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KEF的老旗舰??

KEF Maidstone R109
by Chris Binns
Issue 3 - November 1999

There cannot be many people with even a mild interest in hi-fi to whom the initials KEF mean nothing. From budget systems to esoterica, the company has held a high profile in the market place for many years. I should imagine that even if you have never actually owned a pair of KEF loud-speakers you could probably name at least one model, utter all, you have nearly forty years worth of product to choose from. Founded in 1961 by the now legendary Raymond Cooke, KEF (short for Kent Engineering and Foundry) quickly established an innovative approach to loudspeaker design that would keep them in the limelight for years to come. Their approach was novel in so much as they were one of the first companies to use synthetic materials in the cone assemblies of their drive units: Polystyrene and melinex being two early examples. One of the first products to emerge from this development work with these materials was the now legendary B139 bass unit. Due to the companies policy of making their units available to other manufacturers this radical design became something of au acoustic icon - if a loudspeaker design used one of these you knew that it was serious about low frequencies.
Several years later, in collaboration with the BBC, Cooke developed the drive units that would be pivotal in the design of the highly successful and influential LS3/5A, the B110 and T27.
These groundbreaking units incorporated materials such as Bextrene and Neoprene, the characteristics of which displayed several advantages over conventional paper based diaphragms. The new devices were superior in stability over a considerably wider range of both temperature and humidity. They exhibited low coloration and were suitable for mass production to a consistent standard within close tolerances. These developments changed the course of loudspeakers for the next decade or so and provided the basic template for numerous uncoloured designs throughout the seventies.

When you bear in mind that at a conservative estimate, the B110 and T27 units found their way into some three million speakers world-wide, I think it is entirely fair to say that, on this evidence alone, KEF have been something of a major influence in audio. The KEF company's auspicious first years were followed by a whole series of innovations. The sixties saw another first in their incorporation of computer technology in designing both cabinets and drive units. KEF were also the first company to use separate enclosures for each drive unit, as exhibited in the Reference 105's which were first produced in the late seventies. The eighties saw the introduction of the coupled cavity bass loading system which gave more control over drive units at frequency extremes. More recently in the early nineties, they introduced the Uni-Q driver. Not always without a degree of controversy these ideas have helped and sometimes shaped the art of loudspeaker design in the last three decades.

To the best of my recollection I have owned three different KEF loudspeakers. At least one pair (104aBs) are remembered with both affection and admiration for surviving the rigorous and unreasonable demands of student life, whilst maintaining a degree of dignity regardless of the sometimes questionable material fed to them. Post college, in the environs of the recording studio, I remember being absolutely floored by the awesome power of the KM-1 active studio monitors. Their enormous cabinets each boasted no less than four 15" bass units and a total of 1.6 Kilowatts of amplification.

When a company with a track record such as KEFs decides to launch a flagship i.e. the culmination of everything that they know about loudspeaker design, the very least we should do is sit up and take notice.

