"Jim Carr" wrote in message
news:tVq8d.12196$mS1.2969@fed1read05...
"Porky" wrote in message
t...
From a practical standpoint, the question isn't whether Doppler shift
exists in a loudspeaker, the real issue is whether or not it's audible,
and
if it is audible, whether or not our hearing has a mechanism to
compensate
for it.

How could the ear/brain possibly compensate for it? There's no way to
analyze a sound to know if it's distorted unless you know how the sound is
supposed to be in the first place. Take the classic whistle on a train.
Unless you know the pitch is supposed to stay constant, how can you know
the
sound is affected by Doppler? You can't.

The point is that everyone hears the Doppler shift in a train whistle,
but when comparing a "live" sound to it's replica being reproduced by a very
accurate loudspeaker system, under the closest to ideal conditions possible,
there is a great deal of disagreement as to whether there is any audible
distortion produced by the speaker system, and even more as to whether any
of that is due to Doppler shift. J B Lansing, Altech and others have done
considerable experimentation with "live vs reproduced" sound, and the matter
of realism seems to get very close under the best conditions, so close that
even highly trained expert listeners have trouble telling the difference. If
it were otherwise, we wouldn't be having this discussion! :-) That argues
that either our hearing mechanism compensates for any Doppler distortion
that might be present, or that it isn't audible even if it does exist.


As for the "real" issue the discussion always been esoteric. I don't think
anyone really thinks there is anything practical that can be done about
it.

As to it being an esoteric discussion, it has certainly become one, but
the original question was "Do speakers create Doppler distortion when
producing both a HF tone and an LF tone at the same time?", and there is
nothing esoteric about that question. If audible Doppler distortion does
occur in a speaker, then there must a number of ways to minimize it, so this
discussion does have some possible practical application, assuming that
anyone can prove that we actually hear Doppler distrotion in a speaker when
listening to music.