Troops need better hearing protection.

• Author: Jean, Grace V.
• Position: INSIDESCIENCE+TECHNOLOGY

WRIGHT-PATTERSON AIR FORCE BASE, OHIO--It is mistakenly thought that vision is the most important of the five senses. In reality, hearing is the one that dominates and clues humans in to their surroundings.

On the battlefield, troops' auditory perception takes a beating. The Veterans Affairs Department compensates servicemen more than $1 billion annually for hearing loss-related problems. But even as the Defense Department provides measures to prevent hearing damage, troops complain that using such devices limits their ability to fight effectively because their environmental acoustic cues are muffled or distorted. For those reasons, some troops choose to forgo wearing earplugs at the cost of long-term aural disabilities.

In an effort to improve--and protect--troops' hearing ability on the battlefield, scientists at the Air Force Research Laboratory are studying how the human auditory system locates and processes sounds. They are translating their findings into technologies that not only will provide troops with 3-D audio displays but also will preserve their acoustic health.

When a noise occurs, the sound waves arrive at one ear before the other. Humans are sensitive to that interaural time delay of 10 to 800 microseconds. The brain processes the staggered signals to help pinpoint the location of the noise, said Richard McKinley, principal engineer at the lab's battlefield acoustics branch.

[ILLUSTRATION OMITTED]

Inside an anechoic chamber, 277 Bose loudspeakers are embedded in a geodesic sphere that is suspended in midair by netting. In its center rests a chair where subjects sit with microphones inside their ear canals and listen to chirps. Scientists measure how the sounds change when they reach the ears.

Based upon those studies, researchers have figured out how to reproduce spatially distanced sounds in a stereo headset using high-speed digital signal processors. Normally when sound is piped through headphones, its directional quality is lost. The resulting surround-sound effect is great for listening to a favorite CD, but not so practical for military pilots who have to monitor multiple radio channels. Though they can increase the volume of certain frequencies to help distinguish the conversations, the voices still overlap each other.

By spatially separating the radio input so that one voice seems to emanate from someone standing 30 degrees to the left, and the other voice 30 degrees to the right, for example, an operator can...