The more you turn up the volume in your earbuds, the harder your ear works to turn it back down, a process that ultimately leads to "listener fatigue," according to new research by Longmont-based Asius Technologies.
The local audio engineers -- led by inventor Stephen D. Ambrose -- have also created a gadget that can fight the fatigue and allow listeners to hear "louder" music even with the volume turned down. The same technology can be applied to hearing aids.
"Audiologists have been recently imploring us to turn down our personal listening devices," said Ambrose, who will present his discovery Saturday at the Audio Engineering Society convention in London along with his colleagues Robert Schulein and Samuel Gido. "We discovered why we have to be told this. We don't have to be told not to touch a hot stove; that is something that we get pretty easily. So why would we have to be told to turn down these personal listening devices?"
The answer, the Asius engineers found, has to do with the ear's ability to dampen volume when the pressure generated by sound waves in the ear canal become dangerous. And those sound pressures are much greater when the speaker in the ear -- such as an earbud -- actually seals off the ear canal. Essentially, plugging the ear canal creates a closed cylinder, and the speaker works as a piston.
"When a sound wave is moving just through the air, it acts a lot differently than if a 'piston speaker' is sealed into a cylinder, which your ear canal is," Ambrose said.
Sealing a speaker in an ear canal can increase the pressure on the eardrum by up to 1,000 times compared with the pressure created by a speaker on a headphone that's not sealed in the ear, the researchers found. To defend against these pressures, the body triggers a defense known as the stapedius reflex, when muscles in the ear flex to cut the sound waves that pass from the eardrum into the inner ear.
"Paradoxically, the protective reflex makes loud volumes seem lower than they really are," said Asius Technologies' Gido, "potentially prompting the listener to turn up the volume even more."
The result is listener fatigue or, literally, tired ears. Ambrose has a long history of experiencing this fatigue himself. He's the original inventor of wireless in-ear monitors -- which are now used almost universally by stage musicians to hear a particular sound mix while they're performing -- and he's spent years engineering in-ear monitors for everyone from Michael Bolton and Clint Black to Bon Jovi and Steve Miller.
"I've mixed on stage with lots of different professional bands," Ambrose said. "And we noticed that after three hours of performing, our ears would ache."
Ambrose has now figured out a way to tweak earbuds and hearing aids to eliminate the audio fatigue, and the fix can also increase the vibrancy of the sound. The tweak amounts to creating a hole in the device that is then sealed with a gossamer membrane -- a sort of mock eardrum, or tympanic membrane -- that is able to absorb the more forceful sound waves from the speaker, taking the pressure off the real eardrum.
"The fake tympanic membrane allows the closed system to feel like it's open and sound like it's much more vibrant," Ambrose said.
Ambrose has tested the idea by jury-rigging -- and later refining -- the hearing aids of one of his longtime friends, Gary Moore.
"He drilled this hole and put in this little membrane," Moore said. "And every time he's changed something, my hearing has gotten better."
Moore has noticed that he doesn't have to take out his hearing aids anymore to "rest his ears," but he's even more excited about the changes he's noticed in his ability to understand speech. He used to have difficulty distinguishing words such as care, tear, bear and there, he said, and he had a hard time understanding higher-pitched voices.
"I'm very excited," said Moore, who attributes his chronic hearing loss to years working in a cement plant. "This is revolutionary to me."
Ambrose said he's getting similar responses from other people who use hearing aids.
"Hearing-aid wearers have been able to turn their hearing aids down by half or two-thirds because now the lower volumes sound much better, much louder, much more balanced and they're hearing a lot more details."
Ambrose and his colleagues are also working on creating a housing for an in-ear speaker that would, essentially, be made entirely of the fake tympanic membrane. The ear piece looks like a tiny balloon that inflates in the ear, sealing the canal.
Ambrose expects that his group's discovery will spur more research into the ear's protective reflex.
"We didn't just happen upon a gadget," he said. "We happened upon a whole field of study."
Contact Camera Staff Writer Laura Snider at 303-473-1327 or firstname.lastname@example.org.