Porky wrote:


I would go so far as to say that anything generating sound and in motion
relative to the listener will generate Doppler shift, but in the special
case of a speaker reproducing a complex waveform consisting of more than one
pure tone, the velocity of the source relative to the listener is
effectively zero, and therefore no Doppler shift will be generated, because:

Tell me if this is equivalent or not: There is Doppler type
mixing between two frequencies if and only if the pressure
in the far field due to them is a different function of the
velocity of the piston. Where the transfer function is flat
in the Fourier sense, nothing mixes. That is what it all
boils down to in the end. That is not at all the same as
the standard argument because it won't happen in a tube and
the standard argument says it will.

Also, a single tone cannot produce Doppler distortion so I
am definitely wrong about that. Yikes! I see why. The
definition I've been bandying about for a linear system is
actually the definiton of a linear, time invariant system.
The system we are considering must be time variant in terms
of the impedences involved. This is getting wierd.

Can this yield what I've been asking for, a general
expression for far field pressure as a function of piston
velocity that includes the Doppler distortion? I'm not sure
yet, but I'll be thinking about it. It is straightforward
for any two frequencies, however, and is left as an exercise
for the student. :-)


Bob
--

"Things should be described as simply as possible, but no
simpler."

A. Einstein