"Phil Allison" wrote in message
...

"Porky"

"Arny Krueger"

That's the listener riding the same train as the whistle.


It seems to me that the train/whistle anology is not a valid one for
this
purpose, because the train's motion and the whistle's sound are not
being
reproduced by the same source, as happens in a loudspeaker producing a
complex waveform.


** How so ? The whiste is mounted on the train.


If you make a recording of the train approaching and receeding from your
listening position and play it back, you will hear exactly the same
Doppler
shift you heard when the train went by, and this can be confirmed by
measurement. Conversely, if you make a recording of the whistle from the
train and play it back on a speaker moving down the tracks at the same
velocity as the train, you will hear the same doppler shift you heard
from
the passing train, even though there is no shift in the actual
recording.


** No kidding.


The above logic actually has little to do with Doppler distortion in a
speaker, but the fact remains that the train/whistle in not a valid
anology!


** I saw no relevant facts go by - must have just whizzed past on an
express train .......


Making the assumption that a speaker produces Doppler shift because a
whistle on a moving train does is a rationalization not based on the
actual
physical facts.


** You rationalisations are far more extensive and non logical.



Even moving the whistle back and forth in approximation of a
moving speaker cone is not a valid anology, because the whistle's back
and
forth motion is not generated by the sound coming from the whistle, as
it
would be in a speaker reproducing a complex waveform.


** Huh ? Since when is a cone's motion *produced* by sound ???



You're actually dealing with two separate sources producing separate
waveforms.
Mounting the whistle on the speaker cone still won't be a valid anology
because the
waveforms are not being reproduced by the same mechanism, two separate
sources again.

The only valid anology for what happens with a speaker reproducing a
complex waveform would be some other single entity that is capable of
reproducing the same complex waveform. Any suggestions?


** Lay off the weed.

The sound produced by the speaker happens because the speaker is driven
by a single complex waveform, thus there is a single source for the sound.
The sound that comes from a train whistle is generated by the whistle, and
the motion imparted to the whistle comes from the train's motion, two
separate sources. If you move the whistle back and forth in a manner
approximating that of a speaker cone, you still have two sources, the
whistle's sound and the mechanical vibration of the whistle, if you mount
the whistle on the speaker cone, you have two sources, that driving the cone
and that coming from the whistle. None of those approximates in any way, or
is a valid anology for a loudspeaker producing a complex waveform that comes
from only one source, the complex electrical waveform driving the speaker
motor. All the other anologies have two sources, one for the low frequency
motion and one for the high frequency sound, NOT a valid anology for what
happens when a speaker reproduced a complex waveform. If you don't get that,
then perhaps it is you who should "lay off the weed". You aren't going to
get it until you can differentiate that which comes from two or more
separate simple driving sources and that which comes from a single complex
driving source
BTW, I never said anything about a cone's motion being prodiuced by sound.
I said "a speaker reproducing a complex waveform".