All auditory amplifying systems include a microphone and a speaker. If the sound leaves the speaker and enters the microphone, it becomes re-amplified. Once this acoustic energy - not audible sounds, but acoustic energy - is reintroduced through the system, it develops its own noise or whistle. This is a normal phenomenon which occurs in churches, auditorium and hearing aids, if the sound is amplified. It must be controlled in the hearing aid system to prevent it from interfering with your ability to hear and understand, not to mention annoying others around you. Once the whistle is audible to the hearing aid user, others can also hear it. Controlling feedback is more difficult in hearing aids than auditoriums because the microphone and speaker are so close together.

The high frequencies have the shortest wavelength. It is easier for high frequencies to escape from the ear and re-enter the hearing aid. Most people can hear acoustic feedback, but the hearing impaired person may not, due to the degree of the high frequency hearing loss. Someone else may say, "What is that?" The hearing impaired person does not hear it. When they discover it is their own hearing aid that is whistling, the hearing impaired person may become embarrassed, flustered, and angry over their situation.

Fit of the hearing aid:

It is important that the hearing aid fits properly in the ear. The ear does continue to grow. As the ear grows, the hearing aid no longer fits the ear. The same loudness that was required from the hearing aid for the hearing impaired person to hear and understand, no longer can be maintained because of the whistle. The earmold can be remade, so that the hearing aid properly fits. If it is an in-the-ear hearing aid, it may have to be recased. This can happen every one to three years for most individuals. Increased power requires a better seal. The hearing aid or earmold may need to be remade as often as every 3 to 6 months for severe to profound hearing losses.

Vent size:

The vent is a hole through the hearing aid or earmold, which allows the ear to breathe, or reduce the reverberation that people often have when an object is placed in their ear. As acoustic feedback becomes more of a problem, the vent needs to be reduced in size. Closing the vent reduces the amount of sound that can leak out from the instrument. However, reducing the vent can cause distractions: people can feel themselves or hear themselves walk, voices seem to have more echo, and the ear becomes moist. These problems need to be discussed with the hearing aid professional. Sometimes one must get used to these problems if they are to hear and understand better without the whistle.

 

Reposition the microphone and speaker:

Moving the microphone and speaker further apart makes it more difficult for the sound to re-enter the microphone from the speaker. One may no longer be able to use a smaller hearing aid such as a canal hearing aid. The use of a larger hearing aid such as a full inside the ear or a behind the ear hearing aid increases the microphone/speaker separation. As the hearing loss becomes more severe, it may be necessary for the head to separate the microphone and speaker. This is done by placing the microphone on the one side of the head and the speaker on the other side of the head. The head to becomes the baffle, therefore, reducing acoustic feedback. The microphone and speaker are now connected either by a wire or by a radio signal. This is normally known as a Power CROS hearing aid.

Modify the sound:

Altering the frequency response of the hearing aid so fewer high frequency sounds are amplified can also reduce the feedback. This helps, but unfortunately it also decreases the ability to clearly understand speech, difficult high frequency voices, accents, or understanding in background noise. A new way of modifying the sound is phase-inversion. This is available in some of the new digital hearing aids. Digital instruments will yield more improvements for controlling feedback in the future.

Earwax removal:

Earwax causes sound to bounce back instead of going through the eardrum. A sign that this may be the problem is wax on the tip of the hearing aid. The aid should be cleaned every night. Some people should visit their hearing health professional to have the earwax removed on a regular basis. This should be done at least once a year or as often as every a month. Through history and experience, you will determine what degree of ear care is required for you.

Acoustic feedback problems can be of great irritation because it can occur out of no where: when you smile, when you eat, when you bend over. If you have diligence and a good sense of humor, you will find that you can learn to live with the feedback if it occurs only occasionally.

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