|
Hearing loss from loud noise or music is permanent, but preventable. In the audiology clinic at Children's Hospital Boston, concerned parents often ask how they can keep their child from ending up with a hearing loss. When someone asks "How loud is too loud?" our challenge is to provide clear and understandable guidelines that will help people protect their hearing health.
My interest in the use of personal stereo systems and hearing loss prevention started while I was in graduate school. While doing a student rotation in a clinic one day, I tested the hearing of a fifteen-year-old boy who had a subtle permanent hearing loss. The pattern of the test results were very suspect as being from long-term noise, such as might be seen in someone who just started working in a noisy factory and wasn't using hearing protection. When we asked about different things in his life that were noisy, he pulled out a CD player with headphones and said he listened to his music a lot. When we asked him for the volume level of his earphones, he said, "All the way up! That's where it sounds best." When he asked how loud he could listen and not do more damage, we weren't sure how to best guide him.
It's important to understand that it's not just "how loud" but also "how long" a person listens to loud music that determines whether listening was safe or if it was risky to hearing. The combination of the level ("how loud") and duration ("how long") could help provide safe-listening guidelines.
A useful analogy might be thinking about headphone listening like how fast you drive your car. If we knew a "speed limit" for listening level and duration we could offer reasonable safer-listening guidelines. If we knew how many people out there are "speeding" and why, we could offer ways to curb risky behavior.
To get at these questions, my colleagues and I have undertaken two directions in our studies: one to look at "how fast people drive" and the other to consider a reasonable "speed limit."
One study, with Dr. Terri Ives at Pennsylvania College of Optometry, School of Audiology, has looked at how loud people listen using different headphones in different background noise environments. After looking at listening behavior in 100 people, we know that it doesn't matter if you use an in-ear earphone or an over-the-ear earphone: around 6% of people listen to loud even when it's quiet, and around 80% of people listen to loud when it's noisy (like listening to your headphones when your flying on an airplane). But, if a person uses headphones that block out background noise, fewer people tend to listen too loud. For example, our study sponsor, Etymotic Research, Inc., makes a headphone that's meant to block out a lot of background noise. When people used their earphone, only 20% listened too loud when it was noisy (compared to the 80% who listened too loud when the earphones don't block out background noise). So the type of earphone (over-the-ear vs. in-the-ear) doesn't mean people listen louder, it's the background noise that makes people listen too loud. If a person uses a background noise-isolating earphone, they tend to not turn up their music as high in those noisy situations.
So if background noise causes us to "drive too fast" with our headphones, and some good earphones help us to "drive slower," what's the speed limit? The other study, undertaken by myself and an AuD-PhD student, Cory Portnuff, from the University of Colorado, looks at setting that "speed limit" with MP3 players. We looked at the Apple iPod, iPod Mini, and iPod Nano, the Creative Zen Micro, and the Sansa Sandisk MP3 players, and their output levels using several different kinds of headphones (in-the-ear, earbuds, and over-the-ear). We found that generally, people can turn the level of their music up to 80% of the maximum and listen for 90 minutes without seriously increasing their risk for hearing loss, using the earphones that come with the MP3 players. If you listen at lower levels (like 60% or 70% of maximum) you can listen longer (but not all day) without increasing risk for hearing loss. But if you listen all the way up (at maximum volume level), you can only listen for a few minutes before starting to increase risk for hearing loss.
So, our guidelines for safer listening are to not exceed 80% maximum level if you listen for 90 minutes or less, using the typical earbuds that come with the MP3 player. Using an earphone that blocks out background noise tends to help people listen at more moderate levels (less than 80% for 90 minutes), even when it's noisy. It is very important, though, to know that these sound-isolating earphones also block out important environmental sounds, like car horns and train whistles. You shouldn't use a sound-isolating earphone if you need to be aware of your environment for safety reasons. They are very good to use if you are at a fitness center and want to block out the gym's loudspeaker stereo and listen to your own music, or if you want to listen to the airplane movie at a reasonable level on that cross-country flight. They wouldn't be good to use for listening to your music while walking home through a dangerous part of town.
Certainly, the majority of people will not develop hearing loss from listening to headphones too loud. Our research, and studies published by other researchers, tells us that the number of people who habitually listen too loud for too long who might develop a hearing loss is likely less than 1% (our estimate is that it's around 0.5%). Even if only ½ of 1% of headphone users develop hearing loss from abusive listening, given that about 70 million MP3 players have been sold since 2001, that means as many as 350,000 people could develop hearing loss from using headphones irresponsibly. This is tragic, since this type of hearing loss is permanent and entirely preventable. We hope that current research and education efforts protect the hearing of as many people as possible.
|