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Automobile Silencer

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If you've ever heard a car engine running without a muffler, you know what a huge difference a muffler can make to the noise level. Inside a muffler, you'll find a deceptively simple set of tubes with some holes in them. These tubes and chambers are actually as finely tuned as a musical instrument. They are designed to reflect the sound waves produced by the engine in such a way that they partially cancel themselves out. Mufflers use some pretty neat technology to cancel out the noise. In this article, we'll take a look inside a real car muffler and learn about the principles that make it work. But first, we need to know a little about sound.

 

Where Does the Sound Come From?
Sound is a pressure wave formed from pulses of alternating high and low air pressure. These pulses makes their way through the air at -- you guessed it -- the speed of sound. In an engine, pulses are created when an exhaust valve opens and a burst of high-pressure gas suddenly enters the exhaust system. The molecules in this gas collide with the lower-pressure molecules in the pipe, causing them to stack up on each other. They in turn stack up on the molecules a little further down the pipe, leaving an area of low pressure behind. In this way, the sound wave makes its way down the pipe much faster than the actual gases do. When these pressure pulses reach your ear, the eardrum vibrates back and forth. Your brain interprets this motion as sound. Two main characteristics of the wave determine how we perceive the sound: * Sound wave frequency - A higher wave frequency simply means that the air pressure fluctuates faster. The faster an engine runs, the higher the pitch we hear. Slower fluctuations sound like a lower pitch. * Air pressure level - The wave's amplitude determines how loud the sound is. Sound waves with greater amplitudes move our eardrums more, and we register this sensation as a higher volume. It turns out that it is possible to add two or more sound waves together and...

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