It is tragic that excessive noise has now become a threat to man's hearing even in the pursuit of leisure. I once displayed a "skull protector" on television, and was surprised to receive a request for details from an employee of a Midwest police department. His job was to train department personnel in the use of firearms. He participated in pistol shooting and was also an avid target shooter and hunting enthusiast. Noticing difficulty in hearing women's and children's voices, he went to the Mayo Clinic. He was shocked to be told that the sound waves from shooting had damaged the cells in the nerves of his ears, that it was permanent damage, irreparable. He was told to give up shooting immediately or face the loss of hearing any normal conversation within less than a year's time.
"I also shoot skeet, trap, waterfowl, upland birds and big game. As you can imagine, this hearing deficiency takes a great part of my life away from me and my family."
He wanted the data on the skull protector, to see if his doctors would approve a limited amount of shooting if he wore one.
Perhaps adults must be held responsible for discovering the dangers of their noisy play, but children are also endangered. Children everywhere are being hurt by playing with firecrackers and toy guns, and all sorts of toys equipped with noisemaking devices.
Investigators in Oslo, Norway, proved that about 1 per cent of the 14-year-olds suffered from hearing loss that may have been caused by toys that emit impulse noises. Similar investigations in Denmark showed injuries to hearing in 3.7 per cent of boys ranging in age from 10 to 16. In 1967 the Journal of the Acoustical Society of America reported on the findings of foreign and American research. Investigators at the U.S. Army's Human Engineering Laboratories measured the impulse noises produced by four toy firearms, and suggested these toys pose a potential hazard to hearing. In June of 1966, Consumer Reports warned that the blast of a toy bazooka powered by compressed air might damage the hearing of the children using it. In 1968 the British Standards Institution took cognizance of the danger from toys, and revised its code for safety to include noise levels. Though no precise limits were set, pending additional studies, officials expected that the eventual limit may be 100 decibels at three feet from a child's ear, according to the Manchester Guardian of May 18, 1968.
Amplified music has developed into a threat to hearing, especially for youngsters who listen to it constantly at school, at discotheques, and at home.
It seems that every doctor or audiologist who takes a reading in a live-music discotheque is assured of a newspaper headline about the dangers found therein. Theories abound about why the threat of amplified music makes news, from the one that society is attacking the rebels where it hurts, to the other extreme that there is genuine concern for our youngsters. Whatever the reason, it must be duly noted that no comparable concern exists about the deafening situation in factories and computerized offices. Is it that adults don't matter, or that factory noise is not as exciting as the "big beat"?
It is true that even the unamplified music of the Mabaans sometimes hits 100 to 104 decibels, with final peaks of 106 and 110. However, this music (sometimes from a five-string lyre and a chorus of twenty) beats out only during the two-month spring harvest. The festival singing apparently takes place not more than three times a week, and while it lasts from one to three hours, the total exposure is hardly comparable to the year-round almost daily exposure of "civilized" youngsters.
Amplified music's impact on hearing is a touchy subject, involving the audio industry and teen-agers. Yet it cannot be ignored. Electric guitars and other amplified instruments have produced levels of from 90 to 105 decibels, with peaks of 130 decibels. These amplified sounds are especially hazardous to hearing for speech, because most of the sound energy is in the critical 500 to 3,000 cps frequency range.
This problem, like all noise problems, is international. Levels in Copenhagen nightspots frequented by young people were found to exceed 120 decibels, a definite health hazard.
Unfortunately, the relationship between temporary loss, which is the usual experience, and permanent loss is not yet understood. The head of the division of otolaryngology of the University of Florida tested his daughter and nine other teenagers before and after a rock'n'roll session not long ago. Though he found measurable hearing loss, he did not know whether this was a temporary or a permanent loss if the levels ranged from 106 to 120 decibels.
Though more studies are needed, there seems little question but that prolonged exposure to amplified music poses a threat to hearing. For one thing, we do not know when the temporary loss blends into permanent loss, nor do we know how susceptible any given youngster is to the dangers of intense noise exposure. Another area of investigation should answer this question: if a permanent hearing loss is caused, but it is rated as only an insignificant 5-decibel loss, what happens when the victimized youngster hits middle age? The premature 5-decibel loss, added to the "normal" loss at middle age, may make the difference between a minor loss and deafness.