Development of the Maidstone began in the Autumn of 1995. KEF had already established some reasonably large and well regarded designs, such as the Reference four, but the company had produced nothing suitable for the world arena of high end heavyweight loudspeaker design. By contrast, container loads of large, esoteric loudspeakers were being shipped from the United States. To successfully compete in this market KEF needed to produce a loudspeaker to satisfy an extremely demanding list of criteria. The new unit would have to have a massive dynamic range, wide band width, low coloration, good imaging and overall musical quality plus the capability to deliver high (read realistic) volume levels, with minimum compression and distortion, in a large room. The design team could take some consolation from the fact that physical size and budget constraints did not appear to be too severe. Confronted with this challenge the engineers decided to start with a clean slate. It was not a case of pressing into service existing components designed for other systems. Every part of the Maidstone was drawn up with the final product in mind. Strangely enough, the design solution exhibits a return to more traditional values. With the exception of the Uni-Q, it appears that KEF has omitted many of the other innovations for which it is famous.
The Maidstone, once fully assembled, is large and very heavy. Each of the speakers arrives in two sections, and even in this state it takes two people and a lot of sweat to unpack, move and install them. If you don't believe me yet, maybe you will when I tell you that the complete cabinet is approximately 4ft high by 2ft wide with similar depth and weighs in at around 200lbs, or nearly 90Kgs. The weak hearted or spinally impaired should take notice of these facts and approach installation with some caution.
Each assembled cabinet comprises a bass bin, an upper bass cabinet and the mid I top box. The substantially braced bass bin has an internal volume of a 145 litres and is reflex loaded by two ports, each 100mm diameter and 420mm long, flared to avoid turbulence. KEF supplied a spare bass drive unit - not I might add because there was any likelihood of one failing but because they are proud of it. And so they should be. This is not just another 15" bass unit; it is one of the most beautifully engineered devices I have ever seen. Technically it is something of a masterpiece, incorporating a short (10mm) voice coil immersed in a long magnetic gap. This provides lower distortion and greater stability than the more conventional motor structure which utilises a long coil and short gap. The adopted approach is a lot more expensive to produce, primarily due to the cost of engineering the massive magnet assembly needed to generate and focus the flux evenly. The cone is a slightly flared, bonded pulp structure, terminated in a synthetic rubber suspension and complimented by a double rear spider assembly again aiding stability. This unit covers the bottom end of the frequency spectrum up to about 100Hz.
The two upper sections of the cabinet sit on the bass cabinet, coupled to it by 3 gold plated cup and cone assemblies. The lower of these contains a 10" drive unit built along the same extravagant lines as its big brother i.e. over engineered and dead gorgeous. The internal volume behind this upper bass unit is 14 litres and it works in the range from 100Hz to 400Hz. It also marks the Maidstone's first divergence from conventional practice. A lot of full range speakers step straight from a very large bass driver to a very small midrange unit, which can cause problems with the integration of the units, and the continuity of the bass. KEF have stepped the drivers far more gradually going 15" -10" -6.5". This, and the fact that they all employ the same doping, should produce musically far more coherent results, from the deep bass right up into the low treble. Or so say KEF and it has to be admitted that this is one of the R109's great strengths.

The top enclosure is bolted, via (gold plated) spacers, to the upper bass cabinet which contains a 6.5" Uni-Q driver handling (almost) the rest of the frequency range. The chassis of this unit, like the others, is a high quality die-casting finished to an excellent standard. For those of you who haven't encountered this KEF innovation, the Uni-Q driver demands closer investigation. Their design features a highly developed tweeter situated within the coil assembly of the mid-unit, thus approaching the ideal of a 'single point source' delivering a well behaved dispersion pattern with good phase characteristics off axis - or so we are told.

The overall look of the Maidstone strikes me as something that started out as an ugly functional object, before being tamed to make it more aesthetically acceptable. The 25mm thick (50mm in the bass unit) front baffles are curved in an easy going fashion and veneered in handsome grain matched mahogany whilst the back, top and sides of the cabinets are finished in a satin black. KEF have lavishly adorned the Maidstone's by gold plating virtually all the exposed metal parts. This extravagance is not too much in evidence until you see the back of the units which boast beautifully finished terminal plates and binding posts. There is also what might be mistaken for a nameplate on the top of the mid/HF box. Its true function is to facilitate the addition of a super tweeter, not something commonly encountered in this part of the world except by the RSPCA, but apparently becoming a trend in the far east. One wasn't supplied and I certainly didn't miss it.
The terminal plates are situated on the back and top of the bass cabinet, the former providing input to the crossovers, the latter, output to the mid and top drivers. This adds up to a staggering twenty binding posts per loudspeaker (all gold plated...). With this glut of connections available, various configurations for set-up present themselves. Everything from single wiring (using supplied gold jumpers) through to full 4-way active drive can be accomplished. KEF advocate an approach which lies somewhere in between. They recommend passive bi-amplification, for which, as we'll see, they have good reason.
Below the terminal boards lie the crossovers. One unit serves the two bass sections, the other the mid and high frequencies. Once again, high build quality is evident and KEF's matching of crossover components and drive units is second to none. This usually pays dividends with imaging and presentation of detail. A small amount (± 1 dB) of level adjustment is available for the high frequency energy level, via a screw terminal, to compensate for different acoustic environments (and of course it too is gold plated).

The mid-range cone material is doped polypropylene with a gentle curve whilst the tweeter is a 1" fabric dome, ferrofluid cooled within a neodymium magnet assembly.

