Solving the most common forms of feedback

Since both electronic and mechanical feedback are usually only solved by sending the hearing aid to a repair lab, let's concentrate on the type of feedback that is the most common, and is also the one you can possibly solve yourself. Acoustic feedback occurs when the sound coming out of the ear mold or speaker manages to get back to the microphone, and sets up a "loop" that starts the hearing aid to whistle. Here are some common causes and suggestions for this:

1) Ear wax

A wall of ear wax blocking the ear canal is a very common cause of hearing aid feedback. Sound waves have pressure as they leave the ear mold. Imagine placing the end of a garden hose against a house with the water turned on. The water would spray out in all directions. When the sound pressure leaving an ear mold or hearing aid hits a solid wall of earwax, it also sprays in all directions, including out through the vent or any gaps between the ear mold or shell and the ear canal.

If you have a problem with feedback, have someone check your ear canals for ear wax and get it removed. This is the most common cause of hearing aid feedback

2) Loose fit

Another common cause of feedback is poor and loose fitting ear molds and hearing aids. Many people don't realize that losing ten or twenty pounds of weight can affect the fit of their hearing aid, causing it to fit loosely. If feedback begins right after an illness or a hospital stay, this is often caused by a loss of weight. A new impression and a new ear mold or shell remake may be required, or one of the following suggestions:

a) Test for a fit problem by pressing the hearing aid tighter into your ear with the erasure end of a pencil. If pressing it in stops the feedback, this indicates a fit problem.
b) Try putting Keri lotion or Vaseline around the canal of the hearing aid before inserting it. If it is a small gap, this sometimes helps.
c) Old time hearing aid dispensers used to put a coating of clear finger nail polish on the canal portion of hearing aids to make them fit slightly snugger.
d) Try plugging the vent temporarily with putty or tape. If this helps, fit may be a problem.
e) An ugly, but effective solution for very loose hearing aids is "Poligrip-comfort seal strips". If it doesn't work, they can be removed.
f) Try Comply Soft Wraps. The Comply Wrap is a strip of foam with an adhesive backing to stick onto hearing aids or ear molds. It reduces feedback and improves retention for hearing aids that are too small.
g) The best solution is getting a new better fitting ear mold or shell made. Check availability and prices locally for this, or contact a repair lab for information on how to go about getting it done by shipping your hearing aid and an impression direct to a repair and remake lab.

3) Pointed wrong

One often overlooked problem that sometimes causes feedback is when the end of the hearing aid shell or mold is pointed incorrectly. If the original impression was not made long enough, or the shell technician cut it too short, the mold/shell sometimes points into the wall of the ear canal instead of at the eardrum. The ear canal normally has two bends, kind of like an S curve. The ideal situation is for the end of the mold/shell to extend slightly beyond the second bend, allowing the sound to be "aimed" at the eardrum. If the end of the mold/shell terminates by pointing at the wall of the ear canal before the second bend, the sound is forced back out of the ear just as in the case of pointing towards ear wax. This is best solved by a longer canal, but even shortening, re-pointing, or "belling" the end of the canal may help.

4) Leakage

With custom in-the-ear hearing aids, the sound tube at the end of the hearing aid may be pushed in or have a hole in it from "aggressive" cleaning, the microphone may be pushed in; or there may be a hole in the wall of the vent that goes through the hearing aid. With behind-the-ear aids, there may be a crack or hole in the tubing, especially where it enters the ear mold, or a high power BTE may require a tubing with a thicker wall to prevent leakage.

Beware the Digital Conundrum!

Frequency response adjustments - They may solve your feedback, but can be disastrous for your speech understanding!

There are times that feedback can be solved in other ways than getting a better acoustic seal, but these are sometimes at the expense of hearing well. With digital hearing aids, there are "automatic" feedback controls, and also adjustments that the fitter makes to reduce feedback, but these are not always in the best interest of better hearing.

The most common adjustment to control feedback involves decreasing the high frequencies of a hearing aid. Even in digital hearing aids, most (but not all) of the feedback control methods involve some manner of cutting high frequency amplification. This is the easiest way to stop feedback, because almost all digital programming software includes adjustments for feedback. But it is often at the expense of your hearing ability! If the "cause" of your feedback is poor fit or even ear wax, and your hearing aid fitter does not consider that cause, they will often say "no problem", and reprogram your hearing aid to reduce the feedback.

If you have your hearing aids adjusted for feedback, and wind up not hearing as clearly or as well as you want to, you should consider the possibility that your feedback problem has a cause other than the programming. Before you have your hearing aids reprogrammed to control the feedback, try some of the temporary solutions above for loose fit, such as pressing the hearing aid into your ear to see if the feedback stops.

If your hearing aid professional adjusts the hearing aid for feedback and you still hear as well as before the adjustment, that is good. But if you find yourself straining for clarity after the adjustment, discuss the possibility with them that you may have a fit problem.

There are many possible causes for feedback. It may require a visit to your local audiologist or hearing aid dispenser to solve this, but the information above may help give you the edge in knowledge that it takes to understand and help solve your problem.

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