Annoyed neighbors may take some sadistic satisfaction in knowing that the operator of a powered lawn mower is in danger. Lawn mower noise has been measured at a range of from 92 to 105 decibels, with an average of 97. Two investigators discovered significant temporary hearing loss after 45 minutes of exposure. Aware that this can deafen the susceptible, they suggest that communities not overlook lawn mowers in their hearing-conservation programs.
Perhaps women were once wise to get out of the noise-stressed kitchen, out of their noisy homes and into the business and professional world. Except that there too—as well as coming and going—they are exposed to dangerous noise levels. But by far it is the male who pays the greater price in hearing damage. Men work in noisier occupations, operate the noisy do-it-yourself tools, hunt, commute on noisy highways, and set off the July 4th firecrackers. Civilized male hearing ages faster than that of women. But not so among the Mabaans, where men and women are equally exposed to the same environmental noise. The hearing of the Mabaan male is not significantly worse than that of the female.
There are many signs that the hearing ability of men and women of industrialized cities is declining. One of them is the shift in the baseline for the so-called loudness curves. In 1932 this baseline was zero decibels. In 1956, less than a generation later, this reference point had to be changed to plus-4 decibels. This shift is interpreted by Jansen to mean that the hearing acuity of the general population has diminished.
More and more people are finding it difficult to hear without help. The telephone company installs volume controls for the hard of hearing in hotel lobby phones; it provides optional amplified signal bells and flashing lights instead of bells. The legitimate theater uses electronic speech reinforcement where none was needed several decades ago.
When I was manager of a legitimate theater in Cincinnati I heard criticism of "dead spots" where hearing was supposed to be difficult. I invited an acoustical specialist to attend a matinee performance and advise me. During the intermission he called my attention to two women, of late middle age, sitting in front of him. He had heard perfectly. They had complained to each other that they could not catch all of the dialogue. Here was a strong indication that the problem lay with the listeners' hearing, not the theater, and not mumbling actors. Why do clergymen today need microphones for their sermons? Probably many among their congregations are suffering from partial deafness and do not know it.
Thomas Edison once predicted that as urban noise grew greater (which it inevitably would), the man of the future could eventually be born deaf.
We have long known the condition called presbycusis, age-induced hearing loss. We are now coming close to understanding occupational deafness. But the best evidence that people are having their ears hurt outside of work is the identification of a new category of deafness: sociocusis. Its name means hearing loss caused by a lifetime of living and playing in noisy environments.
Rosen's work in Africa is a challenge to industry's claim that there is an immutable law that adult man loses a specified amount of hearing with advancing age. One way to determine what contributes to loss of hearing with age is to measure the hearing of members of comparative societies: industrialized vs. primitive, quiet vs. noisy.
To verify the existence of sociocusis, someone would have to go through life with an ear plug in only one ear and then check his hearing to see if the protected ear retained significantly more hearing ability than the unprotected ear.
Thanks to the carelessness of a Dutch physician, there is one recorded case history in which a man did go through much of his life with one ear plugged up. Dr. A. J. Philipszoon, chief of the Ear, Nose and Throat Clinic of the University of Amsterdam, reported in 1962 that an 82-year-old man came to the clinic to try to get a hearing aid. The eardrum of his right ear was normal, but in his left ear was found a plug of cottonwool and earwax. It turned out that 32 years earlier, his family doctor, after treating the ear for an inflammation, had neglected to remove the plug of cottonwool. Dr. Philipszoon tested the hearing of both ears. The right ear showed a "normal" loss of hearing due to aging. But the hearing in the left ear was much better. The wax-encrusted plug had acted as an ear-defender for 32 years. "This case shows us 'experimentally,'" Dr. Philipszoon concluded, "that for the onset of presbycusis the noise of every day is a very important factor as suggested by Rosen."
It is estimated that perhaps ten per cent of the population may have "tin ears"—ears so sensitive that the cumulative effect of experiencing the urban noises found in transportation, on the street, and in the motorized home may lead to permanent hearing loss for the critical speech frequencies. Yet there has been no attempt to define an acceptable hearing conservation standard for the general population.