Originally Posted by Dave IV
...In short, the acoustic wave travels in a conical straight line from the exhaust pipe, to the the rear of the bike. There is no magical property causing the wave to “make a U-turn or wrap around” the bike. If you are observing the bike while you and the bike are stationary you will hear the loud exhaust while standing in front of the bike. This is due to reflections (NOT refraction) of the wave from objects near the bike. Once the bike is moving the effect of the reflections is minimized and the loud exhaust will be almost entirely noticeable only from the rear of the bike...
If we were floating 10,000 feet off the ground, not moving, with no clouds or wind, and I was facing a one of these loud Harleys 5 feet in front of me, would I hear none of the sound coming out of the tailpipe? With nothing for the sound to reflect off of, would it then not make any difference what kind of exhaust the motorcycle had? If I'm understanding this correctly, I would hear some sound from the engine but not the sound directed out the exhaust pipe.
OK, I'm not challenging you on this. I'm just curious.