According to the National Institutes of Health, "long or repeated exposure to sounds at or above 85 decibels can cause hearing loss" -- noise louder than city traffic but not as loud as a lawnmower. The louder the sound, the shorter the time it takes to damage hair cells.
At maximum volume, an iPod reaches about 103 decibels, which can cause permanent hearing loss in a matter of minutes while listening through ear buds. In-ear headphones, like the earbuds that come with an iPod, send loud music straight into your ear and directly toward sensitive cells.
Noise-amplifying headphones, such as the kind DJs might use in clubs to hear over background club music, can produce louder sounds and take less time to cause irreversible damage. Just 15 minutes of listening at 100 dB can be harmful, according to the NIH.
Hearing loss among musicians can affect their abilities to discern pitch, perceive loudness, and recognize where sounds are coming from, according to Kathy Peck, executive director of Hearing Education and Awareness for Rockers. Peck said she has noticed a trend among DJs and hip-hop artists losing their ability to hear bass frequencies.
"If you lose your low end, that's like hearing a train go by, so that's very dangerous," Peck said, as opposed to losing the ability to detect high frequencies like birds chirping.
After years of performing, David Beltran has started to notice that he has trouble recognizing lower frequencies through his left ear, and deep voices sound muffled when he talks on the phone on his left side.
The 27-year-old Chicago DJ said that people in his industry often have no choice but to have their headphones at maximum volume for hours at a time -- and they often must stand near monitor speakers, adding to the problem.
"I know a lot of musicians who have experience with some form of hearing damage," said Beltran, who has tried to better monitor his own volume limit since noticing the problem. "When I'm working with other DJs, they'll have it as loud as possible. That to me is a sign that these older guys are going deaf."
PORTABLE MUSIC PLAYERS
For regular iPod users, the negative effects of loud listening might not be immediately noticeable.
"Noise-induced hearing loss or music-induced hearing loss happens very slowly over time," said audiologist Cory Portnuff. "I think in a few years we'll be able to see some effects of music players on hearing, but we're still easily five to 10 years away from seeing larger scale effects."
Portnuff has been studying the effect of portable music players on hearing loss as part of his doctoral dissertation at the University of Colorado. Studies on the hearing effects of portable music players have been around for decades, first looking at cassette and CD players. Portnuff's research is the first to use a monitoring device attached to participants' iPods to take away the unpredictability of self-reporting.