非常好文，HIFI全攻略 [复制链接]

leslie 在 2004-3-13 0:28:19 发表的内容 差不多，看了一半

强啊！
其实我问题全看懂了，回答看不明白，算不算也看懂一半？：（

10.0 Amplifiers:
Note: A receiver contains an amplifier, so the following questions apply to both receivers and amplifiers. In the following text, "amp" and "amplifier" are used synonymously.

10.1 What is Biamping? Biwiring?
10.2 Can amplifier X drive 2 ohm or 4 ohm speakers? How do I raise the impedance of a speaker from (say) 4 ohms to 8 ohms?
10.3 How do I drive more than two speakers with one stereo amplifier?
10.4 How big an amplifier do I need?
10.5 Do all amplifiers with the same specifications sound alike?
10.6 Is this amplifier too big for that set of speakers?
10.7 Where can I get a cheap low-power amplifier?
10.8 Is the stuff sold by Carver really awesome?
10.9 What is a preamplifier?
10.10 What is a passive preamplifier?
10.11 Do I need a preamp? Why?
10.12 Should I leave equipment on all of the time or turn it on and off?
10.13 Do tube amps sound better than transistor amps? FETs?
10.14 What about swapping op-amps?
10.15 Where can I buy electronic parts to make an amplifier?
10.16 Where can I buy audio amplifier kits?
10.17 Where can I read more about building amplifiers, preamps, etc.?
10.18 What is Amplifier Class A? B? AB? C? D?
10.19 Why do I hear noise when I turn the volume control? Is it bad?
10.20 What is amplifier "bridging" or "monoblocking"? How do I do it?

10.1 What is Biamping? Biwiring?
Most speakers are connected to an amplifier by one pair of terminals on each speaker. Within these speakers, a crossover distributes the signal (modified appropriately) to each of the drivers in the speaker.

Some speakers are set up to be either biwired or biamped. A much smaller number allows triwiring and triamping. The same principles apply but use three sets of wires or three amplifiers instead of two. Most speakers that support biamping/biwiring have two pairs of terminals and some mechanism for shorting the two pairs together when used in the normal way. This mechanism is most likely a switch or a bus bar. To help the descriptions below, I will refer to these two pairs as LO and HI (because normally one pair connects to the woofer and the other pair connects to the tweeter/midrange).

Biwiring means that a speaker is driven by two pairs of wires from the same amplifier output. One cable pair connects HI to the amp, and the other cable pair connects LO to the same amp output that you connected the HI cable to. Biwiring is controversial; some folks hear a difference, some do not. The most plausible explanation involves magnetic induction of noise in the relatively low current HI cable from the relatively high current signal in the LO cable. Accordingly, Vandersteen recommends the two cable pairs for a channel be separated by at least a few inches. In any case, the effect appears to be small.

Biamping means that the two pairs of terminals on a speaker are connected to distinct amplifier outputs. Assuming you have two stereo amplifiers, you have two choices: either an amp per channel, or an amp per driver. For the amp per channel, you connect each terminal pair to a different channel on the amp (for example, the left output connects to HI and the right side to LO). In the other configuration, one amp connects to the LO terminals, and the other amp is connected to the HI terminals.

The point of biamping is that most of the power required to drive the speakers is used for low frequencies. Biamping allows you to use amps specialized for each of these uses, such as a big solid-state amplifier for the LO drivers and higher quality (but lower power) amp for the higher frequencies. When you have two identical stereo amps, some folks recommend distributing the low-frequency load by using an amp per channel. In any case, whenever you use two different amplifiers, be careful to match levels between them.

Biamping also allows you to use high-quality electronic crossovers and drive the speaker's drivers (the voice coils) directly, without the series resistance and non-linear inductance of a passive crossover. Biamping which uses the speaker's crossover is therefore much less desirable. Replacing a good speaker's crossover with an electronic crossover has advantages, but involves some very critical tradeoffs and tuning which is best left to those well-equipped or experienced.

See also section 16.0 below, on wire and connectors in general.


10.2 Can amplifier X drive 2 ohm or 4 ohm speakers? How do I raise the impedance of a speaker from (say) 4 ohms to 8 ohms?
Almost any amplifier can drive almost any load if you don't turn the volume up too high. Tube amplifiers are one exception. Some amps clip if you play them too loud. This is bad and damages speakers. Other amplifiers shutdown if they are asked to play too loud. Many will overheat, with bad consequences. However, in almost all cases, it takes seriously loud sound or low speaker resistance (less than 4 ohms) to do damage. Running two sets of 8 ohm speakers at once with common amplifiers represents a 4 ohm load. Four sets of 8 ohm speakers makes a 2 ohm load. Two sets of 4 ohm speakers also makes a 2 ohm load. If you stay sober and don't turn it up past the point where it distorts, you are PROBABLY safe with most amplifiers and most loads. See 10.3 for more information.

You can raise the impedance of a speaker by a few different methods. However, each has drawbacks. If your amplifier won't drive your speakers, AND you are sure that the problem is that the speakers are too low impedance, you might try one of these techniques.

A)
Add a 4 ohm resistor in series with the speaker. This requires a high power resistor, because the resistor will dissipate as much power as the speaker. Doing this will almost always hurt sound quality, too. This is caused, in part, by the fact that speakers do not have constant resistance with frequency. See 10.3 for more information on this.

B)
Use a matching transformer. There are speaker matching transformers which can change from 4 ohm to 8 ohm, but a high quality transformer like this can cost as much as a common receiver. Also, even the best transformer will add some slight frequency response and dynamic range errors.

C)
Use two identical speakers in series. If you have two 4 ohm speakers which are the same make and model, you can wire them in series and make an equivalent speaker with 8 ohm impedance. The sound from that "new speaker" will not be as precisely localized as it would from one speaker, so your stereo image may be hurt. Also, it requires that you buy twice as many speakers as you might have bought otherwise. However, this technique has one side benefit. Two speakers can handle twice the power of one.


10.3 How do I drive more than two speakers with one stereo amplifier?
One amp can drive many speakers. However, there are two limits to this practice. The first is that you can overheat or damage an amplifier if you drive too low of an impedance to loud listening levels. Avoid loading any amplifier with a lower impedance than recommended. Adding two speakers to one amp output loads that output with half the impedance of one speaker. (See also 10.2 above)

The second is that with tube amplifiers, which are uncommon in today's common system, it is important that the speaker impedance and the amplifier output impedance be well matched.

When driving two or more speakers from one amp output, always wire them in parallel, rather than series. Series connection, while safe in terms of impedance levels, can hurt sound quality by raising the impedance that the speakers themselves see. Also, when different speakers are wired in series, amplifier voltage will divide between the speakers unevenly, because different speakers have different impedance-versus-frequency characteristics.

Many amplifiers have connectors for two pairs of speakers. In general, these amplifiers also have a speaker selector switch. Most amplifiers connect speakers in parallel when both are selected, although some less expensive ones will wire the speakers in series. It is common for these amplifiers to require 8 ohm speakers only, because the amplifier is built to drive either 4 or 8 ohms, and two sets of 8 ohm speakers in parallel loads the amplifier like one set of 4 ohm speakers. It is almost always safe to connect one set of 4 ohm speakers to an amplifier with two sets of outputs, provided that you NEVER use the second terminals for any other speakers.


10.4 How big an amplifier do I need?
Unfortunately, amplifier power ratings and speaker power ratings are almost always misleading. Sometimes, they are factually wrong. Speaker ratings are almost useless in evaluating needs.

To start with, sound pressure, measured in dB, often stated as dB SPL, is a function of the log of the acoustic "sound" power. Further, human hearing is less sensitive to differences in power than the log transfer function would imply. This means that the perceived difference between a 50 watt amplifier and a 100 watt amplifier, all else equal, is very small! One columnist said that a 250 watt amplifier puts out twice the perceived loudness of a 25 watt amplifier, but quantitative statements about perception should always be treated with caution. That statement came from Electronics Now Magazine, Jan 1994, Page 87, Larry Klein's "Audio Update" Column, which is also good reading on the subject of required amplifier power.

There is a wide variation in the "efficiency" and "sensitivity" of the various speakers available. I have seen good speakers with under 80 dB per watt efficiency and have also seen good speakers with over 96 dB per watt efficiency, measured one meter from the speaker. This difference of 16 dB represents a factor of 40 difference in power requirement!

So the first step in determining amplifier requirements is to estimate relative speaker efficiency. Other factors include how loud you will want to listen, how large your room is, and how many speakers you will drive with one amplifier. This information will give you a rough starting point. For an example, a typical home speaker will produce 88 dB at 1 watt. In an average room, a person with average tastes will be happy with this speaker and a good 20 watt per channel amplifier. Someone who listens to loud music or wants very clean reproduction of the dynamics of music will want more power. Someone with less efficient speakers or a large room will also want more power.

Past that point, you will have to use your ears. As with all other decisions, your best bet is to get some candidates, borrow them from a friendly dealer, take them home, and listen to them at your normal and loudest listening level. See if they play cleanly when cranked up as loud as you will ever go, into your speakers in your room. Of course, it is also important to be sure that the amp sounds clean at lower listening levels.


10.5 Do all amplifiers with the same specifications sound alike?
Some say that they do. Some say that they don't. Some demonstrated that many amplifier differences can be traced to very slight frequency response difference. Let your own ears guide you. If you want to compare amplifiers, you can do it best in a controlled environment, such as your home, with your music and your speakers. Also be very careful to match levels precisely. All you need to match levels of amplifiers is a high input-impedance digital voltmeter set to AC volts and a test recording or signal generator. For best accuracy, set levels with the speakers wired to the amplifier.


10.6 Is this amplifier too big for that set of speakers?
There is no such thing as an amplifier that is too big. Small amplifiers are more likely to damage speakers than large ones, because small amplifiers are more likely to clip than larger ones, at the same listening level. I have never heard of speakers being damaged by an overly large amplifier. I have heard of 100 watt speakers being damaged by a 20 watt amplifier, however, in really abusive hands. This will happen because when an amplifier clips, it will generate much more energy at high frequencies than normal music would contain. This high energy at high frequencies may be less than the continuous power rating of the speaker, but higher than the actual energy rating of the tweeter. Tweeters tend to be very fragile components


10.7 Where can I get a cheap low-power amplifier?
There are very few available. One source is to buy a cheap boom box and only use the amplifier. Another source is Radio Shack. A third alternative is to buy a car stereo booster and get a 12V power supply for it. Finally, you can build an amp pretty easily if you are handy, but it probably won't be that cheap. Mark V Electronics, for example, sells 20 watt amp kits for under $30 and 80 watt amp kits for under $150. Sound Values has a 60 watt amp kit complete for about $200, and Old Colony sells some amp kits for a bit more. All three, Mark V, Old Colony, and Sound Values kits have been built by satisfied rec.audio.* posters, although quality of the Mark V kit is lower than the others. (See 10.15, 10.16, 10.17)


10.8 Is the stuff sold by Carver really awesome?
Some people really like it. Others believe that it doesn't perform up to specifications. Still others believe that it isn't all that it is hyped up to be. However, much of this is repeated rumor based on older Carver equipment. One of Carver's claims to fame is lots of watts per pound of weight. As with almost everything else, the best policy is to listen for yourself and see what you think.


10.9 What is a preamplifier?
A preamplifier is an amplifying electronic circuit which can be connected to a low output level device such as a phono cartridge or a microphone, and produce a larger electrical voltage at a lower impedance, with the correct frequency response. Phono cartridges need both amplification and frequency response equalization. Microphones only need amplification.

In most audio applications, the term 'preamplifier' is actually a misnomer and refers to a device more properly called a 'control amplifier'. Its purpose is to provide features such as input selection, level control, tape loops, and sometimes, a minimal amount of line-stage gain. These units are not preamplifiers in the most technical sense of the word, yet everyone calls them that.


10.10 What is a passive preamplifier?
A passive preamplifier is a control unit without any amplification at all. It is a classic oxymoron, because it has no capability to increase the gain of the signal. It is only used with line level sources that need no gain beyond unity.


10.11 Do I need a preamp? Why?
The tasks of a preamp are to:

     Switch between various input signals,
     Amplify any phono inputs to line level,
     Adjust the volume,
     Adjust the treble and bass if necessary,
     Present the right load impedance for the inputs, and
     Present a low source impedance for the outputs.

If you have a turntable, you NEED a preamp with a phono input. This is because the turntable has an output which is too small for driving amplifiers and because the output of the turntable requires frequency response equalization. You can't connect any other source to a phono input other than a turntable (phono cartridge). Also, you can't connect a phono cartridge or turntable to any input other than a phono input.

Microphones also require special preamplifiers. Some microphones also require "phantom power". Phantom power is operating power for the microphone which comes from the preamp. Microphone preamps are often built into tape decks and microphone mixers.

If you only have high level inputs, such as the output of a CD player and the output of a tape deck, the main value of a preamp is selecting between inputs and providing a master volume control. If you only listen to CDs, it is plausible to skip the preamp entirely by getting a CD player with variable level outputs and connecting them directly to a power amplifier.

Some caveats apply. One, the variable outputs on a CD player are often lower sound quality than fixed outputs. Two, some sources have high or nonlinear output impedances which are not ideal for driving an amplifier directly. Likewise, some amplifiers have an unusually low or nonlinear input impedance such that common sources can't drive the input cleanly. A good preamplifier allows use of such devices without sacrificing sound quality.

Unfortunately, the only way to be sure that a preamplifier is of value with your sources and your amplifier is to try one.

Almost all receivers contain a phono preamp, a volume control, and input switching. Therefore, if you have a receiver, you may never need a preamp.


10.12 Should I leave equipment on all of the time or turn it on and off?
Some gear draws significant electricity, so you will waste money and fossil fuel if you leave it on all of the time. As an example, a common amplifier consumes 40 watts at idle. High-end gear uses far more electricity, but ignoring that, 40 watts x 168 hours x 52 weeks x US $0.0001 per watt hour (rough estimate) is $35/year. Now add a CD player, a preamp, and a tuner, and it really adds up.

High-end enthusiasts claim that equipment needs to warm up to sound its best. If you care about the best sound, give your equipment at least 20 minutes to warm up before serious listening. Warm up will allow the inside temperature to stabilize, minimizing offsets, bring bias currents up to their proper values, and bringing gain up to operating level.

Either way, good gear will last a very long time. Tubes are known to have a finite life, but good tube designs run tubes very conservatively, giving them life exceeding 10 years of continuous service. Some amplifiers run tubes harder to get more power out, and thereby may be more economical to turn off between use.

Filter capacitors will fail after enough time at temperature with voltage applied. They will last longer if turned off between use. However, like tubes, filter caps can last tens of years of continuous use, as can power transformers, semiconductors, and the like.

Filter capacitors have a funny problem that justified a simple break-in or reforming when they are restarted after many years of rest. It involves bringing up the power line voltage slowly with a variable transformer. For tips on reforming capacitors, consult "The Radio Amateur's Handbook", by the ARRL.

Semiconductors seem to fail more often because of bad surges and abuse than age. Leaving gear off may be best for semiconductors and other surge-sensitive gear if you expect power line surges, as come from an electrical storm or operation of large motors.

Fuses seem to age with temperature and get noisy, but they are so inexpensive that it should not bias your decision. However, some are inconvenient to change, and may require opening the case and even voiding the warranty.


10.13 Do tube amps sound better than transistor amps? FETs?
Lets first list some commonly used active electronic components and their good and bad attributes.

TUBE: (Valve, Vacuum Tube, Triode, Pentode, etc.) Tubes operate by thermionic emission of electrons from a hot filament or cathode, gating from a grid, and collection on a plate. Some tubes have more than one grid. Some tubes contain two separate amplifying elements in one glass envelope. These dual tubes tend to match poorly.

The characteristics of tubes varies widely depending on the model selected. In general, tubes are large, fragile, pretty, run hot, and take many seconds to warm up before they operate at all. Tubes have relatively low gain, high input resistance, low input capacitance, and the ability to withstand momentary abuse. Tubes overload (clip) gently and recover from overload quickly and gracefully.

Circuits that DO NOT use tubes are called solid state, because they do not use devices containing gas (or liquid).

Tubes tend to change in characteristic with use (age). Tubes are more susceptible to vibration (called "microphonics") than solid state devices. Tubes also suffer from hum when used with AC filaments.

Tubes are capable of higher voltage operation than any other device, but high-current tubes are rare and expensive. This means that most tube amp use an output transformer. Although not specifically a tube characteristic, output transformers add second harmonic distortion and give gradual high-frequency roll-off hard to duplicate with solid state circuits.

TRANSISTOR: (BJT, Bipolar Transistor, PNP, NPN, Darlington, etc.) Transistors operate by minority carriers injected from emitter to the base that are swept across the base into the collector, under control of base current. Transistors are available as PNP and NPN devices, allowing one to "push" and the other to "pull". Transistors are also available packaged as matched pairs, emitter follower pairs, multiple transistor arrays, and even as complex "integrated circuits", where they are combined with resistors and capacitors to achieve complex circuit functions.

Like tubes, many kinds of BJTs are available. Some have high current gain, while others have lower gain. Some are fast, while others are slow. Some handle high current while others have lower input capacitances. Some have lower noise than others. In general, transistors are stable, last nearly indefinitely, have high gain, require some input current, have low input resistance, have higher input capacitance, clip sharply, and are slow to recover from overdrive (saturation). Transistors also have wide swing before saturation.

Transistors are subject to a failure mode called second breakdown, which occurs when the device is operated at both high voltage and high current. Second breakdown can be avoided by conservative design, but gave early transistor amps a bad reputation for reliability. Transistors are also uniquely susceptible to thermal runaway when used incorrectly. However, careful design avoids second breakdown and thermal runaway.

MOSFET: (VMOS, TMOS, DMOS, NMOS, PMOS, IGFET, etc.) Metal-Oxide Semiconductor Field Effect Transistors use an insulated gate to modulate the flow of majority carrier current from drain to source with the electric field created by a gate. Like bipolar transistors, MOSFETs are available in both P and N devices. Also like transistors, MOSFETs are available as pairs and integrated circuits. MOSFET matched pairs do not match as well as bipolar transistor pairs, but match better than tubes.

MOSFETs are also available in many types. However, all have very low input current and fairly low input capacitance. MOSFETs have lower gain, clip moderately, and are fast to recover from clipping. Although power MOSFETs have no DC gate current, finite input capacitance means that power MOSFETs have finite AC gate current. MOSFETs are stable and rugged. They are not susceptible to thermal runaway or second breakdown. However, MOSFETs can't withstand abuse as well as tubes.

JFET:
Junction Field Effect Transistors operate exactly the same way that MOSFETs do, but have a non-insulated gate. JFETs share most of the characteristics of MOSFETs, including available pairs, P and N types, and integrated circuits.

JFETs are not commonly available as power devices. They make excellent low-noise preamps. The gate junction gives JFETs higher input capacitance than MOSFETs and also prevents them from being used in enhancement mode. JFETs are only available as depletion devices. JFETs are also available as matched pairs and match almost as well as bipolar transistors.

IGBT: (or IGT)
Insulated-Gate Bipolar Transistors are a combination of a MOSFET and a bipolar transistor. The MOSFET part of the device serves as the input device and the bipolar as the output. IGBTs are only available today as N-type devices, but P-type devices are theoretically possible. IGBTs are slower than other devices but offer the low cost, high current capacity of bipolar transistors with the low input current and low input capacitance of MOSFETs. IGBTs suffer from saturation as much as, if not more than bipolar transistors, and also suffer from second breakdown. IGBTs are rarely used in high-end audio, but are sometimes used for extremely high power amps.

Now to the real question. You might assume that if these various devices are so different from each other, one must be best. In practice, each has strengths and weaknesses. Also, because each type of device is available in so many different forms, most types can be successfully used in most places.

Tubes are prohibitively expensive for very high power amps. Most tube amps deliver less than 50 watts per channel.

JFETs are sometimes an ideal input device because they have low noise, low input capacitance, and good matching. However, bipolar transistors have even better matching and higher gain, so for low-impedance sources, bipolar devices are even better. Yet tubes and MOSFETs have even lower input capacitance, so for very high source resistance, they can be better.

Bipolar transistors have the lowest output resistance, so they make great output devices. However, second breakdown and high stored charge weigh against them when compared to MOSFETs. A good BJT design needs to take the weaknesses of BJTs into account while a good MOSFET design needs to address the weaknesses of MOSFETs.

Bipolar output transistors require protection from second breakdown and thermal runaway and this protection requires additional circuitry and design effort. In some amps, the sound quality is hurt by the protection.

