While most people covet the hours of nonstop music and the snug earpieces, those features, and others, are also the reasons the players may hurt your hearing.
The component that can have the greatest impact is the headphone. In a study published last year in the journal Ear and Hearing, Dr. Brian Fligor of Harvard Medical School looked at a variety of headphones and found that, on average, the smaller they were the higher their output levels at any given volume control setting.
Compared with larger headphones that cover the entire ear, some insertable headphones, like the white ones sold with Apple Computer's iPods, increased sound levels by up to nine decibels. That may not seem like much, but because decibels are measured in logarithmic units, it can mean the difference between the noise output of an alarm clock (about 80 decibels) and that of a lawnmower (about 90 decibels).
The other problem, a second study found, is that insertable headphones are not as efficient at blocking background noise as some larger ones that cover the ear, so there is more incentive to turn up the volume.
To be sure, no one is certain what levels of noise the average MP3 listener is experiencing. But a large study of iPod users between 18 and 54 in Australia last month might provide some insight. The study, by the National Acoustic Laboratory in Sydney, found that about a quarter of the people surveyed kept their iPods at volumes that could cause long-term hearing damage.
The bottom line: MP3 players may increase the risk of hearing loss for some people.