While on a really quiet night, it's possible for the ear to hear an AK-47 magazine being loaded and the rifle being cocked more than a quarter-mile away, wearing the earplugs reduces that distance to just 400-500 feet.
Another solution tried by the Armed Forces, an ear muff-like device with microphones on the outside, addresses this problem, but has the side effect of preventing the soldier from accurately determining the direction that a sound is coming from, a property called localization. That's not a good trait when the enemy could be nearby.
In 2009, Dr. Mead Killion, a noted expert in audiology and founder of Etymotic Research, a company that makes products for the hearing aid and consumer electronics industries, was attending a meeting of the National Hearing Conservation Association, where these hearing injuries were being reported. The problem was not a lack of availability of good hearing protection, but that it just wasn't being used.
Killion's company had developed a chip twenty years ago for the hearing aid industry, that was designed to amplify soft sounds, but have no effect on loud sounds, as long as they didn't exceed 105 dB of loudness (a tolerable level equal to the sounds that an orchestra can sometimes produce).
Another property of the chip was it didn't amplify sounds louder than this level, and, in fact, limited them. Killion thought that these characteristics could be adapted to a new product he referred to as a blast plug, something that might eliminate all of these injuries.
He next married this circuit with an eartip design, originally perfected for Etymotic's consumer headphones, which fit almost everyone. While the eartip seals the ear, the electronics inside compensates by amplifying the soft sounds, thus raising the sound level to what it would be for an open ear.
At the same time, sudden intense sounds -- such as from firearms and IEDs -- are reduced to safe levels by the sealed earplug. Thus, this new invention, named the BlastPLG Earplug, solves the problem: the ability to detect the soft sounds while blocking out the loud sounds.
Realistic field tests were conducted by John Casali, Ph.D. of Virginia Tech, an authority in human factors design, for their effectiveness in allowing soft sounds to be heard (detection) and for their directionality (which permits accurate localization).
The results of the tests proved that the devices provide the same ability to discern soft sounds as though wearing no earplugs at all. And, the localization tests proved they worked nearly as well as the open ear. For most listeners, it seemed as if nothing was in their ears.
Currently the military is testing the product. Drill sergeantsare being fitted with the electronic earplugs at two U.S. military bases. While there's no question that they work, what's being evaluated is whether the troops will be willing to use them. If not, it's just another good idea without a market.
The BlastPLG Earplugs was just awarded the 2011 Design and Engineering Innovations Award at this year's CES.