All said, there is much more difference between individual designs, whether tube or transistor, than there is between tube and transistor designs generically. You can make a fine amp from either, and you can also make a lousy amp from either.

Although tubes and transistors clip differently, a good amp will keep all devices from ever clipping, so this difference should be moot.

Some people claim that tubes require less or no feedback while transistor amps require significant feedback. In practice, all amps require some feedback, be it overall, local, or just "degeneration". Feedback is essential in amps because it makes the amp stable with temperature variations and manufacturable despite component variations.

Feedback has a bad reputation because a badly designed feedback system can dramatically overshoot or oscillate. Some older designs used excessive feedback to compensate for the nonlinearities of lousy circuits. Well designed feedback amps are stable and have minimal overshoot.

When transistor amps were first produced, they were inferior to the better tube amps of the day. Designers made lots of mistakes with the new technologies as they learned. Today, designers are far more sophisticated and experienced than those of 1960.

Because of low internal capacitances, tube amps have very linear input characteristics. This makes tube amps easy to drive and tolerant of higher output-impedance sources, such as other tube circuits and high-impedance volume controls. Transistor amps may have higher coupling from input to output and may have lower input impedance. However, some circuit techniques reduce these effects. Also, some transistor amps avoid these problems completely by using good JFET input circuits.

There is lots of hype out on the subject as well as folklore and misconceptions. In fact, a good FET designer can make a great FET amp. A good tube designer can make a great tube amp, and a good transistor designer can make a great transistor amp. Many designers mix components to use them as they are best.

As with any other engineering discipline, good amp design requires a deep understanding of the characteristics of components, the pitfalls of amp design, the characteristics of the signal source, the characteristics of the loads, and the characteristics of the signal itself.


As a side issue, we lack a perfect set of measurements to grade the quality of an amp. Frequency response, distortion, and signal-to-noise ratio give hints, but by themselves are insufficient to rate sound.

Many swear that tubes sound more "tube like" and transistors sound more "transistor like". Some people add a tube circuit to their transistor circuits to give some "tube" sound.

Some claim that they have measured a distinct difference between the distortion characteristics of tube amps and transistor amps. This may be caused by the output transformer, the transfer function of the tubes, or the choice of amp topology. Tube amps rarely have frequency response as flat as the flattest transistor amps, due to the output transformer. However, the frequency response of good tube amps is amazingly good.

For more information on tubes, get one of the following old reference books, or check out Glass Audio Magazine (see the magazine section of the FAQ for more info on Glass Audio).

The Receiving Tube Manual (annual up to 1970)
The Radiotron Designers Handbook
Fundamentals of Vacuum Tubes" by Eastman 1937, McGraw-Hill


10.14 What about swapping op-amps?
Many components use ICs called op amps as audio amplifiers. Earlier op amps had poor sound quality, especially if misused. Some engineers with a strong background in ICs and op amps learned that they could improve sound if they replaced slow, noisy, low slew-rate, or otherwise bad op amps with better ones. Some less informed people tried doing the same thing and made the sound worse.

One pitfall with op amp swapping is that some op amps are more prone to unwanted oscillation than others. The faster the op amp, the more likely it will cause an unwanted oscillation, which will really damage the sound. For that reason, Joe may succeed in replacing 741 op amps with 5534 op amps in his gear, and you may fail. It is dependent on design, layout, etc.

As technology and design expertise improves, audio op amps get better and swapping is getting less and less useful. Newer op amps are displacing yesterday's best, and sound surprisingly similar to straight wire.

Still, there are different op amps for different purposes. Bipolar op amps are ideal for preamplifiers where noise is critical. The OP-27, OP-37, LT1028, and LT1115 are very well received for phono preamps, head amplifiers, and microphone preamplifiers. Bipolar op amps are also more practical for signals with low source impedance.

FET devices like the OPA604 and OPA2604 have higher slew rate, higher bandwidth, and lower input current. These op amps are better for line-level inputs and high source-resistance signals. Some amplifiers, like the OP-37 and LT1115 achieve higher bandwidth by using less internal compensation. These amplifiers are not unity gain stable, and should not be used in circuits with low closed loop gain or large feedback capacitors.

Some of the better op amps for audio as of today include
(* means highly recommended):

          Single          Dual
          AD845*          AD842
          AD847           AD827
          AD797*          NE5535
          NE5534          NE5532
          OP-27           AD712
          LT1115*         LM833
          AD811           OPA2604*
          AD841           OP249*
          HA5112*
          LT1057
          LT1028
          AD744
          SSM2016

With op amp part numbers, there is a lot of room for confusion.
Here is a guide to the numbers that is often accurate:

Op amp part numbers start with a manufacturer's prefix:

          Analog Devices uses AD
          Burr Brown uses OPA
          Linear Technology uses LT
          Motorola uses MC
          National uses LF and LM
          PMI uses OP
          Signetics uses NE and SE
          TI uses TL

This can be confused because if TI copies a Signetics op amp, they may assume the Signetics prefix, or they may use their own. Fortunately, if the part numbers are the same, circuitry is almost exactly the same, as is the performance. (Note: almost)

The next thing in the part number is two, three, four or five digits. This is invariably the key to the part. If the numbers are the same, the parts are almost surely the same. For example, an LM357N and an LM357J are electrically identical and sound the same.
Next is a letter or two indicating the op amp package and possibly how it has been tested and what tests it passed. Unfortunately, manufacturers haven't standardized these letters. Fortunately, you almost never care. If it is a dual-inline (DIP) package and you are replacing a DIP, you shouldn't have to worry whether or not it is ceramic or molded. Likewise, you rarely care if it has 100uV offset or 4mV offset for audio. Finally, you don't care if it wasn't tested at elevated temperatures because you will use it in your house, inside well ventilated gear.

So in general, an NE5532J is a TL5532N, and an AD827JN will sound the same as an AD827LD. If you aren't sure about some detail, call or write the IC maker and ask for a data sheet on the parts in question. They will always send data sheets for free, and these data sheets contain details on the various part numbers, internal circuitry, and electrical characteristics.


10.15 Where can I buy electronic parts to make an amplifier?
There are many commercial parts distributors that sell only to Corporations. Their prices are often list, their supply is often good, and their service varies. Common ones are Arrow Electronics, Gerber Electronics, Hamilton Avnet, and Schweber Electronics. See your local phone book.

There are also distributors that cater to smaller buyers. These typically have only one office. Some have lousy selections but great prices. In the following list, (+) means that the dealer has a good reputation, (?) means that the dealer has insufficient reputation, and (X) means that some have reported problems with this dealer. (C) means they have a catalog.

        All Electronics Corporation (Surplus, Tools, Parts) (?) (C)
                PO Box 567
                Van Nuys CA  90408 USA
                800-826-5432
                818-904-0524
        Allied Electronics (Full Line of Parts) (+) (C)
                800-433-5700
        Antique Electronics Supply (Tubes, capacitors, etc) (?)
                688 First St
                Tempe AZ  85281 USA
                602-894-9503
        Billington Export Ltd. (Valves and CRTs)
                I E Gillmans Trading Estate
                Billinghurst, RH14 9E3  United Kingdom
                Tel (0403) 784961
        Chelmer Valves (Valves)
                130 New London Rd
                Chelmsford, CM2 0RG  United Kingdom
        DigiKey Corporation (Full Line of Parts) (+) (C)
                701 Brooks Avenue South
                PO Box 677
                Thief River Falls MN  56701-0677 USA
                800-344-4539
        Electromail (Wide range of parts, similar to Radio Shack)
                PO Box 33, Corby, Northants NN17 9EL  United Kingdom
                Tel 0536 204555
        Langrex Supplies Ltd. (Obsolete Valves)
                1 Mayo Rd.
                Croyden, Surrey, CR0 2QP  United Kingdom
        Maplin (European Parts) (?) (C)
                +44 702 554161 (For Orders Only)
                +44 702-552911 (Customer Service)
        Marchand Electronics (?) (Crossover kits)
                1334 Robin Hood Lane
                Webster NY  14580 USA
                716-872-5578
        MCM Electronics (Speakers, A/V Repair Parts, Etc) (+) (C)
                650 Congress Park Dr
                Centerville Ohio 45459-4072 USA
                513-434-0031 or 800-543-4330
        MesaBoogie (Tubes, instrument speakers) (?)
                707-778-8823
        Michael Percy (Connectors, MIT, Wonder Caps, Buf-03) (+)
                PO Box 526
                Inverness CA 94936 USA
                415-669-7181 Voice
                415-669-7558 FAX
        Mouser Electronics (Full Line of Parts) (+) (C)
                PO Box 699
                Mansfield TX  76063-0699 USA
                800-346-6873
                817-483-4422
        Newark Electronics (Full Line of Parts) (+) (C)
        Old Colony Sound (Audio parts and audio kits) (+) (C)
                PO Box 243
                Peterborough NH  03458-0243 USA
                603-924-9464
        Parts Express (Speakers, Cables, Connectors) (+) (C)
                340 East First Street
                Dayton OH  45402-1257 USA
                513-222-0173
        PM Components (High end audio parts and valves)
                Springhead road
                Gravesend
                Kent, DA11 3HD  United Kingdom
                Tel (0474) 560521
        PV Tubes (Valves and Transformers)
                104 Abbey St.
                Accrington, Lancs, BB5 1EE  United Kingdom
                Tel (0254) 236521
        Radio Shack (Parts, Low-End Audio) (+) (C)
        RATA Ltd (Audio parts and cables: Kimber, Ansar, Vishay)
                Edge Bank House
                Skelsmergh
                Kendal, Cumbria, LA8 9AS  United Kingdom
                Tel (0539) 823247
        SJS Acoustics (High-end parts, valves, transformers)
                Ben-Dor
                Lumb Carr Rd.
                Holcombe, Bury, BL8 4NN  United Kingdom
        Sowter Transformers (Mains and output transformers)
                EA Sowter Ltd. PO box 36
                Ipswich, IP1 2EL  United Kingdom
                Tel (0473) 219390
        Tanner Electronics (Surplus Parts) (+)
                214-242-8702
        Toroid Corp of Maryland (Toroidal power transformers) (+)
                (also sells without secondary, ready to finish)
                608 Naylor Mill Rd
                Salisbury MD 21801-9627 USA
                410-860-0300
        Triode Electronics (Tubes, transformers, boxes) (?)
                2010 Roscoe St
                Chicago IL  60618 USA
                312-871-7459
        Welborne Labs (Connectors, Linear Tech ICs, Wima Caps) (?)
                P.O. Box 260198
                971 E. Garden Drive
                Littleton, CO 80126 USA
                303-470-6585 Voice
                303-791-5783 FAX
        Wilson Valves (Valves)
                28 Banks Ave.
                Golcar, Huddersfield, HD7 4LZ  United Kingdom

10.16 Where can I buy audio amplifier kits?
Alas, Heath is no longer making Heathkits. Alternatives:

        AP Electronics (High grade components and kits)
                20 Derwent centre
                Clarke St.
                Derby DE1 2BU  United Kingdom
        Audio Note (Audio parts, kits, and high quality amps)
                Unit 1
                Block C, Hove Business Centre
                Fonthil Rd.
                Hove, East Sussex, BN3 6HA  United Kingdom
                Tel (0273) 220511
        Audio Synthesis (Many kits from Ben Duncan designs) (?)
                99 Lapwind Lane
                Manchester M20 0UT, UK
                061-434-0126 Voice
                060-225-8431 FAX
        Crimson (UK) (?)
        Hafler (+) (may be out of the kit business)
        Hart Electronic Kits (Audiophile kits and components)
                Penylan Mill
                Oswestry
                Shropshire, SY10 9AF  United Kingdom
                Tel (0691)652894
        Mark V Electronics (?)
                8019 E Slauson Ave
                Montebello CA  90640 USA
                800-423-3483
                213-888-8988
        Old Colony Sound (+) (See 10.15)
        Sage Audio (Various kits UK$95 to UK$430)
                Construction House
                Bingley
                West Yorkshire
                England BD16 4JH UK
        Sound Values (+) (See 10.7)
                185 N Yale Avenue
                Columbus OH  43222-1146 USA
                614-279-2383

10.17 Where can I read more about building amplifiers, preamps, etc.?
        Audio Amateur Magazine
                Audio Amateur Publications
                PO Box 494
                Peterborough NH  03458 USA
                603-924-9464
        Analog Devices Audio/Video Reference Manual
        Electronic Music Circuits, by Barry Klein
                Howard D Sams & Co ISBN 0-672-21833-X
        Electronics Australia (Magazine with audio projects)
                AUD47 per year 12 issues, often discounted
                PO Box 199
                Alexandria, Austrailia
                +612 353 9944 or +612 353 6666
        Elektor Electronics (How it works and you-build articles)
                (no longer published in US. Still available in Europe)
                PO Box 1414
                Dorchester DT2 8YH, UK
        Enhanced Sound: 22 Electronic Projects for the Audiophile
                (Some basic projects and some "how it works")
                by Richard Kaufman
                Tab Books #3071/McGraw Hill
                ISBN 0-8306-9317-3
        Glass Audio Magazine
                Audio Amateur Publications
                PO Box 494
                Peterborough NH  03458 USA
                603-924-9464
        IC Op-Amp Cookbook, Third Edition by Walter G. Jung
                ISBN 0672-23453-4, Howard W. Sams, Inc.
        Journal of the Audio Engineering Society (Theory & Experiment)
                Audio Engineering Society
                60 East 42nd Street
                New York City NY  10165-0075 USA
                212-661-2355
        Popular Electronics
        Radio-Electronics
        Radiotron Designer's Handbook, Fourth Edition (old, tube info)
        The Technique of Electronic Music, by Thomas H Wells
                Schirmer Books ISBN 0-02-872830-0
        Vacuum Tube Amplifiers, MIT Radiation Lab series
        Wireless World
        Some of the above titles, as well as a catalog of technical
                        books, are available from:
                OpAmp Technical Books, Inc.
                1033 N Sycamore Avenue
                Los Angeles CA  90038 USA
                800-468-4322 or 213-464-4322

10.18 What is Amplifier Class A? What is Class B? What is Class AB? What is Class C? What is Class D?
All of these terms refer to the operating characteristics of the output stages of amplifiers.

Briefly, Class A amps sound the best, cost the most, and are the least practical. They waste power and return very clean signals. Class AB amps dominate the market and rival the best Class A amps in sound quality. They use less power than Class A, and can be cheaper, smaller, cooler, and lighter. Class D amps are only used for special applications like bass-guitar amps and subwoofer amps. They are even smaller than Class AB amps and more efficient, yet are often limited to under 10kHz (less than full-range audio). Class B & Class C amps aren't used in audio.

In the following discussion, we will assume transistor output stages, with one transistor per function. In some amplifiers, the output devices are tubes. Most amps use more than one transistor or tube per function in the output stage to increase the power.

Class A refers to an output stage with bias current greater than the maximum output current, so that all output transistors are always conducting current. The biggest advantage of Class A is that it is most linear, ie: has the lowest distortion.

The biggest disadvantage of Class A is that it is inefficient, ie: it takes a very large Class A amplifier to deliver 50 watts, and that amplifier uses lots of electricity and gets very hot.

Some high-end amplifiers are Class A, but true Class A only accounts for perhaps 10% of the small high-end market and none of the middle or lower-end market.

Class B amps have output stages which have zero idle bias current. Typically, a Class B audio amplifier has zero bias current in a very small part of the power cycle, to avoid nonlinearities. Class B amplifiers have a significant advantage over Class A in efficiency because they use almost no electricity with small signals.

Class B amplifiers have a major disadvantage: very audible distortion with small signals. This distortion can be so bad that it is objectionable even with large signals. This distortion is called crossover distortion, because it occurs at the point when the output stage crosses between sourcing and sinking current. There are almost no Class B amplifiers on the market today.

Class C amplifiers are similar to Class B in that the output stage has zero idle bias current. However, Class C amplifiers have a region of zero idle current which is more than 50% of the total supply voltage. The disadvantages of Class B amplifiers are even more evident in Class C amplifiers, so Class C is likewise not practical for audio amps.

Class A amplifiers often consist of a driven transistor connected from output to positive power supply and a constant current transistor connected from output to negative power supply. The signal to the driven transistor modulates the output voltage and the output current. With no input signal, the constant bias current flows directly from the positive supply to the negative supply, resulting in no output current, yet lots of power consumed. More sophisticated Class A amps have both transistors driven (in a push-pull fashion).

Class B amplifiers consist of a driven transistor connected from output to positive power supply and another driven transistor connected from output to negative power supply. The signal drives one transistor on while the other is off, so in a Class B amp, no power is wasted going from the positive supply straight to the negative supply.

Class AB amplifiers are almost the same as Class B amplifiers in that they have two driven transistors. However, Class AB amplifiers differ from Class B amplifiers in that they have a small idle current flowing from positive supply to negative supply even when there is no input signal. This idle current slightly increases power consumption, but does not increase it anywhere near as much as Class A. This idle current also corrects almost all of the nonlinearity associated with crossover distortion. These amplifiers are called Class AB rather than Class A because with large signals, they behave like Class B amplifiers, but with small signals, they behave like Class A amplifiers. Most amplifiers on the market are Class AB.

Some good amplifiers today use variations on the above themes. For example, some "Class A" amplifiers have both transistors driven, yet also have both transistors always on. A specific example of this kind of amplifier is the "Stasis" (TM) amplifier topology promoted by Threshold, and used in a few different high-end amplifiers. Stasis (TM) amplifiers are indeed Class A, but are not the same as a classic Class A amplifier.

Class D amplifiers use pulse modulation techniques to achieve even higher efficiency than Class B amplifiers. As Class B amplifiers used linear regulating transistors to modulate output current and voltage, they could never be more efficient than 50%. Class D amplifiers use transistors that are either on or off, and almost never in-between, so they waste the least amount of power.

Obviously, then, Class D amplifiers are more efficient than Class A, Class AB, or Class B. Some Class D amplifiers have >80% efficiency at full power. Class D amplifiers can also have low distortion, although not as good as Class AB or Class A.

Class D amplifiers are great for efficiency. However they are awful for other reasons. It is essential that any Class D amp be followed by a passive low-pass filter to remove switching noise. This filter adds phase shift and distortion. It also limits the high frequency performance of the amplifier, such that Class D amplifiers rarely have good treble. The best application today for Class D amplifiers is subwoofers.

To make a very good full range Class D amplifier, the switching frequency must be well above 40kHz. Also, the amplifier must be followed by a very good low-pass filter that will remove all of the switching noise without causing power loss, phase-shift, or distortion. Unfortunately, high switching frequency also means significant switching power dissipation. It also means that the chances of radiated noise (which might get into a tuner or phono cartridge) is much higher.


10.19 Why do I hear noise when I turn the volume control? Is it bad?
Almost all volume controls are variable resistors. This goes for rotary controls and slide controls. Variable resistors consist of a resistive material like carbon in a strip and a conductive metal spring wiper which moves across the strip as the control is adjusted. The position of the wiper determines the amount of signal coming out of the volume control.

Volume controls are quiet from the factory, but will get noisier as they get older. This is in part due to wear and in part due to dirt or fragments of resistive material on the resistive strip. Volume control noise comes as a scratch when the control is turned. This scratch is rarely serious, and most often just an annoyance. However, as the problem gets worse, the sound of your system will degrade. Also, as the problem gets worse, the scratching noise will get louder. The scratching noise has a large high-frequency component, so in the extreme, this noise could potentially damage tweeters, although I have never seen a documented case of tweeter damage due to control noise.

Some controls are sealed at the factory, so there is no practical way to get inside and clean out the dirt. Others have access through slots or holes in the case. These open controls are more subject to dirt, but also are cleanable. You can clean an open volume control with a VERY QUICK squirt of lubricating contact cleaner, such as Radio Shack 64-2315. Even better is a non-lubricating cleaner, such as Radio Shack 64-2322. With any cleaner, less is better. Too much will wash the lubricant out of the bearings and gunk up the resistive element.

You can also clean some controls by twisting them back and forth vigorously ten times. This technique pushes the dirt out of the way, but is often just a short term fix. This technique is also likely to cause more wear if it is done too often. Try to do it with the power applied, but the speaker disconnected, so that there is some signal on the control.

Sealed and worn controls should be replaced rather than cleaned. Critical listeners claim that some controls, such as those made by "Alps" and by "Penny and Giles" sound better than common controls. Regardless of the brand, however, it is essential that whatever control you buy have the same charcteristics as the one you are replacing. For most volume controls, this means that they must have AUDIO TAPER, meaning that they are designed as an audio volume control, and will change the level by a constant number of dB for each degree of rotation.

