August 5, 2010

Ask the Audiologist

By Tara Hartman, Au.D, CCC-A
Audiology Consultants, P.C.

What is that whistling and squealing sound that comes from hearing aids?

The whistling sound that hearing aids sometimes make is called feedback. Feedback can occur for many reasons, and it is normal for hearing aids to squeal at certain times. The problem with feedback is that it is often perceived by others as well as the hearing aid user and it can be rather annoying and disruptive. It also drains battery life quickly. In order to stop feedback we need to understand what causes it.

Feedback occurs when amplified sound exits the speaker or receiver and is picked up by the microphone and reamplified. This creates a feedback loop and it’s perceived as a squeal or a whistle. Think about somebody holding a microphone in a large room and they walk a little too close to the speakers. Everyone cringes at the loud squeal the microphone system produces.

The same thing happens with the hearing aids. There is a microphone and speaker very close together, and if any of the amplified sound gets reflected back through the microphone, feedback will occur. Some people will put their hand over their ear and force feedback to occur because the sound has nowhere to go except back through the microphone. This is how many people test to see if their hearing aids are working, but it is not the best method to use because it is working against what we are trying to accomplish. We want to reduce whistling, not create it.

So why does it happen in some hearing aids but not others? As hearing care professionals, we have to find ways to keep all that amplified sound in your ear. The more power or volume a hearing aid has, the harder it is to keep all that sound in. This is why turning up the volume on your hearing aid can cause more squealing. Most digital hearing aids come with feedback management systems to help reduce whistling by detecting it quickly and canceling it out. This has been a huge advancement in hearing aids, and it has allowed us to fit a variety of styles and sizes without too many feedback problems. Older styles of hearing aids, on the other hand, did not have this cancellation
technology, so we have to find other ways to keep the sound in the ear canal. Usually this requires a tight fit in the ear or plugging up the vent hole so sound does not leak out of the ear. Ears continue to grow and change shape throughout our lifetime so hearing aids can become loose over time, and that may allow the sound to escape back through the microphone. Remaking the hearing aid or ear mold may be required; otherwise the option is to turn down the hearing aid which may compromise your ability to hear. Other methods of controlling feedback is to add a sponge around the canal portion of the hearing aid or ear mold to seal off the ear canal or to add a clear coating to the hearing aid that builds up the shell for a tighter fit. In severe cases, it is sometimes best to consider purchasing newer hearing aids that have feedback management technology so you can get the volume you need without the whistling.

If you experience feedback, contact your audiologist so he or she can help you find ways to manage it.

Filed Under: Health & Wellness

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