How a Muffler Works

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Here's what the inside of a muffler looks like and how it works.

A muffler is used near the end of the exhaust system on a vehicle to reduce the noise emitted by the engine. The noise comes from the combustion chamber, and travels through the exhaust stream.

The muffler has a series of perforated tubes, baffles and a trap door that redirect exhaust gases. As the gases travel, sound waves are either absorbed, or reflected and destructively interfered, cancelling them out.

The exhaust gas continues to flow around in the muffler and out the tail pipe. However, most mufflers pose as a restriction for an internal combustion engine, because the exhaust gases have to travel around, back in a reverse direction and then out the tail pipe. This is known as reverse flow or turbo style muffler.

Many mufflers are accompanied upstream by a resonator, that reduces certain frequencies of sound in the exhaust stream before it enters the muffler. On the outside, it looks like a small tube increasing to a large diameter tube, and then back down to exhaust pipe diameter.

Mufflers work on the principle of destructive interference and absorption. The walls of the muffler are made of two layers of stainless steel, which help reduce vibration and absorb sound. Some mufflers have a fiberglass material around the perforated tubes to help absorb sound.

Destructive interference occurs when a sound wave is reflected off a surface and interferes with the inbound sound wave. The high amplitudes interference with the low amplitudes, and the net amplitude becomes zero. Baffles are strategically distanced to cancel out certain frequencies.

The muffler illustrated in this video was from a 2001 Toyota Corolla. It features a spring loaded passive exhaust flap. The flap opens once pressure is built at higher RPM's, allowing the majority of exhaust gases to enter into the third and final chamber, before exiting the tail pipe.


Purchase tools used in this video to dissect your own car parts:
Angle Grinder (aka snap ring pliers):
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(Canada)
3/8" Ratchet set:
(US)
(Canada)
Screwdriver set:
(US)
(Canada)

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