Badly designed circuits will wear out volume controls very quickly. Specifically, no volume control is able to work for a long time if there is significant DC current (or bias current) in the wiper. If the output of the control goes to the input of an amplifier, the amplifier should be AC coupled through a capacitor. If there is a capacitor there, it might be leaky, causing undesirable DC current through the volume control.

If you have a circuit with no blocking capacitor or a bad blocking capacitor, you can add/replace the capacitor when you replace the control. However, get some expert advise before modifying. If you add a capacitor to a device which doesn't have one, you will have to make other modifications to insure that the amplifier has a source for its bias current.


10.20 What is amplifier "bridging" or "monoblocking"? How do I do it?
When you're told a stereo power amplifier can be bridged, that means that it has a provision (by some internal or external switch or jumper) to use its two channels together to make one mono amplifier with 3 to 4 times the power of each channel. This is also called "Monoblocking" and "Mono Bridging".

Tube amps with multiple-tap output transformers are simple to bridge. Just connect the secondaries in series and you get more power. The ability to select transformer taps means that you can always show the amplifier the impedance it expects, so tube amp bridging has no unusual stability concerns.

The following discussion covers output transformer-less amps. Bridging these amps is not so simple. It involves connecting one side of the speaker to the output of one channel and the other side of the speaker to the output of the other channel. The channels are then configured to deliver the same output signal, but with one output the inverse of the other. The beauty of bridging is that it can apply twice the voltage to the speaker. Since power is equal to voltage squared divided by speaker impedance, combining two amplifiers into one can give four (not two) times the power.

In practice, you don't always get 4 times as much power. This is because driving bridging makes one 8 ohm speaker appear like two 4 ohm speakers, one per channel. In other words, when you bridge, you get twice the voltage on the speaker, so the speakers draw twice the current from the amp.

The quick and dirty way to know how much power a stereo amp can deliver bridged to mono, is to take the amp's 4 ohm (not 8 ohm) power rating per channel and double it. That number is the amount of watts into 8 ohms (not 4 ohms) you can expect in mono. If the manufacturer doesn't rate their stereo amp into 4 ohms, it may not be safe to bridge that amp and play at loud levels, because bridging might ask the amp to exceed its safe maximum output current.

Another interesting consequence of bridging is that the amplifier damping factor is cut in half when you bridge. Generally, if you use an 8 ohm speaker, and the amplifier is a good amp for driving 4 ohm speakers, it will behave well bridging.

Also consider amplifier output protection. Amps with simple power supply rail fusing are best for bridging. Amps that rely on output current limiting circuits to limit output current are likely to activate prematurely in bridge mode, and virtually every current limit circuit adds significant distortion when it kicks in. Remember bridging makes an 8 ohm load look like 4 ohms, a 4 ohm load look like 2 ohms, etc. Also, real speakers do not look like ideal resistors to amps. They have peaks and dips in impedance with frequency, and the dips can drop below 1/2 the nominal impedance. They also have wildly varying phase with frequency.

Finally, some amplifiers give better sound when bridged than others. Better bridging amps have two identical differential channels with matched gain and phase through each input, left and right, inverting and non-inverting. Simpler bridging amplifiers have one or two inverting channels, and run the output of one into the input of the second. This causes the two outputs to be slightly out of phase, which adds distortion. There are also other topologies. One uses an additional stage to invert the signal for one channel but drives the other channel directly. Another topology uses one extra stage to buffer the signal and a second extra stage to invert the signal. These are better than the simple master/slave arrangement, and if well done, can be as good as the full differential power amp.


Back to main index - Continue to 11.0 CD Players, CDs, Turntables, and LPs

16.0 Wire
More than any other topic, speaker cables and equipment interconnects seem to use up rec.audio.* bandwidth echoing the same theoretical arguments, testimonials, and opinions. Controversy can be stimulating, educational, and also amusing. Please try to keep postings aimed at one of those three goals, and avoid the insults and emotion. Also, try to avoid echoing a common position or principle, as described below.

16.1 Do speaker cables matter?
16.2 What speaker cables are available and how good are they?
16.3 What can I use for budget speaker cables?
16.4 What can I use for budget speaker connectors?
16.5 What about interconnects, such as the cable between tuner and amp?
16.6 What about Phono Interconnects:
16.7 Is there really a difference in digital interconnects?
16.8 Can I make very good interconnects myself?

16.1 Do speaker cables matter?
To avoid confusion and repetition, here is some terminology. Cables are connectors attached to wires. Wires generally have multiple conductors optionally surrounded by a shield and outer insulating covering. Cables can introduce noise into the signal, act as a filter (and thus change the frequency response of the system), and provide nonlinearities from improper (intermittent/loose) connections to or between the connectors.

It is quite scientifically conceivable that some cables do cause a difference in sound, because of the differences in DC resistance, interconductor capacitance, and connector attachment alone. The effects of exotic conductor weaving and materials are not so well established. In general, these effects (once we eliminate DC resistance), seem to be small. However, if your system is at least fairly good, then some folks have observed (although not in an experimental, double-blind sense) significant differences in system performance with different cables. The effects are said to be quite system specific; the only real guideline is to try them and see which ones seem to sound better in your system.

Roughly speaking, the price ranges for speaker cables is low (under $1/ft), medium (under $6-8/ft), and high (up to $100/ft and more). Try to arrange it so you can trial such cables; at several hundred dollars per set, experiments can be expensive.

In any system or experiment, it is essential that the differences between cables be separated from the differences between connectors.

You should have an EXTREMELY solid connection between cable and speaker. Speakers operate at very low impedances, so that bad connections will create significant artifacts or signal losses at any power level. For example, if the connection has a linear resistance of just 1 ohm, the speaker damping factor may be changed, and the bass may suffer If the connection contains imperfect metal oxides, then a slightly rectifying junction will block the signal, producing compression, distortion, and other non-linear effects.

There are many magazine articles on cables with various perspectives which are worth reading, including:

        "Speaker Cables: Testing for Audibility"
              Fred E. Davis
              Audio, July 1993, pgs. 34-43

16.2 What speaker cables are available and how good are they?
There is a wide range of speaker wire available, ranging from 30ga zip cord (~$.10/ft) to exotic wires costing over $300/ft. The material used ranges from copper to oxygen-free copper (OFC) to silver. (There are a bunch of others as well.)

Oxygen-free copper is probably NOT any different from common copper in sound. If you hear a difference between two cables, it is not a difference between oxygen-free and common copper.

Resistance may be significant for speaker cables. The higher the resistance, the more the cable will affect the sound, all else equal. The resistance characteristic of metals is called resistivity. The resistivity of copper is 1.7 microohm-cm. Silver is very slightly lower, 1.6. Gold is a bit higher, 2.4.

Silver and gold are different from copper in other ways than resistivity. Gold does not oxidize in normal environments, so gold contacts will not need periodic cleaning and will not create rectifying junctions. Silver will oxidize, but the oxide of silver is conductive, so oxidized silver will still make good contact. Copper oxide is a bad conductor. Oxidized copper contacts may insulate, may conduct, or may rectify. Copper is a bad material for cable terminals, but this may or may not mean anything for the conductor itself.


16.3 What can I use for budget speaker cables?
First, a few words on terminology. Wire is sized by AWG or BS gauge number. Larger numbers represent smaller wire. AWG 40 (also called 40 gauge) is as fine as human hair. AWG 12 is 2mm or .081" diameter. Some wire is classified as solid, because it contains one strand per conductor. Other wire is called stranded, because it consists of many strands per conductor. Stranded wire is far more flexible than solid wire. Most wire is made from drawn copper. Some wire is sold that is claimed to be made with a process that produces oxygen-free copper. Oxygen-free copper has a different metallurgical structure than common copper and may or may not conduct current better.

Some critical listeners have reported excellent sound from large diameter solid copper wire, such as home wiring "Romex 12-2". At least one expert has said that common 18-gauge solid copper hook-up wire sold by Radio Shack also works very well. Also recommended on a budget is Sound King wire, a 12 gauge oxygen free copper stranded cable. This is available from MCM Electronics for $.39/ft.

Scientifically, thinner wire has more resistance than fatter wire, so fatter wire will have less resistance-related effects. Resistance effects can be eliminated by using at least 12 gauge wire, particularly for long runs. Of course, shorter runs are always preferred, because they come much closer to the ideal zero-length wire, with no resistance, no capacitance, no inductance, and no change in signal.


16.4 What can I use for budget speaker connectors?
The worst connectors are push-down, or spring terminals. Screw terminals with solid copper wire are much better. Gold-plated binding posts and gold spade lugs are inexpensive by audiophile standards and are extremely stable. Binding posts with spade lugs can be tightened to get a very good mechanical joint, and may offer the lowest electrical resistance of any connector.

Gold plated banana plugs and jacks are very good speaker terminals. Good ones are more expensive than gold spade lugs, however, they also provide a bigger area of contact, and are more convenient when you must frequently reconfigure the system. Banana plugs should be periodically monitored for corrosion and loss of spring tension. Monster offers a banana-plug connector with an expanding center pin that forms an even better connection than common gold banana plugs. At approximately $25 per pair, the Monster banana plugs aren't a budget connector.

All else equal, connectors with gold surfaces are better than connectors with any other surface. This is for two reasons. First, gold is extremely inert, meaning that unless gold is exposed to very harsh chemicals or harsh vapors, it will not corrode or oxidize. It will remain a pure, low-resistance conductor. Second, gold is quite soft, so that if a gold-plated connector is squeezed between two metal surfaces, it will deform slightly to fill scratches and voids, giving a very broad, low-resistance contact area.

Corrosion of connectors is often a problem. Gold-plated terminals and connectors somewhat avoid this problem; problems with other connectors can be mitigated by unplugging and replugging the connector on a regular basis, cleaning the contact areas with a pencil eraser, or by using a contact enhancer such as Cramolin or Tweek. When you use a contact enhancer, be very sure to follow the directions, and avoid spreading enhancer about your equipment.


16.5 What about interconnects, such as the cable between tuner and amp?
Line-level interconnects conduct smaller signals than speaker cables; the typical signal ranges from -2V to +2V (the CD output standard) with currents in the microamps (the corresponding values for speaker cables attached to a largish power amp might be -70V to +70V and currents of many amps). Line-level interconnects can be divided into single-ended (or unbalanced), and balanced interconnects. Home audio is almost always single-ended interconnects.

Single-ended interconnects almost always use a form of the RCA connector (or phono plug). RCA plugs form fair to poor connections that degrade with time as corrosion works into the metal-metal contact and as the spring tension of the connectors relax. Gold-plating reduces the effect of corrosion and locking RCA connectors solve most of the mechanical problems. However, these premium phono connectors are rare and expensive. For example, a gold-plated Vampire locking RCA plug costs approximately $23/pair. If RCA connectors weren't a de facto standard, we'd recommend against them.

Unbalanced interconnect wires vary in geometry, material and price. Cheaper wires have a single conductor (normally stranded) and a shield and cost $.20-$2/ft. Medium (complexity and price) wires have two conductors (often arranged as a twisted pair) surrounded by a shield and cost from about $3-$20/ft. Exotic wires have all sorts of geometries and materials (such as stranded silver conductors, or ribbon cable braided around a core, or in one extreme case, a tube filled with mercury!). Prices may be as high as $200-$300/ft.

Balanced interconnects have three conductors: two for the signal one for ground, and additionally a shield. The standard connector for balanced cable is the ITT/Cannon XLR connector, which is quite good mechanically (they lock). Equivalent connectors are also available from Switchcraft, Neutrik, and other vendors. If you have to run cables longer than 12 feet or 4 meters, the greater noise immunity of balanced interconnects is often a good idea. For this reason, balanced connectors are standard equipment in professional installations such as studios, public address systems, and broadcast stations. There is not much variation in balanced cables. The three brands mentioned above are known to be rugged, high quality and moderately priced. Slightly weaker imported connectors are available, but they aren't dramatically cheaper. Better connectors are also easier to assemble and have a more durable cord strain-relief.

For most systems, the most important aspect of a cable are the mechanical reliability of the connectors; in particular, the joint between connector and wire, and the joint between connector and socket. Typically, interconnect cables are short. It is worth getting just the right length; cables often come in .5 meter increments. With quite good systems, some people observe differences in sound between various interconnects. This is quite system-specific and the same advice as given above applies: try several brands. Most good dealers will loan interconnects for home evaluation.

In cables where the shield does not carry the signal or ground, the shield is normally only connected to ground at one end. In systems where there are significant differences between ground levels on various components, it may make a difference which way such cables are connected. Typically, the end where the shield is grounded should be at the source of the signal. Often, such cable has arrows on it pointing in the direction of the signal flow. In any case, try both orientations.

There are many objective reasons why cables might cause differences in sound by interacting with the drivers in the signal sources as well as by providing non-linear effects in the RCA connector. Most of these effects are again related to interconductor capacitance and resistance, and the quality of the shielding provided by the "shield" conductor. In balanced cables the quality of the "twisted pair" inside the shield is also important. One might note that a shield protects from only capacitively coupled interference, and not from any magnetic field interference. The twisted pair in a balanced line provide some magnetic rejection, as does steel conduit. However, steel conduit has other characteristics which make it undesirable for audio in general.


16.6 What about Phono Interconnects:
Phono interconnects are part of the link between a cartridge on a turntable and a preamp (or head amp or receiver). They are a special case of line-level interconnects because the signal is much lower, typically 1 to 50 millivolts. They are also intended to operate into a higher impedance, typically 47K ohms, and form part of the capacitive load for the cartridge.

The low signal levels mean that the shielding of the cable, and the presence of a separate drain/shield are more important, as is a good ground. A separate solid ground should come along with the cable as a separate lead co-routed with the cable.

In addition, the low signal levels make a good solid connection to and through the connectors MUCH more important, because of the greater sensitivity to low-level nonlinearities.

Wire capacitance is often ignored in line-level interconnects; however, in a phono interconnect, it may constitute half of the total capacitive load of the cartridge. Obviously, then, two cables with significantly different capacitances should sound differently. In this sense, the "right" cable for one cartridge may be too low or high in capacitance for another cartridge.

For low-impedance cartridges (most moving coil cartridges), the wire must have low resistance to prevent cartridge unloading and frequency-dependent signal loss. In addition, as the signal levels are quite low, shielding is important.

Unfortunately, copper shields do not block stray magnetic fields, so in the case of phono cables, careful routing may be even more effective at reducing hum than special wire.


16.7 Is there really a difference in digital interconnects?
There are now three kinds of digital interconnects that connect transports to D/A converters: coax, plastic fiber (Toslink) and glass fiber (AT&T ST). In theory, these should sound EXACTLY the same (bits are bits). However, this assumes good circuit design (in particular, the clock recovery circuits of the DAC, and careful consideration of electronic noise) which may be compromised because of cost considerations or ignorance. Note: different signaling schemes are used on plastic and glass fiber.

In any case, some people claim to hear a difference; of those who do, most seem to prefer the glass fiber. However, the technology of fast digital data transmission in consumer electronics is evolving very quickly now. Any specific recommendation should be treated with suspicion until the industry matures.


16.8 Can I make very good interconnects myself?
Yes. You will need to be the judge of whether or not they are as good as $100 interconnects, but it is easy to make interconnects that are better than the $2.00 set which comes with new equipment.

There are two necessary ingredients: two-conductor shielded cable and RCA connectors. There is a lot of debate over what is the best cable, but in general, the lower the capacitance per foot, the better. Choice of insulation is harder. There may be an advantage to polypropylene or teflon over polyester or rubber, but even that is debatable. If you are buying wire from an electronics distributor, some have successfully used Belden 1192A microphone cable. It is rubber insulated, so very flexible. Another recommended cable is Belden 8451. This is a polypropylene cable with foil shield. Finally, consider Belden 89182. This is foamed teflon insulated, so very low capacitance, and foil shielded. If you plan to make a long cable, this low capacitance cable may be the best choice.

There is also a variety of RCA connectors available. A good connector would be gold plated and machined to tight tolerances. A poorer connector will not fit as well, will make poorer contact as the connecting surface oxides, and will lose its springiness with use.

When wiring the cable to the connector, use one wire for signal, (the tip of the RCA connector) and one wire for ground (the shell or outer conductor of the RCA connector).

Some cables use a foil shield which is difficult to solder. These cables typically have a drain wire parallel to the foil which can be used for soldering. Others use a braided shield.

Regardless of which type of wire you have, connect the shield or the shield drain wire to ground on only ONE SIDE. This will stop noise picked up by the shield from causing ground noise.

It can be a touchy job soldering RCA connectors. Before you use your new cables, check with an ohmmeter or a continuity tester to make sure that you have not accidentally sorted the signal and ground leads together, either with a stray drop of solder or a loose wire strand.


Back to main index - Continue to 17.0 The Press

9.0 Speakers:
9.1 What should I listen to when evaluating speakers?
9.2 What should I listen for when evaluating speakers?
9.3 Why use a subwoofer? Will it help? One or two?
9.4 How do you connect a subwoofer to a stereo?
9.5 What do I need for surround sound?
9.6 GREAT speakers for LOW price.
9.7 What speakers should I consider in the $XXX/pair price range?
9.8 Can you build better speakers than you can buy?
9.9 Where can I read more about speaker building?
9.10 Where can I buy speaker drivers?
9.11 Where can I buy loudspeaker kits?
9.12 How can I improve the sound of my speakers?
9.13 How can I replace/re-cone my old speakers?
9.14 What computer programs can I use to design speakers?
9.15 Can I magnetically shield my speakers for use near a TV?
9.16 What are all of these abbreviations people use for speakers?
9.17 What are fluid-filled (fluid-cooled, ferro-fluid) tweeters?
9.18 Should I use spikes under my speakers? Pennies under the spikes?
9.19 How do you couple speakers to speaker stands?
9.20 What is a Sealed, Ported, Bass Reflex, Acoustic Suspension, Bandpass, and Coupled Cavity Speaker? Which is better?
9.21 What is the best material to make speaker boxes out of? Why?
9.21b What is the best "stuff" to fill a speaker cabinet with?
9.22 What size fuse or circuit breaker should I put in my speaker to protect it from damage?

9.1 What should I listen to when evaluating speakers?
The most important thing is to listen to recordings that you *know*. Any good salesman will play you recordings that highlight that particular speaker. Do not be embarrassed about bringing a stack of CDs with you to the hi-fi shop.

Do not spend your valuable listening time switching between a dozen pairs every 3 seconds. If you are shopping at a quality store, the dealer will, from the description of your room, your size requirements, your musical tastes, and your budget, be able to show you a couple of pairs that will be close to what you want. Spend several minutes listening to each. When you think you're close, don't be embarrassed about spending half an hour or more listening to the speakers. You're going to have them in your home for a lot longer, and many speakers will cause "listening fatigue" after a short time. Make sure you really like them before you hand over money.

One thing to try is well recorded "Spoken Word" records; most people have a very good ability to tell when a speaking voice sounds unnatural, even if they've never heard the person speaking live. If you play an acoustic instrument, find something that features that instrument solo, or in a small group; make sure it really sounds like it should. Almost everyone has heard a live piano. Piano can be very revealing.

Blues, jazz, folk, or 'easy listening' music with simple instruments and a female vocalist is also revealing. Well done female singing voices provide a very good test of a system's response. Try something simple and soft, which will let you hear any noises coming from the system; and something complex, with lots of instruments all happening at once, to make sure the system doesn't go muddy when things get complicated. And, of course, try a few of your favorites, and see if you like what happens with them.

If a sales person suggests some music to listen to, the odds are that it isn't the most revealing. Sales people tend to suggest things which sound great. Anything you own and like is good, because you know it and are happy to listen to it carefully. No matter how good the recording, if you don't like Opera, you won't listen to it as carefully as your favorite, scratchy, 1940's rhythm and blues.

Most important is to listen to something you are familiar with. Even if a recording is flawed (and what ones aren't?), how is it different from your normal setup? Some of the most important differences are "Gee, I never heard that instrument before!"


9.2 What should I listen for when evaluating speakers?
When comparing two speakers side-by-side, doing an AB comparison, be extremely careful to match the levels before evaluating. A slight level difference can make one speaker sound better, even though the difference may not be perceived as a level difference. Some claim that you will be influenced by a difference of less than 1/2 dB!

First and foremost, the sound should be natural. If you listen to vocals, close your eyes and try to picture someone singing in the same room with you. Does it sound realistic? Likewise with instruments. You selected recordings of instruments that you like and have heard live. Do they sound like what you remember them sounding like live?

