Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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Re: A really big can of worms

Posted by MAD MAN HARJU on January 3, 2005 at 09:37:49

In Reply to: Re: A really big can of worms posted by Soundmind on January 3, 2005 at 05:46:04:

“Engineers and scientists don't work on "could", they work on IS.”
“…what more knowledgeable people will pass off with a laugh.”

Did you also laugh when Otala and later Walt Jung presented their theories of TIM and SID, because before that it was never heard of, among your kind of people, that amplifier stress at high frequencies could cause audible effects. Today this is accepted and a part of every good engineers “checklist”.

“Scientists establish the absolute criteria beyond which further improvement cannot be usable because of the limits of human perception…”

Is the limit of human perception really reached yet? Take as an example our ability to distinguish changes in the direction to a sound-source of less than ONE degree in the frequency-range around 2 kHz. This corresponds to a time difference between the ears of 10 us or a frequency of 100 kHz. This would imply that the phase and frequency response of a system is important beyond 100 kHz.

“Take my word for it, if you can hear it, it CAN be measured.”

Nobody knew how to measure the effects of SID before Walt Jung showed how to do.
And what I am pointing at is just the fact that I can (and many others with me) hear differences but our current measurement methods don’t reveal this. That is why we are looking at different measurement methods to se if they correlate with what we hear, and since this is yet to be proven we must say “could be causing”.

BTW People “who work on IS” ONLY will never be the ones who bring the progress into new territory.

And about the really big can of worms with cables that you brought up, my take is like this; I think that much of it is exaggerated but that there are very small differences, which may depend of a number of reasons. A cable is also a capacitor connected in parallel with the load, and the capacitance isn’t that linear regarding to frequency and amplitude. Well not even good capacitors are that so why would a cable be that. (And maybe, just maybe, skin-effect can be a small part of what might cause the capacitance to change and hence causing phase modulation and that is perceived as “time smear”). And we all know that a frequency response that is modulated by signal-amplitude cause signal dependent phase modulation. And then we have the issue of the inductance of the cable witch also can be non-linear regarding to frequency and amplitude.

And a part of the “problem” may in some cases be just an interaction issue, the pre-amp or amplifier with or without a feedback loop might not work well with that particular load.

And when we are talking of loads, why do people of your kind Soundmind persist on making measurements of power-amplifiers with a purely resistive load? The answer I usually get is that every loudspeaker is different and there is no point to try to make measurements with a load that resemble an average load. This is to be blunt JUST PLAIN WRONG.

Loudspeakers (and I mean all loudspeakers) store quite significant amounts of resonant energy, and for relatively long periods of time (tens to hundreds of milliseconds) and this back-EMF interacts with the non-linear amplifier and creates new distortion terms. Just ask any skilled loudspeaker designer. And amplifiers connected to these real loads will not behave as nicely as measured with a purely resistive load If we use LCR networks that simulate the overall impedance of the speaker in our measurements we get a bit closer to the real thing, but to get all the way we need to measure with real loudspeakers and preferably with several different loudspeakers.

And again Soundmind you haven’t addressed my examples of what could be causing the things we hear. You are just so hell-bent on insisting that “if you can hear it, it CAN be measured”. It doesn’t matter how much we tell you that we hear differences that don’t relate to the measurements. And as long as we hear differences we have to seek answers.

And yes I’m also very suspicious when somebody comes with a “new” explanation to some of the things I’m hearing. But I almost get MAD when somebody is trying to tell me that I can’t be hearing what I’m hearing because we can’t measure it.

BTW Last time I checked my hearing, my threshold of hearing was almost 10 dB lover than the normal hearing limit in the range of 1000 to 3000 Hz. But I don’t hear as good as I used to in the high frequency range with my hearing starting to fall of above 15 kHz, due to age and exposure to loud sounds. But my hearing did fall of above 18 kHz already at an age of 15 so I haven’t lost so much or the years…

Enjoy Creating / Mad Man Harju

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