The Noise Haters

"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.

Loud noise also causes a number of unpleasant bodily sensations, such as vibration of the head and eyeballs, loss of vision, loss of equilibrium and heating of the skin. A noise of 160 decibels can kill rats and mice. Explains Knudsen: "The body temperature rises to a lethal level. It's the conversion of sound energy into heat that kills." In humans, at sounds near and above 160 decibels, the stirrup (one of three little bones in the middle ear) may be driven through the small "window" in the well of the inner ear. Possible result: meningitis, from infection of the fluid in the inner ear.

Even low-intensity tones can be dangerous if they are pure, i.e., if their frequency is limited. The reason: pure tones form a concentration of sound energy within the ear. The most "sensitive" frequencies--those which the body can least tolerate--occur, says Dr. Knudsen, within the octaves of 300-600 cycles per sec. and 600-1,200 cycles (middle C is 261.6 cycles). Warns Dr. Knudsen: "Anyone who lives in an environment where the intensity at these frequencies consistently reaches 85 decibels [for example, alongside a busy jet airport] should have hearing tests--because damage is possible. If the level stays at 90 decibels or above, damage will definitely result."

Psychological Effects. Workers in noisy surroundings often complain of such apparently psychogenic ailments as nausea, fatigue, headache, loss of neuromuscular coordination, and reduced sexual desire. "Noise can and does drive some people to distraction," says Dr. Knudsen. "If noise does nothing more than interfere with sleep --and this it does on a gigantic scale--it is a menace to good health." Knudsen carefully catalogued causes for his own middle-of-the-night awakenings, found that 75% were the result of noise. Most common culprits: auto horns, barking dogs, ambulance sirens, chirping birds. Dr. Knudsen's solution: earplugs. The plugs could not cope with sirens and extra-loud auto horns, but they attenuated all noise by about 30 decibels, cut his nightly awakenings in half.

Studies also show that noise adversely affects human efficiency. The Air Force's Dr. von Gierke says: "It impairs both manual dexterity and accuracy." A normally accurate, responsible aircraft mechanic may unconsciously rush, through his work, do a slipshod job, if he happens to be working in the neighborhood of a whining jet exhaust. When officials of Aetna Life Insurance Co. cut office noise levels 14.5% by installing acoustic wallboard, they found that typists' errors dropped 29%, machine operators' errors fell 52%, employee turnover decreased 47%, and absenteeism declined 37.5%.

What's Being Done? Noise costs U.S. industry an estimated $2,000,000 a day in workmen's compensation (for noise-related injuries), lost man-hours and decreased efficiency--but industry has been slow about putting in adequate controls. U.S. airlines, for example, balk at installing adequate jet noise suppressors, estimate that reduced engine power would cut payloads by 13 passengers per plane. Truck-line operators remove factory-installed mufflers in the mistaken belief that vehicle performance is sharply improved. Despite growing public pressure for noise abatement, few U.S. cities have adequate noise-control ordinances.

One of the few bright spots in the U.S. is somnolent Memphis, which has won 14 "Quietest City" awards from the National Noise Abatement Council for a strict program that requires thrice-yearly inspection of car brakes and mufflers, permits horn honking only in emergencies, and prescribes fines for people who keep noisy pets. But more needs to be done, says Physicist Knudsen: "The reduction of noise results in increases in output of labor and in human well-being that usually more than justify the cost of reducing the noise."

* The unit for measuring relative loudness of sounds, the decibel is approximately the smallest degree of difference that, a human ear can detect between the loudness of two sounds.

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