"Don Pearce" wrote in message

On Fri, 6 Aug 2004 07:47:24 -0400, "Arny Krueger"
wrote:

The only way to verify this is to look at the phase as well as the
amplitude of the sidebands.

That's one way, but it's a very hard row for me to hoe.

So, you decline to believe that the relative amplitudes of the
sidebands are different and relevant, as the frequency has increased?


No, not at all. But I am not convinced that with the complex
interactions of a speaker you can reach your conclusion as simply as
you have. Non-linearities of various orders can cause a multiplication
function which results in phase modulation. But to put this down to
Doppler effect is a leap too far for me.

I agree that the actual acoustical measurements may or may not show a
Doppler effect. At best the Doppler distortion is relatively small in the
face of the massive AM effects.

If I turn the volume up, the AM effects seem to get stronger, both overall
and proportionately. And, this is a relatively linear driver being driven
over a wider frequency range than it would be used in a good design.

If I got anything worthwhile out of this, it is the concept of using 3 tones
to separate AM distortion from FM distortion. But you still need an
underlying clear instance of FM distortion to make it worth the trouble. I
suspect that a lot of the purported jitter measurements we've seen are
actually pretty suspect because the common measurements confuse AM and FM
distortion.