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In alt.music.home-studio,rec.audio.tech,rec.audio.pro,
(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. As far as our
super-excursion speaker is concerned, the location that's generating
the high pitched sound is moving forward and backward several feet.
If you still don't believe that this scenario validates the
train-whistle analogy, why not make the bass waveform move at the
speed of, oh say a train, and have the high pitched signal on top of
it be, oh say the sound of a whistle.
The scenario described in this thought experiment would *certainly*
produce doppler shift in the higher signals. If you made the bass
carrier sound low enough frequency and loud enough, you would even be
able to hear the weeeooohhweeeoooh modulation of the higher frequency
as the source of that sound (the surface of the speaker cone) is
moving towards and away from you. It follows reasonably that this also
happens with regular speakers, but to a lesser extent.
The question of whether it's a relevant, measurable, or hearable
distortion is a separate issue from whether it physically exists.
Forgive me if this has already been discussed to this point, I didn't
have time to read the entire thread.
I made what I considered to be a similar 'extreme' post, but your
woofer cone moves an order or two of magnitide greater distance than
mine does. So I commend your post, it needed to be said.
As far as not having time to read the whole thread, I've been
participating, so it's a sad commentary on where I'm spending my time.
Someone should have just said at the start "Bob Cain (and a few
others here) is in denial about the existence of Doppler effect in
speakers" and I wouldn't have tried so hard...
Ken
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http://mindspring.com/~benbradley
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