"I hate noise," says Los Angeles Physicist Vern O. Knudsen. "Noise is a human plague."
What concerns blunt, balding Dr. Knudsen—and many another U.S. scientist—is that the U.S., already perhaps the loudest nation in the world, is growing still noisier. Ever more numerous jet planes scream overhead, unmuffled trucks roar through city streets, sports cars whine along once placid suburban roads, and missile-age workers are being exposed to the highest and most dangerous noise levels in history. "Noise," says Physicist Knudsen, "is the bane of our existence."
Old Noise Hater Knudsen, former chancellor of the University of California at Los Angeles, is a crusader whose stamp-out-sound vendetta started 38 years ago while he was a graduate student at the University of Chicago, where he earned his doctorate with a thesis on the physics of hearing. With his trusty, ever-present sound-level meter, Knudsen tours the world, makes surprising discoveries. He once measured a noise level of 90 decibels* at a U.C.L.A. faculty tea. In the surf at Santa Monica, he registered a 3-ft. breaker at 80 decibels from a distance of 50 ft., and noted that the high-pitched, cracking noise made by shrimp often climbed to 90 decibels. He unromantically recorded a measurement of 92 decibels on the trail near the bottom of Niagara Falls.
Knudsen next turned to traffic, found that, even from 200 ft. away, a truck barreling along Los Angeles' San Diego Freeway pushed the needle up to 91 decibels —which is still twelve decibels lower than an accelerating Lexington Avenue bus in midtown Manhattan. At 92 decibels, New York's Times Square is probably the world's noisiest intersection; London's Oxford Circus registers 87, and Paris' Place de la Madeleine 90.
Physical Effects. Doctors agree with Physicist Knudsen that noise is a hazard to physical health. The most obvious danger: deafness. "The Good Lord in his mercy provided the majestic elephant and the lowly ass with ear flaps that would at least partially close the ear canal," observes Knudsen. "But man, poor creature, was not so favored."
A pistol blast, close up, can rupture an eardrum, and similarly sudden, unexpected sounds produce widespread, potentially harmful changes in bodily activity, as the body's defensive mechanism reacts to the unknown stimulus. Blood and intracranial pressures rise, perspiration increases, muscles contract sharply, flow of saliva and gastric juices is radically reduced, and digestion ceases. Even short-term exposure to high-intensity noise—above 135 decibels—can cause a breakdown in the ear's sensitive basilar membrane.
Few humans are ever exposed to such severe noise intensities. But some occupations (e.g., airline pilots, aircraft workers, riveters, boilermakers) require constant exposure to dangerously high sound levels. Such prolonged exposure, says Knudsen, results in a degeneration of the organ of Corti—part of the middle ear's acoustic apparatus—and a decrease in the number of ganglia, or nerve cells, in the ear. The U.S. Air Force's Dr. Henning E. von Gierke warns that continued exposure to 135 decibels of noise for longer than ten seconds once a day, or to 100 decibels for more than eight hours a day, may result in permanent hearing loss.