Audiology experts agree hearing loss is increasing. According to the American Speech-Language-Hearing Association, the number of Americans age 3 and older with some form of auditory disorder has more than doubled since 1971, from 13.2 million to about 30 million today. Of those, one-third are said to be people with noise-induced hearing loss.

Hearing experts warn improper use of iPods and other personal stereo systems can dramatically heighten the risk of hearing loss, particularly in young people.

Hearing aid specialist Don Ling from Miracle-Ear in Burton says those who should be concerned are people who are genetically predisposed to hearing loss -- technically called nerve deafness -- or who have health issues that may contribute to hearing loss.

"Most of those people probably won't know who they are until it's too late," Ling said. "So you want to be careful in your youth."

Typically, people start to experience hearing loss in their 60s, Lind said. But he said he is seeing more baby boomers in their 50s and expects that trend to continue.

The newest personal stereo gear presents two problems that concern hearing experts. The newer "earbuds" that fit snugly inside the ear put that sound only a tiny distance from the inner ear.

Digital technology makes it possible to play music in these devices without the signal distortion produced by, say, a transistor radio.

The other issue is that the newest iPods are capable of holding up to 15,000 songs and being able to play for up to 20 hours on a fully charged battery.

"If you use them at high volume for eight hours there's no doubt you could have damage," says Flint Township ear, nose and throat specialist Bobby Mukkamala. "There's a point where even resistant ears will break down."

Less expensive earbuds do not block background noise, meaning users often have to turn up the volume to hear music over ambient sound.

Noise-canceling headphones - of both the bud and over-the-ear type - actively capture and remove background noise.

Eytmotic's noise-canceling earbuds for iPods costs $149, according to the company's Web site. Bose's widely advertised QuietComfort 2 outside-the-ear noise-canceling headphones list for about $300.

Best Buy's Web site advertises seven noise-canceling headphones ranging in price from $44.99 to $199.99. The Flint Township store had only three last week: a Phillips over-the-ear set for $44.99, a Sony over-the-ear version for $49.99 and the bud-type with this feature for $99.99.

Mukkamala says young people aren't the only ones turning up the volume to block background noise.

"Earbud type headphones without noise-cancellation are more harmful than over-the-ear headphones without it.

"I tell patients that (head) phones with noise cancelation are becoming more readily available and less expensive. This is a much better way to drown out ambient noise."

With noise-canceling headphones, a safe listening range is considered to be 65-70 decibels, the level of normal conversation. At that level, a person could listen indefinitely without worrying about hearing loss.

The trend toward more people reporting hearing loss predates the iPod. It can be traced to the dawn of the industrial age, says Pam Mason, American Speech-Language-Hearing Association director of audiology professional practices.

These new devices merely add to a daily din of environmental noise that includes traffic, construction, jets, nightclubs, leaf blowers and surround-sound home theater systems.

"By age 65, about a third of the population will experience some age-related hearing loss," or presbycusis, said Brenda Lonsbury-Martin, the association's director of research and science.

"Old-age hearing is an accumulation of exposure to loud noise, exposure to ototoxic drugs (more than 130 medications, including some commonly used drugs, can cause or contribute to hearing loss, according to ASHA), smoking and a number of things that accumulate over time. Once this loss starts to occur, if you continue to add noise insult, you're more at risk."

Hearing damage occurs when loud sound destroys tiny hair cells in the inner ear. These cells are responsible for converting sound waves into electrical impulses, which are then sent to the brain. Once 25-30 percent of these cells disappear, Lonsbury-Martin said, a person starts to experience hearing loss.

Mukkamala said young people who haven't been exposed to noise in the military or factory-settings and report hearing loss are getting their exposure at concerts and in bars - and from listening devices.

Some recent warnings about hearing loss and personal music devices cite research on portable CD players by Brian J. Fligor, director of diagnostic audiology at Children's Hospital in Boston. In the case of one brand of player matched with a particular brand of earphone, he found that listeners could get a sound dose as high as 120 decibels.

This is comparable to the sound level at a loud rock concert or sandblasting; it could lead to the risk of hearing damage after 7.5 minutes of exposure.

Preliminary data on iPods and similar devices have found lower maximum levels - above 100 decibels (the noise volume of a chainsaw; risk of hearing damage after two hours), but not higher than 115 decibels (a football game in a loud stadium; risk of hearing damage after 15 minutes), Fligor said.

The sound, rather than being diffused at a football game or convert venue, is traveling a tiny distance from your earbud to your eardrum.

Hearing damage isn't the same thing as hearing loss and the effects of temporary exposure to loud sound don't have to be lasting "if you pay attention to your ear health," said Lonsbury-Martin.

She said the advice to a personal stereo user who experiences muffled or dulled hearing after listening would be the same as for any person coming out of a loud environment: Don't go back until the symptoms pass. And guard against similar exposure in the future.

Mukkamala said a ringing in the ears after loud-noise exposure is common.

"Usually, the ringing is what we call temporary threshold shift. The ringing should stop and hearing be perceived to be normal after a few days.

"If the ringing persists, there may have been a permanent threshold shift, which indicates there has been damage to the inner-ear hair cells."

Fligor's findings with CD players led him to prescribe as a safe portable stereo dosage one hour per day at 60 percent of maximum volume, a level that would fall below the 85 decibel mark at which the Occupational Safety and Health Administration says the risk of hearing damage begins. Fligor notes that this is meant more as a guide to self-regulation than a hard and fast rule.

Individual tolerances and preferred listening levels vary, he said.

Even if iPod users were to limit listening to an hour per day, experts agree, ambient noise -- on city streets or even in an office setting -- could challenge efforts to keep the volume down to 60 percent of maximum.

In informal research, Wichita State University audiologist Ray Hull asked students to take off their headphones in the name of science. Taking readings with "a fairly sophisticated" sound level meter, Hull found typical listening levels approaching 120 decibels.

While some people just prefer to listen to their music as loud as possible, Hull said, another factor is at work as well.

"A person can be listening at 60 percent volume, but then as the person's auditory system adapts to the intensity of the sound, the perception of the intensity is that it is becoming less, so the response is to continue to turn the volume up," Hull said.

Audiologists agree that it is important to guard against this desensitization by minding the volume dial rather than simply trusting your ears.

A good measure for how loud is too loud: "If you're standing across an elevator cab - that's about three feet away - if you can hear someone else's music, that person is giving themselves a hearing loss," said ASHA's Mason.

Mukkamala is one of the 42 million who have bought Apple's iPod. He said he listens to music while exercising. "I try to limit my loud music to Enya and not 50 Cent, but Enya doesn't quite motivate me on the treadmill as much as 50 Cent."

He said he has his hearing checked every year. "So far, so good."

By Ron Krueger
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