An estimated 20 million American men, women and children are exposed to dangerous levels of sound every day. Audiologists are now particularly concerned because hearing loss is increasing at an alarming rate among children.
People once developed noise-induced hearing loss most often between the ages of 40 and 50, according to the current issue of American Health. Today, however, many doctors are attending to teen-agers with hearing problems.
In a study which tested the hearing of 1,495 Fountain Valley, Calif., children in the second, eighth and 10th grades, scientists discovered hearing failure rates ranging from 7 percent in the youngest group to 13 percent among the older group. Ten years ago the overall dysfunction rate was 3 percent.
"Loud noise wears down the delicate hair cells in the inner ear, which translate sound into nerve impulses," said Dr. Alice Suter, a Cincinnati audiologist who worked for the now-defunct noise abatement office of the Environmental Protection Agency.
"If the noise is really high, as in an explosion, it can destroy the hair cells outright. At slightly lower levels -- a rock concert, for instance, or a noisy industrial job -- the damage is slow but steady. Occasional exposure to this type of noise isn't bad, but if it happens over and over again, permanent damage can occur," Dr. Suter added.
How much noise is too much? The danger zone begins at 80 to 85 decibels (dB), the volume of a minibike or a rattling sink garbage disposal. People should limit their exposure to continuous sounds louder than this, or wear protective devices.
Common sources of dangerous noises include: Jet engines 140 dB; rock concerts, 90 to 130 dB; amplified car stereos, 140 dB at full volume; portable stereos, 115 dB at full volume; power mowers, 105 dB; jackhammers, 100 dB; subway trains, 100 dB; video arcades, 100 dB; power saws, 95 dB; electric razors, 85 dB; crowded school buses, 85 dB; and school recesses-assemblies, 85 dB.
Performers playing rock music run a very high risk. Pete Townshend, a guitarist for the British rock group, the Who, suffers from permanent ringing in his ears, a condition known as tinnitus. Before the group's 1989 tour, he was forced to rehearse inside a soundproof booth to preserve what hearing he had left.
Kathy Peck is another musician with damaged hearing. In 1984, her punk rock band warmed up an audience for the rock group Duran Duran in Oakland. She woke up the next day with a ringing in her ears that wouldn't go away. Today, Ms. Peck, who has lost 40 percent of her hearing and wears a hearing aid, is active in an organization called Hearing Education and Awareness for Rockers (HEAR). It is dedicated to persuading musicians to reduce the volume and wear hearing protection. "Rock and roll is like a sport," said Ms. Peck. "You should wear your protective gear."
Listening to rock and roll through headphones can also be hazardous. At full volume, a portable stereo can emit about the same level of sound as an average rock concert.
Dr. William Clark of Washington University's Central Institute for the Deaf in St. Louis calculates that about 80 percent of all children own such stereos. "There's strong evidence that 5 percent to 10 percent of children habitually turn the sound up to destructive levels," he said.
Of the 20 million Americans who put up with dangerous noise daily, about 9 million are exposed on the job, including 5 million factory workers plus construction and agricultural workers, firefighters, musicians, and truck drivers.
If people can learn to live more quietly, doctors believe it is possible they may avoid the "natural" hearing impairment that comes with age. When scientists examined tribesmen living in the Sudan under Stone Age conditions not long ago, they discovered virtually no deterioration in the hearing of elderly tribe members.