One minor reservation about the crossover layout. I might be out of line here, but it seems to me that in a speaker of this quality particularly bearing in mind the unused space behind the top section of the cabinet, that there would be advantages in externally mounting the cross-over? If there is any evidence of electronic components being microphonic (and I firmly believe that there is) surely the last place you would want to situate them is inside a bass cabinet - especially one generating the volume levels of which the Maidstone's are capable.
Finally on the construction front, the bass cabinet is supplied with cones which screw into the bottom plate. The front ones are quite a bit taller than the rear, thus tilting the system back by a few degrees. As one would expect, the Maidstone comes with a full and lavishly presented handbook for installation and operation - yet again typical of the attention to detail throughout the whole system.
In spite of their size, the KEF's are not especially sensitive: 91dB is specified, along with a 4-ohm load. KEF's Conjugate Load Matching is not in evidence here - a lot of their earlier models incorporated circuitry to ease the load on the amplifier and thus make them easier to drive. Ironically I think we can safely say that the Maidstone is something of a power hungry monster, and the preference for bi-amping is understandable.
The system I used with the big KEF's comprised the Meridian 508.24 for CD replay and the Linn for vinyl. These were coupled with the Pass Labs phono stage, Primary line stage and mono blocks, which rose to the occasion admirably. It is rare that I'm able to safely unleash over 300 watts into any loudspeaker but it was clear that the Maidstone's were having a good time with them. Connections were made with Chord Company Chorus and Odyssey which did sterling service. Towards the end of the listening, and feeling the demand to try something a little more exotic (and in keeping with a twelve grand speaker) I prised a set of the ruinously expensive Nordost SPM from the editor's sticky grasp. And yes, it made a big difference, building on the already impressive performance.
The Maidstone's need plenty of space around them which was no problem fore and aft but unfortunately in my room I could not quite give them the clearance they deserved to the sides. They constantly reminded me of the fact, so be warned, you will need a lot of space.
The first thing you notice about the sound of the Maidstone's is the sheer, enormous scale that they present. There is an impact to music that a good large speaker can provide by way of a combination of dynamics, bandwidth and effortlessness that can be totally addictive. The Maidstone's are good. There is a sure footedness to their presentation that instils a confidence not available from lesser designs. To be more specific, the Maidstone puts all the fundamentals in the right place, and at the right time, with such authority that all other aspects of the performance fall into place.

Rhythmically complex music, such as Peter Gabriel's soundtrack to The Last Temptation of Christ is conveyed in a fashion that leaves no doubt as to who is in control. The drummers, all twenty of them! As the music builds up, and each successive layer of percussion is added, there has been a sense of doubt with many systems that they might lose the plot or even their bass units when things start getting frantic. Not so with the Maidstone's. I have never heard a speaker remain so totally in control with this music, even at really frightening levels. They manage to pass it off with a slight sense of arrogance as in "is that the best that you can do?" No problem. There is something about the combination of the two bass units that gives music of this sort both the weight and agility which makes it so exciting. In my experience a single large bass driver cannot successfully deliver both of these qualities. Likewise, large scale orchestral works such as Brahms' Symphony Nos. 3&4' are beautifully reproduced, again with that sensation of immense scale countered with poise, and where called for, drama. It was impossible for me to listen to just one movement, I had to play the whole thing through. By contrast, small scale recordings such as the Shostakovitch string quartets (all of them!) were reproduced with an intimacy that was enthralling, combined with a lush but accurate string tone, built on the resonant presence of the instrumental bodies. Although there was plenty of depth, the Maidstone's found it difficult to define a convincing lateral image of the instruments, resulting in a lack of precision across the soundstage.

