s attached to the muffler on a passenger car to reduce the sound produced Mufflers are installed within the
exhaust system of most
internal combustion engines. Mufflers are engineered as an acoustic device to reduce the
loudness of the
sound pressure created by the engine by
acoustic quieting. Sound reduction techniques used in mufflers include: reactive silencing, resistive silencing, absorptive silencing, and shell damping. The noise of the hot exhaust gas exiting the engine can be abated by a series of passages and chambers lined with roving
fiberglass insulation and/or resonating chambers
harmonically tuned to cause
destructive interference, wherein opposite sound waves cancel each other out. The operation of an internal combustion engine produces distinct pulses of exhaust gas that exit through the exhaust pipes and the muffler. For example, a four-cylinder engine will have four high-pressure pulses for each operating cycle, a six-cylinder engine will emit six high-pressure pulses, and so on. Higher backpressure can also help
nitrous oxides (NOx) emission reduction in some engines. When engine performance is the main concern, the exhaust pipes and muffler should be large enough to facilitate breathing as well as small enough to create a high exhaust flow. Some
aftermarket mufflers claim to increase engine output and/or reduce
fuel consumption by slightly reduced back pressure. This usually entails less noise reduction (i.e., more noise). Greater muffler flow may increase engine power, but excess muffler flow capability provides no additional benefits and can be more expensive as well as being noisier. ==Regulations==