A new type of earbud takes advantage of your ear’s natural reflexes, giving you the same audio fidelity at a lower volume. And it takes away that physical strain.
Listener (or hearing) fatigue is the name for that discomfort and pain you might feel when using in-ear headphones, hearing aids, or any device that seals off the inner ear.
This past Saturday, Stephen Ambrose, Robert Schulein, and Samuel Gido of Asius Technologies described how sealing a speaker in the ear canal substantially boosts sound pressures and how a modified ear-tip can help alleviate that effect.
But first, a little physiology and physics. Sound waves are pulses of alternating compressed and expanded air molecules. Our ears interpret these alternating pulses as sound.
When the waves enter a sealed ear canal, they produce a dramatic boost in sound pressure levels. That boost triggers the stapedius (or acoustic) reflex – a defense mechanism in the ear that dampens the transfer of sound energy from the eardrum to the cochlea (auditory portion of the inner ear) by as much as 50 decibels.
"Paradoxically, the protective reflex makes loud volumes seem lower than they really are," Gido explains, "potentially prompting the listener to turn up the volume even more." The ear drum, already shaken by the oscillations, is further impacted by the boosted volume.
Since the acoustic reflex doesn’t protect the ear drum from excessive shaking, the repeated activation of the tiny muscles involved in the reflex results in physical strain.
To counter the oscillations, the team developed a way to use a synthetic membrane technology outside the ear drum to take the brunt of all the pounding. That ‘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.
This membrane tech can be applied in two ways (watch a video about them):
- One involves a retrofit for existing in-ear headphones. In the past, small holes have been drilled into earbuds to alleviate pressure. Stretching a thin film of medical-grade polymer over these holes reseals the ear environment, yet provides a sacrificial membrane to absorb the abusive pressures.
- For more sound pressure reduction, Asius also developed a small, inflatable seal called the Ambrose Diaphonic Ear Lens (ADEL). Pictured above, it’s a tiny ear-sealing balloon that uses a tiny pump to inflate the polymer membrane. The Asius Diaphonic Pump converts sound waves into a direct-flowing stream of molecules, which fills the membrane using only energy from the headphone speaker.
The flexible polymer membrane behaves like a second ear drum, which is more compliant than the real ear drum, says Gido, allowing it to direct excess sound energy away from sensitive ear structures. He also says the lens maintains desirable audio fidelity and prevents feedback.
"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," says Ambrose. "The fatigue couldn't simply be ‘fixed in the [audio] mix' because it now appears to be a physiological phenomenon," he adds. "It wasn't a problem with electronics, but rather mechanics."
The buds aren’t for sale yet, but Popular Mechanics and Sound+Vision have given them a try.
The work, supported by the National Science Foundation, was presented at the 130th Audio Engineering Society convention in London on Saturday.
Image: fully inflated ADEL / Asius Technologies, LLC
This post was originally published on Smartplanet.com