Traditionally the Uni-Q drivers have excelled at image definition, to the extent that it wasn't essential to be square in the middle of the loudspeakers. This is where I suspect that the width of the room was upsetting the situation but unfortunately I didn't have the opportunity to try them in a wider one. Besides, moving them would have been a nightmare! I have heard them produce lateral images (although not of the exaggerated, pinpoint variety so fashionable at present), so this will have to remain a 'listen to them in your own room' judgement.
A session which remains highlighted in my memory of these loud-speakers occurred late one night, listening to the Naxos recording of Arvo Part; Fratres. This eerie music has a quiet, pensive beginning which grows to a thunderous dynamic crescendo before dying down again, all within the first movement. It is intensely emotional stuff, and I was left enthralled and not a little scared, particularly as I was in the house alone.
As you will probably gather, I was enjoying myself. I had to force myself to explore some of the other possibilities using ancillary equipment that I had on hand, because every time I went into the room I just wanted to listen to more music. I did get round to bi-amping the Maidstone's with two Naim NAP 250's, and this proved to be a good match, sounding a little tidier and more controlled, although lacking the drama and sense of scale that the Primary valve amps could generate. The attributes of the Naim amplification shone through, with good rhythmic delivery and timing. I began to wonder what four NAP 135's would sound like... but there just wasn't time, and by this stage I felt as if I already had a good feel for the KEF's capabilities.
It was also interesting to observe the reaction of other people, especially those not interested in hi-fi. The normal response to a pair of loudspeakers the size of the Maidstone's is an immediate 'How much do they cost?' closely followed by remarks concerning the justification of such expenditure, prior to a cursory listen. These KEF's elicited somewhat different behaviour. Possibly because of the grand scale with which they reproduced music, the normally casual listener was often seduced into a longer relationship. At one stage whilst the review pair was in residence, what started as an evening barbecue instead became an intensive listening session. I ended up with eight people present (none of them remotely interested in hi-fi), rifling my music collection for requests, and wallowing in the sheer enjoyment of the sound, to the virtual exclusion of conversation. This continued until just after 5 o'clock in the morning!
There is no doubt that the Maidstones are remarkable. Like any esoteric product, they demand skill and patience in setting up, and the choice of suitable amplification is certainly a limited one. Yet again we are confronted with a product that demands the agility and subtlety of a small amplifier combined with the sheer muscle and current drive of a much larger unit. Fortunately because they work so well with bi-amplification, this dichotomy is not the problem it might otherwise be. Similarly they are demanding of the room. These loudspeakers excel at presenting music on a large scale and in order to achieve their full potential they need plenty of space to breathe.
Have KEF met their design objectives? Yes, I believe they have. The Maidstone's did all the things that you would expect a large loudspeaker to do and with supreme confidence. Are they value for money? I just don't know That depends on your particular outlook and circumstances, I know that I spent as much time as I possibly could listening to the Maidstone's, and when the time came for them to go I realised that there was going to be a considerable period of readjustment. I still miss them.

TECHNICAL SPECIFICATIONS

Product Description: 4-way, stacked enclosure loudspeaker.

Drive Units:
Bass: 380mm doped paper cone, double suspension, under hung voice coil.
Bass/Mid: 250mm doped paper cone, underhung voice coil.
Midrange: 160mm doped polypropylene cone.
Tweeter: 25mm ferrofluid cooled, fabric dome.

Cabinets:
Bass: 145 litre, 25mm braced MDF, 50mm baffle. Reflex loaded.
Bass/Mid: 19 litre, 25mm braced MDF.
Mid/Treble: 6.5 litre, 25mm braced MDF.
Crossover Frequencies: 100Hz, 400Hz, 2.8kHz
Frequency Response: 35Hz - 20kHz ± 3dB. -6dB - 30Hz.
Sensitivity: 91dB/w
Maximum SPL: 118dB
Power Handling: 400 watts
Impedance: 4 Ohms
Weight: 87kgs
Dimensions (WxHxD): 600 x 1188 x 671 mm
Finish: Mahogany / Black Satin (Other veneers available to special order.)
Price: £12000

一、KEF的发展

KEF位于英国Kent郡的Medway河畔。KEF的全名是Kent Engineering Fonndy，是肯特郡的一个公司。我们介绍的R-109 MAIDSTONE梅德斯通，梅德斯通就是KEF工厂所在地。KEF建于1961年，是由原来在英国广播公司工程部担任技术主管雷蒙德•库克（Raymond Cook）创办的，到今天已有近40年的历史，不论是在我国、在英国、还是在世界上都可以算是历尽沧桑的老厂了。

20世纪80年代曾经看到伦敦出版的《High Performance Loudspeakers》一书。在这本专论扬声器的书中涉及到KEF至少有4次---5次之多。

