Hearing aid silences 'howl' from feedback
Tuesday 22 September 1992
THOUSANDS of people who suffer from 'howls' in their hearing aids could benefit from a new device to be launched in Britain next week, writes Susan Watts.
People with severely impaired hearing often find they must turn up the volume on their hearing aids so much that the microphone picks up sounds from the device's own loudspeaker, producing a howling feedback effect.
High frequencies cause the worst howls, so manufacturers have tried to alleviate the problem by limiting these in the sound their hearing aids amplify. GN Danavox, the Danish hearing aid maufacturer that paid the pounds 1m development costs, tried the device on 30 profoundly deaf people.
Many reported hearing high pitched sounds they had never heard before. One 10-year-old said she had heard 'a ghost' creeping up behind her. This turned out to be the wind.
The device feeds its own continuous test signal through the hearing aid, but at too low a volume to be heard. The hearing aid monitors the way the test signal is altered as it bounces around the ear canals.
This gives the device a clear picture of how ordinary sounds will echo around the ear, so it can produce a signal that is the exact equal and opposite of these unwanted sounds, cancelling them out almost immediately before they can cause feedback.
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