by Neil Bauman, Ph.D.
Hearing aids produce feedback, which can sound like your hearing aids are squealing or whistling. This happens for one reason only–the sound output from your hearing aid amplifier is feeding back into the microphone (hence the name “feedback”).
There are a number of causes of feedback.
- 1. Your hearing aids are not properly adjusted and consequently are pumping too much power into the higher frequencies that you can’t hear (which are more prone to feedback). (I mentioned this one in my article of January 8, 2006.)
- 2. You have too much wax in your ear canal. This prevents the earmold going in far enough and sealing properly. Hence the amplified sound leaks out (which gets back to the mic and produces feedback).
- 3. Your earmold is too small. As a result, it doesn’t fit tightly enough. Some earmold material shrinks over time making them become loose. Other times your ear canal expands. For example, it could expand if you are a new hearing aid wearer, or if you have lost weight.
- 4. You didn’t insert the earmold/hearing aid properly. If it doesn’t seat properly and get a good seal, it can cause feedback.
- 5. If you have a Behind the Ear (BTE) hearing aid, you may have a cracked tube or earmold that lets the sound leak out.
- 6. Your vent is too big. Depending on your hearing loss, you may be able to get away with a large vent, or you may not be able to have any vent at all. Typically you want the largest vent you can get away with as this lets your ear canal breathe and reduces the occulsion effect (like you were hearing in a barrel). One nice solution is to have earmolds with big vents and then plugs of varying sizes that you can insert to reduce the vent size to one that works for you. This is what I have. My earmolds came with a very large vent built in, and a series of 6 plugs I can insert ranging from big bore to small bore to no vent at all.