我国的扬声器厂家多家超过40年的历史，可惜都没有取得像KEF这样世界范围内的知名度。为了学习和借鉴，让我们看一下KEF 40年来有些什么重要产品和技术建树。

1）大胆采用新材料

在20世纪40年代KEF最早推出的三分频扬声器箱中，中频单元、低频单元采用了3×Polystyrene（聚苯乙烯）振膜；高频采用了Mylar（聚酯）振膜。20世纪60年代中期，KEF又采用了人造橡胶中频单元的折环，还采用了一种Bextrene振膜（一种轻、薄而坚韧的纤维材料，耐高温，防潮）。在扬声器业内流行一句很有名的话：“扬声器的问题，某种意义上就是材料问题。”一种新的优良的材料的选用往往会改变扬声器的面貌。事实证明这话是很有道理的。回想我们在20世纪60年代初开始介入扬声器，正是以纸盆工艺研究开始的。KEF一开始就抓住了一个材料问题，说明了他们的大胆与创新，也说明了他们一开始就抓住了关键。

2）LS3/5A的坚实基础

LS3/5A称为英国一代扬声器的典范、经典之作。关于LS3/5A我们已经讲了很多，这里就不再重复，但是KEF为3/5A提供了高频单元T27。KEF和英国其他公司一同成为LS3/5A的制作厂家。一家好公司会生产某件好产品，某件好产品又会使该公司名声大振。几十年来，音箱的名牌、型号多如牛毛，但经过岁月的洗礼，风韵犹在宝刀不老的音箱实在不多。LS3/5A不久前停产，还引起许多人的感慨和怀念，足见其影响深远。

3）开创用计算机分析扬声器的特性

只有很少数的扬声器工厂会认真去做研究发展，KEF算是一家。20世纪70年代初，KEF开始用计算机分析检测扬声器的振动。除了在极低的频率条件下，振膜呈刚体活塞振动，到了高频振膜呈现分割振动，即在振膜上每一点的振幅和相位都不尽相同，而我们用肉眼简直无法观测。KEF率先采用了激光扫描的办法，拾取扫掠点的信号（振幅和相位），再用计算机分析，可以看到在一定频率下，一定时间振膜振动模式。这样就可以寻找出扬声器振膜设计上的缺陷以及工艺制作中的不均衡和偏差。这项技术在英国其他扬声器公司也被采用，例如B&W公司，日本亦有公司采用。我国却没有哪个扬声器采用这个技术。在20世纪80年代，我曾经与天津大学力学系佟景伟教授合作对一个耳机振膜作了激光扫描计算机分析，取得了很好的效果，当然具体方法与KEF并不完全相同。

4）UNI-Q同轴共点技术

同轴共点（UNI-Q）技术是KEF在扬声器设计上的一项专利发明。由于一只扬声声器难以重放全部的音频频率，所以采用几只不同频段的扬声器（低频、中频、高频）组成一只音箱，来重放全部频率。但是由于不同位置扬声器的摆放，相位不一致，指向性不一致，会产生一些干扰，而且时间也先后不一致，也会产生相位变化。

同轴扬声器一定程度上解决了上述难题，刚开始高频单元悬置在中频或低频单元的前面，轴线是一致了，但是不同音频的时间差没有解决，而且还有一定的相互干扰。后来有了改进，将高频单元放在中频、低频扬声器的后面，磁路中用一个号角连接，它避免了放在前面的相互干扰，但是时间差的问题仍没有解决。由于钕铁硼磁体的出现，扬声器磁路可以做得很小，将这样的高频小单元放在中频或低频扬声器的中间，即所谓UNI-Q技术。

图18-31是这种UNI-Q技术剖面图。由图可以看见这种UNI-Q技术与另一家英国扬声器公司的同轴技术有异曲同工之妙。高频单元是放在低频单元的导磁柱之中。

图18-32是三种音箱的示意图，依次为同面式、同轴式和相合式，即同轴同时式（UNI-Q）。

图18-33是一个UNI-Q单元剖面示意图。研制扬声器的人一眼就可以看出其中的奥秘。能实现UNI-Q的关键在于低频单元的导磁柱要足够大，高频单元足够小，小到可以放进去。

5）耦合音腔（Coupled Cavity）技术

这项技术一直沿用至今。“耦合音腔”顾名思义，就是利用扬声器音箱内一对互连的音腔来达到某一种功能，而KEF则运用此技术在低频之上。长期以来，扬声器设计者对直立柱形扬声器设计都有一种顾虑，那就是由于前障板变得修长，导致在选用低音扬声器单元时受到很大的限制，而单元口径大小，自然与低音的排放量和伸缩性具有直接的关系，所以一般来说，座地柱形扬声器的低音分量会相对减少，而“耦合音腔”就正好是针对这个问题而设计出来的解决妙法。

