The Science of iPods and Hearing Loss

After having had a lawsuit leveled at them for claimed hearing loss resulting from iPod listening, Apple has responded by upgrading iPod firmware to allow people to reduce the maximum volume level in their iPod. Great response from Apple, right? Wrong. Infinite Loop asks whether this may be an admission of guilt regarding the lawsuit, as does Lifehacker, and and one definitely has to wonder whether this insufficient solution is simply a quick response to the lawsuit.

Apple's response provides so little guidance on how to set the limit that it is near useless to concerned parents of children who use iPods or to concerned iPod listeners. Here's why.

First, Apple provides no guidance on what level to set the iPod and what it means for how long someone can listen to their iPod at that level. Consider that whether a sound is damaging depends on both the level the sound and how long the sound is heard. Listening to a sound for twice as long is the same as doubling the power of the sound with respect to hearing damage. What does this mean? To properly set the level, you have to know how long the iPod will be listened to in a day; equivalently, after the level has been set, you need to know how long you can safely listen to that level in one day.

National standards by OSHA and other groups have guidlines for sound exposure and hearing protection. A sound at 85 dBA can be safely heard for 8 hours. Great, so what level is that for an iPod? Well, it depends on what you are listening to your iPod with, but for now let's assume you are using the iPod earbuds. According to Harvard doctor Brian Fligor, 85 dBA is just below the 60% mark on the iPod nano volume control (indications are that it will be at an even lower setting on larger and more powerful iPods). So, at a 60% volume setting you can listen for  8 hours, but that time will halve for every 3 dB increase in sound level (that's a doubling of power). Again according to Filgor, a volume setting of 80% on the nano produces a 98 dBA level, producing a safe listening duration of 23 minutes! What about full volume? 111 dBA and 1 minute of safe listening. Complete data is shown on the right and is from this paper in The Hearing Review.

The case is even worse if you listen to your iPod (like I do) with insert earphones like the Etymotic ER-6is and Shure earphones. Acoustic measurements indicate that levels are approximately 7 dB higher at the eardrum with those listening devices. This means that for the same volume setting, insert earphones cut the safe listening time by 4.

So, you can now see where the firmware upgrade is inadequate. It does not ask whether the person is listening with insert earphones or earbuds--Apple's software should tell people that limits should be set lower if inserts are used. Secondly, they don't give any guidance at all as to how long the iPod can be used at that maximum setting. Right now, providing the volume control limit ability is like being given medicine with no guidance on dosage or how often to repeat a dose. If Apple wanted to, they could design firmware that would embed a sound level meter inside the iPod and beep when the daily safe limit of sound exposure has been reached.

The latest Hearing Review issue has several excellent articles on music and hearing loss, including "Portable" Music and Its Risk to Hearing Health and The Medical Aspects of Noise Induced Otologic Damage in Musicians. The articles are easy to understand by the average person. One researcher offers the following evidence that portable music players cause hearing damage. Dr. Fligor saw a 15-year old patient who had significant wax in his right ear. After removing the wax, hearing thresholds were measured in both ears. The ear that didn't have the wax showed a 20 dB hearing loss at 4kHz while the ear with the wax was normal. The teenager said that he listen to his portable music player at full volume, and Fligor concludes that the most likely explanation for the loss in the one ear was the music player--the ear with wax didn't have loss because it was protected by the wax which naturally reduced the loudness and protected that ear. The audiogram for this child is reproduced on the right, and the yellow highlight shows the 20 dB difference in ability between the two ears at 4 kHz.

Concerned? Data suggests that you can listen to your iPod at 50% volume indefinitely, and at 60% volume for over 4 hours. You will be tempted to go well above that if listening in an already noisy place, like on a subway or an airplane, but consider the consequences if you do and maybe leave the iPod off until you get to a quieter place.

Comments

[Terri Ives, Sc.D., Au.D.]

Dr. Fligor and I finished our iPod study data collection on "Does Earphone Type Affect Hearing Risk". The results of which were presented in part at the American Auditory Society Meeting 2006 and at the Noise-Induced Hearing Loss in Children at Work and Play Conference 2006.

Don't forget that just because a combination of an insert earphone and an iPod can put out higher SPL it doesn't mean that people actually turn it up to that level. In fact, we found that using the insert type, like the ER6i when in background noise caused people to keep the levels much more safe and sane. No surprise if you think about it.

[Greg]

Thanks for the information the Apple site was useless when trying to figure out a safe volume level. I have tinnitus and try to be careful with my hearing. Protect your ears you'll miss them when they're gone!

[Juno888]

For me i could say any more about that coz i want be, neutral person.