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发表于 2011-3-9 01:42
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Nelson Pass的电流功放 和 全频补偿网路法
继续老pass的阻尼
Why is that? First, such drivers are able to takeadvantage of acoustic and suspension resistance to achieve some or all of thedamping that they need to prevent excessive overhang because their moving massis very light. With their efficient motors, even a high source impedance isoften enough to give critical damping. Second, their impedance curve tends toreflect their needs – more current both at low frequency resonance and in thetreble, two areas where frequency response has fallen off with increasedspeaker impedance. If you want, the current through the voice coil can be madeconstant regardless of the variations in the acoustic environment. The voicecoil force is invariant whether the cone is loaded into a horn, sealed box,bass reflex or whatever else you care to mount it in.
那么是什么原因呢？
一、这些单元可以受益于声学阻力和悬挂阻力来达至部分甚至全部的阻尼效果，足以防止过度振幅，因为振膜移动质重“太轻”，加上高效的磁束，即使信源内阻较高，通常都可以给与“恰当的阻尼量”。
二，全频的阻抗曲线通常是反映它的需要——低端共鸣区和高端需要更多的电流，因为这些区域的阻抗较高。若有需要，音圈的电流可以不管声学环境变化而做到恒定的电流。即使单元装任何箱体结构，号角、密封、倒相或任何箱体，音圈发出的能量不变。
4 Third, they are very easy to adjust in the upper midrangeand high end where you typically run into peaking problems. Most of thesedrivers are too hot in the upper midrange and quite a few of them fail to makeit to 20KHz. With a simple parallel network, you can arrange for a midrange dipfollowed by an increase at the top, evening out the loudspeaker response. With thehigher quality drivers, you more than not simply want an equalized “shelf”where everything above a specific frequency is evenly attenuated.
三、它们的高中音频段和高频段很容易调整，其它的单元通常会振幅到顶。大部分全拼都在“中高段”着火而不能到达20KHz。做个并联的网路，可以把中频陷掉部分、高频推高一点….推到标称频率上限以外。有了高质量的单元，一定想等化一下，令某频率以上的相应平顺化。
The adjustments for damping at the low end and themid/high peaking are easily accomplished using R, RC or RLC (resistor/inductor/capacitor)networks wired in parallel with the output of the amp. You occasionally see thissort of equalization with full-range high efficiency drivers usingvoltage-source amplifiers, but there the elements are paralleled and thenplaced inseries with thedriver. With a current source, the equivalent circuit becomes the elementsplaced in series and then paralleled with the driver.
这个等化调整是需要做个阻抗、阻容或阻容感抗网路，并联在输出端（跨接在单元两端），这种网路，在电压源功放驱动的全频是常见的，但是却是原件并联，串在信号通道中。在电流源功放则是网路原件串联但是与单元并联。
Of course with a current source, there's the addedbenefit that the resistive element of the speaker cable and the connectionpoints can be made to largely disappear. To obtain the best results, theloading network is placed close to the driver instead of the amplifier. The followingpages will show what we found with a variety of full-range efficientloudspeaker transducers when we drove them with an active current source andexperimented with parallel networks to shape the response to our liking.
毋庸置疑，有了电流源功放，更有利的是喇叭线材和接触点的电阻成份仿佛消失。要效果靓尽。这个网路会尽量放在单元附近，而不是放近功放。后面会告诉你，我们在这些不同的高效全频身上如何利用主动的电流源功放和实验出来的网路为频响曲线“整容”成为我们“心中美女”。
Most of the examples we will examine do not require true current source amplifiers, onlyamplifiers of quite high output impedances. Most of these cases will be happywith an output impedance of approximately 47 ohms or so and prefer 47 ohmsloaded in parallel with the output of a current source. That being the case,you can build a Thevenin Equivalent of such a current source by placing a largeresistor (here later referred to as R0) in series with the output of a highwattage voltage source amplifier and get similar results.