KEF先在扬声器音箱上下两端各设一个开了排气孔的音腔，如图18-34所示，跟着以一对同口径的低频单元，以相对方式互相击荡，结果大量的低频便会朝着预先设定的前障板上的排气孔排放出去。这样便大大加强了扬声器在低频上的表现。而且亦解释了KEF的座地柱形扬声器，为什么可以经常营造出超越它们体型和单元直径的低频，还依赖于它们另一外表特征，就是特大口径的低频反射孔。由图18-34可见，这种结构上下两只低频扬声器装在箱体中部，磁路用一柱相连，保持稳固，声从倒相口发出。这种结构有省障板的一面，也有结构复杂的一面，支持的轴会对辐射有影响。

二、寂寞后的辉煌

KEF在20世纪70年代推出Reference SERIES 104，这是代表KEF技术的参考系列，后来又陆续推出105、103、101、105/2；80年代又推出旗舰107。90年代，KEF虽然不断推出新产品，但看不到它好的代表性的作品，有点销声匿迹的感觉，形形色色的传闻也不少。但是人们都知道KEF是一个有实力、有创新精神的扬声器公司。利用计算机分析测试扬声器一直是处于领先地位的公司。我们终于在2000年以前到了KEF新的大型旗舰式音箱，Mode 109 The Maidstone。果然从气势上，音质上都得到人们良好的评价。

“他山之石，可以攻玉”，我们对国外好的扬声器、音箱不只是一味赞美，看看它们好在哪里，有什么可借鉴和学习的地方。

二、Mode 109的概况

它是一个大型扬声器箱，在KEF也是空前的。以15英寸（φ380mm）扬声器为低频扬声器的大型机，而且是四分频5路扬声器系统。因为中频段是UNI-Q,看起来是4路，实际上是5路。在机箱上还有一只超高频扬声器以求更宽的重放频率。Mode109扬声器系统由三个独立的箱体构成，稍微有些倾斜，除了高频单元以外，都是KEF自行开发的。这就说明了KEF不只是一个箱体装配厂，而是自己也生产扬声器单元。
粗看和流行风格有所不同的是外形不是那种细长、苗条，而是比较宽。

三、Mode 109的几个技术特点

对于Mode 109 KEF发表一段自述：“最近4年推到市场的KEF参考系列充分体现了KEF扬声器设计的哲学，通过精心制作，通过科学设计，通过优良产品工艺达到优越的音质。”R109/Modestone系统是为了重放全频带大动态的音乐信号。采用大口径扬声器使低频扩展和得到足够的响应，巨大的精确度，低失真，低染色。

1）激光扫描图

图18-35是SP145 UNI-Q单元的中频锥体激光扫描图。图上所显示的是3.11Hz时锥体的振动模式。在锥体上的弯曲波从音圈到折环，被具有阻尼性能的折环材料所阻尼。这种激光扫描的一种方案是利用全息干涉法，得到全息干涉条纹图，再将全息干涉条纹图由摄像机和图像处理接口板直接输入计算机自动处理，将图像经高频滤波去掉噪声成分，再经条纹细化提取中心线坐标，再经曲面拟合，绘图、打印图形。早期用全息干涉法分析扬声器振膜的振动，但是全息图不是振膜的实际振动图形，只有激光扫描法才能看到真实的振动。

2）SP1405低频单元和有限元

从图18-36分析这个扬声器单元有这样一些特点：
1）是铸铝的，这保证了盆架的坚固性和一致性。
2）音圈是短音圈。短音圈的概念是指音圈绕线部分的长度远小于导磁板的厚度。其目的是保证音圈振动处于磁场均匀的线性部分。
3）双定心支片
一场扬声器只有一只定心支片，这只SPI1405却有两只定心支片，以限制振膜严格沿轴向振动。
4） 非饱和磁路
导磁板的缺口形成非饱和磁路，其目的也是为了减少失真。
5）曲线形振膜