Your very first impression should be something like "what nice sound". If your initial gut reaction is "gosh, what a lot of detail", the system is likely to be heavy in the treble (often interpreted by beginners as "more detailed") and you'll probably find that annoying after a while. If your first reaction is "hey, what powerful bass", then the system is probably bass-heavy, rather than ideal. The most common mistake for beginners is to buy a system with REALLY powerful bass, because it sounds "impressive" at first. After a while, though, you'll get tired of being thumped on the head by your music.

Not to say that good bass and treble aren't important. But your first realization should be that the music is all there, and that it comes together as good music, without one particular part trying to dominate it. Sit back and listen to it for a bit. You should be able to pick out the individual instruments if you want. They shouldn't force themselves on you, and you should also be able to hear the music as a single piece, the sum of its parts, without feeling like each of the instruments is trying to grab your attention away from the others.

You should check how things sound with the amp turned up, and also with it turned down to a fairly low volume level. Some speakers which sound very nice at low levels begin to sound confused, like they can't cope, when turned up. On the other hand, some sound nice loud, but sound thin and bodiless when you turn them down a bit. With the spoken word or female vocalist, listen for "sibilance", a pronounced 'hiss' at the end of 's' and 'z' sounds. It shouldn't be there. Most planar speakers just can't play very loud. Whatever you hear, do some auditioning at the maximum volume you anticipate ever wanting.

It is acceptable and sometimes desirable to switch the stereo to mono to evaluate naturalness. Mono is a good test of both the room and the speakers. The image should be rock-solid dead center, and not move with signal or level. If it isn't perfect mono, it will be nearly impossible to create a good stereo.

A speaker in a large box is capable of producing low frequencies at higher volumes with more efficiency than a small box, but that doesn't mean that a small box can't have great bass, it just won't be as efficient and can't play as loud.

Good speakers can "recreate a natural stereo sound stage", placing some instruments to the left of the left speaker, some sounds in the middle, and some to the right of the right speaker. Poorer speakers make it harder to localize voices.


9.3 Why use a subwoofer? Will it help? One or two?
One reason to get a subwoofer is to add bass to a feeble system. A second reason is to move the lowest frequencies to a separate driver, and thereby reduce a particular kind of distortion caused by the nonlinear mixing of different sounds, called "intermodulation distortion". A third is to increase the power handling ability of the system and the overall reliability. All are valid reasons, but it isn't so simple.

To improve the sound of a good speaker system, a subwoofer must "integrate smoothly" into the system, extending the bass without causing peaks or dips. Many subwoofers have a crossover that goes between your amp and your main speaker which sends the lows to the subwoofer and sends the higher frequency signals to the main speakers. This may damage the perfect sound of a good system, it may sound similar, or it may sound better.

Most good small speaker systems have a bass peak at resonance, which attempts to compensate for the absence of lower bass. Like it or not, this is the only way to make a small system sound realistic. If the small system is done well, the improvement you will get from a subwoofer will be small, but still real and, to many, significant.

Correctly done, a good subwoofer will enhance the sound of a good small-box system. Done wrong or haphazardly, anything is possible. Even a fine large speaker system might benefit from careful addition of a subwoofer. However, the better the original system, the more likely it will be that a modest subwoofer will do more harm than good.

Low frequencies travel less directionally than high frequencies, so many people say that only one subwoofer is required for good sound. This is true to some extent, but not completely true.

There are a few reasons for getting two subwoofers. Some feel that you need two subwoofers to accurately reproduce the stereo image, no matter how little low-frequency stereo information there is. Others feel that two subwoofers are much easier to set up in a room, less likely to excite standing waves in the room, and give smoother sound.

A third reason is that two subwoofers can produce twice the sound of one. Finally, even though subwoofers produce very low frequency sound and very low frequency sound is non-directional, subwoofers also have output at 100 Hz, and sound at 100 Hz is directional, so two subwoofers will give a slightly better stereo image than one. Assuming, of course, that the two are separated by at least two feet.

Finally, even though original source signals rarely contain any music with stereo components below 50Hz, there may be some noise component with low-frequency out-of-phase noise. This unusual noise might add a sense of space to a recording if it is reproduced by a system in which the woofers are very far apart.

It is still true that a single good subwoofer, correctly added to a system will help the sound but two will probably help more.


9.4 How do you connect a subwoofer to a stereo?
Many subwoofers contain their own amplifier and crossover. For these, take the preamp output and feed it into the subwoofer amp input and also into the main amplifier.

For other subwoofers, just run them in parallel with your main speakers, or combine them into your system with your own bass amplifier and crossover.

Some A/V receivers contain a splitter specifically for use with subwoofers. If you have one of these, you will either want a separate amplifier for your subwoofer or an amplified subwoofer.

Consult the manual which comes with the subwoofer.


9.5 What do I need for surround sound?
"Surround Sound" has referred to a number of different products over the years. Many mass-fi receivers have "Surround Sound" buttons that do little more than muck up the imaging.

In recent years the term "Surround Sound" has become synonymous with the surround systems produced by Dolby Laboratories. Dolby Surround comes in several flavors, such as passive surround (which simply decodes the phase information and sends it to the rear speakers) and the more advanced system called Pro Logic. Pro Logic system uses computer circuitry to route directional information to the appropriate speakers.

Generally, one needs at least two more speakers beyond the main stereo pair. Advanced Pro Logic systems such as the Lexicon and Fosgate can accommodate several more speakers beyond the two additional ones (usually placed in the rear). Often one can find Pro Logic systems with two front, two rear, two side, as well as a center channel speaker for dialogue.


9.6 GREAT speakers for LOW price.
I was just approached (accosted?) by a couple of kids driving a van that said they had some GREAT speakers to sell. They are overstocks, used by major recording studios and DJs or even hot, and they normally sell for $1000/pr, but they'll let me have them for just $399. Am I getting ripped off?

Yes, you most certainly are. The speakers these people sell are none of what they describe. They are never used in studios. There might be one or two DJs out there that use them because they can't afford anything else. They are not overstocks, and in all likelihood, they are NOT HOT!.

Are they good speakers? No, they're, at best, no better than the big boom boxes you find in $400 rack systems in department stores. They are worth no more than what the kids paid for them ($100/pr).

The speakers go under names like "Acoustic Monitor DB IV", "Acoustic Linear", "Pro-Poly", "Audio Reference 4350" and so on. They all "feature" things like "liquid cooled 3" tweeter", poly-cone 12" woofer, fantastic (but impossible) frequency response, 98 db/watt sensitivity, and so on. The brand names are remarkably similar to reputable firms, but different enough to delay law suits.

These speaker are made by a couple of manufacturers with the intent of being sold exactly this way. They cost the kids in the van about US $100 a pair, and the kids are given minimal training about what kinds of stories to use, what parking lots are the most likely to generate sales (department store parking lots near colleges in September is a great time for these guys). Anything over the US $100 the kids paid is pure profit.

Stay away, you're getting ripped off.


9.7 What speakers should I consider in the $XXX/pair price range?
This is probably the most commonly asked question on rec.audio, and also the most impossible to answer. The market keeps changing, everyone has different tastes, and no one has the time to listen to even 10% of the products available in any country. Also, many good products are only available in specific regions or countries.

If you really want recommendations and are willing to listen to the opinions of others, check the past few issues of Stereophile Magazine. Although they are strongly biased towards very expensive gear and have their own particular other biases, they do steer you to some very good equipment in their frequently-updated list of "RECOMMENDED COMPONENTS".


9.8 Can you build better speakers than you can buy?
Some people can build better than you can buy. These people are either experts, golden ears, extremely well equipped, inspired, or a combination of the above.

Some companies have plans available to entice you into buying their drivers: Audio Concepts, Audax, Dynaudio, Focal, KEF, and Scanspeak. Your success rate with these plans will probably be very good IF your cabinetry skills are very good and IF you follow the plans precisely. If you deviate (as everyone does), anything is possible.

Stereophile has published three different plans designed by Dick Olsher which are similar two-way ported systems. A recent one of these was in Stereophile Nov '90, pages 94-127. Audio Magazine published a plan called "The Pitts" by Ken Kantor, in Audio, Nov '88 pages 65-71 continued in Dec '88 pages 73-77. This plan is a two-way sealed box.

I have built one published design and one manufacturer's design. I believe that both met my expectations. They took me a long time to build, taught me a lot, were fun projects, and sounded good when finished.

I also believe that a commercial system which cost what my parts cost will never sound anywhere near as good as the one I build. If you consider $2/hour for my time, however, building is financial suicide.

Designing your own system is even more a can-of-worms, and should be left to those with either a strong stomach, a very forgiving ear, infinite resources, or excellent guidance.


9.9 Where can I read more about speaker building?
   Europe's Greatest Speaker Designs
           Solen Electronique
           4470 Avenue Thibault
           St.-Hubert, QC J3Y 7T9 Canada
           Voice 514-656-2759
           FAX 514 443-4949
   High Performance Loudspeakers by Martin Colloms
   Speaker Builder Magazine
           Audio Amateur Publications
           PO Box 494
           Peterborough NH 03458 USA
           603-924-9464
   Synergetic Audio Concepts Classes and Newsletters
           Syn-Aud-Con teaches classes on Audio and Acoustics
           12370 W. Co. Rd. 100 N.
           Norman IN 47264 USA
           812-995-8212
   The Loudspeaker Design Cookbook, Fourth Edition
           by Vance Dickason (C) 1991
           ISBN 0-9624-191-7-6
           $29.95 + $2.00 S&H from
                   Old Colony Sound Lab
                   PO Box 243
                   Peterborough NH 03458-0243 USA
                   603-924-9464
           $25 + $2 S&H (sale price as of 3/24/94) from
                   Madisound
                   8608 University Green; Box 4283
                   Madison WI 53711 USA
                   608-831-3433

9.10 Where can I buy speaker drivers?
        A & S Speakers (Broad line)
                3170 23rd Street
                San Francisco CA 94110 USA
                415-641-4573
        Audio Concepts (Their own kits plus drivers)
                901 South 4th Street
                LaCrosse WI 54602 USA
                800-346-9183 or 608-784-4570
        Phil Baker (Surplus cabinets only)
                546 Boston Avenue
                Medford MA 02155
        Bandor Design & Development Studios (Aluminium coned speakers)
                11 Penfold Cottages
                Penfold Lane
                Holmer Green
                Bucks, HP15 6XR  United Kingdom
                Tel. (0494) 714085
        DBS Audio (Speaker kits and crossovers)
                PO Box 91, Bury St.
                Edmunds, Suffolk, IP30 0NF  United Kingdom
                Tel (0284) 828926
        Drexler Audio Systems (Bandor Speaker Distributor)
                14 Rose Lane
                Rosemont PA 19010
        Falcon Electronics (Drivers and cross overs)
                Tabor House
                Mulbarton
                Norfolk, NR14 8JT  United Kingdom
                Tel. (0508) 78272
        Faraday Sound (Concrete loudspeaker cabinets)
                248 Hall Road
                Norwich, NR1 2PW  United Kingdom
                Tel. (0603) 762967
        Gold Sound (Broad line including pro speakers)
                PO Box 141
                Englewood CO 80151 USA
                303-789-5310
        Madisound (Broad line)
                8608 University Green
                Box 4283
                Madison WI 53711 USA
                608-831-3433
        Meniscus
                2442 28th Street SW Ste D
                Wyoming MI 49509 USA
                616-534-9121
        Parts Express
                340 East First Street
                Dayton OH 45402-1257 USA
                513-222-0173
        Solen Electronique (Airborne, Audax, Ceratech,
                Dynaudio, Eton, Lpg, Morel, Peerless,
                Scan-Speak, Seas, Solen, Vifa)
                4470 Avenue Thibault
                St.-Hubert, QC J3Y 7T9 Canada
                Voice 514-656-2759
                FAX 514 443-4949
        The Speaker Co (Large range of drive units plus speaker kits)
                Unit 9, Waterside Mill
                Waterside, Macclesfield, SK11 7HG. United Kingdom
                Tel. (0625) 500507
        Speakers Etc.
                1828 West Peoria Avenue
                Phoneix AZ 85029 USA
                602-944-1878
        SRS Enterprises (Pyle, Pioneer)
                318 South Wahsatch Avenue
                Colorado Springs CO 80903 USA
                719-475-2545
        Wilmslow Audio (Kits and drive units. KEF, Dynaudio, Audax, SEAS,
                        Peerless, Scanspeak, Morel)
                Wellington Close
                Parkgate Trading Estate
                Knutsford, Cheshire, WA16 8DX  United Kingdom
                Tel (0565) 650605
        Zalytron (Broad line including kits)
                469 Jericho Turnpike
                Mineola NY 11501 USA
                516-747-3515

9.11 Where can I buy loudspeaker kits?
        Audiocab (Speaker kits and cabinets)
                9 Skewbridge Close
                Wooten Bassett, Swindon, SN4 7DW  United Kingdom
                Tel (0793) 848437
        Audio Concepts, Inc. (Wide range of kits. Catalog available)
                (see 9.10, above)
        Fried Products (Parts kits starting $550. Catalog available)
                (Emphasizes high-end transmission line speakers)
                (Parts kits have plan, crossover, and driver)
                1323 Conshocken Road
                Norristown, PA  19401 USA
                610-277-1014 or 800-255-1014
        IPL Acoustics (Kits using SEAS, Morel, Audax, and Visaton)
                2 Laverton Road
                Westbury, Wiltshire, BA13 BRS  United Kingdom
                Tel (0373) 823333

        Mahogany Sound (Parts kits and Woodstyle kits)
                (Parts kits have plan, crossover, and driver)
                (Woodstyle kits also have 3/4" MDF veneered boxes)
                (Prices $150/pair to $500/pair. Catalog available)
                (Two way, three way & subwoofer kits)
                2610 Schillingers Rd #488
                Mobile AL 36695 USA
                205-633-2054
        Tabula Rasa (Wide range of speaker kits)
                1 Silkin Dalton Close
                Broadfield, Crawley
                W. Sussex, RH11 9JD United Kingdom
                Tel. (0293) 531190

Also see above, under suppliers for speaker drivers.


9.12 How can I improve the sound of my speakers?
The best way to change the sound of your speakers is to change where you put them. Ideally, the speakers should be located at ear level, in front of you, squared off between you. It's then a matter of fiddling with a) the angles, b) the distance apart, c) the distance from you, and d) the distance from the wall. Just moving the speakers around in the room or putting them onto stands can make a major difference. For more on speaker placement, see 13.1 below.

Other than that, speaker modifications can be a can of worms, or can produce very subtle changes, which you might prefer. For example, you might improve a speaker by adding some cross braces of 1"x1" wood from left to right and from front to back. This will stiffen the cabinet and reduce speaker cabinet wall vibrations, which probably hurt sound quality. Alas, this will be most effective with lower-cost and poorly built speakers.

Along similar lines, some claim success putting lead wire or epoxy putty on thin parts of the speaker to damp out resonances. You can try doing this to the thinner parts of the speaker "basket" or frame, or to the front "baffle" or supporting panel.

Still another "tweak" is to add sound deadening felt pads to the inside walls of the speaker. Instead of felt pads some advocate sand-filled latex coatings on the inside walls of speakers. Others advocate ceramic tiles held in place with "thinset". Still others rave about commercial products like AC Glop, Acoustic Magic, and Bostik Sheet. However, the people who rave about these products tend to be the same people who sell them.

Any change along the lines of adding felt, cross-bracing, or putty will have subtle effects on the sound.

For the brave at heart, you can replace old or cheap drivers with better ones, but the results of this one change can be very dissatisfying if you happen to get the wrong type of driver for that application, and may never sound right, even if you use a similar driver. Speaker system design is still somewhat of a science and somewhat of an art. Throwing paint on a canvas often makes a mess.

Whatever change you try, don't "burn your bridge" home. Be sure that you can undo whatever change you did, just in case. Many tweaks to good speakers, no matter how well thought through, will correct for one flaw, but create others, or correct a flaw that the designer had cleverly used to his advantage.


9.13 How can I replace/re-cone my old speakers?
The best chance of success is to buy an identical replacement speaker driver from the manufacturer of the system.

Second choice is to buy the exact same driver from a distributor. This is sometimes difficult because it is hard to learn exactly what driver the manufacturer used. In addition, EVEN IF the manufacturer used stock speakers, they might have used matched pairs or selected speakers by hand for an exact set of specific characteristics.

There are companies that rebuild drivers, but they charge quite a bit. I have heard $75 per driver. This is rarely done for anything but very expensive commercial drivers. Speaker manufacturers will often sell owners the materials that they need to repair a speaker. If you are handy with delicate things, it is worth a try.

In addition to speaker manufacturers, there are companies which sells rebuild kits for approximately $30 per pair, containing new foam, a special glue, and instructions. If you have a blown or distorted voice coil, this still won't help. A few netters have used rebuild kits from this company successfully. Contact:

                Stepp Audio Technologies
                PO Box 1088
                Flat Rock NC 38731 USA
                800-747-3692

Two other vendors of speaker repair parts are:

                Parts Express (sells 8", 10", 12",
                & 15" repair kits)
                340 E First St
                Dayton OH  45402-1257 USA
                513-222-0173

                Simply Speakers
                P. O. Box 22673
                St. Petersburg FL 33742 USA
                800-767-4041 or 813-571-1245

Some speaker manufacturers have very good warranties. Electro-Voice warranties all professional products for life. KEF has a similarly broad warranty on their speakers. Contact the manufacturer first.


9.14 What computer programs can I use to design speakers?
There are many useful programs available, but none are complete without a good knowledge of speaker design. Further, you will NEED to supplement any program with hand tweaking for the best sound. Finally, no simulation program is ever useful without good model parameters, and the parameters which manufacturers give you are often imperfect, so many good designers strongly recommend your own lab measurements. The Loudspeaker Design Cookbook (see 9.9) tells you how to measure a speaker, and also gives enough theory to feel confident with a good program. You can get a lot done with a simple spreadsheet and the equations in a book like The Loudspeaker Design Cookbook.

For more information on programs for speaker design and on speaker-design hardware, such as measurement systems, get the archive "sahfsd02.doc" from directory:
usenet/rec.audio.high-end/Software on "ftp.uu.net ". In addition, there are other interesting audio-related files in that directory. Look around.


9.15 Can I magnetically shield my speakers for use near a TV?
You probably will need to buy speakers that are made with an integral magnetic shield. Magnetic shielding is usually done by either shielding the speaker magnet or by cancellation of the magnetic field very close to the magnet, or by both. Shielded speakers are NOT built by lining the enclosure with metal. While it sounds like a good idea, it doesn't work.

A common magnet shield is a mild steel cup around the magnet. This is the cheapest shield, and is usually fairly ineffective. It also will interfere with the speaker's critical magnet gap, so this type of shield can hurt speaker performance by shorting the magnetic field and reducing the magnetic flux density in the gap, which can reduce efficiency and affect the speaker's low frequency performance.

Cancellation is done using a reverse-polarized magnet glued to the back of the main magnet. If done right, it can almost completely cancel the rear stray field. In some cases it can also increase the magnetic flux density in the gap, which may or may not be desirable.


9.16 What are all of these abbreviations people use for speakers?
Most of these parameters are well documented in the Loudspeaker Design Cookbook. (see 9.9) In summary:

Fs  Driver free air resonance, in Hz. This is the point at
     which driver impedance is maximum.
Fc  System resonance (usually for sealed box systems), in Hz
Fb  Enclosure resonance (usually for reflex systems), in Hz
F3  -3 dB cutoff frequency, in Hz

Vas  "Equivalent volume of compliance", this is a volume of
        air whose compliance is the same as a driver's
        acoustical compliance Cms (q.v.), in cubic meters

D   Effective diameter of driver, in meters
Sd  Effective piston radiating area of driver in square meters
Xmax Maximum peak linear excursion of driver, in meters
Vd  Maximum linear volume of displacement of the driver
        (product of Sd times Xmax), in cubic meters.

