How physics will make earphones less painful

As most people know, a few hours of having an ear bud in their ear leaves them sore and unable to listen any longer. Scientists have figured out what happens during 'listener fatique,' and designed pump-action ear buds that can solve the problem. Find out how you can rock and roll all night, and party every day.

Sounds are nothing more than pressure waves in the air. When they hit the ear, they travel down through the ear canal and knock into the ear drum. This is a membrane - like the top of a drum - that vibrates as the pressure waves hit it. That vibration is passed down, through a series of tiny bones, farther into the ear, to the cochlea. The cochlea is a spiraling space, filled with fluid and lined with hairs. The vibration hits the fluid, the hairs move, and their movement triggers electrical signals that finally make it to the brain and let us know that we're listening to our Star Wars ringtone again, and we need to pick up the phone.

In theory, it shouldn't matter whether we're listening to sounds a thousand miles away or wedged in our ear. In practice, we can listen to the far-away sounds all day without discomfort, while a relatively short span of listening to an ear bud or a hearing aid leaves listeners sore. Scientists thought that the sound was magnified in the ear, or that there was some kind of electrical problem with the devices. It turns out, the problem was the structure of the audio device, and the physical response of the inner ear. When the ear is blocked by an ear bud, a sealed chamber between the device and the ear drum. This chamber, with its lack of any form of pressure-release, increases vibrations intensely.

The ear responds to what it perceives as a loud noise by engaging the acoustic reflex. Tiny muscles pull even tinier bones away from the ear drum, so that it has to vibrate more dramatically to get the same signal across. Other tiny muscles pull other bones away from the cochlea, further dampening the signal. The sound is made softer, and the listener turns up the volume even more. This massive amount of pressure on the ear drum, and the fatigue of the muscles involved in the acoustic response, causes pain in the inner ear; listener's fatigue.

There are a couple of physics fixes for the problem. Both of them involve taking some of the pressure off of the ear drum by building oscillating barriers between it and the origin of the sound. This problem, the sealing of the ear, has caused problems in the past for people with hearing aids. Humans are used to hearing their own voice a certain way because it reverberates through their heads. This is one of the reasons we're so shocked when we hear ourselves on recording devices. The voice we hear isn't the one that's reaching other people. When a portion of the ear is sealed off, a person's own voice sounds muffled. This is why some people with hearing aids talk loud. They can't hear themselves correctly, even if they have no trouble hearing anyone else. Engineers have relieved the pressure by drilling holes in the hearing aid, but often this leads to the wearer hearing squeaks and squeals as air rushes through the holes. Since a person with headphones doesn't need to hear their own voice, scientists propose sealing off those holes, not with solid plastic, but with a flexible film barrier that provides a buffer between the sound and the ear drum.

Another design is a little more high-tech. Engineers want to try sending the earbud down the ear canal with its own little inflatable balloon. The balloon will inflate to fill the ear canal by pairing the outward flow of pressure from the speaker in the bud with a hole to take in inward flowing air outside the sound port. Once the balloon is inflated, it will do the same thing as the film. It will absorb some of the pressure that would otherwise batter the ear drum and cause the acoustic reflex to kick in. (And people thought pumps were going to be limited to sneakers in the nineties.)

Read the paper about the discovery at Asius Technologies.