I have seen the Doppler Effect cited as the reason for loud pipes having little effect on safety.
Doppler was an Austrian physicist and mathematician who first enunciated the principle known as the Doppler effect in 1842.
Doppler effect
n.
A change in the observed frequency of a wave, as of sound or light, occurring when the source and observer are in motion relative to each other, with the frequency increasing when the source and observer approach each other and decreasing when they move apart. The motion of the source causes a real shift in frequency of the wave, while the motion of the observer produces only an apparent shift in frequency. Also called Doppler shift.
OK, I'm no scientist, but this looks like it has questionable applicability to the VOLUME, as perceived by the observer, of a sound, as they move together. There is also the issue of windows up, radio on, exhaust pointed backwards, not forward, which side of the bike the exhaust is on etc. Is the Doppler Effect really the primary issue here anyway?
