Big Audio Dynamite

The air inside the Nashville Convention Center is literally trembling.

Sound pressure waves launched by hundreds of bass woofers surge through the room at 1,132 feet per second. The waves combine with each other, bounce off the walls, flutter your clothing and quake through your body. The ambient noise inside the main hall is nearly 130 decibels, the threshold of pain.

Along the back wall, nearly 200 cars crammed with car audio equipment are about to compete in a stereo-vs.-stereo competition called dB (decibel) Drag Racing. Teams from around the county have spent months building their stereos until they are several times louder than a commercial airliner's jet engine.

When it's time to race, a microphone is placed inside the windshield. Doors are bolted or strapped shut to prevent sound pressure from escaping. An announcer says "Go," and the stereo is blasted by remote control for a cheering crowd.

Nobody is allowed inside a car when it's in competition; the sound waves are deafening and potentially lethal. Windshields blow out, batteries explode -- it's part of the fun.

Hundreds of dB Drag events take place every year, but this is the world finals, the event at which every competitor's amplifiers and ambitions are cranked to 11. Here, high-end car audio manufacturers pimp products and scout for new talent. Over there, Hooters girls mesmerize bassheads. In the staging area, obsessive stereo enthusiasts fistfight over proper design rules. And everywhere, everybody is practically screaming -- because that's the only way to be heard over all the ever-present bass.

And in this world, where bass is boss, the reigning boss of all bass is a 65-year-old Ahwatukee woman.

Alma Gates stands proudly by her baby, her Ford Bronco, showing it off to fans who know her name but call her "Ma." She and her son Patrick form the nucleus of Team Gates, the most famous competition team in car audio.

"Our Bronco defies most people's imagination," says 23-year-old Patrick. "If you're not into car audio, you don't understand it. We're building the loudest nonexplosive object on Earth here. The threshold of pain is about 132 decibels. A gunshot is about 145. The threshold of pressure is about 161. Above that, you start seeing bodily damage. We're the first ones to ever really [break 170 decibels]. Short of putting a rat in there and closing the door, we're not really sure what it can do."

The Bronco's laptop-calibrated stereo includes 26 batteries powering 48 amplifiers and an equal number of woofers. The truck weighs 16,000 pounds and is packing about $200,000 worth of equipment. To lock in sound pressure waves, every nonessential part of the vehicle has been stripped out, every crevice filled with high-density foam. The windshield is three inches thick, and the airtight doors are closed by 600-pound pistons. The stereo has 48,000 watts of power, the same as a fair-size radio station, all pounded into the passenger cab of a reinforced Ford truck.

This is the third generation of the Team Gates Bronco. Their earlier, quieter versions set car audio records in 1996 and '97 and made the names Alma and Patrick Gates known to just about every hard-core basshead in the world. Then they were defeated in 1998.

The dB Drag World Finals in Nashville marks their return to competition to regain their championship title.

"I'm not nervous," says Alma.

"We're either going to win, lose or screw up," figures Patrick.

When a speaker woofer fluxes, it creates a wave that expands outward like a rock thrown in a pond. The human ear interprets this wave as sound, but recognizes frequencies only between 20 and 20,000 hertz. At the low end of the human range, the threshold is fortuitously set so you do not hear certain environmental noises (such as your heartbeat) all the time.

If you take dozens of high-powered woofers, make them flux in perfect synchronicity, then trap their sound inside a confined space, the pressure wave can become a tsunami.

"A lot of people don't realize the amount of pressure that builds up," says Team Gates lead designer Scott Owens. "The doors alone are taking a couple thousand pounds of pressure. It's tough to make [the truck] strong enough to handle it."

Team Gates calls the truck "The Beast." It is a monster truck in the literal sense, and far more complex than simply a bunch of speakers and woofers shoved into a truck bed. Constructing a vehicle for SPL (sound pressure level) competition requires an obsessive exactness, thousands of dollars and countless hours of devotion.

The key is maximization. The designer must pull the maximum amount of current from the batteries, which in turn must produce the maximum amount of power from the amps, which must push the loudest possible sound from the woofers, which must be arranged in a manner that maximizes their collective force.