大部分这里研究的例子都不需要电流源功放，只要功放有足够的“输出内阻”（哈！？老Pass真的发烧？）
大部分的单元都喜欢内阻在47欧的功放或者搞个47欧并联在单元上。如此搞法，你，可以做个等效Thevenin 电流源功放，只要在电压功放串个大电阻(就叫做R0 吧)在输出线上就行。（老余按: 前年我搞过，串了个50欧在喇叭红线上，效果不明显，因为是蛋鸡而不是晶体佬用晶体机，无晶体机也。）
I’m not saying it will equal a spiffy First Watt F1 (beingClass A and no feedback and all), and your resistor will run hot. On the otherhand, you probably already have such a voltage
source amplifier and some of thesespeakers are quite cheap, allowing you a taste of these forbidden pleasureswithout high expense. I want to emphasize that this does not serve as any sortof comprehensive guide to designing systems around this approach. You can buildup the examples and they will probably measure about the same. But rememberthat we are mostly restricting ourselves to the sealed box case forsimplicity’s sake. In the real world and most of time, these drivers are usedin an enclosure that also utilizes the back wave of the driver. Additionally,the best measured curve is often not the best sounding one so be prepared totry various values to get satisfactory sound.
我不是在卖我的靓机 First Watt F1 的广告（它是全A类无负回输JJ），同时你这个电阻会发热。另一方面，你可能已经有部电压源功放和几个鸡级单元在手，可以花费无几，试试这只螃蟹。我强调，这篇“有字天书”不是个设计电流源功放的工程指导，你可以试试做，可能和我的结果一样过瘾，但提醒你我们是用密封箱体做实验，因为操作简单。回到真实世界，多数箱体都利用振盆背后的声压加强低频。还有，测量曲线最美妙的时候，并非最靓声的时候。所以准备几个不同数值，搞到自己满意为止哈！
5 Amplifier / Loudspeaker / EQ network Model The following schematic will bereferenced through the rest of the article: This diagram shows a current-sourceamplifier, the simplified model of the loudspeaker's impedance and the generalizednetwork that we can parallel with the speaker to enhance its performance. The speakermodel consists of L2/R2/C2 that model the fundamental resonance, and R3/L3 giveus its DC resistance and high frequency inductance. A good example of this isthe simulation of the Pioneer b20fu20-51 driver. The values L2 = .05 H, R2 = 27ohms, C2 = 300 uF, R3 = 7 ohms and L3 = .1 mH give a reasonable facsimile ofthe measured free-air impedance curve shown below.
功放／喇叭／等化网路模组
下面的线路图是个标准参考图：让你知道电流源功放、等效喇叭单元阻抗特性和并联的等化网路的结构来加强效果的概念。喇叭单元的等效电路包括L2/R2/C2 模拟基本的F0 谐振，R3/L3是直流阻力和高频的电感。例子：先锋b20fu20-51单元。L2=0.05H，R2=27欧，C2=300uF， R3=7欧；
L3=0.1mH是自由空气阻抗曲线的仿真
6 Unless otherwise noted in this discussion, we will beaddressing the driver mounted in a sealed box of a given volume, as it is theeasiest design to consider. Horns and rear-loaded acoustic systems are morecomplicated to simulate and measure and the test results are more difficult toduplicate and interpret. One advantage to a sealed box for fullrange drivers isthat the excursion becomes limited below resonance, which can reduce distortionparticularly at higher levels. Driven by a voltage source, we usually see aresponse loss anywhere from - 6 to -15dB at low-frequency resonance and atreble that increases or declines (or both) depending mostly on the coneconstruction and voice coil inductance. Driven by a current source, we notethat the bottom end is bumped up at resonance and the top end is increased whencompared to the performance of the voltage source.
除非特别标明，全部都是把单元装在特定容量的密封箱体，因为容易考量。号角和背负箱体结构难以简单模拟、测量，而且测试结果难以重复和解读。全频在密闭箱的好处是在F0以下振膜震动受控制，减低失真——尤其是大音量时。用电压源功放通常会看到低频有-6到-15dB 的滚降但高频却增加或减少（看锥体的结构和电感量）。电流源驱动的话，对照电压源功放，我们看见低端F0 附近丰满了，高端增加了。
Let's assume that we want to achieve optimal frequencyresponse for a given system. This is not necessarily the best-sounding system possible but causes lesssubjective arguments. We can trim the damping "Q" of the lowfrequency roll-off knee by trying different values for R0 (L0 = 0 in this case) until it flattens out to ourtaste. Most of the drivers we worked with were happy with values from about 22ohms to about 47 ohms. It is surprising that so little damping gave suchdramatic results but as previously pointed out, this category of loudspeaker respondswell to small amounts of damping.
