拜年！再实话实说，来砖 [复制链接]

原帖由 远去的村庄 于 2012-1-27 22:58:00 发表 请问拾音时会有反电势存在吗？

反电势是相对于电力推动而言。拾音时相当于单纯发电机原理。

原帖由 神农 于 2012-1-27 13:15:00 发表 楼主何不把你制作的功放来个巡回试听，确实好的话还怕没人识货？

前面只做了定性分析，具体到实用系统须定量对应调整的。
不是简单的一台功放就能解决问题。被动分频音箱有局限。
这个系统包括电子分频，多路精确修正功放和对应的音箱。
现在确实没时间和精力搞运动。
谢谢支持，有机会来北京，欢迎指导。

原帖由 znd06 于 2012-1-27 22:08:00 发表 浦东兄聪明，实践出真知。 这不等于它没有发出电流，刚才动的那一下子消耗在电阻上。如果是驱动信号，就会有所抵消。从外部看，喇叭呈阻抗升高，如果驱动电压恒定，则实际驱动电流减小。 个人认为开关功放也是有提升空间的，同理。 一切建立在实验基础之上，那来的帽子呦。

朱兄请蛋顶、蛋顶！！！


我引的是bebear的帖，指的当然是他，不会是你。


老浦东滴肚肠是直的，不喜讲违心话，更不喜拉帮结派，有话直说，望勿见怪。


喇叭的反电动势是客观存在，但不宜片面化，只看电压不谈电流，因为“功率”才会影响声音，光看空载电压是没有意义的。


就拿前面俺举的例子来说吧，要在0.1欧姆电阻上产生1伏电压，就需要10瓦的功率，喇叭如果拍一下就有如此强的能耐，发电机早就该改变结构了。


音响界的前辈们早已深知这些，也想出了很多行之有效的克制手段，从功放到喇叭结构都有采用，动圈喇叭中的铜短路环就是有效手段之一。


早上随便乱侃，得罪得罪。

怪我没看仔细，该自罚。
影响声音的确实是不够起眼的，实时伴生的反向电流。前面说到：以往总想克服，抑制，是和我的区别。所举假设仅为交代明白直接些，切勿对号入座。也很希望你能来京交流。搞点花雕、加饭没问题，哈哈

不错的文章，讲得很深入。

据专家研究（民科不算），反电动势虽然很弱，在物理上基本没啥动静，但却有可能影响到功放的负反馈电路，从而放大其影响，这种失真据说叫做“界面互调失真”，Interface Intermodulation Distortion，这些都是至少20年前的研究了。

POWER INTERFACE IIM

We all know Matti Otala, a Finnish researcher who discovered the origin of an obscure type of distortion, Interface Intermodulation Distortion (IIM). This new form of distortion, found as a result of a new measurement method, is caused by the amplifier design: the bandwidth of each stage, group propagation time, delay introduced by the various stages with impact on the feedback loop action during transients. Among the different measurement schemes proposed to prove the existence of this type of distortion, there is no lack of interest in those that simulate the appreciable energy caused by the counter-electromotive force of the loudspeaker and the acoustic enclosure, which is re-injected -- not as a voltage but as an energy -- into the output of the amplifier -- while the amplifier itself is reproducing a different frequency.

Actually, the classical measurements (harmonic distortion, intermodulation distortion according to the SMPTE norms) do not allow detecting it. The basics of this method, which was proposed about 20 years ago by a team of researchers from the University of Musashi, Tokyo, are still relevant today. They are depicted, with some extensions, in Fig. 2.

The method consists of injecting a 1kHz signal at the input of the amplifier under test to obtain a nominal 15W power into the load at the output. This is either a pure resistive 8-ohm load or a loudspeaker. A low output impedance power generator, in turn, through a non-inductive 250-ohm / 1000W resistor and a LC filter to suppress the 1kHz band (self-induction of 7.5mH/15A plus capacitor 3.3uF), inserts a 50Hz signal into the terminals of the load or the loudspeaker. You thus recover the composite signal present at the load or loudspeaker terminals. This signal is then fed into an audio spectrum analyzer.

As shown in the figure, the composite signal is returned to the amplifier and its input, because it contains a feedback loop. By injecting a second signal into the load, with a frequency much lower than the signal being amplified, the counter-electromotive force is simulated which the loudspeaker would inject into the amplifier.

This secondary signal follows very closely in the time domain and the amplitude domain the envelope of the signal being amplified, and is then more or less quickly attenuated and quickly decreases in frequency. These two effects are the result of the electromechanical damping of the moving mass, the air load of the membrane, and the mechanical friction which slows down the movement until the moving parts return to their rest position.

Curve #1 in Fig. 3 shows the original composite signal across the purely resistive load, on the left side of the 50Hz signal, and a small residual harmonic (100Hz) from the low-frequency power generator. Curve #2 shows the result from a high-quality amplifier with no IIM distortion, phenomena whatsoever. Curve #3, on the other hand, shows an amplifier having excellent harmonic and intermodulation distortion figures (like an average value of 0.008% at half power in the middle of the audio band and slightly more above that) but showing, under these test conditions, large problems of IIM distortion under power.

It is interesting to note, in passing, that this same amplifier, when tested with a slightly larger power output, changes its behavior and produces, as seen in Curve #4, an even higher IIM with a completely different shape than in Curve #3. The fact that these results vary widely from one amplifier to another makes us wish to know its impact on the sound reproduction quality of each.

It has been effectively shown on the spectrum analyzer that listening to amplifiers with anomalies as bizarre as those seen in curves #3 and #4 have a lack of finesse, bad timbre, or sound inexplicably "hard." However, many tests have shown that amplifiers with relatively high distortion levels because of low feedback factors can present, in this type of power IIM distortion, strong disruptions without being unpleasant to listen to -- far from it. That is the case for the model of which the measurement is shown in Curve #5, a mono triode amplifier equipped with a 10A/801A triode.

要不说“地球人都知道”呢。怎么应对才是根本。

经典负反馈电路就是对治"静态漂移"和"反电动势"的

哈哈，很少同意LPD的观点，但这回同意了。
不知道是不是喝多了，哈哈。。。
音响最大的问题不在功放，而在拾音器和喇叭。
反电动势是客观存在的，但不是楼主描述的那样，深度负反馈对反电动势有很强的抑制作用，不要误解。

我也觉得LPD说得有道理，电流与电压的关系！