New Device May Protect Ears from Listener Fatigue

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2011-05-13 09:42

Listener fatigue results from being subjected to a continuous barrage of sounds of varying frequency and volume. It can result in discomfort and pain for some people when using in-ear headphones, hearing aids, and other devices that seal the ear canal from external sound.

The prevention is not always to not use the device, especially if it’s due to a hearing aid. Turning down the volume is always recommended for in-ear headphones to help prevent injury to the ear and hearing, but some listeners will experience pain and discomfort from use of in-ear devices even at low sound volume.

Sound engineers may have found the cause of listener fatigue due to in-ear devices and a potential solution.

In two separate papers and a presentation at the 130th Audio Engineering Society convention in London on May 14th, 2011, Stephen Ambrose, Robert Schulein and Samuel Gido of Asius Technologies of Longmont, Colo., describe how sealing a speaker in the ear canal dramatically boosts sound pressures and how a modified ear-tip can help alleviate, or even eliminate, that effect.

Using physical and computational models, the researchers show that sound waves entering a sealed ear canal create an oscillating pressure chamber that can produce a potentially dramatic boost in sound pressure levels. This boost appears to trigger the acoustic reflex which is a defense mechanism in the ear.

The acoustic reflex can dampen the transfer of sound energy from the eardrum to the cochlea by as much as 50 decibels. The acoustic reflex does not protect the ear drum from the excessive shaking that can occur with the oscillating pressures.

"Paradoxically, the protective reflex makes loud volumes seem lower than they really are," adds Gido, "potentially prompting the listener to turn up the volume even more."

The resulting physical strain of the oscillations in the pressure chamber and the repeated activation of the tiny muscles involved in the acoustic reflex are what the researchers believe may lead to listener fatigue.

Ambrose and his colleagues developed a way to counter the oscillations by using a membrane outside the ear drum to take the brunt of all the pounding. This "sacrificial membrane" disrupts the excessive pressure waves, protecting the ear drum and preventing the triggering of the acoustic reflex, ultimately leading to lower, safer listening volumes.

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