Whistling sound coming from hearing aid

Whistling, or Feedback, is a common problem with many hearing aid users. Several things influence whether it happens or not, when it happens, and how often it happens.
1. The size of the hearing aid and how it relates to the distance between where the sound goes into the hearing aid and where it comes out.
2. The amplification mechanism as compared to the overall circuitry of the hearing aid.
3. How high the volume is turned up.

Hearing aids provide a one way in and a one way out pathway for sound. The sound goes into the microphone, becomes amplified, and then goes out through the speaker to the ear drum.

Sound, however, moves in all directions unless something is blocking it from moving. This means that some of the amplified sound that will come out of the speaker can go back into the microphone again and become re-amplified. This can happen if the hearing aid isnt fit properly. It can be that the hearing aid is too loose in the ear, or the earmold isnt filling the enitre canal or if the vent is too large and it is allowing sound to travel back to the microphone.

The louder the sound, the farther it can travel and the more quiet the sound gets as it travels. Sound that is amplified by a typical ITE or ITC hearing aid doesnt have far to go to reach the microphone again - and then perhaps start to whistle.

Since BTE (behind the ear) hearing aids are much larger, they have less of a chance of feedback - the distance that the sound must travel to reach the microphones again is much more than the distance for a smaller hearing aid. This is why BTE's are recommended for more severe hearing losses because the hearing aid's volume can be turned up and you dont have to worry about that annoying whistling sound as much.

If his hearing aid is giving off alot of feedback, the hearing aid might be turned up louder than the hearing aid was intended to amplify. It might mean that he needs newer and more powerful hearing aids. It might also mean that his hearing aids do not fit properly, and they need to be refit. Either way, I would advise that he see his audiologist or professional and see if they cannot fix the problem.

Thanks. I don't think my dad has a BTE. His hearing loss is profound- so maybe the hearing aids are turned up too much.

Thanks again for the detailed answer.