More than half of American high school students surveyed reported some signs of hearing loss, a finding audiologists blame on ubiquitous iPod, other MP3 players and portable DVD players.

A new poll commissioned by the American Speech-Language-Hearing Association suggests more high school students in the U.S. show some form of hearing problem, to a level that surpasses that of the previous generation.

The unsettling thing is that noise-related hearing loss is permanent, according to Brenda Lonsbury-Martin the association's chief science and research officer.

Extended portable music listening could lead to hearing loss.

Symptoms include:

• Turning up the TV or radio.
• Saying "what" or "huh" during regular conversation.
• Experiencing ringing in the ears.

It's clear that Apple's iPod and similar devices have revolutionized how people listen to music. Music fans can listen in many more places, for much longer and at loud settings.

It's not clear what is causing the hearing-loss symptoms.

American Speech-Language-Hearing Association president Alex Johnson

"If you think of this exposure as being kind of a dose of noise, that the longer you're exposed to it over a longer period of time probably increases your risk," said the association's president, Alex Johnson, in Washington.

"Our greatest concern, of course, is for students."

Earphone design matters

Nevertheless, the U.S. poll of 1,000 adults and 301 high school students found those over 18 tend to listen to their iPods for longer periods than students.

Over the last 10 years, audiologist M.J. DeSouza in Toronto has noticed a difference in her practice. She used to see mainly toddlers and seniors, but now people of all ages make appointments.

"Even people in their early thirties are coming in and they're saying, 'You know, I'm just not hearing as well as I used to,'" said DeSouza. "When we do the hearing test, it turns out to be noise-related hearing loss."

Earbud-style headphones are part of the problem, according to audiologists. People tend to pump up the volume when there is a lot of background noise, such as on subway rides.

• FROM JAN. 5, 2006: Townshend says kids will be all right if they turn down the volume

They recommend:

• Turning down the volume.
• Listening for shorter periods of times.
• Wearing headphones that fit over the ear.
• Seeing a certified audiologist for hearing loss symptoms.

The U.S. poll was conducted during the last two weeks of February. Results for high school students have a margin of error of plus or minus 5.8 percentage points. For adults polled, the margin of error is 3.2 percentage points.