"Bob Cain" wrote in message

Randy Yates wrote:

"*IF* a system is linear, then it will not exhibit the Doppler
effect" is a true statement. However, get this:

T H E S Y S T E M I S N 'T L I N E A R !!!!!!!!!!!!!!!

Well, Randy, many people are saying that it is and produces
FM distortion anyway.

That could be both true and confusing, no?

Note carefully, (for thine ist a beanhead): the "system" here is
defined to be the entire electro-mechanical path from the speaker's
electrical input to the acoustic receiver's input.

This is a critcal point.

**** you, and I say that with all due respect. The system
here is everything from the face of the piston on out.

Out how far? Until we get to the receiver, there is no Doppler distortion
from that piston. Once we get to the receiver, there is Doppler distortion.
But judged all by itself fixed in space, the receiver can be
distortion-free.

Nothing that occurs before that can be contributory and must
be eliminated in some way from any experiment designed to
catch Doppler at work.

It would be nice to eliminate that, but in the real world of acoustic
measurements...

Again, give me a mathematical expression which describes in
a quantitative way what should be measured at a distance
from that speaker as a function of the motion of that speaker.

Asked and answered, but it takes a little reading in standard references.

Until that is done, "Doppler distortion" is not supported in
theory.

But it was all done 30 or more years ago, in the JAES.

I sincerely hope no one will say that it isn't
required because you see evidence of frequency modulation.

Where else might that FM come from?

According to a recent post, even that evidence may not
really indicate frequency modulation but can be accounted
for by non-linearity in the driver.

Except, that the driver does not evidence that nonlinearity unless the
distance between the diaphragm and the receiver is varying.

I don't know the
intricasies of modulation theory but it was said by someone
who does that the data shown does not carry the signature of
this supposed effect.

At this point all sorts of things have been said. Me, I trust my
experimental data, Halliday and Resnick, and the JAES.

Until "Doppler distortion" is supported in theory, and I
hope all know by now what qualifies as a theory, there is no
basis for it and no basis for correct interpretation of any
measurement data.

So get thee to the library and study up!

This is just basic science, folks.

Sometimes you just got to do your reading.