Re  Driver DC resistance (voice coil, mainly), in ohms
Rg  Amplifier source resistance (includes leads, crossover,
        etc.), in ohms

Qms  The driver's Q at resonance (Fs), due to mechanical
        losses; dimensionless
Qes  The driver's Q at resonance (Fs), due to electrical
        losses; dimensionless
Qts  The driver's Q at resonance (Fs), due to all losses;
        dimensionless
Qmc  The system's Q at resonance (Fc), due to mechanical
        losses; dimensionless
Qec  The system's Q at resonance (Fc), due to electrical
        losses; dimensionless
Qtc  The system's Q at resonance (Fc), due to all losses;
        dimensionless

n0  The reference efficiency of the system (eta sub 0)
       dimensionless, usually expressed as %

Cms  The driver's mechanical compliance (reciprocal of
        stiffness), in m/N
Mms  The driver's effective mechanical mass (including air
        load), in kg
Rms  The driver's mechanical losses, in kg/s

Cas  Acoustical equivalent of Cms
Mas  Acoustical equivalent of Mms
Ras  Acoustical equivalent of Rms

Cmes The electrical capacitive equivalent of Mms, in farads
Lces The electrical inductive equivalent of Cms, in henries
Res  The electrical resistave equivalent of Rms, in ohms

B   Magnetic flux density in gap, in Tesla
l   length of wire immersed in magnetic field, in meters
Bl  Electro-magnetic force factor, can be expressed in
        Tesla-meters or, preferably, in meters/Newton

Pa  Acoustical power
Pe  Electrical power

c   propogation velocity of sound at STP, approx. 342 m/s
p   (rho) density of air at STP 1.18 kg/m^3

9.17 What are fluid-filled (fluid-cooled, ferro-fluid) tweeters?
These tweeters are built almost exactly the same as other tweeters. They look and act almost exactly the same, too. The only difference is that they have a small, controlled amount of a special fluid inserted into the gap between the magnet and the voice coil.

One big effect of adding this fluid to a tweeter (or to any speaker) is that it makes the voice coil capable of dissipating more heat. This means that the speaker can have a lighter voice coil, for better performance, or a higher power rating for the same voice coil. The other big effect of this fluid is to add mechanical damping. The frequency response and transient response of the driver will change, possibly for the better.

In addition, this fluid may help center the voice coil, may lubricate the voice coil, and may help keep dirt out of the gap. This fluid will not increase the magnetic field, concentrate the magnetic field or otherwise change the magnetic circuit. Nor will it cushion impact if the voice coil bottoms.

The fluid used for this purpose is often called "ferrofluid". It consists of sub-microscopic particles of magnetic material suspended in special oil. This fluid stays in the gap because of the strong magnetic pull of the magnet. There is some debate over whether these fluids can dry out with time. Manufacturers claim that the oil used is non-volatile.

It is possible to use ferrofluids in mid-range drivers and woofers. However, as tweeters tend to have the most fragile voice coils, tweeters have the most to gain from ferrofluid. There are various different fluids on the market, some of which have characteristics tailored to tweeters, some to woofers, etc.

It is very risky to blindly add fluid to a driver. It may not be compatible with the adhesives used in the driver, may not be practical with the particular driver layout, and is impossible to remove. Permanent driver damage is possible.


9.18 Should I use spikes under my speakers? Pennies under the spikes?
| Spikes prevent speakers from rocking. They also couple the speaker directly to the floor. Spikes will pierce carpet. Some spikes will damage carpet. Most will just put a small hole in the carpet which is invisible. Putting a heavy speaker directly on carpet will cause a permanent mark on the carpet. Spikes can prevent this.

If you have a pretty hardwood floor, then spikes will definitely damage the finish. A rigid disc under the spike will distribute the load and lessen the damage. Any coin should work fine. Using a coin will not change the speaker/floor interaction. Do not use a coin with a carpeted floor. Alternatives to spikes for wood floors are Blu-Tack and similar products. (see 9.19)

If your floor is extremely rigid, then the spikes will make the speaker more rigid. If the floor is more conventional, such as a suspended floor or a wooden floor over joists, spikes can have a positive or negative effect, depending on the resonant characteristics of the floor/speaker system.

The counterforce resulting from a forward cone motion in a speaker may try to move the speaker backwards, but spikes will have little or no effect on this. Most audible effects from spikes are due to coupling the speaker to the floor, so it will be less likely to resonate on its stand. Some argue that in most cases, spikes will have no audible effect at all. Try it for yourself.


9.19 How do you couple speakers to speaker stands?
Ideally, your speakers should sit flat on the speaker stand or floor. They shouldn't see-saw back and forth if nudged.

One good way to accomplish this is to use a small dab of putty under each corner of the speaker. There are a few common putties used for this, but all share the properties of being very elastic and staying flexible indefinitely. These putties are inexpensive, removable, and reusable.

| Try either Blu-Tak, which is available in the UK from office supply stores for cleaning typewriter elements, Faber Castell UHU Hold-It, which is available in the US from office supply stores for holding up pictures, and DAP's Fun-Tak, which is sold in hardware stores for holding up pictures, or Pritt Buddies..

9.20 What is a Sealed, Ported, Bass Reflex, Acoustic Suspension, Bandpass, and Coupled Cavity Speaker? Which is better?
All are "direct radiator" enclosures, so called because the sound is produced directly from the driver (the "radiator") without the assistance of a contrivance such as a horn.

SEALED BOX:
The simplest direct-radiator system. The rear of the driver sees a sealed enclosure, and none of the rear output of the driver contributes to the sound output. Depending upon how stiff the mechanical suspension is vs how stiff the enclosed air in the enclosure is (and that's a function of the size of the box), you can have either an Infinite Baffle enclosure, in which the mechanical suspension is the dominant source of system stiffness and the box is large; or an Acoustic Suspension enclosures, where the air in the box is the dominating stiffness, and the box is small.

Sealed boxes tend to be the lowest efficiency systems for a given box size and bass cutoff frequency.

VENTED ENCLOSURES:
Also the same as Bass Reflex, Ported, or Passive Radiator. Here, an aperture in the box provides a means for the rear output of the cone to contribute to the total output of the system. However, it only contributes over a very narrow range of frequencies. In fact, in a properly designed system, the front output of the cone is reduced at the same time the output of port increases, so the port DOES NOT ADD to the output of the woofer, it REPLACES the output of the woofer at these frequencies. This, if done properly, can significantly reduce distortion and increase power handling at very low frequencies, a region that can be difficult for drivers.

Vented systems can be up to 3 dB more efficient than a sealed box system that has the same bass cutoff frequency and size.

BANDPASS:
These are compound systems in that they have at least two enclosures: one on the front and one on the rear of the driver. The enclosure on the front, which looks remarkably like a vented box (because it is), acts as a low pass filter, and, can couple the output of the woofer more efficiently to the outside. They have several useful advantages. For example, the front enclosure can be used as a very effective acoustic crossover, filtering out mechanical noises generated by the woofer, something no electronic crossover can do. For very low frequencies, such an acoustic crossover can be far less expensive and more easily designed than an equivalent electronic crossover.

They are called "bandpass" because the combination of the rear enclosure and the driver form the high pass portion while the front enclosure forms the low pass section. Making the bandwidth of the system narrower raises the efficiency of the system.

COUPLED CAVITY:
A variation of bandpass and vented systems, they are the results of a designers attempt to solve specific problems. They consist of two or more rear enclosures, each coupled to the next by a vent. Each enclosure/vent combination is another resonant system, and the combination is, essentially, a high order, multi-tuned resonant system.

Generally, these systems have quite complex response and are difficult to design. No comprehensive theory on their operation exists like that for sealed, vented and bandpass systems.


9.21 What is the best material to make speaker boxes out of? Why?
An ideal speaker cabinet material would be very stiff, so that it would not tend to move with variations in box air pressure. It would also be very well damped, so that if it ever does deflect from air pressure, it will come back to the original position without resonating. It would also have a very high resonant frequency (supersonic), so that low frequency box air pressure would not cause it to resonate. An attractive material is preferred, and additional credit is given for a material which is easy to cut, glue, and finish. A great material would be cheap, too. Finally, it would be nice if the material were light, because we all have to move our speakers sometimes, and it's hard to appreciate good speakers with a sore back.

With all of those attributes, it would seem that no material is perfect. However, there are many materials that have enough of the above good attributes to make excellent speaker cabinets. Yet each has advantages and disadvantages.

In the list of good speaker box materials below, letters are used to indicate which attributes the material possesses.

        S = Stiff
        D = Damped
        H = High Resonance
        A = Attractive
        M = Machinable
        C = Cheap
        L = Light

MEDIUM DENSITY FIBERBOARD (MDF): SDMC This is the most practical material for quality speakers. It is harder to find than plywood, but most lumber yards can special order it. It cuts very nicely and has a smooth surface. It takes veneer very well. However, bring a helper when you pick the stuff up. One sheet is very heavy. MDF is harder on tools than common wood, but easier than particle board. This is the material that many great speaker makers use. US $45 for a 4'x8'x1" sheet. Density: 50 lbs/cu ft.

POLYCARBONATE (LEXAN): DML A clear or solid-color polycarbonate box can look strikingly good. However, this is not a cheap material. To locate it, look in the classified directory under PLASTICS. US $60 for a 1'x1'x1" sheet. Density: 75 lbs/cu ft. Acrylic (Plexiglass) is cheaper than Polycarbonate, but weaker and poorer damped (not recommended).

CORIAN, FOUNTAINHEAD, AVONITE, SURELL, GIBRALTAR: SDA Regardless of the brand, these synthetic countertop materials come in a wide array of colors and look beautiful. They are hard to buy, and harder to work. They take special glue to bond and require wet sanding with very fine paper to finish. You can tap it, but it's too brittle for wood screws. Corian is acrylic mixed with powdered aluminum triwwwte clay filler. Avonite, Gibraltar, and Surell are polyester resin mixed with the same clay filler. US $26 per 1'x1'x0.5". Density: 100 lbs/cu ft.

MARBLE: SDHA One challenge with marble speaker enclosures is cutting holes for the drivers. A carbide bit on a router will work, but it will dull quickly. Marble is also difficult to glue, so bracing is difficult. But it sure is pretty when you're done! US $25 to $45 per 1'x1'x1.25". Density: 160 lbs/cu ft.

PLYWOOD SHEETS SPACED AND FILLED WITH SAND OR LEAD SHOT: SDAMC If you have time on your hands and want a great impractical box, try this. Make a simple box out of common plywood. Then glue cleats on the outside of the box to space the outside plywood from the common plywood. Glue hardwood-veneered plywood to the cleats and pour sand or lead shot into the spaces between the cleats. It won't be light, but with the filler, it will be extremely well damped. In addition, if you use strong cleats and glue well, the box will be extremely stiff. One person used different size Sonotubes as an alternative to plywood, and filled the space between them with sand. Be sure to sterilize the sand in your oven before putting it in the box.

ALUMINUM SHEETS SPACED AND FILLED WITH ALUMINUM HONEYCOMB (Aerolam): SDHL Airplanes use this material for flooring. Next time a plane crashes in your neighborhood, see if you can get the wreckage for your next speaker project. You can't get a better, light-weight material. Celestion has exploited this for some great products. If you're really ambitious, you can make your own sandwich out of high-quality plywood faces and a thick honeycomb core. You will probably need an epoxy to glue the honeycomb to the plywood. A home-brew sandwich is easier to cut and glue than Aerolam.

FORMED CONCRETE: SDHC There are tricks to working concrete, such as to cast braces, rebar, and steel-wire right into the mix. Also, some concrete is better damped than other. Remember to oil your concrete forms so that they can be removed. Most concrete speakers use an MDF front panel, but you can pour one if you use cardboard tubes or plywood rings to mold the concrete into the shape of a speaker cutout. Alternately, you can make a common veneered plywood speaker box and cast concrete inside it for stiffening.

Any box can be improved by making the walls thicker, by bracing the walls, and by stiffening the walls. The stiffness of a material goes up as the cube of the thickness, so a slightly thicker material is much stiffer. A thicker panel will also have a higher resonant frequency because the stiffness goes up faster than the mass.

Consider lining the inside of your speaker with ceramic tile, attached with thinset mortar. You can get tile remnants cheaply. They are easy to apply and can be added as an afterthought to an imperfect box. However, be sure to attach all braces before tiling, because it is hard to attach anything to tile.

Also consider bracing any weak parts of the box. For example, all joints will benefit from a wooden cleat. The back of the box will benefit from stiffeners where the speaker terminals are attached. Most importantly, brace the front panel, or make it out of a double thickness of material.


9.21b What is the best "stuff" to fill a speaker cabinet with?
The following discussion will focus on practical facts on speaker cabinet stuffing and on sealed systems. Theory is limited help in selecting speaker stuffing. Vented system do share a few of these same issues and will also be mentioned, but the goals and physics of stuffing a vented box are different than those of a sealed box.

NHT speakers use polyester fill. Some use a Danish polyester that mimics the properties of fiberglas very closely. Excluding this special poly, there are two kinds of polyester available: pillow stuffing, and audio-spec polyester.

Forget pillow fill. It's cheap and easy to get. If you use enough, it will damp the midrange, and that's a lot better than an empty box. But it has little effect on lower frequencies. Some fabric stores sell "Super Good Stuff" from Stearns Technical Textiles. This is a common, inexpensive material that is said to perform as well as audio-spec polyester.

For lining the walls of a vented enclosure to reduce internal reflections, or filling a transmission line to absorb the back wave, highly absorptive wool or fiberglas are ideal. However, these materials do not provide the desired results in a sealed system. They will provide more reflection absorption than polyester, but the latter is quite good in this regard in the critical midrange. In a sealed system you don't want absorption at lower frequencies anyway; you want damping and isothermal conversion. (Author's note: I have tried "all-out" efforts using fiberglas lining and polyester fill to achieve the best of both worlds. I found little practical benefit over polyester alone.)

Most professional designers agree that practical experience, combined with trial and error is the best way to get optimum stuffing material, quantity, and method for a given design. This is why good designers routinely experiment with fill in the development of a new system. If you are designing a system that differs substantially in shape or volume or source impedance (passive crossover) from one of known reference, you will need to experiment to get best performance.

Adjusting the filling is the last step in getting bass right, and is used mostly to fine-tune the system Qtc and resonance. As increasing amounts of polyester are added to a sealed box, the resonance and Q gradually go down. This can be shown mathematically to be due in roughly equal parts to the effects of simple resistive damping and isothermal conversion. At some point, a minimum is reached, and further material reverses the trend by taking up volume. An experienced designer can find the optimum amount of fill in a few trials by monitoring the impedance versus frequency curve as stuffing is added or removed.

Filling also has the important effect of reducing internal reflections, to reduce standing waves and comb filtering. However, the amount of filling has comparatively little effect on this.


9.22 What size fuse or circuit breaker should I put in my speaker to protect it from damage?
Most modern speakers consist of a box containing more two or more drivers interconnected through a network of inductors, capacitors, and resistors. One fuse or circuit breaker in series with that array can't possible protect all drivers.

Conventional circuit breakers are a very bad choice for speaker protection. They add series resistance, series inductance, and lousy electrical contacts, all tending to degrade performance. Moreover, breakers have a trip characteristic that does not match the damage mechanisms of speakers.

Fuses are a better choice, but still are not very good. This is because speakers have complex thermal behavior. Loud playing will warm up the voice coil making it more sensitive to damage. No fuse takes this into account correctly. A fuse will do a better job of protecting tweeters, but is still not perfect.

If you want to protect a speaker with a fuse, use the lowest current, fast-blow fuse which will not blow during normal listening. This may trip prematurely in a very loud passage, or may degrade sound quality, but it is your best bet for fuse protection. For a woofer, start with a 1 Amp fuse and work up. For a tweeter, start with 100mA and work up.

There are also cheap tweeter protectors available which contain a light bulb and a resistor potted in a small tube. They work pretty well, and if you reduce the tweeter network's series resistance by a few tenths of an ohm, they are not terrible for the sound. But they are audible and not failsafe.


Back to main index - Continue to 10.0 Amplifiers

12.0 High Fidelity Systems
People frequently use the term "Stereo" to refer to a sound reproduction system. To be more accurate, we will use the term High Fidelity System to refer to a pile of equipment including at least one source, at least one amplifier, and at least one speaker. Common sources are turntables, CD players, tape players, tuners, and receivers.

12.1 What is a receiver?
12.2 What is a tuner?
12.3 How should I go about selecting a system?
12.4 How can I improve the sound of my stereo?
12.5 Do I want a combo system or separate components?
12.6 How can I get better FM radio reception?
12.7 How good are these compact FM antennas?
12.8 What makes the best FM radio antenna?
12.9 What about power line conditioners?
12.10 How can I reduce vibration sensitivity?
12.11 What equipment can I buy that is 100% made in the USA?
12.12 Should I buy "xxx"? Which is better: "yyy" or "zzz"?
12.13 What is Surround Sound? Pro Logic?

12.1 What is a receiver?
A receiver is a tuner, power amplifier, and preamp combined. A common receiver has inputs for a turntable, a CD player, a tape deck, and perhaps one or two other sources. It has selector switch(s), tone controls, and a volume control. A receiver may have outputs for two speakers, or for more.


12.2 What is a tuner?
A tuner is a radio receiver which can not directly connect to speakers. Sometimes, the radio in a tuner is higher quality than the radio in a receiver. A tuner may or may not receive the AM broadcast band, but 99.999% will receive the FM broadcast band. Some also receive short wave bands, frequencies used for long-distance rather than for local commercial broadcasts.


12.3 How should I go about selecting a system?
If you're looking to buy something, the first step is to figure out what you can spend. If you're looking for a whole system, this gets tricky, because you have to allocate amounts for the different components. The most popular current rule-of-thumb for a single source system (speakers, amp, 1 something-player) is to divide the money about equally among the three parts. If you want several players, you'll have to decide whether they are all equally important, and so deserve the same amount of money; or whether some are less important, in which case you can spend less on them and put the savings elsewhere.

This rule isn't hard-and-fast. It's just meant as a starting point so you don't have to listen to every possible combination of equipment. If you are building around a CD player, you might spend a bit less on the player and a bit more on the speakers. If you are buying turntable (or something else which plays by physical contact) on the other hand, it might be good idea to put a bit extra into the player. The reason for this is that if you skimp on the turntable, then when you come to buy a better one you may find that your records have been worn out by the cheap player. If you skimp on the speakers, on the other hand, then when you can afford better speakers the music will still be there on your records.

Another perspective says that you should spend the most you can on your source, as the sound can never be better than what you get off of the record/CD.

See also 9.1, 9.2, and 11.1 for information on what to listen to and what to listen for when evaluating speakers, turntables, CD players, tape recorders, and systems in general.


12.4 How can I improve the sound of my stereo?
The cheapest improvement you can make, and perhaps the most effective, is to position your speakers carefully and correctly. See 13.1, below. This will improve the frequency response flatness, making it easier to hear every instrument and voice. Setting speaker position correctly can also improve the three-dimensional recreation of a stereo image.


12.5 Do I want a combo system or separate components?
Combo systems used to be cheap jokes; that's not always true now. Some sound very nice; there are even some made by "audiophile" companies, and they sound even nicer. They've got lots of advantages. They take up less space. The controls tend to be well-integrated, especially if they are remote-controlled. Therefore, they are easy to operate; this can be a major plus if some of the people who'll use it are afraid of, or not very good at, technology. Also easy to set up, and don't leave millions of wires dangling all over everywhere.

If you do go for a combo, get a brand name; either an audiophile company, or a good "consumer electronics" company. Brand-X combos are generally overpriced and unpleasant. If possible, buy it where you can listen to it first, such as a "real" hi-fi shop. Mid-range hi-fi shops sell combos, as a way of introducing beginners to quality sound.

In most good combos, the speakers are the weak link. If you do go for a combo, you can almost always improve the sound drastically by buying a set of better speakers. Better speakers start in the $100-$200 price range. Some of the best combos come without speakers, forcing you to do this. A good combo with replacement speakers will give you very pleasant music.

Sounds good, you say, so why do people bother with components? Well, you can get better sound with a component system -- but usually at the expense of convenience and size. A good component system will normally require a mixture of boxes from different makers to get the best results, so you've got to spend more time listening to things. However, if you listen to your music seriously, then the performance of a component system is the reward for that extra work.

Components are harder to set up and operate. However, as noted, you can get better sound. You also get more flexibility. If, for example, you decide you want a better CD player, you just replace the CD player. With a combo system, you've got to replace the whole system. If your component tape deck breaks, you can remove it from the system and take it in for repair or replacement. With a combo, the whole system has to go in for repair or be replaced.

When you want to add some new recording medium to your system (laserdisc, VCR, DAT, DCC, MD, ...), if you've got components you just go buy the appropriate box. Many combo systems do not have places (or many places) to attach extra bits, so again you could be looking at replacing the whole thing. With a component system, you can add a turntable; most modern combos can't cope with turntables any more. Do you have a record collection?

