[[Image:Exhaust pipe muffler.JPG|thumb|right|
▲[[Image:Exhaust pipe muffler.JPG|thumb|right|Dual [[tailpipe]]s attached to the muffler on a passenger car]]
▲Mufflers are installed within the [[exhaust system]] of most [[internal combustion engine]]s, although the muffler is not designed to serve any primary exhaust function. The muffler is engineered as an [[acoustics|acoustic]] [[soundproofing]] device designed to reduce the [[loudness]] of the [[sound pressure]] created by the engine by way of [[acoustic quieting]]. The majority of the sound pressure produced by the engine is emanated out of the vehicle using the same piping used by the silent exhaust gases absorbed by a series of passages and chambers lined with roving [[fiberglass]] insulation and/or resonating chambers [[harmonic]]ally tuned to cause [[destructive interference]] wherein opposite sound waves cancel each other out. An unavoidable [[side effect]] of muffler use is an increase of [[back pressure]] which decreases [[engine efficiency]]. This is because the engine exhaust must share the same complex exit pathway built inside the muffler as the sound pressure that the muffler is designed to mitigate.
Some vehicle owners remove or install an [[Aftermarket (automotive)|aftermarket]] muffler when [[engine tuning]] in order to increase [[Power (physics)|power]] output or reduce [[Fuel economy in automobiles|fuel consumption]] because of [[economic]] or [[Environmental quality|environmental]] concerns, recreational pursuits such as [[motorsport]] and [[hypermiling]] and/or for personal [[Aesthetics|aesthetic]] [[Acoustics|acoustical]] preferences. Although the [[Law|legality]] of altering a motor vehicle's [[Original equipment manufacturer|OEM]] exhaust system varies by jurisdiction, in most [[Developed country|developed parts of the world]], modification of a vehicle's exhaust system is usually highly regulated if not strictly prohibited.