Turn up your iPod, turn down your hearing

Personal digital music is one of today’s hottest trends. Everywhere people sport the telltale white “earbuds” and cords of the biggest musical trend of all: the iPod.

The iPod, made by Apple Corporation, is the flagship of personal music, the harbinger of a new generation of personal music listening, but the iPod generation may be losing their hearing, without even knowing it.

Noise-induced hearing loss occurs in response to excessively loud noise. It usually develops slowly and without creating symptoms. If it occurs gradually over a long enough time, the victim may not even realize that their hearing is ebbing away.

“I listen to my iPod every day, probably for at least an hour at a time,” said Portland State student Andrea Demas.

“I have [the volume] up at least three-fourths of the way,” Demas said. “It’s pretty loud.”

Two factors contribute to iPod-related noise-induced hearing loss: volume and duration.

The decibel is the unit used to measure a sound’s intensity. The typical iPod can generate sound volume at a level of 100-130 decibels.

In comparison to the iPod, motorcycle noise at a distance of 30 feet is about 80 decibels. The intensity level in the front row of a rock concert is about 110 decibels. The noise created by a military jet taking off is about 140 decibels for 100 feet.

The United States has long held industrial safety standards for loud noise. In industry, workers must be protected against noise levels exceeding 85 decibels.

While European iPods are required by law to cap volume at 100 decibels, no such standards exist in the U.S.

According to Susan Doucette, an audiologist with Legacy Health System, every three to five decibel increase cuts safe exposure time in half, effectively doubling the risk of the listener receiving a toxic dose of noise.

For today’s earbuds, a safe daily dose of listening at moderate levels may only be around 30 minutes.

As duration of exposure to loud noise increases, the auditory system becomes fatigued. According to Doucette, the result is a temporary condition known as threshold shift, which is accompanied by a stuffy feeling in the ears, dulled hearing and ringing in the ears, called tinnitus.

“When I take my iPod off, my ears usually have this generally muffled feeling,” Demas said. “Sometimes it feels like I’m not hearing things very well.”

“Repeated episodes of threshold shifts or even a single incident of intensely loud exposure can result in a permanent loss of hearing and permanent tinnitus, due to damage to the tiny hair cells in the inner ear,” Doucette said.

Audiologists suggest that the best way to protect one’s hearing is to limit both the decibel level and the duration of exposure.

“It’s also important to remember that the effects of noise exposure are cumulative over your life,” Doucette said.

Ears damaged by one episode of loud noise do not return to their normal pre-noise baseline. The next time abnormal noise exposure occurs, fresh damage is superimposed on the existing deficit.

“Some folks also have tender ears,” Doucette said. “It takes very little to damage their ears and they end up with a permanent hearing loss and very bothersome tinnitus.”

There is currently no way to predict how individuals will respond to noise, or exactly how much noise exposure, if any, can be considered safe. Since most people do not walk around with personal sound meters, Doucette said the best approach is one of caution.

“If your ears feel stuffy or ring following iPod use,” Doucette said, “you had it up too loud or for too long.”

Users in the U.S. turn the volume up to dangerous levels, often to cover background noise. The typical user who rides TriMet and turns their iPod up loud enough to drown out the noise of the bus and their fellow passengers is exposing their ears to a sound level capable of causing hearing loss.

The iPod’s loudness problem is made worse by its earbuds, which have replaced traditional headphones.

Studies suggest that the kind of headphone used with any sort of personal music system greatly affects the risk of noise-induced hearing loss. The closer the headphone is to the eardrum, the higher the sound levels the system is capable of producing.

Conversely, external headphones fit loosely, covering the ears with pieces of soft foam. A later iteration featured soft plugs that sat loosely in the opening to the ear canal. In either case, the danger of delivering too much sound straight into the ears was much lower.

Because an iPod’s earbuds fit so deeply into the ear canal, the volume of air in the canal and the distance between headphone and eardrum is reduced. This effectively doubles the relative level of noise exposure and can reduce by one-half the amount of time for safe listening.

A spiral-shaped structure in the inner ear, the cochlea, is filled with fluid and lined with microscopic hair cells. The hair cells are what respond to auditory signals and then work with the brain to create a perception of sound.

Although remarkably tough, hair cells are easily damaged by excess noise, and do not regenerate once they are gone. Researchers continue to search for a way to repair or re-grow damaged auditory hair cells in humans, but so far with little success.

According to the National Institute on Deafness, at least 30 million Americans currently have some degree of hearing loss. Over the last 20 years, environmental noise has doubled every decade, a combined effect of city congestion, automobile noise and electronics, all contributing to hearing loss.

Many personal music devices, such as the Sony Walkman, include safety precautions in their instructions. Apple Computer recently developed a free software package to provide iPod users with a method to limit the system’s volume. The software update is available as a free download at www.apple.com/ipod/download.

Once installed, the software utilizes a combination code to allow parents and users to set and lock volume limits on the iPod. The new volume-limiter update works with earphones, all accessories that plug into the iPod headphone jack and the iPod Radio Remote.

On March 29, 2006, the American Academy of Audiology responded to Apple’s action by stating that this software package could help users listen to their iPods in a responsible manner.

What else can people do to protect their hearing?

“Kids – and adults, for that matter – need to realize that if they want to listen to their iPod all day, they must keep it a low level,” said Myron Smith, another Legacy audiologist. “If they want it louder, they need to limit the time. They can’t have it both ways and keep on enjoying the music.”