In a study published in December 2004, Brian J. Fligor, Sc.D., and L. Clarke Cox, Ph.D., at Boston University measured the volume levels of six portable CD players, through both the original headsets, if any, and five others purchased separately. At their highest settings, most of the 35 possible player-headset combinations were loud enough to cause irreversible noise-induced hearing loss if used regularly for as little as a few minutes per day.

The measurements were done shortly before iPods became popular. Fligor, now director of diagnostic audiology at Children’s Hospital Boston, said preliminary results indicate that the volumes produced by iPods and other MP3 players are “in the same ballpark” as that of the CD players.

In a separate study published in April 2005, Warwick Williams of Australia’s National Acoustic Laboratories measured the noise emanating from the personal music players of 55 randomly chosen passers-by in two busy city intersections. The volume averaged about 86 decibels–a bit too high, say Consumer Reports’ noise experts, for extended daily listening. Some players were turned up much higher than that.

At maximum volume with the included headphone, nearly all the MP3 players we rated exceeded 85 decibels in our tests at an external lab, and some exceeded 100, a level that can damage hearing even after short periods of time. To avoid hearing loss, our experts say you should never set your music player’s volume higher than 85 decibels, about the same level as a vacuum cleaner or a noisy restaurant. Be sure to judge the volume conservatively: Music you like tends to sound softer than an annoying sound with the same decibel level.

Many players in our MP3 Ratings have built-in volume limiters that take the guesswork out of safe listening. Some models have a preset safety level, which can be activated via the player’s menu or an on/off switch. All iPods and some Creative models allow you to custom-set the volume limit, as well as protect the setting with a pass code–a nice touch for concerned parents. We recommend setting the maximum volume between 1/2 and 3/4 of the volume bar’s full setting. But be aware that the loudness of individual songs can vary significantly, depending upon genre, equalizer setting, and how the song was recorded.

Our experts say that people whose living and working environments are otherwise quiet can safely listen to 85-decibel music for several hours a day. But if you’re regularly exposed to other loud sound–whether from machinery, transportation, or live music–you should wear hearing protection at those times if you want to enjoy music from your portable player at other times. That’s because damage from noise exposure is cumulative. If you have any concerns about hearing loss, see an audiologist soon.