BEHAVIOR
Cuts the noise coming from car and truck engines. Unless, of course,
some young driver cuts holes in it.
HABITAT
The muffler lives at the end of the combustion process, beneath the
back end of the car.
HOW IT WORKS
Exhaust gases are piped into the muffler at elevated pressures and then pass out the tailpipe. The escape of high pressure exhausting into the atmosphere generates noise.
Noise is suppressed inside the muffler by destructive interference. Sound energy reflects off the inside of the muffler and tends to cancel itself out. This is the principle of noise-canceling headphones: two identical sound waves that are exactly out of phase with each other can cancel each other.
Exhaust gases enter the muffler’s first chamber where they escape into a resonating chamber. The resonator is designed to reflect sound waves back at incoming waves so the two waves interfere with each other.
Exhaust and sound escape to a second chamber for further dampening.
The exhaust has to flow through small holes in the pipes inside the muffler, thus reducing the noise further.
The body of the muffler is a sandwich of metal with a layer of insulating material between them. This helps noise reduction by absorbing sound.
A different design for a muffler is the straight-through or glass pack muffler. Combustion gases enter through a perforated pipe inside the muffler. The gases escape through the perforations into a chamber filled with sound-absorbing material (fiberglass, for example) and then out the tailpipe. The straight-through design reduces back pressure, making the engine more efficient.
The design of mufflers is a balance between suppressing noise and reducing power output by the engine. Like sticking a banana up the tailpipe, a muffler creates back pressure, which retards exhaust gases
and decreases engine output. Too much exhaust restriction in the muffler will cause noticeable reduction in power.
INTERESTING FACTS
The silencer or muffler was invented by Hiram Percy Maxim. He used the same technology to invent the silencer for firearms. His father, Sir Hiram Stevens Maxim, was a more famous inventor. He invented the
machine gun and the modern spring mouse trap, and had pre-Wright Brothers success getting a steam-powered airplane to take off.
Library of Congress Cataloging-in-Publication Data
Sobey, Edwin J. C., 1948–
A field guide to automotive technology / Ed Sobey.
Published by Chicago Review Press, Incorporated
814 North Franklin Street
Chicago, Illinois 60610
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