If you're really not sure, components are the safer bet; if you're going to make a mistake, that's probably the better way to be wrong. But, if you're sure that a combo would be best for your needs, it can be a totally reasonable choice.

Now, some people may be tempted by one-maker 'component sets', particularly the modern, miniature ones. They tend to be equivalent to combos. Most use non-standard connections, rather than the normal twin phono plug, so that it's likely you can't swap or add components anyway. Even where they use standard interconnects, they may rely on non-standard interconnections for control purposes. In a few cases, they also rely on sharing power, with a power supply in only one of the boxes and the rest taking low-voltage connections from that. And, no one maker makes the best everything. By default, assume that they will have the same disadvantages (and most of the same advantages) as combos. If it's important for it to work with "standard" components from other makers, be sure to ask before you buy.

And, if you're in doubt, go for separate components.


12.6 How can I get better FM radio reception?
A. Use a (better) antenna. (See 12.7 and 12.8 below)
B. Use a (more) directional antenna. (See 12.7 and 12.8 below)
C. Aim your directional antenna. Rhombics are ungainly to move, but Yagis and dipoles are small enough to point right at the station. With the dipole, to tune in a station to the East, run the antenna North-South. With a Yagi, point the individual elements North-South with the smallest element on the East end.

12.7 How good are these compact FM antennas?
For receiving, small is ugly. The bigger the antenna (all else equal) the better. Of course, all else is never equal, but these fancy, expensive mini antennas tend to be awful. Some compensate for their small receiving structure with a small antenna signal amplifier. However, the quality of that amplifier is often no better than the quality of the amplifier in your tuner or receiver, so the antenna just gives you a stronger signal, complete with stronger noise.

All of that said, some compact FM antennas can work better than a simple dipole in some situations. They tend to have an internal amplifier, which helps with weak signals. Some are directional. Some aren't. If possible, be sure that whatever you buy can be returned for a refund if it doesn't work out well for you.


12.8 What makes the best FM radio antenna?
Although there is no "best" antenna for everyone, one of the most directional is the "rhombic". Being very directional, this antenna can select one weak station out of many strong ones, or one group of stations originating from a general direction. In addition, very directional antennas are good at reducing multipath interference, a problem which is more severe in cities with tall buildings.

This antenna is very long, and made up of four pieces of wire with feedline at one end for antenna connections and a resistor at the other for termination. Rhombics for FM broadcast band use are at least 15 feet (4.5 meters) long, but can be made fairly narrow, less than 3 feet (1 meter) wide. A more narrow antenna will be more directional. A longer antenna will give a stronger signal.

Another very directional antenna is the "yagi", which looks just like a common TV antenna. You can even use a common TV antenna as a very good FM antenna. The FM and TV bands are very close together. It has the advantages of being cheap, directional, and easy to rotate.

One of the simplest and easiest to make antennas is the folded dipole, made from 300 ohm twin lead. It is approx. 58" long. This antenna is surprisingly good for receiving signals in a moderately strong signal area. Folded dipoles come with many tuners and receivers as a standard accessory. They are also available for approximately $2 at audio and department stores.

Whatever antenna you have, you can often get it to work better for specific stations by moving it. In the case of the folded dipole, sometimes it works better vertically, and other times it works best horizontally. Sometimes, you can get that one elusive station to come in perfectly if you bend the two ends of it at funny angles. Don't be afraid to experiment. One warning. As atmospheric conditions change, the best antenna placement may also change.

An excellent reference book on antennas is printed by the American Radio Relay League (ARRL). It is called The ARRL Antenna Book. Currently in its 16th edition, it is a 736 page large, illustrated paperback. It costs $20 plus s/h. It has fairly complete antenna theory, practical information such as charts, drawings, comparisons, and tips on construction and adjustment. The ARRL is founded and chartered as a non-profit organization to better amateur radio, and antennas are a vital part of amateur radio.

    American Radio Relay League
    225 Main Street
    Newington CT 06111 USA
    203-666-1541

Also useful:

    Practical Antenna Handbook by Joseph J. Carr
    Tab Books #3270/McGraw Hill - ISBN 0-8306-3270-3

12.9 What about power line conditioners?
Each home and each outlet has slightly different power line impedance and power line noise. Each amplifier is affected by power line impedance and power line noise differently. Power line conditioners try to reduce this line noise. Some also change the power line impedance in a way which is supposed to be better. We will leave it to your ears to decide if these devices help the sound of your system enough to justify their expense.


12.10 How can I reduce vibration sensitivity?
Some complain that heavy foot falls will cause skipping or more subtle sonic problems with CD players or turntables. If you have these problems, there are a few different things which you can try to reduce the problem. One is to add weight to the rack which holds the equipment. Heavier things move slower. If you can get the motion slow enough, it won't cause sonic or tracking problems.

Another solution is to add rubber or elastomer (Sorbothane) cushions under the CD player or turntable. This might make it better, but might also make it worse. Experiment.

A third solution is to increase the coupling between the rack and the floor using spikes, which concentrate the weight on a very small area. Another way to increase the coupling between the rack and the floor is to use a plastic adhesive like HoldIt, sold under the UHU trade name in office supply stores.


12.11 What equipment can I buy that is 100% made in the USA?
There are many lines of equipment that are carefully hand crafted in the USA. Unfortunately, these systems are usually the high-end ones. Some US companies also make gear in the far east. When in doubt, ask. Some US audio manufacturers are:

    Adcom (some made in Japan)
    Audio by Van Alstine
    Audio Research
    California Audio Labs (CAL)
    Carver (some made in Japan)
    Jeff Rowland
    Krell
    Mark Levinson
    McCormack
    McIntosh
    Parasound
    Proceed
    PS Audio
    Spectral
    Waida

12.12 Should I buy "xxx"? Which is better: "yyy" or "zzz"?
We can provide facts and opinions (and you get to decide which is which :-), but we can't recommend if, or which way, you should jump, because we don't know what your priorities are. (That won't stop us from trying, though!) For example, if you are considering a used item at a low price vs. a new one at a higher price, one of us might say "go for the new one because of the warranty", when another would say that you can fix it yourself if it breaks. They're both right.

This also applies to speakers. One may have very good, flat bass, but only go so low, where the other may go lower, but have less flat frequency response. Which is better? Depends on the buyer. Good speakers are carefully designed to achieve a balance of performance that matches the priorities of the designer. Some designers put much of their budget into appearance. Some designers put their budget into very high efficiency. Others strive for the smallest box which can deliver an acceptable low frequency performance. Do you really want people on the network making that decision for you?


12.13 What is Surround Sound? Pro Logic?
In an effort to make movie soundtracks more dramatic and engaging, Dolby Labs created a signal encoding which encodes more than just two channels of audio onto the stereo signal. Many popular receivers and home-theater systems include the required circuitry to decode these signals. These components are referred to as Pro Logic, Dolby Pro Logic, or Surround Sound components. Very few audio recordings contain this encoding, but it is very common with movie soundtracks and some network TV programs.

Best Surround Sound reproduction requires five separate speaker systems, but some improvement is claimed from a surround sound receiver and three speakers over two speakers. In its best implementation, surround sound will give a fuller sense of being in the middle of the action. The quality of the image is a function of the recording, the broadcast quality, and the choice of reproduction components.

For more information on surround sound, get:
The soundtrack comes after you...
which is available by anonymous FTP from ftp.csn.org as:
/Laserdisc/ld03



Back to main index - Continue to 13.0 Listening Rooms and Houses

13.0 Listening Rooms and Houses
13.1 How should I place speakers in my room? What size room is best?
13.2 How do I wire a house for sound?
13.3 Where can I read more about listening room construction and tuning?
13.4 What is white noise? What is pink noise?

13.1 How should I place speakers in my room? What size room is best?
You are after two important, distinct goals: flat frequency response and good three-dimensional image. At your disposal is the room size, the room shape, speaker height, speaker placement, listening position, and room treatments. Even though good speakers are essential to good sound, room effects are also extremely important. In many cases, the differences in room effects will be more noticeable than spending twice as much on speakers!

For smoothest bass response, a listening room should be as large as possible, have dimensions as unrelated as possible, and should be optimally damped. Although nothing is ever ideal, there are a few room dimension ratios that are better for listening rooms:

        Height          Width           Length
        1               1.14            1.39
        1               1.28            1.54
        1               1.6             2.33

If your room isn't shaped like that, don't worry. These effects are not major.

Also for smooth bass response, woofers should be at distances from the nearest three room boundaries that are as different as possible. In some cases, the line dividing the listening room into left and right halves must be considered a room boundary. Also, for smooth bass response, the listener's ears should be at distances from the nearest three room boundaries that are as different as possible.

All of this is essential because a wall near a speaker boosts the bass from that speaker at some frequencies. If a speaker is the same distance from three walls, then some frequencies will be emphasized much more than others, rather than slightly more.

For best three-dimensional image, a listening room should have good symmetry about the plane between the two speakers. This means that if one speaker is in a corner, the other speaker must be in a corner. If this symmetry is not right, the first reflection from the wall behind one speaker will be different from the first reflection from the wall behind the other speaker and critical parts of the stereo signal will be damaged.

Also, no large object should block the path from speakers to listener or from speaker to speaker. Speakers should be elevated so that tweeters are at listener ear height. The distance between speakers should be no greater than the distance from each speaker to the listener. Finally, the tweeters should be aimed at the listeners.

A normal box-shaped listening room with bare walls will have "slap echo" which will reduce intelligibility. A good cure is randomly-placed wall hangings consisting of small rugs spaced an inch or so away from the wall to increase sound absorption. Another cure is convex-shaped art objects on the walls to disperse harmful reflections. If money is available, commercial room treatments such as "Tube Traps" and "RPG Diffusers" are also valuable, but many of the benefits of these exotic devices are available with simpler techniques.

As a general rule, in a good room, speakers and listener can be close to room boundaries with minimal adverse effects. In a bad room, a good strategy is to place both speakers and listener as far away from room boundaries as possible.

An excellent starting point for speaker placement is to measure the listening room diagonal dimensions. Divide that measurement by three. Put each speaker that distance from a corner, on the room diagonals.


        I----------------------------------I
        I                                  I
        I                L                 I
        I                                  I
        I       S                 S        I
        I                                  I
        I----------------------------------I

Place your listening position midway between the two speakers and approximately half way from the speakers to the wall. Be sure that there is nothing in the "triangle" formed by the listening position and the speakers.

Try this and then move things 12" (30cm) at a time to see if you can improve the sound. Your ears will be a better guide than any commonly-available instruments. To keep track of what you are doing, take notes. To remember exactly where you put the speaker on the floor, a practical trick is to mark the floor with a sewing needle and thread.

13.2 How do I wire a house for sound?
A fundamental principle of physics is that the farther a signal travels, the more the signal will be degraded. Translate this to mean that the shorter the wire, the better. Understanding this, the idea of running speaker cable between every room of the house isn't as attractive as it first seems.

If you still decide to wire your house for sound, you should do it at the same time you're wiring for telephone and electricity. It is possible to wire a house after the walls are closed, but it becomes very difficult.

It is economical to use common house wire (Romex, UF, NM, etc) for speaker wire in the walls, but this may violate building codes. Check with an electrician or inspector first. It will also confuse future electricians, so label the wire clearly, all along its length.

If you want to make your house like a recording studio, it is best to use the techniques of recording studios. When studios run long lengths of sound cable from one room to another, they drive the cable with 600 ohm line amplifiers. They also use shielded, twisted-pair cable. They only connect the shield at one end of the cable. Finally, they use balanced inputs at the other end of the cable.


13.3 Where can I read more about listening room construction and tuning?
        "Building a Recording Studio" by Jeff Cooper
                Mix Bookshelf
        "Handbook for Sound Engineers"
        "The Master Handbook of Acoustics" by F Alton Everest
        "Sound Engineering 2nd Edition" by Don and Carolyn Davis;
                Howard W. Sams & Co. (C) 1990
        "Good Sound" by Laura Dearborn
                Introductory, but clear and accurate
        "Sound Recording Handbook" by John M. Woram
                Howard W. Sams & Co. #22583
                Excellent General Reference
        "Audio Technology Fundamentals" by Alan A. Cohen
                Howard W. Sams & Co. #22678
                Overview of Audio Theory
        "Introduction to Professional Recording Techniques"
                by Bruce Bartlett
                Howard W. Sams & Co. #22574
        "Modern Recording Techniques" by Hubar and Runstein
                Howard W. Sams & Co. #22682
        "Sound Studio Production Techniques"
                by Dennis N. Nardantonio
                Tab Books
        "The Uneasy Truce Between Music and the Room"
                F. Alton Everest
                Audio, February 1993, Pgs. 36-42
        "Coloration of Room Sound by Reflections"
                F. Alton Everest
                Audio, March 1993, pgs. 30-37

13.4 What is white noise? What is pink noise?
"White noise" is characterized by the fact that its value at any two different moments in time are uncorrelated. This leads to such noise having a flat power spectral density (in signal power per hertz of bandwidth), and is loosely analogous to "white light" which has a flat power spectral density with respect to wavelength.

Pink noise has flat power spectral density per PERCENTAGE of bandwidth, which leads to a rolloff of -3 dB/octave compared with white noise.

There are many reasons for using pink noise in audio testing. One is that music has an average spectral content much closer to pink noise than white noise. Another is that pink noise can be readily measured with constant Q bandpass filters and naturally leads to flat plots on logarithmic frequency scales - which correspond to the equally tempered musical scale.

Pink noise is often used with 1/3 octave band filters to measure room acoustics. This idea has merit since 1/3 octave is a convenient number near the limit of our ears ability to detect frequency response irregularities, and because averaging measurements over 1/3 octave bands smooths out the numerous very narrow peaks and dips that arise due to standing waves in rooms.

Another term you'll hear about is Gaussian noise - this is noise with a Gaussian amplitude probability density. Gaussian noise has the amazing property that linearly filtering it preserves its Gaussian amplitude density and that sums of Gaussian random variables are again Gaussian. The two terms shouldn't be confused. It is possible to have Gaussian white or pink noise.


Back to main index - Continue to 14.0 Recording

14.0 Recording
There are more different recording systems available today than ever before. Digital and analog are both available to the consumer. With the advent of consumer digital recorders, used pro analog recorders are becoming available for surprisingly low prices. Now may be the time for you to buy a microphone and recorder and make your first!

14.1 What is DAT? What is its status today?
14.2 What is DCC? What is its status today?
14.3 What about writable compact discs? What is the status today?
14.4 What are Dolby B, C, and S, HX Pro, and DBX? Are they compatible?
14.5 What is the best cassette deck under $400?
14.6 What is PASC? Can I hear the effects?
14.7 What is SCMS? Can I hear the effects?
14.8 How can I bypass SCMS?
14.9 What's this about a tax on DAT?
14.10 Is it legal to copy an LP, CD, or pre-recorded tape?
14.11 How do I clean and demagnetize tape heads?
14.12 How do I adjust a tape recorder for best results?
14.13 Where can I get new pinch rollers or drive belts?
14.14 What is a good rubber (pinch) roller cleaner?
14.15 How can I program a recorder to tape a radio broadcast?
14.16 Will CrO2 or Metal tapes damage a deck made for normal tape?
14.17 Why do my old tapes squeak in my car cassette deck?
14.18 Is VHS Hi-Fi sound perfect? Is Beta Hi-Fi sound perfect?
14.19 How do HiFi VCRs compare to cassette recorders? DAT recorders?
14.20 What is the difference between VHS HiFi and Beta HiFi?
14.21 Is there any good reason to buy a HiFi VCR for common TV shows?
14.22 What is the best cassette tape?
14.23 What is the best Reel-to-Reel tape?
14.24 What is Type I, Type II, Type III, and Type IV cassette tape?

14.1 What is DAT? What is its status today?
DAT (Digital Audio Tape) is currently the standard professional digital format for 2-track digital recording. DAT had a short-lived consumer presence, but never "made it". As digital recorders have no tolerance for clipping, using a DAT recorder takes a slightly different knack. The results can be worth it, however, as DAT format offers the same resolution and dynamic range as CDs. DATs record for up to 2 hours on a tape, and can run at three different sampling rates: 32 kHz, 44.1 kHz (for CD), and 48 kHz (the DAT standard).


14.2 What is DCC? What is its status today?
DCC is Philips' attempt to modernize the regular cassette. DCC decks can play analog cassettes, and can record new Digital Compact Cassettes. They use stationary heads (DATs use rotary heads as do VCR's), and although they are digital, they use lossy compression to fit all the data on the cassette. Although DCC sound quality is far better than the 1960 standard cassette, the DCC does not have the sound quality present in DAT or CD. DCC may be a good choice for consumers who want to assemble mix tapes for cars or walkmans, but is not suitable for any professional applications. As of December 1992, DCC is very new, DCC equipment is very expensive, and the ultimate future of DCC is not assured.


14.3 What about writable compact discs? What is the status today?
Recordable CD's are available, but are very expensive. Blank discs sell for approximately $35 each, and the recorders start at around $6,000. These units are mostly used by recording studios and other audio professionals.


14.4 What are Dolby B, C, and S, HX Pro, and DBX? Are they compatible?
Dolby B, C, S, and DBX are techniques for increasing the signal/noise ratio of recordings. All work in similar ways: they compress the dynamic range of the sound during recording, then expand it back upon playback. As much as we would like it to be otherwise, you only get correct reproduction if you use Dolby B to play back a Dolby B tape. Same for Dolby C, Dolby S, and DBX. Dolby HX Pro is the exception.

Dolby B works mostly with higher frequencies; it increases their levels during recording and decreases their levels, and the levels of high-frequency noise such as tape hiss, during playback.

Dolby B tapes can be played back without Dolby B processing, but high frequencies are over-emphasized and the sound will be excessively bright. This can be compensated for to some extent by turning down the treble control. Audio novices often remark that commercially recorded tapes recorded using Dolby B sound dull when played back with Dolby B; this is because they are accustomed tothe boosted high frequencies they hear when playing these tapes without Dolby.

Dolby C achieves greater noise reduction (about 8-10 db) than Dolby B by working with a greater range of frequencies and altering relative levels more; this means that playing Dolby C tapes back with no Dolby processing or with Dolby B, leads to very bad frequency response and a sound that most people find unpleasent. Dolby C may also be more sensitive to variations among decks in exact frequency response, alignment, etc. Some people find that tapes recorded using Dolby C sound best only when played back on the deck on which they were recorded.

Dolby S works with an even broader range of frequencies than Dolby C, and achieves slightly greater noise reduction. Its has three advantages over Dolby C: (1) many people find that tapes recorded and played back using Dolby S sound closer to the original than tapes done using Dolby C; (2) tapes recorded using Dolby S don't sound awful if played back on Dolby B decks, and (3) Dolby S seems to be less sensitive to variations among decks.

DBX is similar to Dolby B, C, and S, but uses the same compression on all frequencies, high and low. However, DBX is mostly used in the professional market. Very little home DBX equipment is available, and some of that home equipment is no better than comparable Dolby B home systems. All DBX systems are compatible with all other DBX systems, but incompatible with Dolby. A DBX tape will sound terrible without DBX processing during playback.

All compression/expansion systems suffer two problems. One is due to the fact that compressors can't compress a loud signal before they have heard a bit of it, so that little bit of loud signal will get through uncompressed. Likewise, quiet passages will not be expanded until after they are detected. These delays give rise to an audible problem often called "breathing".

The other problem inherent in all compression/expansion systems is that if there are any frequency response errors in the tape recorder, they will be made worse by the compression/expansion. For example, if there is a 2dB dip in frequency response at 1kHz in the tape recorder, this will be accentuated to a 4dB dip if the compressor is using a 2:1 ratio. So compression/expansion trades noise for frequency response error. For that reason and the previously mentioned breathing, some people prefer to use their recorder without any noise reduction at all. They prefer a bit of noise to the other errors.

Dolby HX Pro is not noise reduction and does not use compression or expansion. HX Pro is a technique developed by Dolby Labs to increase tape headroom by decreasing the bias when recording signals with a large high frequency component. This allows better transient response, particularly on less expensive tapes, and requires no processing when the tape is played back. Dolby HX tapes can be played back on any system with no decrease in quality.


14.5 What is the best cassette deck under $400?


14.6 What is PASC? Can I hear the effects?
PASC (Perceptual Audio Sub-band Coding) is a data-compression algorithm. It increases the length of recording that can be stored in a given number of data bits by eliminating sounds that the developers' research claims can not be perceived by human listeners. Its most important component is the omission of quiet sounds that occur at the same time and near the frequency of louder sounds. It provides up to a 4x increase in the length of recordings a given digital medium can hold; this is essential to allow full-length digital recordings on DCC (and on MD, which uses a different compression technique). It is not necessary to translate CD data to analog before compressing it using PASC, nor the reverse.

