My stock type exhaust has always had some kind of resonant drone in it at
just about highway speed. So I tried a calculation based on a lot of
guesswork. The piece of pipe from the rear of the stock muffler to the tip
is maybe about a yard, give or take. At 2700 rpm each pipe receiving 5400
exhaust pulses per minute, or about 90Hz.
I'm not sure what the speed of sound in moving exhaust gas is, but lets say
that it's the same 1100 feet/sec as in air. A quarter of a wavelength of 90
Hz is just about 3 feet. Can anyone remember their organ pipe theory from
physics? Are organ pipes 1/4 or 1/2 wave?
This would suggest that almost anything you did to break up these straight
pipes, a resonator or something, would alter this resonant effect.
Interesting theory? Comments?
Stu
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