On Wed, 11 Aug 2004 11:47:23 -0400, "Arny Krueger"
wrote:
"Scott Dorsey" wrote in message
If the motion of the cone perfectly follows the waveform, and
the air is not compressable,
Air is compressible, even water is compressible, and that's why the
speed of sound in air and water are finite.
the pressure waveform that results in
the air will be a perfect representation of the original wave.
Scott, I think you've missed a critical point. A speaker is a transducer,
and that means that in the process of following the waveform ideally, the
results in the air can be a little different than what was intended.
If you can somehow arrange for perfect coupling so that the woofer
excursion perfectly matches the input signal, doppler effects should
be a non-issue.
If you made a transducer that increases and decreases the air
pressure without using physical movement, there would be no doppler
distortion. You could have two valves that alternately open and close,
connected to a source of compressed air and the other to a vacuum,
which would cause increase and decrease in air pressure without
movement, but this doesn't seem practical for good audio reproduction.
The problem is that the cone moves, and its movement is significant
in relation to the speed of sound in air.
No. Imperfect woofer excursion is more along the line of AM effects.
Unfortunately this does not go along well with
accurate frequency response in the real world.
I think that this issue of imperfect cone motion has some light shed on it
by contemplating a system with a tweeter, versus a system that lacks one. In
both cases the respective signals are transduced into the air with ideal
waveforms. The Doppler comes from the fact that the HF gets transduced into
the air from a platform with large-scale motion due to some other signal.
The tweeter does not have this situation.
It's like the train whistle. The whistle itself need not be affected by its
motion through the air. The fact that the whistle is moving w/r/t the
listener
AND that the speed of sound is finite, and that the speed of the
train is a significant percentage of the speed of sound...
is the root cause of the Doppler effect.
A lot of stuff has already been covered (and uncovered and
discovered and recovered...) on "another forum." If anyone wants to
read some "background info" before posting further (I suggest it just
to see what has already been rehashed), read these threads "Drum dB's"
and "Doppler Distoriton?" on alt.music.home-studio:
http://groups.google.com/groups?dq=&...oogle%2BSearch
or
http://makeashorterlink.com/?R2DD35609
http://groups.google.com/groups?dq=&...oogle%2BSearch
or
http://makeashorterlink.com/?H2ED62609
And a heads up, "Porky" over there is quite similar in demeanor to
"Phil Allison" here on RAP.
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