These are excerpts of Nelson Pass's paper. I made my comments in BLUE color. This gets very technical, that's the reason I put it in separate post.
PAGE 2....................I tested a 10 foot sample of each cable type using the Fig. 3 setup. I drove the cable by a high source impedance and measured the voltage across it, showing its series impedance. This voltage, referenced to a 0.1 ohm non-inductive resistor and measured from DC to 100kHz, clearly shows the cable impedance's resistive and inductive components (Fig. 4). For the twin lead types, inductive and "skin effect" (an additional high frequency resistance effect) components begin to show up at about 1kHz; they increase the impedance, causing high frequency loss in addition to the cable's resistive losses. Interestingly, all the twin lead types have similar cable inductance values, approximately 2uH per 10 feet, and in the region just above the audio spectrum they are nearly identical. Fig.4 shows below 20kHz they fan out to their respective resistance values. The lightest wire, #24, clearly has the most loss, while Fulton cable has the least...........................
PAGE 3............The existing literature covers the subject quite well. However, I think you will find it useful if I briefly touch on the effects of this series impedance as it relates to frequency response and damping factor 4, 5, and 6.The performance context lies also in the amplifier's source impedance and the loudspeaker's load impedance. The system's performance will depend on the complex sum of the impedances involved:
Z source + Z connections + Z cable + Z load
I have been talking about these impedance forms a voltage divider effect that cause not only amplitude change, also phase change due to the complex impedance.
The speaker has generally been designed to be driven by a voltage source, so our ideal premise requires source and cable impedance to be very small compared to speaker impedance. In this case, the speaker's design dominates the performance as intended so the variations in the loudspeaker's impedance do not interact to produce frequency response deviations. Fig. 5 gives an example of such a case, where the aberration is relatively minor; however, Fig. 6 shows the effects with one particular loudspeaker (which really exists) where the deviation is dramatic.
Just as the cables have an inductive element, so do the amplifiers which drive them.
In tube amplifiers the output transformers provide the inductance whereas in most solid state designs the designer has deliberately provided inductance in the form of a coil for added circuit frequency stability. The reason that damping factor (8ohm/output Z) has been traditionally quoted at low frequencies is not only because much of our interest in damping centers on the woofer, but also because this coil destroys the damping factor at high frequencies. In fact, examples exist of solid state amplifiers which quote damping factors of 500 or greater at 20Hz but which have damping factors on the order of 15 at 20kHz. More recently a few designs (Threshold, Audio Research, Yamaha) have dispensed with output coils, giving them more constant damping factors across the audio band. The new IHF test standards call for measurement of damping factor at all audio frequencies.
This explain low inductance cable does not help the sound as the output inductance of the amps are very high and damping factor at high frequency is very low even they spec high damping factor.
PAGE 4..................... the advent of wide bandwidth power amplifiers has demonstrated other new effects; several amplifier designs (stable with reactive loads such as capacitors) oscillate into low inductance cables with a variety of results. Threshold Stax, and Electro- Research designs behave violently, while others acquire oscillation-caused colorations, usually either a hard, etched, high end or warmth and thickness in the vocal range (due to low order intermodulation sidebands and harmonics)..................
He talked about how they had problem keeping their amps stable. They just don't know how to tame their amps. You'd be surprised how many of those amp designers don't really know electronics. They just pick a circuit, change a little here and there and call it their own. There are only very few topology used in all the amps, you read enough circuit diagrams, you can tell right away what topology. My suspicion is they blind copy and don't really know the circuit.
PAGE 4.......................... as amplifier output stages increased in bandwidth beyond 5MHz, the two effects met and resulted in various forms of sonic problems, fuse blowing, and worse. At Threshold we first ran across the problem with the mating of our 400A and Polk sound cables which caused fuse blowing (due to oscillatory cross-current conduction) with great regularity.
He talked about their amps have sonic problem with those low inductance cables when their amps are at the edge of instability.
After a period of confusion, Matt Polk and I realized independently that the lack of a characteristic termination was causing the problem. Polk developed and patented a "damper" consisting of a .047uF capacitor and 6 ohm resistor in series placed across the loudspeaker, while I used the same network but with .1uF and 5 ohms. The results of this network are seen in Fig. 8 where the resonance in the pulsed waveform is damped out, restoring stability to an otherwise oscillating amplifier. .....................
Here they use band-aid to fix the problem, The right way to do is to design the amp to be stable without external help.
PAGE 5..............Frankly, I found it difficult to assess the results except at the extremes of performance. For 10 foot lengths with properly terminated cables and speakers with inductive high frequency characteristics, the differences between low inductance cable and twin conductor are extremely subtle and subject to question. With a low output inductance amplifier and a Heil tweeter (whose impedance is a nearly perfect 6ohm resistive) the difference was discernible as a slightly but not unpleasant softening of the highest frequencies
His judgement on the sound. But as I said, if the amp is designed to be stable from ground up, result is going to be a lot better as I have experience. It's quite a big difference.
Speaker cables matter when you have the right amp and speakers. You just have to know what you are doing. It will not help if the amp is just not up to par or the speaker is easy to drive. But this is a given, if you don't have good component, you might as well use lamp cord.
If you have a high end amp with a lot of big output transistors ( key to have high damping factor at high frequency), and you drive a hard to drive speaker, then the low inductance cable really shines.
Own designed power amp, own designed preamp, JM LAB Spectral 913.1 speakers, Rythmik F12SE sub.
Not hooked up: Nakamichi Stasis PA-7 power amp, Velodyne VA1210 sub, Kef Reference Series center, Kef Bookshelf speaker, Monitor Audio bookshelf speaker, Infinity rear speakers. Acurus 3X200W amp.
Last edited by alan0354; 11-26-2019 at 03:29 AM.