Arny Krueger wrote:
"Bob Cain" wrote in message

I've got an argument that so far has withstood some scrutiny
which shows that Doppler distortion in a myth.

What would refute it and point out any flaw in the reasoning
would be the dynamical expression for the time varying
function of the pressure wave in an infinite tube with an
ideal piston as a function of an arbitrary, time varying
function of the force applied to that piston.

Fool that I am, I'm kinda stuck down here in the real world. Forget the
math, forget the long-winded discussions, the question that interests me
most is whether or not there's Doppler distortion where it really matters -
in the sound field in front of the speaker.

Well, surprisingly enough, Phil actually made the good point that the woofer
position does not directly follow the input signal, but that the excursion
at lower frequencies is exaggerated. This is indeed the reason that we get
Doppler distortion. But, how do we compensate for this? And can we, even?

Of course, reducing the bandwidth to each driver and reducing the driver
excursion as much as possible are crude ways around the problem.

A more exaggerated example of the distortion, though, is found in coaxial
speakers where the moving woofer cone is used as the horn for the tweeter.
Here, though, I am not sure the math model is quite so easy, and it would
be interesting to see if anyone can model the boundary effects near the
moving woofer cone.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."