ruffrecords writes:

PenguiN wrote:
The sound produced by the speaker happens because the speaker is driven
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.

What if we take this to the extremes with a thought experiment:

Picture the largest loudspeaker in the universe sitting outside

somewhere. It's so big that it has a maximal excursion of several
feet. Now picture a very low bass signal played on that speaker at
almost maximal volume. The speaker cone is vibrating
in-out-in-out-in-out.
Now add to that signal a small, high pitched, low amplitude waveform.

The two waveforms are added together so that it seems like the higher
pitched wave is "riding on top of" the bass wave.


What gets added are the instantaneous pressures. The air pressure
produced is exactly the same as two separate speakers at the two
frequencies. There is no such thing as doppler distortion.

Consider this gedanken: Place a 4-inch speaker on the cone of a 14-foot
speaker. Now, the two speakers are fed different signals. Is there
Doppler? Yes. Use the one 14-foot speaker for both frequencies. Is there
Doppler? Left as an exercise for the student.

Granted, there will be differences, but the lack of doppler will not
be one of them. One of them will be the dispersion characterstics of
the high-frequency signal.

The difference between receiving two such summed signals electrically
versus acoustically is that one has the physical phenomenom of the
propagation of sound through the air in one case and not in the other.
Similarly, an electronic receiver may have other types of non-linear
distortion (e.g., clipping) depending on the circuit and parameters
that an acoustic receiver would not have. The two do not necessarily
have to agree with one another - there are different physical processes
that occur in each.

Get out a physics book and read about Doppler. The explanation of
how the observed wavelength changes when there is a relative velocity
between the source and observer should make you a believer that this
is precisely the scene in a speaker reproducing two frequencies.
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
, 919-472-1124