boom car
n. A car equipped with an extremely powerful stereo system that is being played with the volume and bass levels turned up and the car windows rolled down.
The acoustic terrorism fostered by boom cars runs counter to the desire of most Americans for peace and quiet. The Census Bureau notes that noise is Americans' No. 1 complaint about their neighborhoods. Noise levels have risen sixfold in major U.S. cities in the past 15 years, and automobiles are the largest source of noise.

Peace-loving citizens need to reclaim the streets. Some have already begun: In Chicago, boom cars that can be heard from 75 feet are subject to seizure and their owners may be fined $615. Buffalo, Cleveland and Pittsburgh also are cracking down on boom cars. In Papillion, Neb., owners of car stereos that can be heard from 50 feet away can earn themselves three months in jail.
—Ted Rueter, “Today's boom cars are nothing if not acoustic terrorism,” Los Angeles Times, March 27, 2002
1988 (earliest)
The "boom cars" — windows open with their supercharged stereos at full blast — regularly cruise up and down in front of William Bailey's house on 25th Avenue S in St. Petersburg. Their young occupants drive slowly and sometimes stop to talk to friends — sonically assaulting nearby residents in the process.
—Joseph Galarneau, “Sound effects,” St. Petersburg Times, July 17, 1988
Boom cars are also called ground pounders, street pounders, or (rarely) trunk thumpers and no wonder considering the brain-liquefying power of some of these car stereo systems. A decent home stereo might pump out 200 watts, but boom car units often boast 1,000 watts of power, and systems with 2,000 or even 3,000 watts have been recorded. As a point of reference, the human pain threshold for noise is 120 decibels (dB), but these rolling sonic factories can hit 140 or even 150 dB. Because decibels are measured on a logarithmic scale, the sound level doubles every 10 dB, so (it turns out) 150 dB would be the equivalent of standing next to a 747 with its jet engines at full roar.

(For the record, I should note that the "winner" in this contest may be the 48,000-watt absurdity installed in a Ford Bronco a couple of years ago. According to Wired magazine, it could reach 175 decibels (two and a half times louder than the 747) and the vehicle's occupant would actually die (and most unpleasantly, too) if he was insane enough to crank up the system to its top volume.)
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