Using earphones to listen to your iPod or similar music player? Don't crank up the volume too high for too long. That's the word from a conference called Noise-Induced Hearing Loss in Children at Work and Play.
Two studies on iPods and similar devices will be presented Thursday at the conference, being held in Cincinnati.
The first study comes from Cory Portnuff, Au.D., a graduate student at the University of Colorado at Boulder. Portnuff's team conducted a series of tests to determine exactly how long and how loud people could safely listen to iPods and similar devices with different types of earphones. Those headphones included earbuds, sound-isolating headphones (which reduce background noise), and regular over-the-ear headphones.
The key finding: The higher the volume, the more you should limit your listening time, with the recommended limits varying somewhat depending on the type of headphones you're using.
If you listen at 10 percent to 50 percent of maximum volume, the researchers say you can listen as long as you want, regardless of headphone type. But if you push the volume to 80 percent of maximum, the researchers recommend limiting your daily listening time as follows:
If you turn down the volume just a bit, to 70 percent of the maximum, the researchers suggest more generous time limits:
The time limits from Portnuff's team are related to the sound output levels of each type of headphone. For instance, they say earbuds put out about 5.5 more decibels than headphones that sit on top of the ears, on average. Their study also shows higher outputs for sound-isolating headphones.
The maximum listening times "represent the amount of time that a typical person could listen to their MP3 player every day without greatly increasing their risk of hearing loss," the researchers write.
The study doesn't show why the recommended daily time limits are slightly lower for stock iPod earbuds than for earbuds in general.
The researchers note that some people's ears are more sensitive than others.
"Today, however, we have no way of predicting who has 'tough' ears and who has 'tender' ears," write Portnuff and colleagues. They warn that "hearing loss occurs slowly and is often not noticed until it is quite extensive, so early prevention is the key."
The second study comes from researchers including Brian Fligor, Sc.D., CCC-A, of Harvard Medical School. Fligor also directs the diagnostic audiology program at Children's Hospital Boston.
He and his colleagues studied 100 graduate students with normal hearing. The students sat in a sound-testing booth listening to music through several types of headphones. Their job: Set the music volume to a comfortable level.
Meanwhile, the researchers either kept the booth quiet or piped in background noise, such as noise recorded in an airplane cabin. The students listened at fairly tame levels under quiet conditions.
But when the booth got noisy, they tended to turn up the volume to riskier levels unless they were wearing sound-isolating headphones.
Takeaway? Watch the volume. And if you're going to be in a noisy setting, sound-isolating headphones may help you keep the volume at safer levels.
SOURCES: Noise-Induced Hearing Loss in Children at Work and Play, Cincinnati, Oct. 19-20, 2006.
By Miranda Hitti
Reviewed by Louise Chang, M.D