In article ,
(Jay) wrote:

Alan Baker wrote in message
...
No. You're assuming that the compression portion of the wave is equal in
shape to the rarefaction portion of the wave, and thus can be cancelled
by a rarefaction from another engine in close proximity.

But this is highly unlikely to be the case.

Isn't this the case for a sinusoid? If I excite an air mass with a
speaker being driven by a sinewave which moves the paper cone in a
sinusoid fashion, and then I have a microphone whose diaphragm is made
to move in the same manner because of the excitation of the air mass,
and I read a sinewave, then wasn't the air mass moving in a sinewave.
Now I do this for with a bunch of speakers, all playing tones but
which are multiples of the lowest frequency, wouldn't this also be the
case? The combined sound would be that of a pulse jet ripping apart
the air. "Super position does hold."

This web page has some great intuitive animation:
http://www.gmi.edu/~drussell/Demos/s...rposition.html

One weakness of my above explanation is that air does not respond in
an entirely linear fashion, so maybe superposition doesn't entirely
hold. This is what they're depending on with the "throw your voice"
technology where they're "mixing" 2 ultra-sonic (and directable)
sounds and having them produce a sum (inaudible) and difference
(audible) sound at the intersection.


The weakness in your argument is assuming that a pulse jet produces
anything close to a sine wave.

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."