A muffler is designed to absorb the extremely harsh noise from an internal-combustion engine. A catalytic converter is a reaction chamber designed to reduce toxic emissions. They are required on all vehicles in the United States and in most other countries.
Some motorists install aftermarket exhaust mufflers and/or disable the catalytic converter to produce a distinctive humming or roaring sound from their vehicle.
A roaring exhaust system can be heard and felt over a wide distance, rattle windows and travel through walls. Millions of people are adversely affected by this noise.
Flowmaster "American Thunder" 40 Series
Marketed as "the most aggressive sound street and strip muffler in Flowmaster's product line."
The biggest sellers of after-market exhaust systems are Flowmaster, Magnaflow and Borla. Flowmaster claims its performance exhaust systems produce "an aggressive muscle car sound." Meineke Car Care Center's website has a section that allows vehicle owners to sample different sounds from their own line of aftermarket mufflers. Midas signed a deal with Flowmaster to carry their entire line of muffler systems.
Aftermarket exhaust systems are advertised in custom car magazines, auto racing events, and product placement on cable television shows such as Horse Power and Muscle Car on Spike TV (Viacom).
These companies are members of the Specialty Equipment Market Association (SEMA). Representing dealers and installers, they have lobbied against proposed noise-pollution ordinances in communities across America. SEMA created the 'Congressional Automotive Performance and Motorsports Caucus' enlisting members of congress to support their agenda. They also enlist automotive enthusiast clubs to lobby on their behalf on political issues.
From the October 2004 issue of Hot Rod Magazine: "Every hot rodder owes Conrad Wong (left) of SEMA a debt of gratitude. He's the guy representing us in Washington to preserve our hobby from political scum, and he went on Power Tour to spread the word."
In most states, modifying the muffler for the explicit purpose of making it louder is illegal.
SEMA had lobbied to rewrite the noise code in California to stifle law enforcement. It required police officers to measure exhaust noise with a decibel meter using the dB(a) standard, which does not measure low frequency noise.
Citations were often challenged in court because the meters must be certified and calibrated for its readings to be used as evidence. In addition, police officers must be properly trained to use the expensive equipment. The result was that less motorists were cited for noise violations.
A new law was passed (27150.2 VC) that does not require law enforcement to use sound level meters to test for excessive noise. The citation is based on officer's judgment. This enforcement enforcement measure is called 'plainly audible standard' that allows an officer to determine noise levels.
In New York City, noise offenders can be cited if the exhaust noise is plainly audible at 150 feet.
China does not require catalytic converters on vehicles. Auto manufacturers do not install them as standard equipment to avoid the increased cost of production. The resulting air pollution is so bad that its citizens wear breathing masks in major cities.
Magnaflow offers loud exhaust systems for large SUVs, including the Hummer and Cadillac Escalade.