How Motorcycle Mufflers Work

Introduction

Mufflers on motorcycles serve the same purpose as they do on cars and other automobiles--muffling the noise made by the vehicle and creating a softer hum to the engine's operation. A set of tubes inside the muffler act to cancel out noise by reflecting the sound waves.

Sound and Motion

The way a motorcycle's sound is produced is fairly straightforward. It is all linked to the engine, where high-pressure gas must be shot out of the exhaust valve whenever it opens. This high-pressure gas rams into other lower-pressure gas, and this results in sound moving quickly down the pipe and creating a loud sound. This pressure is registered in the human ear as motion due to the vibrations that occur when it hits. The air pressure level determines how loud the sound ultimately is, because greater air pressure level creates more vibrations within the eardrum and thus a greater sound.

Destructive Interference

How the vibrations get canceled and the sound reduced is a process that relies on something known as destructive interference. Destructive interference cancels waves out by essentially replicating them, because it is possible to create a sound wave that is precisely proportionally opposite to the existing wave that is making all the fuss, and a wave that is entirely out of phase with the initial wave will result in an interference that causes no sound to be heard, because the two waves will hit the ear at the same time and cancel each other out.

The Resonator

Within the muffler's set of tubes is the resonator. This is the key to noise canceling, as it is the resonator that operates to create a reflected sound wave that will cancel out the frequency of the first sound wave. It works by allowing the first wave to enter the chamber, where it then hits the wall of the muffler at its end and then comes barreling back out of the area through which it initially entered. In this process, and due to the precise length of the chamber, the first wave exits the resonator exactly when the following wave bounces off the chamber's outside. It is all timed so that the high and low pressure parts of the waves interact and negate each other.