Asius’ ADEL earbud balloon promises to take some pressure off your poor eardrums

Novel device with rock ‘n’ roll roots may protect listeners from potential dangers of private listening devices and hearing aids

May 16, 2011

Engineers investigating “listener fatigue”–the discomfort and pain some people experience while using in-ear headphones, hearing aids and other devices that seal the ear canal from external sound–have found not just what they think is the cause, but in addition a possible solution.

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

“We tried for years to show down the amount but still experienced audio fatigue, even on the lowest levels shall we get by with on stage,” says Ambrose, who was leading the improvement of in-ear monitors for greater than 35 years as a musician and audio engineer for leading artists and movie studios. “The fatigue couldn’t simply be ‘fixed within the [audio] mix’ as it now seems to be a physiological phenomenon,” he adds. “It wasn’t an issue 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 which may 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 within the ear that dampens the transfer of sound energy from the eardrum to the cochlea–the auditory part of the internal ear–by up to 50 decibels, but doesn’t protect the ear drum from the excessive shaking.

“Paradoxically, the protecting reflex makes loud volumes seem under they are surely,” adds Gido, “potentially prompting the listener to show up the quantity much more.” The ear drum, already shaken by the oscillations of the pressure chamber, is further impacted by the boosted volume.

The resulting physical strain, at the side of the repeated activation of the tiny muscles taken with the acoustic reflex, are what the researchers believe could lead to listener fatigue.

To counter the oscillations, Ambrose and his colleagues developed the way to use an artificial membrane technology outside the ear drum to take the brunt of your entire pounding. This “sacrificial membrane” disrupts the excessive pressure waves, protecting the ear drum and preventing the triggering of the acoustic reflex, ultimately resulting in lower, safer listening volumes.

The papers describe two approaches for introducing the recent membrane technology. The best involves a retrofit that may be applied to existing in-ear headphones and builds upon earlier studies of hearing aids. For many years, audiologists have known that sealed ear canals create distracting uncomfortable side effects, resembling the occlusion effect that causes one’s voice to sound muffled. In years past, audiologists drilled small holes within the earbuds of hearing aids and other audio devices to relieve the pressure; however, the holes also brought about squealing feedback effects and diminished sound quality.

Ambrose discovered that stretching a skinny film of medical-grade polymer over these pressure-alleviating holes reseals the ear environment, yet provides a sacrificial membrane to soak up the abusive pressures. In accordance with the conclusions of the new 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. The ADEL™, which seems like a tiny ear-sealing balloon, uses a singular, miniaturized technology called an Asius Diaphonic Pump™ to inflate the polymer membrane.

The pump, developed with support from NSF’s Small Business Innovation Research program, converts the alternating, compression-expansion waves of sound right into a direct-flowing stream of molecules, filling the membrane using only minimal energy from the headphone speaker. The pump has enough force to both inflate the ear lens and keep the device comfortably within the ear canal for so long as the device is worn.

“The lens maintains desirable audio fidelity, especially at bass frequencies, and stops feedback,” says Gido. “The flexible membrane vibrates with the oscillating sound pressure within the sealed ear canal and radiates excess sound energy out of the closed space in front of the ear drum. In a way, the flexible polymer membrane behaves like a second ear drum, that’s more compliant than the genuine ear drum, allowing it to direct excess sound energy far from the sensitive structures of the ear.”

The pump takes benefit of a physical property called an artificial jet, a column of fluid that erupts when an acoustic wave passes through a small hole.

Sound waves are compression and rarefaction waves–specifically, symmetric pulses of alternating compressed and expanded air molecules. Our ears interpret the alternating pulses as sound.

“As sound waves go through any given small hole, the alternating pulses emerge and retract in the course of the orifice like a small air-piston, hitting and knocking the encompassing air molecules forward like billiard balls,” says Ambrose. “Other molecules take part the stream from the edges end result of the low pressure created by the flow. This leads to a sustained jet of air.”

By integrating an inward flowing jet into the side of the sound port, Asius transformed a normal synthetic jet right into a real pump able to harvesting and storing inflation and deflation pressures.

“Our support of the diaphonic valve-on-a-chip and its capabilities for harvesting audio energy to couple communications into the ear arises from both the innovative components of the proposed technology in addition to the societal impacts,” says Juan Figueroa, the NSF program director who has overseen Asius’s grant. “The development will allow users improved hearing at all times, instead of being forced to live with reduced hearing over and over again as a consequence of device-related listener fatigue.”

The brand new technologies emerged from Ambrose’s experiences as a recording artist and audio pioneer. In 1976, Ambrose invented what would become the SoundSight MicroMonitor, the primary high-fidelity, custom in-ear monitor (IEM), a headphone for monitoring amplified music during concerts.

While the small size, improved sound and other advantages caused wide adoption of the IEMs, users realized early on that extended listening could end in uncomfortable fatigue within the ear, and infrequently pain. The experiences weren’t unique–hearing-aid users, battlefield soldiers using in-ear protection, and others using sealed-ear-canal devices reported similar experiences.

“From the start, I knew something must 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 within the ear that nobody ever dreamed were possible.”

The researchers corroborated observational data with a working laptop or computer simulation of the effect, incorporating data from functioning ear canals, cadavers and fluid dynamics models.

Since the reflex is muscular, the researchers believe the repeated engagement and disengagement causes the tiny muscles to fatigue, resulting in much of the pain and discomfort linked to listener fatigue. The researchers have submitted applications to conduct extensive studies to figure out the role these factors play in contributing to hearing loss.

“With the assistance of Jay Kadis from Stanford University, we confirmed that the our devices prevented the acoustic reflex from triggering, and the lower volume levels merely sounded louder since the ear was now more sensitive–more sensitive, yet less vulnerable to higher volumes. And, without the reflex, the stapedius muscle was now not being constantly tired out from overuse. We knew we had a discovery and an answer that might help everyone from professional performers to hearing-aid wearers.”