A muffler (North America) or silencer (outside North America) is a device for reducing the amount of noise emitted by a machine such as an internal combustion engine or a gun. The first was invented by Hiram Percy Maxim to silence guns. When used on internal combustion engines, the engine exhaust blows out through the muffler.
Mufflers usually contain a series of baffles to absorb sound. They are a common piece of equipment on automobiles, usually slung under the rear of a car, but many diesel-powered semi trucks have large mufflers mounted vertically behind the cab.
Catalytic converters also often have a muffling effect.
While the goal is to absorb energy that would otherwise be released as sound into the environment, mufflers do force engines to work somewhat harder pushing exhaust gas through them. Therefore, it is a common engine tuning practice to replace stock mufflers with versions that require less energy to force the gas through (usually described as lowering the “back pressure”). Such accessory mufflers can often increase a vehicle’s power, but usually at the cost of less effective noise suppression.
For a muffler/silencer as fitted to a gun, see Suppressor.
Source: Wikipedia – The Free Encyclopedia