The new findings regarding the sound volumes selected by music-playing teens today are similar to findings 20 years ago when Walkman audio cassette players first came onto the market, Portnuff said. "One of the concerns we have today is that while Walkmans back then operated on AA batteries that usually began to run down after several hours, teenagers today can listen to their iPods for up to 20 hours without recharging them."
A 2006 study by Portnuff and Fligor indicated a typical person can safely listen to an iPod for 4.6 hours per day at 70 percent volume using stock earphones. But listening to music at full volume for more than five minutes a day using stock earphones increased the risk of hearing loss in a typical person, according to the study.
The 2006 study also concluded that individuals can safely listen to iPods for 90 minutes a day with stock earphones if the volume is at 80 percent of maximum levels without greatly increasing the risk of hearing loss, he said.
Loud music can potentially damage delicate hair cells in the inner ear that convert mechanical vibrations, or sound, to electrical signals that the brain interprets as sound, said Portnuff. "Over time, the hair cells can become permanently damaged and no longer work, producing hearing loss."
Everyone does not share the same risk of hearing loss, he said. Some people are born with "tougher ears" that allow them to listen to music relatively safely for longer periods. In contrast, those with "tender ears" may suffer ear damage even if they follow MP3 listening recommendations. "There is really no way of knowing which people are more prone to damage from listening to music," he said.
"Damage to hearing occurs when a person is exposed to loud sounds over time," said Portnuff. "The risk of hearing loss increases as sound is played louder and louder for long durations, so knowing the levels one is listening to music at, an
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University of Colorado at Boulder