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.
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