Causes and cures for listener fatigue

LONDON—Speakers from Asius Technologies of Longmont, CO, reported their findings at the 130th Audio Engineering Society Convention on the cause of “listener fatigue” that some people experience when using hearing aids, in-ear headphones, and other devices that seal the ear canal. In addition, Stephen Ambrose, Robert Schulein, and Samuel Gido described new approaches to reduce the condition, which can cause discomfort and pain.

In separate presentations on May 14, the investigators reported that sealing a speaker in the ear canal dramatically boosts sound pressures. Using physical and computational models, the researchers showed that sound waves entering a sealed ear canal create an oscillating pressure chamber that can produce a potentially dramatic boost in sound pressure levels.

Data from the models, coupled with laboratory observations, suggested that this boost triggers the acoustic reflex, a defense mechanism in the ear that dampens the transfer of sound energy from the eardrum to the cochlea by as much as 50 dB, but does not protect the eardrum from the excessive shaking.



To counter the oscillations, Ambrose and his colleagues developed a way to use a membrane outside the eardrum to bear the brunt of the pounding. This artificial membrane disrupts the excessive pressure waves, thereby protecting the eardrum and preventing the triggering of the acoustic reflex.

Another, simpler solution, the researchers said, involves using a modified ear-tip that can help alleviate, or even eliminate, listener fatigue.