Rob, I have another question. I really hope I'm not bothering you while being engaged in some of your groundbreaking developments (of course I am!
), but my issue is really earthshatteringly important, and you are the only person able to solve it.
I remember you stating that every electronics component has an impact on the sound, even resistors, cables, solder joints and plugs. My own experience tells me the same. My favorite headphone to date, the HiFiMan HE1000, sounds dramatically better with a replacement cable (with silver conductors in my case). Another dynamic headphone, the Sennheiser HD 800, reacts almost equally sensitive to cables (although its original cable isn't really bad), different cables alter the sound in different ways.
You seem to be right: The human hearing is much more sensitive than commonly believed. Nevertheless, it's amazing that such tiny signal deviations «survive» on their way through a sound transducer with its infinitely greater signal corruption. But that's how it is, and I don't expect you to have an answer to that.
However, since you're in possession of extremely sensitive measuring equipment:
Have you ever measured the effect of cables on the signal? I'm explicitly not speaking of electrical values such as capacitance or inductance, but measurable signal alterations with some likelihood to have an audible impact. In what way do cable geometries and conductor materials alter the signal shape? I can somehow reproduce how abrupt impedance steps and maybe even sharp corners (e.g. from cable plugs) may produce «transmissionline resonances», but even with those it's unclear how they print themselves on the signal. With conductor materials it's hard to find any explanation in the first place. Silver is the better conductor than copper. So what? Increase the copper conductor's cross-section accordingly and you get the same resistance! Moreover, differences in the tenths of ohms absolutely don't matter with (say) headphones with load impedances of e.g. 35 ohms. And resistance per se is frequency-neutral.
However, I can't help but confirm the notion that silver conductors tend to sound treble-friendlier than copper conductors. What's the cause for this? And how would it translate into measuring results? As far as I know, silver and copper conductors measure absolutely indentical in the audio band – with sine waves. Do silver conductors take more care of the signal, or do they add treble? (Unthinkable!) Are copper conductors unable to transfer an electrical audio signal adequately, without audible losses? Is there a conductor material at all that guarantees absolute signal integrity?
I'm somewhat familiar with the skin effect and have «heard» it in my own cable experiments. However, according to the classic electroacoustics doctrine it's reserved to the ultrasonic range. Now even if it causes a tiny treble roll-off in the audio band (let's assume it!), how can it have a decisive impact on the perceived sound quality when at the same time the signal on its way has to run through any arbitrary sound transducer which may in fact benefit from it due to synergetic effects? It seems the skin effect is always perceived as negative (well, according to my experience after all). How can this be? It seems that it's more than just a treble roll-off, it may in fact have a separate quality. How does it measure, if it's real?
Regards
Marcel