May 13, 2011
Protect Your Hearing
(Ivanhoe Newswire) "“ Engineers investigating "listener fatigue"- the discomfort and pain experienced while using in-ear headphones, hear aids, and other devices that seal off the ear canal from outside sounds- have found the cause, and a potential solution.
Researchers believe that sealing a speaker in the ear canal dramatically boosts sound pressures, and a modified ear-tip can help alleviate or eliminate that effect.
"We tried for years to turn down the volume but still experienced audio fatigue, even at the lowest levels we could get by with on stage," Stephen Ambrose of Asius Technologies of Longmont, Colo., was quoted as saying. "The fatigue couldn't simply be 'fixed in the [audio] mix' because it now appears to be a physiological phenomenon. It wasn't a problem with electronics, but rather mechanics."
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.
Data from the models coupled with laboratory observations suggest that the 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 decibels, but does not protect the ear drum from the excessive shaking.
The resulting physical strain, along with the repeated activation of the tiny muscles involved in the acoustic reflex, are what the researchers believe may lead to listener fatigue.
Ambrose discovered that stretching a thin film of medical-grade polymer over the pressure-alleviating hole reseals the environment, yet provides a sacrificial membrane to absorb the abusive pressures. Based on the conclusions of the recent papers, the membrane-hole modification appears to eliminate the overpressure effects that impact the users of many headphones, hearing aids and other devices.
For greater sound pressure reduction and potentially improved sound quality, Asius also developed a more advanced corrective device: a small, inflatable seal called an Ambrose Diaphonic Ear Lens (ADELTM). The ADELTM, which looks like a tiny ear-sealing balloon, uses a novel, miniaturized technology called an Asius Diaphonic PumpTM to inflate the polymer membrane.
"From the beginning, I knew something would have to be done about this audio fatigue factor," says Ambrose, though he had trouble proving that pressures were so extreme. "I invented the diaphonic pump partly to prove that audio volumes could create static pressures in the ear that no one ever dreamed were possible."
Because the reflex is muscular, the researchers believe the repeated engagement and disengagement causes the tiny muscles to fatigue, leading to much of the pain and discomfort associated with listener fatigue. The researchers have submitted applications to conduct extensive studies to determine the role these factors play in contributing to hearing loss.
SOURCE: 130th Audio Engineering Society convention held in London, England, May 14th, 2011