假定我们想要完美的频响曲线，不一定是最好声的，但可以避免争论。
我们可以改变R0（那么在这里L0=0）来改变阻尼的低频滚降的“Q”，直到我们喜欢为止。大部分测试的单元都在22欧到47欧附近。这么少的阻尼就可以有这个效果真真大吃一惊，这些喇叭对这么少的阻尼“反应良好”。
Usually we also want to adjust the upper midrange andhigh end. Often these drivers will exhibit an upper-mid peak followed by adecline before the upper-most treble is reached. We can compensate for this byour selection of R1, C1 and L1, which can be used either to create a shelf or adip to flatten out the response. With these models in mind, we measured all thesample speakers of interest, developing networks to optimally flatten out theirresponse with a current source, and comparing this with the same speaker drivenby a voltage source. We used a Vidsonics “virtual crossover” substitution boxto play with the parallel loading and took both near-field (from an inch or so)and far-field (from 1 meter) response measurements using Mlssa. Again, theresults here are not necessarily the best sounding ones achievable and I am notattempting to address this subject as such, given the wide range of sourcematerial, listening environments and subjective tastes. Typically, these exactnetwork figures are not the ones listeners will subjectively prefer. Usuallythis is because listeners tend to prefer a higher value for R1 than is shown onthe table. If you decide to use one of these networks, consider the possibilitythat R1 is the minimum value and use a switch or high-power (5 watt)potentiometer to variably increase the value to as much as twice R1. Less oftenyou might consider a different value for L1 to trim the treble.
通常我们都会调调高频到中高频段。这些单元都会在稍高的中频大叫但在高频却滚降。我们可以调整R1，C1和L1，把这些谷和峰抚平。参照这个概念图，我们把选择部分来设计网路，搞平滑他们在电流源功放的频响，与电压源比较。我们用了个Vidsonics “虚拟分音网络”代换箱体，来把弄这个并联的网路，用Mlssa测试远场响应（1米）和近场（1寸）响应。再说一次，平滑响应并非一定靓声。这里不准备讨论靓声这个部分，因为很多音源、房间、主观的因素影响。典型的结果是，这些改动都不太受欢迎。他们都较喜欢大的R1效果。如果使用这个网路，先用最小的数值，然后慢慢调到两倍。有时候可能考虑用不同的L1去砍高频。
I repeat: Consider this as an experimental guide and agood starting point. Be prepared to change the values to suit your needs andremember that these figures were obtained in stuffed sealed enclosures in alarge room placed well away from the wall. Your results will certainly vary.Also remember my comments reflect off-hand reactions. Please do not treat themas reviews.
在重复：这是实验记录，作为一个基准来开始是不错的。所有数值都需要准备改动，还有记住这是有吸音的密封箱体，在大房间摆位、离墙摆放。你的结果不会一样。同时我的说法是即时反应，并非试听报告。
7 The following table shows the values that resulted inimproved frequency response curves with current sources for different speakersin different sized boxes: * Mini-Me is the Lowther Mini-Medallion rear loadedhorn enclosure. Horn is the KleinHorn, a 20 foot long 30 Hz rear loaded hornwith a 30 sq ft mouth. Article to follow shortly.
后面的表格是我们测试后，用电流源功放、不同箱体容量，达到好曲线的数值。Mini Me是lowther Mini-Medallion背负号角箱体，号角箱体是Klein Horn——6米多长的30Hz背负号角响，3平方米号嘴。这些以后再说。
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以下是各个具体单元的解说，我就不翻译了（全翻，老pass可能有意见了）
这个并联网路的做法，理论上对信号相位不影响，可能值得学习。等化串在信号通道还是有点忐忑......., 配晶体机，50欧......，惹人遐思.......
还有就是：这里说明单元的振盆质重对单元的Q值影响是绝对的，越大质重，除了反应慢，还有越需要阻尼、F0 摆幅越大——喇叭单元F0 附近的倒灌电能越大。
[ 本帖最后由 henry余 于 2011-3-9 02:49 编辑 ] |
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