The spectrum of the sound from the engine does indeed have several
strong harmonics that rise up from a random noise floor. I think
you'd be able to cancel the periodic components of the noise leaving
the random part behind. If I had to guess, you'd get rid of the buzz
and be left with the roar. So with cancelation it might be similar to
a jet turbine in sound.

Regards

p.s. As far as synchronization, if I understand correctly, most of the
simple forms of these motors are started with a spark, but then carry
on self sustained operation at the natural frequency of the pipe. You
could however use a spark to ignite the charge slightly early and thus
force synchronization.


"Pete Schaefer" wrote in message news:%gc6c.32308$J05.219351@attbi_s01...
I guess you're talking about interference patterns and such. All that stuff
is irrelevant. The noise coming from a pulse jet will only have a couple of
periodic components. The rest is a bunch of quasi-random, aperiodic noise
resulting from some extreme turbulence. While turbulence phenomena are
chaotic in nature and not truly random, you might as well treat them as
random for this case. You never get a periodic interference pattern setting
up.

"Regnirps" wrote in message
...
As for summing, there is nothing mysterious. If you put two engines near
each
other you will sum in some places and cancel in others, but the location
varies