You CAN hear PASC, but it is very difficult, since it is not a distinctive noise (like a hiss) nor a consistent diminution (like a notch in a speaker's response), but a broad, uncorrelated dropout in a changing collection of sounds that are masked by sounds that you can hear very easily.

Since it is lossy, repeated PASC recording will cause progressive loss, and this signal damage may become easily noticeable. This is a side effect that recording companies hope will have the effect of discouraging piracy via DCC.


14.7 What is SCMS? Can I hear the effects?
SCMS (Serial Copy Management System) is a copy-protection system intended to stop rampant piracy of commercial recordings to digital tape. SCMS allows the home taper to copy from a CD to a digital tape, but prevents anyone from digitally copying that new digital tape.

You CANNOT hear SCMS.


14.8 How can I bypass SCMS?
There are professional devices used by engineers to manipulate the digital bitstream, but they cost several hundred dollars and are not cost effective for consumers. If you need to make perfect digital copies of digital copies, buy a professional digital recorder. Pro models do not have SCMS, are more durable than consumer recorders, and may have better quality electronics than consumer models.


14.9 What's this about a tax on DAT?
Every digital audio tape recorder and every blank digital tape sold in the USA is priced to include a "premium" or "tax". This tax is collected by the US Copyright Office and distributed to the recording artists and record companies that own the copyrights to commercial music. These fees are supposed to repay them for lost royalties.

Many believe that this "tax" is illegal, because it represents an assumption that the buyer will use the recorder and tape to violate a copyright, and not to record their own works. A founding principle of the USA legal system is that everyone is assumed innocent until proven guilty.

If you believe that this law is unjust, write your elected representatives.


14.10 Is it legal to copy an LP, CD, or pre-recorded tape?
In the US today, it may be legal to copy LP's, CD's, etc. for your own private use (such as to copy a CD to play on your walkman). UK law specifically prohibits this, but it is almost never enforced. It is definitely not legal in the US, UK, or almost anywhere else, to copy these sources for commercial purposes, or to give the copies to others.

It is as of yet unclear whether you own the rights to sell or give away a copy of a recording if you made the copy on media which was sold with an included digital audio tax.


14.11 How do I clean and demagnetize tape heads?
First, a caution: DAT recorder tape heads are VERY fragile. Before cleaning the heads on a DAT recorder, get specific recommendations from a very knowledgeable source that is intimately familiar with DAT head cleaning. In the internet, a good source is the DAT-Heads-Digest FAQ. For more information on DAT-Heads-Digest, see section 20.2, below.

To clean tape heads, use pure isopropyl alcohol and lint-free swabs. Wipe the metal parts of the transport with alcohol (DON'T wipe the rollers!) and allow them to dry. Throw the swab away after use. Be exceedingly careful when cleaning the heads on a DAT. DAT heads are notoriously easy to misalign by incorrect cleaning.

Practical tape head demagnetizers are available for under $10. Try to find one with a plastic coated tip. If you can't find one which is plastic coated. you can slip a drinking straw or plastic tube over the tip for the same effect. This plastic will prevent the demagnetizer from scratching the head.

Before plugging in the demagnetizer, remove all tapes from your working area and unplug the recorder. Hold the demagnetizer away from the recorder as you plug it in. Slowly bring the tip of the demagnetizer up to the tape head and slide it back and forth across each tape head for five one-second strokes. Then pull it away from the head slowly and go on to the next. After demagnetizing the heads, use the tip on each metal tape guide with a similar five strokes. Last, slowly pull the demagnetizer far away from the recorder and unplug it. Recording engineers use a demagnetizer before each recording session.


14.12 How do I adjust a tape recorder for best results?
Adjusting a tape machine for best results usually requires special equipment and test tapes. Unless you know what you're doing, leave it for a pro. If you are serious about doing it, buy the service manual for your particular tape recorder. It will list a detailed procedure, as well as describe the correct test tape and tools.

As for setting of record levels, it is best to experiment with different levels on different tape brands. Different formulation will reach saturation for different levels. Generally speaking, the transients on a Chrome tape should peak at about +6 dB above 0, though some formulations can take significantly hotter signals.

14.13 Where can I get new pinch rollers or drive belts?
         Projector-Recorder Belt Company
         Whitewater WI USA
         800-558-9572

14.14 What is a good rubber (pinch) roller cleaner?
Teac RC-1 available from
         J&R Music World
         59-50 Queens-Midtown Expressway
         Maspeth NY 11378-9896 USA
         800-221-8180 or 718-417-3737
Tascam Rubber Cleaner RC-2 available from:
         Tape Warehouse
         Chamblee GA
         1-404-458-1679

14.15 How can I program a recorder to tape a radio broadcast?
Radio Shack and Panasonic make a clock/radio/cassette that can be set to record at a specific time. Radio Shack also sells 120 minute cassettes, which can be used for 60 minutes per side. The recorders are not high quality, and the long tapes are fragile, but it works.

You can buy "appliance timers" at hardware stores that will start and stop an appliance at a specific time. Radio Shack sells fancier versions of the same thing for more money. Gadget freaks love "X-10" control systems. These can be configured to do the same thing. All require a recorder that can be left in RECORD mode. Such recorders are identified by a "TIMER" switch on the front panel. Many cassette decks have a TIMER switch for use with timers.

Memorex sells a "CP-8 Universal Remote" with a built-in timer. Available for approximately $90.00 from either:

        Crutchfield
        1 Crutchfield Park
        Charlottesville VA 22906 USA
        800-955-3000 or 804-973-1811
                or
        J&R Music World
        59-50 Queens-Midtown Expressway
        Maspeth NY 11378-9896 USA
        800-221-8180 or 718-417-3737

This can be set to start a recorder at a particular time. As the recorder will be started from a remote control rather than by the power line voltage, no timer switch is required. Radio Shack has a very similar product available for $99.95, may be less on sale.

Damark also sells a learning remote with a built in on/off timer and sleep timer. It can learn 17 commands per device on a total of 5 devices and should be great for taping a few shows. They also sell a 8 device remote with timer. As Damark sells close-outs, these items may not be available in the future.

        Damark
        7101 Winnetka Avenue North
        PO Box 29900
        Minneapolis MN 55429-0900 USA
        800-729-9000 or 612-531-0066

There is a similar learning remote available from MCM Electronics. They call it a Lonestar Learning Universal Remote, item 80-450, $24.95 on sale.

        MCM Electronics (Speakers, A/V Repair Parts, Etc) (+) (C)
        650 Congress Park Dr
        Centerville Ohio 45459-4072 USA
        513-434-0031 or 800-543-4330

Another timer-remote is the Fox 800 (approx. US $80 retail). The Fox 800 was spotted at Damark 800-729-9000 for $30 in March of 1995.

There is also a Carver remote with timer.

For the true nerd, there's the programmable remote sold as a Scientific Calculator, the HP-48. Audio remote control software for this fine adding machine exists. For more information, consult the HP-48 FAQ. The HP-48 FAQ contains pointers to a few remote control programs. The FAQ is archived at site rtfm.mit.edu in /pub/usenet-by-group/comp.sys.hp48

Use a VCR for audio-only recording. Hook the audio in to the output of a radio, tuner, or receiver. You may also have to connect some video signal to the VCR so that the sync circuits work correctly.


14.16 Will CrO2 or Metal tapes damage a deck made for normal tape?
No. They will work fine. They are no more abrasive than common tape and may actually be less abrasive than very cheap tapes. Recorders which are designed for CrO2 or Metal tape have different bias settings and equalization settings to take best advantage of the greater headroom and to give flat response with these different types of tape. However, they use similar if not identical heads as less expensive tape recorders. Almost all tapes are in some way lubricated, and these lubricants minimize wear and squeaking.


14.17 Why do my old tapes squeak in my car cassette deck?
One problem that will cause this is "binder ooze". The binder is the glue which holds the oxide particles to the backing. With time, this binder can ooze forward and actually get past the oxide particles, so that there is sticky stuff on the surface of the tape. When this sticky stuff goes past the heads, it can cause a slight stick, which will sound like a squeak. You won't feel it with your fingers, but it is there. If you have a prized tape with this problem, consider baking the tape in a home oven at a very low temperature, like 150F. This might cure the problem by drying out the binder.


14.18 Is VHS Hi-Fi sound perfect? Is Beta Hi-Fi sound perfect?
The HiFi recording format is subject to two different problems: Head-switching noise and compression errors.

To get perfect reproduction, the FM subcarrier waveform being played back by one audio head must perfectly match the waveform from the other head at the point of head switching if a glitch is to be avoided. If you record and then play the tape on the same VCR under exactly the same conditions, you have a reasonable chance of this working. But if the tape stretches just a bit, or you play it on another VCR whose heads are not in exactly the same position, or the tracking is off, the waveforms will no longer match exactly, and you will get a glitch in the recovered waveform every time the heads switch. This sounds like a 60 Hz buzz in the audio, which is often audible through headphones even if not through speakers.

The same glitch will occur in the video waveform too, but since head switching always happens during vertical retrace, you won't see it.

The wonderful signal to noise ratio of VHS HiFi is achieved through the use of compression before recording and expansion after playback. The actual signal to noise ratio of the tape itself is about 35 dB and a 2.5:1 compressor is used to "squeeze" things to fit. Like all companders, this produces audible errors at certain places on certain signals, such as noise "tails" immediately after the end of particularly loud passages.

Worse, compressors often have problems simply getting levels right. That is, if you record a series of tones, starting at -90 dB and working up in 1 dB increments to 0 dB, and then play them back, you will almost invariably have level errors. The trend from soft to loud will be there but the steps won't be accurate. Two or three of your tones might come out at essentially the same level, then the next one takes a big jump to catch up or even overshoot.

For music, the result will be that the relative levels of some instruments, passages, etc. will not be accurate.

This doesn't matter as much for movies, which tend to have steady volume level. Also, movie enjoyment is rarely hurt by these level errors. VHS and Beta HiFi is fine for reproduction of movie and tv soundtracks. They are also perfectly fine for non-critical audio applications. But VHS and Beta HiFi are not serious competitors to DAT, CD, open-reel analog tape, or even a high quality cassette deck.


14.19 How do HiFi VCRs compare to cassette recorders? DAT recorders?
VHS HiFi and Beta HiFi are analog recording formats which use modulation techniques to record a video signal and a stereo audio signal on a videocassette. The audio capabilities typically surpass that of the "linear" audio tracks found on all video recorders, thus the "HiFi" designation. "HiFi" is essential for getting good sound quality on your video recordings and out of pre-recorded videos.

HiFi is also touted as an excellent audio recorder for audio-only (no picture) applications. On paper, the specifications are typically superior to analog cassette but inferior to DAT. In reality, the quality of HiFi video recorders is better than low quality cassette recorders but not as good as high quality cassette recorders when they are used with noise reduction systems. In no case can a HiFi video recorder compare to DAT. It suffers from generational loss and audible noise.

Many people use VHS HiFi for recording radio broadcasts, since VCRs often have built-in timers and can record for up to 9 hours. If you use a HiFi video recorder to record from an audio-only source, beware that some decks will not function properly without a video signal for synchronization. If you are interested in very good quality sound, use a deck with manual level control.


14.20 What is the difference between VHS HiFi and Beta HiFi?
VHS HiFi uses "depth modulation"; Beta HiFi uses "frequency modulation".


14.21 Is there any good reason to buy a HiFi VCR for common TV shows?
If you do not own a stereo TV, the purchase of a HiFi VCR will give you the capability to listen to stereo TV broadcasts to your system.

14.22 What is the best cassette tape?
One simple answer to this question is that the best tape is the tape which was used to align your tape recorder. A second simple answer is that more expensive tapes are frequently better in terms of quality of the backing, durability of the oxide, accuracy of the shell and guides, and life.

Background: When you make a tape recorder, you build electronic circuits which have specific, non-flat frequency response. These circuits correct for the non-flat response of the tape heads, the recording process, and the tape. These circuits can be adjusted after the recorder is made, but adjustment is tricky, and may or may not be successful with every tape made. The designer of the tape recorder picked one tape as their standard when they did the design, and built that recorder to work well with that particular tape. It may work better with a different tape, but it won't necessarily sound the best with what one person calls the best sounding tape.

From a review of frequently given answers to this question, it is obvious that almost every brand of tape has its advocates. Many brands also have their detractors. Maxell and TDK tend to have a strong following, but that is in part because they own a large share of the US tape distribution market.


14.23 What is the best Reel-to-Reel tape?
See 14.22. Just as cassette tape recorders are set up specifically for one type of tape, reel-to-reel tape recorders are equalized and biased so that they are best with one specific brand and model of tape. Just as more expensive cassette tapes will last longer and have less noise than cheaper ones, you can expect fewer dropouts, better quality control, and lower noise from more expensive reel-to-reel tapes.

The major brands in reel-to-reel tape include Ampex, Scotch (3M), AGFA/BASF, and Maxell.


14.24 What is Type I, Type II, Type III, and Type IV cassette tape?
These are IEC (International Electrotechnical Committee) standards. They provide broad standards for all tapes, and end the need to align a deck for an individual tape. Type 1 is for normal "iron oxide" tapes (Fe2O3), Type 2 is for high-bias "chromium oxide" tapes (CrO2), Type 3 (obsolete) is for FeCr (ferric chrome), and Type 4 is for Fe (Metal). Type 2 tapes tend to be more expensive than type 1, and type 4 tapes are the most expensive. This is because type 2 tapes tend to have less noise and flatter high frequency response than type 1, and type 4 tapes tend to have even flatter highs and even less noise.

Some Type 1 tapes are more expensive than other Type 2 tapes, and may be worth the extra price. More expensive tapes come in better shells, have better lubrication, fewer dropouts, smoother frequency response, and better uniformity from tape to tape. Even though the types imply a particular tape formulations, the type really refers to the tape performance. For example, some iron oxide tapes have an unusual oxide formulation with very small grains that conforms to the type 2 standard better than the type 1 standard. These tapes will be labeled type 2, but may not have any chrome in them.

Most modern cassette recorders sense the tape type by the holes in the back of the housing and adjust bias and equalization to compensate for the differences. A few top cassette recorders (the Revox and several Nakamichis) automatically align to a particular tape by recording test tones and then setting their own equalization.

In practice, each brand and model tape is slightly different. For the very best recordings, adjust your recorder for the tape you use most, or buy the tape which works best in your recorder. Manufacturers adjust each recorder for a specific tape at the factory. So the best tape might be the one referenced in the recorder owner's manual. In a recording studio, it is common to align the bias and equalization for the specific tape used, and stick with that tape.


Back to main index - Continue to 15.0 Mail Order

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就是不知道在说些什么。

倒，e文，看不懂

19.0 Miscellaneous:
19.1 What do I need to know about warranties?
19.2 What is blind testing? Non-blind? Double-blind?
19.3 Where can I get a service manual for brand XXX?
19.4 Where can I get good repairs on brand XXX?
19.5 How can I take 115V gear over to a 230V country or vice versa?
19.6 Are there really good deals in country XXX?
19.7 How do I find out how much an XXX is worth?
19.8 Do people really hear those differences?
19.9 Why do people disagree on what is the best sound?
19.10 How do I contact the manufacturer of XXXXX? How do I get repair service on XXXXX? How do I get replacement parts?

19.1 What do I need to know about warranties?
Warranties have a few basic components. The first is the term of the warranty. The second is what is covered. The third is who supports the warranty. The fourth is what restrictions.

Term is fairly self evident. What is covered is more detailed. In audio electronics, typically everything is covered with a "parts and labor"" warranty. Often mechanical components such as tape heads are covered by different terms, such as shorter terms on labor and longer terms on parts. Likewise, speaker warranties vary widely, from unconditional with no term limit to a basic 30 days parts and labor.

Some warranties come from the manufacturer. Others come from the dealer. Still other warranty support is available with certain premium charge cards.

A common restriction on some warranties is that the equipment is not covered unless it is sold by an authorized dealer. A few dealers have lied about being authorized dealers. Equipment sold by an unauthorized dealer is almost always sold completely legally. This unauthorized dealer may, in fact, be fully authorized to sell, but not authorized to sell manufacturer's warranties. In buying gear this way, dealers can get it cheaper, and provide the service themselves. This kind of gear, with a full warranty from the dealer is referred to as gray market equipment. Manufacturers discourage buying from these gray market dealers, but the risks are fairly low. If the dealer is local and well established, the risks are minimal.

If you buy equipment mail-order, a dealer warranty may be a pain in the neck, especially if you have to ship the gear to the dealer more than once to get it fixed correctly. Then again, some factory service requires shipping gear far away at your expense, too.

Frequently, home audio equipment is sold with a warranty restriction that if the gear is used commercially or in any profit-making enterprise, then the warranty is void. This is to protect the manufacturer from having to frequently repair equipment meant for light service. Professional audio equipment often comes with very liberal warranty terms, such as lifetime parts and labor. Professional gear takes heavy use and severe wear from constant transportation. It is expected to be able to take this abuse.

All gear, electronic and mechanical, is known to have three principal failure modes: abuse, infant failure, and end-of-life failure. In addition, a few of the failures occur at random.

Infant failure occurs in the first fifty hours of use, and is the principal responsibility of warranties. Infant failure is frequently caused by defective parts or a design defect.

Abuse failure is that caused by a person who pulls a cable too hard, bangs the equipment on the table, pushes the controls too firmly or too fast, or does anything else which the manufacturer did not expect. These are the gray areas of warranties. They do not represent a manufacturing defect in the manufacturer's eyes, but they do leave you with a broken device. To get the best chance of coverage against this kind of failure, select a brand or a dealer with a very liberal warranty policy.

End-of-life failures are rarely covered by warranty. Tape heads have a finite, calculable life, as do rubber rollers, speakers, cables, batteries, bearings, and motors. The life of some of these components can be extended by intelligent care. For example, the life of common rechargeable batteries can be extended by good recharging practice. Likewise, some cleaners can dry out rubber, and will lead to premature failure. Don't expect warranty support for any of these problems, and if you get it, feel lucky.


19.2 What is blind testing? Non-blind? Double-blind?
If you want to compare pieces of equipment, recordings, or people, you could run an experiment. You could select an experimenter to initiate various trials, select some subjects to listen to the sounds, and then ask the subjects questions about what they hear. However, if you want meaningful results, it is necessary to set up the experiment correctly, and ask the right questions.

One of the major problems with any experiment is that the subjects may become aware of the experimenter's hypothesis and allow this awareness to influence their behavior. One technique for preventing such bias is to keep the person who conducts the experiment unaware of the hypothesis of the research. Unfortunately, experimenters invariably form SOME hypothesis of what's going on, and these hypotheses affect how they deal with subjects.

A more reasonable solution involves allowing the experimenters to know the true hypothesis but somehow keeping them ignorant of the specific experimental condition of each subject. This is known as a Partial Blind Experimenter technique. An example of this is that the person running an experiment knows that the main experimenter wants to determine which connecting cables are best at signal carrying, but would not know which cables are being used at any given time during the experiment.

It is also important for subjects not to become aware of the experimenter's specific hypothesis. Subjects often become highly responsive to any cues, intended or unintended, in the research situation that suggest what they are supposed to do to appear normal or "to make the study come out right." This problem can be present in judgment experiments, particularly those in which each subject is exposed to more than one variation of the stimulus. Such a procedure, by its very nature, increases the probability that the subject will begin to guess which aspects of the experiment are being systematically varied by the experimenter.

Many studies avoid this problem with what is called a Blind Subject technique. Using this approach, subjects are not told specifically what the hypotheses are. Additionally, subjects are not told what specific experimental conditions they are in. For example, a subject might be told that he/she is supposed to determine which stereo system sounds better, when in fact the experimenter wishes to examine which color or appearance of the same components looks better to subjects.

When both a Partial Blind Experimenter technique and a Blind Subject technique are used at the same time, this is called a Double Blind experiment. Double Blind experiments have higher probability of producing statistically valid results than Partial Blind Experimenter alone, Blind Subject alone, or other techniques. Double Blind experiments are highly recommended.


