Can You Hear Me Now?

Credit: NIST/Erik Secula

If you or a family member uses hearing aids, you may have first-hand experience with the problem of feedback, an annoying whistling or whining sound that the devices can sometimes make. 

Newer hearing aids have been designed with feedback cancellers, but these fixes can inadvertently introduce other issues: distortions and lower quality for the amplified sounds produced by the aids. This is especially a problem for “open-fit” aid models, which don’t plug up the user’s entire ear canal. Open-fit models are popular because they tend to sound more natural as well as being more comfortable and less visible.

To help manufacturers come up with new ways to deal with feedback and sound quality issues in open-fit devices, researchers at NIST, in collaboration with the U.S. Department of Veterans Affairs (VA) and other organizations, are working to create tests and tools that manufacturers can use as standards when making and improving their designs for removing feedback in hearing aids. What’s needed in particular, researchers say, is a standard way to detect persisting feedback and to measure the resulting sound quality, which can be described on a scale that ranges from “bad” to “excellent.”

To conduct their tests, NIST scientists use a large and extremely quiet room called an anechoic chamber, designed to avoid practically all bounce-back of sounds off the walls, floor, and ceiling. In the center of the room, and sporting the hearing aid being tested, is a life-sized manikin head and torso. The manikin sits in front of a loudspeaker that produces the sounds used to test the aids.

This hearing aid standardization work for testing feedback cancellers could help millions of Americans. Hearing loss affects 1 in 3 people between the ages of 65 and 74 and nearly half of those 75 and older, according to the National Institutes of Health (NIH). Hearing problems are also by far the most prevalent service-connected disability among American veterans, according to the VA.