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New earphone technology could be the answer to 'listener fatigue'


May 17, 2011

The ADEL features an inflatable tip, that is said to minimize or eliminate discomfort in the ears of music listeners (All images: Asius Technologies)

The ADEL features an inflatable tip, that is said to minimize or eliminate discomfort in the ears of music listeners (All images: Asius Technologies)

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It's no big secret that wearing in-ear devices, such as stereo earphones or hearing aids, can cause the ears to hurt over time. According to the engineers at Colorado's Asius Technologies, however, this isn't due simply to a poor fit or high volume levels. Instead, it's caused by an "acoustic reflex," that no amount of earbud-reshaping or decreases in volume will alleviate. There are reportedly ways of minimizing or even eliminating what's known as "listener fatigue," though – these include a flexible membrane, and even an inflatable ear-tip device created by Asius.

Based on physical and computational models used by the researchers, it was found that sound waves create an oscillating pressure chamber, when entering an ear canal sealed with an in-ear device. This triggers a defense mechanism in the ear, in which tiny muscles work to dampen the transfer of sound energy from the eardrum to the cochlea – this does not protect the eardrum from excessive shaking, however. Because the reaction lowers sound levels reaching the cochlea by as much as 50 decibels, it can cause listeners to compensate by turning up the volume even higher, thereby subjecting their ear drums to even more shaking.

The strain on both the ear drums and the muscles are what the Asius team believe causes the discomfort.

One approach to the problem involves modifying existing earbuds or hearing aids by stretching a thin film of medical-grade polymer over already-existing holes in the devices, which are designed to equalize pressure inside and outside of the ear. This "sacrificial membrane" absorbs the sound pressure created by the music or other audio, thereby keeping the pressure chamber effect from occurring.

Another approach, which is said to better reduce pressure and potentially offer superior sound quality, is to use Asius' Ambrose Diaphonic Ear Lens (ADEL). Named for company founder Stephen Ambrose, the ADEL is essentially a tiny polymer membrane balloon that is built into in-ear devices, and inflates into place within the ear canal.

The device is inflated via a built-in Asius Diaphonic Pump, which creates air pressure by forcing sound waves through a tiny opening. "As sound waves pass through any given small hole, the alternating pulses emerge and retract through the orifice like a small air-piston, hitting and knocking the surrounding air molecules forward like billiard balls," said Ambrose. "Other molecules join in the stream from the sides due to the low pressure created by the flow. This results in a sustained jet of air."

Once inflated, it acts almost like a shock absorber for the ear drum. "The lens maintains desirable audio fidelity, especially at bass frequencies, and prevents feedback," said Asius' Samuel Gido. "The flexible membrane vibrates with the oscillating sound pressure in the sealed ear canal and radiates excess sound energy out of the closed space in front of the ear drum. In a sense, the flexible polymer membrane behaves like a second ear drum, which is more compliant than the real ear drum, allowing it to direct excess sound energy away from the sensitive structures of the ear."

There's no word yet on commercial availability of the ADEL. A more detailed explanation of the technology, however, can be found in the Asius video below.

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

WHAT THE HELL!?!?! I\'ve got no doubt that this guy has a good understanding of acoustics and middle ear mechanics, but there\'s some scandalous marketing happening here. In the first part of the video, the ear\'s reflex movements (large) decrease after removing the acoustic seal... But this is because the sound levels of the low-frequency content (which are effective in evoking the middle ear reflex) would have decreased dramatically. A fair comparison would have been to measure the sound levels in the canal with and without a proper acoustic seal, then compare the eardrum movements when the sound levels of the stimulus (the music) are the same across all frequencies.... I can\'t see how this device, which is basically a low-frequency compliance, would be any different from an inner ear canalphone with a leak or pressure tube to reduce the acoustic seal at low-frequencies!!! The moral of the story is - don\'t listen to loud bass! Even though clinicians and researchers claim that low-frequency tones wont cause hearing damage as much as high-frequency sounds, low-frequencies will evoke the middle ear reflex and cause the listener to turn up the music. But I can\'t see the need for this \'clever\' membrane, when a hole and a tube through the canalphone would have been just as good.

Daniel Brown

It is an acoustic peak limiter. The extra energy it takes to stretch the added diaphragm absorbs the peaks, keeping them from triggering the ear\'s reflex. In itself - not a bad idea. Stretch a condom-like device over your earbud to control the instantaneous peaks that are largely inaudible anyway, but cause the damage.

Since this could be made part of the earbud, it is not a bad way to help prevent today\'s kids from blowing their hearing out, as they are doing now.

However, this can also be done in various ways to the audio signal, either peak limiting it before or after recording. In fact, most of the professional in-ear monitor systems include a very good peak limiter as part of the signal chain to control the peaks.

If such a limiter were built into the player (as it should be), it will work with any earbuds - not just the special ones. As an audio engineer, I have seen a very simple peak limiter deigned just for this purpose that could be added to players for a very small cost.


It may appear that the ADEL device is essentially a port, but ports have been used in sealed in-ear devices for a long time and they do not ameliorate the sealed canal issues. If the port is large enough to vent low frequency energy, the perceived sound loses its bass content. This device provides a user-adjustable compliance that provides greater acoustic impedance than a hole but still reduces the static pressure changes that are generated by a driver diaphragm whose movement modulates the volume of the ear canal, thereby compressing the air trapped in the sealed space. This pressure modulation is in addition to the sound wave which oscillates around the average or static pressure, which in a sealed ear is also increasing and decreasing unlike the condition of an open ear canal in which the static pressure is constant.

I have heard this device and it indeed provides an \"open\" sound - more like an outside-the-ear loudspeaker than any headphone or canalphone I have ever heard.


Not to sound argumentative, but how does a membrane act as a \"peak-limiter\"? I\'d have thought that it\'s compliance would be high at low-sound levels, but then stiffen at higher levels (larger diaphram displacements - i.e. a nonlinear compliance that clips), effectively increasing the low-frequency pressure in the ear canal for high-levels (the opposite of a peak-limiter). I\'m obviously missing something, and I\'d appreciate it if I could be put straight.

Daniel Brown

Wow, I\'ve never heard that ear drum displacements cause fatigue, nor that the acoustic reflex causes fatigue. This article is so full of phony baloney pseudo-science I would almost think it is a prank.


NO WAY. You want to put what is effectively a balloon next to my eardrum? No thanks.

Conus Wister
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