Acoustic feedback has been described as “whistling,” “howling,” “screeching,” “screaming,” “squealing,” “whining,” “ringing,” “humming,” “buzzing,” “oscillating” and by various other names. The high-pitched whistling of a hearing aid experiencing acoustic feedback is an irritating sound for the hearing aid wearer and for nearby individuals. It is a normal problem for hearing aid industry, just need the users or professional to treat it correctly.
BASIC PRINCIPLES OF ACOUSTIC FEEDBACK
Thus acoustic feedback is a circle of amplification, where amplified sound is continuously re-amplified to the point at which a tonal squeal occurs. The specific tonality of the squeal is determined by the electronic characteristics of the amplifier combined with the acoustic characteristics of the microphone, the room and the loudspeaker. Due to the varied dimensions, and the reflection and absorption characteristics of different structures, different rooms produce squeals with different tonal characteristics.
Though the example of acoustic feedback at the beginning of this section was applied to a public address system, the same principle applies on a smaller scale to a hearing aid. Amplified sound transmitted to the ear canal from the receiver is radiated out through the vent, or via various other pathways (such as acoustic leakage between the earmold or hearing aid shell and the wall of the ear canal via a pathway called slit-leak), back to the microphone. Then it is amplified and re-radiated out of the ear canal, where it is picked up again by the microphone, re-amplified and so forth. Figure 1 shows a schematic representation of the acoustic feedback pathway in an ITE hearing aid that can lead to acoustic feedback. Figure 2 illustrates an ITE hearing aid in place in the ear, showing potential acoustic leakage pathways. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4172233/
Almost all hearing aids will create feedback when something is placed next to the microphone. For example, when wearers cup their hands over their hearing aids while they are in the ears, they will usually whistle. Properly fitted hearing aids should not whistle during ordinary wear when there is nothing near the microphone.
Causes of feedback whistling include:
- hearing aids that are not seated properly in the ear.
- loose-fitting hearing aids.
- blockage in the ear canal such as earwax.
- excessive jaw movement with chewing, smiling
Any time there are gaps between the hearing aid case and your ear, sound from the end of the hearing aid can leak out of the ear canal and find its way back into the microphone.
HOW TO REDUCE HURT OF WHISTLING OR FEEDBACK
- Reduce the volume,
- Re-seat the hearing aid, dome or eartip properly in the ear,
- Change bigger size dome or eartip, or change to close dome or eartip,
- Change the appropriate length sound tube.
- Remove the earwax and clean the ear cannal
- Consult the professionals.