19.3 Where can I get a service manual for brand XXX?
The most reliable source of supply is the manufacturer's sales office in your country. Here is a list of company contacts that may be helpful in the US. (Please send additions & corrections etc. to neidorff@uicc.com)


    AOC            800-775-1262
    Cannon            516-933-6300
    Casio            201-361-5400
    Daewoo            800-782-4922
    Emerson Radio        800-388-8333
    Sanyo/Fisher        213-605-6756
    General Electric    800-447-1700
    Goldstar        800-222-6457
    Hitachi            800-526-6241
    JVC            800-252-5722
    Kenwood            213-639-9000
    Philips/Mag/Sylvania    615-475-8869
    Mitsubishi/Akai        714-220-1464
    NAD            617-762-0202
    NEC            201-882-9008
    Nutone            800-543-8687
    Onkyo            201-825-7950
    Panasonic/Quasar    215-741-0676
    RCA            317-231-4151
    Samsung            800-542-1302
    Sanyo            800-421-5013
    Sharp            800-526-0264
    Sony            800-282-2848
    Soundesign        800-888-4491
    Teac            213-726-0303
    Teknica            800-962-1271
    Toshiba            201-628-8000
    Zenith            312-745-5152

Alternately, contact one of the repair parts dealers listed in section 10.15 above. MCM and Parts Express offer free catalogs which can be very helpful for locating parts.


19.4 Where can I get good repairs on brand XXX?


19.5 How can I take 115V gear over to a 230V country or vice versa?
Some equipment is available with an international power supply, which can be rewired by any serviceman to either power line voltage. If you expect to be moving abroad, look for this kind of equipment. Often, the same model is available both as US only and as International. Some equipment will be rewirable and won't say it. Adcom amps are known to be rewirable.

If you know that your gear is limited to one power line voltage, you can order a new power transformer for that receiver, CD player, amplifier, or tuner which will be wound differently. Contact the manufacturer's local service center. This can be very expensive. A new transformer for a 40 watt receiver would wholesale for under $25 but cost $75 from a service center.

Another alternative is to buy a power transformer that will convert 115V to 230V and vice versa. This is only practical for smaller gear. Larger power amps require prohibitively massive and expensive transformers. Also, the addition of a transformer may hurt the sound quality.

Here are some common transformer models and 1992 list prices. Power ratings are total line current multiplied by line voltage (2A at 115V is 230 watts). Larger transformers cost more. Some of the costlier transformers are constructed with plugs and jacks for immediate use. Those marked * have wire leads and need safe connections to be used.

Before spending money, check into other things about audio in the new country. Broadcast frequencies are slightly different in some countries than in others, so a receiver or tuner bought in one country may not be able to receive some or all of the stations in another country. The US separates the AM broadcast band frequencies by 10kHz while the UK uses 9kHz. Similarly, the US separates FM stations by 200kHz, where the UK has stations on a 50kHz spacing pattern. It MAY be very simple to modify a receiver from US to UK spacings, but may not. Last, but not least, some equipment will NOT work well on 50Hz power.

        Step Down (230V in, 115V Out)
                MagneTek/Triad  N1X*    50 Watts        $11.83
                Stancor         P-8620* 50 Watts        $14.16
                MagneTek/Triad  N3M     85 Watts        $29.95
                Stancor         P-8630  85 Watts        $43.65
                MagneTek/Triad  N6U*    200 Watts       $25.72
                Stancor         P-8632  200 Watts       $51.80
                MagneTek/Triad  N5M     250 Watts       $42.60

        Step Up (115V In, 230V Out)
                Stancor         P-8637  85 Watts        $43.10
                MagneTek/Triad  N150MG  150 Watts       $49.46
                MagneTek/Triad  N250MG  250 Watts       $54.69
                Stancor         P-8639  300 Watts       $55.51

The Stancor and MagneTek Triad lines are carried by large electronic distributors.


19.6 Are there really good deals in country XXX?


19.7 How do I find out how much an XXX is worth?
There is a "Blue Book" for used audio equipment called "Orion Blue Book-Audio". This guide lists both a wholesale and a retail value for most audio gear.

                
        Orion Research Corporation
        1315 Main Avenue Suite 230
        Durango CO  81301 USA
        303-247-8855

Last I knew a guide costs $169. Each Nov, a new book is printed. After June, the old book is discounted. If you need a single quote from the Orion Blue Book, send a polite request to:

                al@qiclab.scn.rain.com

and you may get a quote back by e-mail.


19.8 Do people really hear those differences?
Who knows? They sure think that they do.


19.9 Why do people disagree on what is the best sound?
There are at least three different measures of what is "Perfect Sound". All three have advocates, and all three are right, in their own way. In general, whether they admit it or not, most listeners fit into one of these three preference groups:

1. It must sound like live music. These people know what voices sound like in person, they know what instruments sound like without any amplification, and they have heard orchestras perform unaided by sound systems. They want to accurately reproduce that sound.

2. It must sound like the recording engineer wanted it to sound. The recording engineer listened with extremely good equipment to the sound coming out of the microphones, and mixed them together for what he, at that time, felt was artistically correct. It may not have been the same as live, but it was exactly what he wanted. In the extreme, people like John Fogerty used to audition his final recording mix in his truck to see how it would sound through a common, lousy stereo.

3. It must give me the most pleasure. No matter how good or bad live sounds, no matter what the recording engineer intended, if buy some equipment will give me more listening pleasure then it must be the best.


With these three perspectives, it is clear that no one system will satisfy everyone. Add to that confusion the variable that everyone likes a different kind of sound, has heard live music under different conditions, and has a different idea of what the engineer intended. There is an enormous range of possibilities.

Another set of reasons is that people look for different things to be right. Some want strong bass; others want male voices to sound like male voices; others want violins to sound like violins. Systems rarely do everything equally well. Speakers (in particular) are compromises. Look for the speaker where the designer had your priority first. You are perfectly right to select speakers based on YOUR personal taste.

Confounding the situation further, we all say the greatest things about the stuff we already bought. To do otherwise would be to admit that we are either stupid or deaf.

Still another reason is that most people haven't heard enough variations. Until you hear a system that can truly reconstruct the three-dimensional accuracy of a stereo image accurately, you may never realize that it is possible. Some excellent recordings contain enough information that with a good enough system, you can hear up-down, in-out, and left-right distinctions very clearly. However, we will never experience this until we are fortunate enough to hear such a fine recording on a very good system.

Finally, some of us really can't hear much difference. We aren't deaf, but we don't have a well trained ear, don't know exactly what to listen for, and may even have slight hearing deficiencies, such as bad sensitivity to high frequencies which comes with older age, or hearing damage from listening to loud sounds (machinery, rock concerts, etc).


19.10 How do I contact the manufacturer of XXXXX? How do I get repair service on XXXXX? How do I get replacement parts?
Some magazines publish lists of contact phone numbers for the manufacturers of equipment. In the US, Consumer Reports has a small listing in each issue and a more comprehensive listing in their March issue. Also, Audio Magazine has an exhaustive listing in their October "Equipment Directory". In Europe, look in "What HiFi?".

You can find many addresses by reading ads in hifi magazines. You can also find out by asking at your friendly local hifi shop, especially if you've built up a relationship with them.

There is a book called the "Electronics Industry Telephone Directory". It comes out yearly and is available in some libraries. Many reps from parts distributors pass them out for free. If you want a copy and are willing to pay for it, call Harris Publishing, 800-888-5900 or 216-425-9000.

The directory of the Electronic Industries Association is similarly useful. You can reach the EIA at 202-457-4900.

A good source for parts and service is often the manufacturer's repair center. The best way to locate one near you is to look at the literature which came with your equipment when it was new. Failing that, see the ideas mentioned above in 19.10.


Back to main index - Continue to 20.0 Net Protocol

18.0 Retail:
18.1 Should I use an up-scale retail store?
18.2 Should I use a discount store?
18.3 Is it right to negotiate price?
18.4 How can I negotiate price effectively?
18.5 It sounded great in the store. Is it great?
18.6 Do sales people try to trick the customer?
18.7 How can sales people trick the customer?
18.8 What should I ask the sales person?
18.9 How do I impress the sales person?
18.10 How do I get the best service from a sales person?

18.1 Should I use an up-scale retail store?
This is probably the best place to listen to gear in a controlled environment, next to your home. This is the best place to find expensive, high quality gear. This is the place which is most likely to have a good policy on home trials and a liberal return/upgrade policy. This is also likely to be the most expensive place to shop. One exception to this is that these stores have the ability to sell demos, returns, and discontinued gear at very advantageous prices.

Some up-scale dealers will negotiate price on large systems or expensive purchases. It never hurts to ask.

There are definitely better and worse local hi-fi stores. If you find a really good one, it is probably worth the extra money to buy from them, rather than from discounters. A really good store will not push you to buy what they want to sell. A really good store will allow you to take your time with your decision. A really good store will not distort the truth in describing equipment. A really good store will help you get the most out of your purchase by showing you how to set it up. They will tell you what placement works best for the speakers. (Don't believe them if they tell you to put them anywhere.) A really good store also selects their lines carefully. They don't want dissatisfied customers or warranty returns any more than you do. A really good store will also have technical equipment and/or skilled technical people that can perform tricky adjustments correctly, such as cartridge and tonearm alignment.

Due to the nature of the customer, a hi-fi store in a shopping mall is likely to use high-pressure sales techniques. They know that the majority of their customers are distracted easily by 299 other stores. Most of their sales go to customers that come in for 3 minutes, select something, and leave. There are exceptions to this, of course, but if there was a good generalization, it would be to look elsewhere. There are stores in large buildings, small buildings, private homes, shopping plazas, and every other conceivable venue. Search from among these to find one that meets your needs and fits your style.


18.2 Should I use a discount store?
If you need to listen carefully before making up your mind, discount stores can be very frustrating. If you know exactly what you want, then this can be a great place to save money. Don't expect knowledgeable sales help or after-sale support. Be sure to ask about the warranty (see 19.1 below on warranties).


18.3 Is it right to negotiate price?
Most people feel that it is fair to negotiate. Some feel that it is fair to lie in negotiating, as the sales people frequently lie to you also. Others think that lying to get a lower price is an immoral practice. It may even be illegal, an act of fraud.

Some people feel that if you negotiate over price, you encourage stores to mark prices artificially high, so that the stores have room to negotiate. Others feel that in negotiating, you are asking the store to accept a lower profit, or asking the sales person to take a lower commission and are directly hurting them.


18.4 How can I negotiate price effectively?
A great source of information on this topic is available from books on buying a new or used car. However, some very helpful general tips include:

Know the competition and the dealer. Know the gear. Know the prices available elsewhere. Believe in your research, not their words. Stand your ground. Be nice to the people but hard on the deal. Be prepared to walk away if they won't agree. Expect their lines and prepare responses in advance.
For example, expect the dealer to claim that the Nakamichi deck is the best cassette deck on the market. Be ready with a reply such as at that price, you can buy a DAT machine which has better frequency response, lower signal to noise ratio, etc.
18.5 It sounded great in the store. Is it great?
Never let anyone else pick stereo for you. Especially not speakers. They all sound different, and you don't need a golden ear to hear the differences. Listen for yourself and ignore what the sales people say.

If you are still unsure, ask the sales people to let you take the gear home for a home trial in exchange for a large deposit. Home auditioning takes 99% of the risk out of store auditions.


18.6 Do sales people try to trick the customer?
Some do and some don't. Some will treat unpleasant customers badly and treat friendly people well. Most sales people aren't wealthy. They sell stereo to make a living. If they can sell you a more expensive piece of equipment or a piece of equipment with a higher profit, they will make more money. Usually, this figures into everything they say. Some sales people claim to be altruistic.

Some sales people really are open and honest. They may starve with this approach, or they may have a nice enough personality, a good enough product line, a good enough store behind them, or enough technical background to overcome this "limitation".


18.7 How can sales people trick the customer?
Often, a customer will trick him or herself without help. We are often swayed by appearance, sales literature, position of the equipment in the show room, and our own desire to buy what others will like.

Some times, the sales person will actively try to push a particular piece of equipment by demonstrating it against another piece of equipment which is inferior or defective.

Some sales people will demonstrate a set of speakers while simultaneously driving a subwoofer, even though they are not telling you this. With the subwoofer, it probably will sound better.

Some sales people will demonstrate one set of speakers louder than others. Louder almost always sounds better.

Most stereo buyers go into the store, spend a few minutes selecting what they want, lay down big bucks, and leave. They don't need to be tricked. They don't listen carefully. They trust the sales person's choice as best in their price range. For non-technical reasons, these people are the most likely to be satisfied with their purchase.


18.8 What should I ask the sales person?
What do you want to know? Seriously, the best questions are those which the sales person can answer without distorting the truth. Don't ask a sales person to compare their brand to a brand they don't sell. Don't ask "how good is the ...". Ask questions of fact.

Here are some questions you may want to ask:

If I don't like it can I return it for a full refund? Can I try this out at my home in exchange for a deposit? What does the warranty cover? For how long? What do I need to know to set this up for best sound? Do I get a manufacturer's warranty with this? Where do I take this to get it repaired under warranty? Where do I take this to get it repaired out of warranty?
18.9 How do I impress the sales person?
Why would you want to? You have money and he doesn't.


18.10 How do I get the best service from a sales person?
Be honest with the sales person. Set some reasonable request and ask them to meet it. For example, say that you will buy this if you can try it at home first and listen to it side-by-side with a piece from another store. Alternately, say that you saw the same thing at store Z for $xx less, but you will buy it from the guy if he will match the price.


Back to main index - Continue to 19.0 Miscellaneous

看不明，英文都还给老师了。

看不动

L版，实在大长編大論了‧看过一部分、觉得不似是近代的文章‧也不是出自资深发烧友的手笔‧但作为对HIFI及器材的基本認識，资料却很宝贵‧

俄~~~~~~~~~~~~~~~~~~~~~~~~~~~没看懂，哪位翻译一下：）

坛上的E文高手翻译出来益街坊啦。

17.0 The Press:
17.1 Which magazine should I read?
17.2 Which reviews are better?
17.3 Is Consumer Reports right?

17.1 Which magazine should I read?
Which ever one you like. None are absolutely objective. Here's a list of some common ones:

        Audio Amateur ($20/yr 4 issues) (Do-it-yourself)
                Box 576
                Peterborough NH  03458 USA
                603-924-9464
        Audio Critic (US $24/yr 4 issues) (High-end)
                PO Box 978
                Quakertown PA  18951 USA
                215-538-9555 or 215-536-8884
        Audio Magazine (US $24/year 12 issues.  Mid-fi)
                Subscription Office: PO Box 53548
                Boulder CO  80321-2548 USA
                800-274-8808, 303-447-9330
                Editorial Office: 1633 Broadway
                New York, NY  10019
                212-767-6000
        Audio Observatory (US $15/year 12 issues)
                22029 Parthenia Street
                West Hills, California  91304
        Audiophile Voice ($18/year 4 issues)
                Subscriptions: Michael Tantillo
                        132 Beach Avenue
                        Staten Island 10306 USA
                        Phone 718-351-9365
                Editorial Office: 2001 Palmer Ave Suite 201
                        Larchmont, NY  10538-2420 USA
                        Phone 914-833-1417
                        FAX 914-834-4070
        Bound For Sound (US $18/yr 12 issues) (High-end)
                220 North Main St
                Kewanee IL  61443 USA
                309-852-3022
        Car Audio and Electronics ($19.95/year 12 issues)
                Avcom Publishing Ltd
                21700 Oxnard Street
                Suite 1600
                Woodland Hills CA  91367 USA
                818-593-3900
        CD Review (Music Reviews; all tastes, only CDs.)
                $19.97 per year 12 issues
                PO Box 588
                Mount Morris IL  61054 USA
        Glass Audio ($20/yr 4 issues) (Do-it-yourself, tubes)
                Box 576
                Peterborough NH  03458 USA
                603-924-9464
        Hi-Fi Choice (Mid-end. Comparative reviews with graphs,
                        tables, and subjective commentary;
                        'Buying Guide' section)
                Dennis Publishing Ltd.
                14 Rathbone Place
                London, W1P 1DE, UK
                +44 71 631 1433
        Hi-Fi News and Record Review (Broad. Good new record
                        reviews. Good equipment measurements)
                Subscriptions Department
                        Link House Magazines Ltd
                        1st Floor
                        Stephenson House, Brunel Centre
                        Bletchley, Milton Keynes MK2 2EW, UK
        Hi-Fi World  (Friendly, lower-mid-end magazine)
                (reviews and "how things work" articles)
                Audio Publishing Ltd
                64 Castellain Rd
                Maida Vale
                London  W9 1EX, UK
                +44 71 266 0461
        In Terms Of Music  (Emphasizes music reviews, new)
                PO Box 268590
                Chicago, IL 60626  USA
                312-262-5918
        International Audio Review (US $38/yr, 12 issues?)
                2449 Dwight Way; Box 4271
                Berkeley CA  94704 USA
        Positive Feedback (US $25/yr 6 issues) (high-end)
                Oregon Triode Society
                4106 N.E. Glisan
                Portland OR 97232 USA
                503-235-9068
        Sound Practices (US $20/yr 4 issues) (Do-it-yourself)
                Box 180562
                Austin, TX   78718
                (512) 339-6229    Voice/Fax
                72411.533@compuserve.com
        Speaker Builder ($25/yr 6 issues) (Speaker projects)
                Box 576
                Peterborough NH  03458 USA
                603-924-9464
        Stereophile (US $35/yr 12 issues) (High-end)
                208 Delgado
                Santa Fe NM  87501 USA
                800-238-2626 or 505-982-2366
        Stereo Review (US $6.97/yr 12 issues.  Lower end/mass
                        market)
                Subscription Office: PO Box 52033
                Boulder CO  80323-2033 USA
                Editorial Office: 1633 Broadw
                New York, NY  10019
                212-767-6000
        The Absolute Sound (US $46/yr 8 issues) (High-end)
                Subscription Center: Box 6547
                Syracuse NY  13217 USA
                800-825-0061
                Editorial Office: 2 Glen Avenue
                Sea Cliff, NY  11579
                516-676-2830
        The $ensible Sound (US $20/yr 4 issues) (Mid/High-end)
                403 Darwin Drive
                Snyder NY  14226 USA
                716-681-3513 or 716-839-2199
        Ultra High Fidelity (UHF) (High end, no advertising)
                Box 65085, Place Longueil
                Montreal PQ  J4K 5J4  Canada
                514-651-5720
        What Hi-Fi (Mid-to-high End; comparative, subjective
                        reviews. Contains it's own buyer's guide
                        with recommendations)
                 Haymarket Trade & Leisure Publications Ltd
                 38-42 Hampton Road
                 Teddington, Middlesex, TW11 0JE, UK
                 +44 81 943 5000
                 US Enquiries should go to:
                        Eric Walter Associates
                        Box 188
                        Berkeley Heights NJ  07922 USA
                        201-665-7811

17.2 Which reviews are better?
Some reviews are so colorful and exciting, that they make great journalism and fun reading. Lets ignore these for now, even though they have their place.

Beware of reviews from magazines that advertise the same product. The likelihood of bias is too high. Unfortunately, that rules out 99% of the reviews in magazines.

Stereo Review has a bad reputation for loving everything made by every advertiser. Even high-end journals such as Stereophile and The Absolute Sound can be influenced.

A classic example of misleading reviews occurs with equipment submitted to a magazine for review. The manufacturer may send the editors a carefully built, adjusted piece for review. The magazine will honestly rave about it. The manufacturer will then send the design off-shore for more economical manufacture and assembly, and the quality will suffer. Lower quality components will be substituted for prime parts. Adjustments will be made to wider tolerances or will not be made at all. The design may be completely changed to make it more manufacturable. You will unknowingly get a completely different piece than reviewed.

Home auditions with one or two candidates from each of a few dealers are your best guide to be sure that you get what you want and pay for.


17.3 Is Consumer Reports right?
Consumer Reports is the most objective testing lab we have ever found. Unfortunately, they are also the world's least specialized testing lab. They market their testing to the average consumer. The average consumer will not hear some of the subtle differences which audiophiles hear. For that reason, Consumer Reports ignores issues that others feel vital.

Consumer Reports also insists on basing their audio testing predominantly on lab measurements. Although lab measurements do tell many differences between devices, interpreting lab measurements for best sound is difficult or impossible. For example, it is very hard to compare two speaker frequency response curves and tell which will sound better. Some $3000 speaker frequency response curves look worse than some $600 speaker curves, even when tested in the same setup. On the other side of the issue, Consumer Reports has improved its test methods, and will continue to improve. Expect the accuracy of their reviews to improve with time.

The Consumer Reports frequency-of-repair data base is larger than any similar data base published and can be trusted as well as any statistic.


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英文考试我每次都不及格。

每个字.....................................................................................




母，我都认得，就是不知道讲什么。