振动膜是由纸浆制成的，采用橡胶折环纸锥表面喷涂一种专门的特殊涂料，纸浆仍是扬声器振膜最主要的原料。纸浆的优点在于密度比较小，有适当的内阻尼，因此音质柔和，纸浆的缺点是刚性不够大。而喷涂一种化学涂料的好处是提高了纸盆表面刚性。仍保持了纸盆密度小，适当内阻尼的优点。

振膜是曲线性的，振膜的几何形状决定了扬声器的频率响应。而振膜的设计过去多根据经验并制成模具，制作纸盆，做成扬声器再测试。这种方法费时、费力、费钱。有时要反复试制几套模具。计算机技术的发展，用有限元法可以解决振膜设计的难题。

将振膜分成若干个有限元，每一个元的振动方式可以找到，有可计算的数字模型和方程式，再用计算机完成有限元的计算，大量的费力、费时的劳动被计算机完成。输入各种几何、物理数据，就可以得出扬声器的频响曲线等参数。因此说，有限元法的出现，解决了扬声器锥体传统的试凑方法，利用一种有效的数学方法。很遗憾的是，国内扬声器厂家只有个别采用过有限元法。除了KEF，欧美许多扬声器公司都采用这种方法。很遗憾的是，国内扬声器厂家只有个别采用过有限元法。

图18-37是低频单元SP1405在300Hz时的激光扫描图，由图可见在折环处有轻微的变形，是向非刚体变化的象征。根据这个住处可将低频分频点定为100Hz。

中低频单元型号是SP1406。SP1406同样是一个短音圈长缝隙磁路系统，喷涂纸锥和铸铝盆架。SP1406在R-109音箱中是中低频单元，它重放100Hz—400Hz一段的声音，图18-38j SP1406在560Hz激光扫描图，表示在560Hz开始突变。

6）箱体设计

箱体设计得相当坚固。是主流派的做法，除了振膜振动，不希望箱体振动，不增加染色。

低频箱采用145l、25mm厚的中密度板；面板用50mm厚度的中密度板中频箱；中低频箱都用25mm厚的中密度板。3个箱体组合在一起，箱体内充有阻尼材料，用于吸收驻波，吸收高频行波。附加阻尼使低频衰减。

R-109的障板宽度是一个特色。从当前的审美观念看，箱体前面大多以瘦长苗条为主。R-109较宽，当然也是为了380mm扬声器的安装与稳固，而且指向特性不错。同时我们看到对箱体的有限元分析，显然面板宽了，但指向性控制在更宽的频带范围。图18-39是类似R-109 UNI-Q箱体的有限元分析，显然面板宽了，但指向性控制在更宽的频带范围。图18-39是类似R-109 UNI-Q箱体的平面障板上活塞的偏轴响应，此曲线表明偏离15º、30º、45º的偏轴声压响应。

图18-40则是活塞装入R-109 UNI-Q箱体时的偏轴响应，15º、30º、45º水平偏轴响应。
图18-41是对UNI-Q箱体采用有限元法的示意图。

四、昂贵的价格

R-109每对售价约19万元人民币，尽管重放音质优良，技术含量很高，但也是一对昂贵的音箱。常常有人问，好音箱为什么那么贵，除了一般产品的生产成本、宣传广告成本外就是这种箱体的技术含量。为试制、研究这样一个音箱投入的人力、物力、智力是很多的。图18-42是R-109各单元的频响曲线和箱体阻抗曲线图。

听过R-109的人对其声音表现评价都很高：“独特的音色”、“出色的声音”、“高音中具有独特的魅力”。这里又有一个问题，有人问R-109这类旗舰类音箱为什么做得这么大。道理其实很简单，好的优秀的大音箱使你得到一种震撼力，这种感觉是任何小音箱所无法感受到的，这就是“曾经苍海难为水，除却巫山不是云”。小型音箱自有小型音箱的优点和魅力，但将小型箱体作为音箱发展方向是难以说服人的。

我们评述KEF R-109的优点，也是为找到借鉴之处，但不等于我们认为KEF一切都好，例如前几年看到的一种装有椭圆扬声器的音箱，就使我们难于理解。KEF的成功很大程度上在于以技术研究的忠实，不仅拥有许多优秀的工程师，还有许多大学作为他们的顾问。产品从研究到生产有2年—5年的时间差，我想这是最值得效法、学习、推崇的。