Learn How Your Ears Protect Themselves

Our ears have a built-in defense system to protect themselves against loud noises continued over a period of time. In the middle ear there are two tiny muscles that contract by reflex when loud sounds occur that would injure the inner ear and cause loss of hearing.

One of these muscles contracts to reduce the vibration of the eardrum when noise exceeds a certain level. The other cuts down on the movement of the stirrup bone in the middle ear, reducing the intensity of the vibrations it transfers to the fluid of the inner ear. This is to protect the delicate structures located there, in the organ of Corti, where vibrations are converted to electrical impulses that travel up the auditory nerve to the hearing area of the brain.

Noise too loud continued too long, however, causes the gradual death of more and more cells in the inner ear. These cells do not regenerate, and the resultant hearing loss is permanent. As aural insult follows aural insult, more and more damage is done without the victim realizing what is happening. Most speech is within the range of 300 to 3,000 cycles per second, but most noise-caused hearing losses begin at 4,000 cycles. Since this is above the speech range, hearing is being eroded without the victim's knowledge.

As overexposure to loud noise continues, the listener's ability to hear human speech is affected. The victim then starts to complain that everybody is mumbling. He asks people to repeat themselves. Too late, it dawns on him that his hearing loss is serious.

Studies indicate that more than 5,000,000 Americans under 18 years of age have permanent hearing problems. One university reported that 60 percent of more than 4,000 freshmen tested had hearing impairments. One test that compared the hearing quality of Americans and African tribesmen revealed that the tribesmen, in their less noisy environment, had better hearing.

Scientists measure sound in terms of decibels. A whisper generates about 30 decibels. An average conversation reaches 60. City traffic, workplace noise, electrical appliances, airports-such environments generate noises from 70 to 170 decibels. No more than 70 decibels can be tolerated for 24 hours without damage. "All your allowable exposure," one engineer said, "can be used up in just one hour at 90 decibels." Another specialist in the field claims that heavy ear mufflers in combination with ear plugs are the best protection.

One researcher tested the effects of alcohol on hearing in noisy environments. It was discovered that the ear muscles that contract to deaden loud noises do not respond as quickly when the subject has been drinking liquor. Moreover, he is more tolerant of loud noises and as a consequence suffers more hearing loss than does the person who is sober. Sedatives also relax these defensive ear muscles and interfere with their reflex action when exposed to noise.

"Those kids who go to lots of rock concerts," one doctor who treats ear problems said, "I'd like to see them 30 years from now."

By then it will be too late.