Understanding motorcycle noise through physics
Thursday, July 17, 2014 - 7:01 am

To The Editor:

Let me first state that I am no fan of excess and unnecessary motorcycle noise.

I wish those who purposely and illegally increase the sound from their bikes would be regularly ticketed. Their frequently cited “right to ride safe” should not impinge upon my right to peace and quiet. At my quiet country home I hear them approaching from miles away, and enjoy the sound until they are miles past.

With that said, I must take issue with the Sound Off poster who claimed recently in the post “Sight versus sound” that there is a “scientific reason” why the loud pipes serve as no warning to those ahead, and asks, “Explain to me the physics involved when a noise is generated behind something, how it possibly can travel to a vehicle ahead of it?” That statement demonstrates sadly how very little general science knowledge there is among the public.

Okay, here is the explanation: The motorcycle can be heard ahead as well as behind, and all ‘round because it is not going faster than 1,125 ft/sec or 767mph, which is the speed of sound in 68 degree air.

If the motorcycle could do so, and surely it would if it could, then it would indeed be going faster than its own sound and therefore not be heard ahead, but only behind and in a cone spreading outward behind it. Since motorcycles, even at their normal full throttle, cannot and do not go faster than sound, then it stands to reason that some of the sound they produce goes out ahead of them, behind them, and all ‘round them, which even the most basic observation will demonstrate as true.

Should you or other readers of this column still not believe this, I advise you to stand quietly beside -but not in the road. Listen as cars, trucks, and motorcycles go by. Can you hear them before they get to you? Are the motorcycles louder than the other traffic before they get to your observation point?

Why do you suppose that is? There will be a quiz on this tomorrow.

John Wolfe