It has been 11 years since I last wrote about feedback, so I thought it was time to return to that topic.

Most of us have memories of the sound of a hearing aid squeaking loudly in church. Many times, the actual feedback tone was at a high frequency the person wearing the hearing aid could not hear. Those nearby were embarrassed for the one with the whistle and many came away from this memory with the firm resolve to never wear hearing aids “if it was going to sound like that and I was going to look like that I won’t.” It was a common reaction.

The good news is that a great deal has changed in hearing aid technology related to feedback.

If fear of feedback is keeping you from hearing better, remember that technology today is not your grandparents’ hearing aid!

Feedback is essentially the factor of any sound system. It occurs when sound that travels through a microphone to speakers is continuously picked up by the microphone and re-amplified. We also probably remember the school principal or teacher at an assembly holding a microphone that got too close to a speaker. The wild squeak that came from the amplified speaker on the stage happened when the cycle of input from the microphone repeated itself rapidly until the system basically shouted, “I can’t do this anymore!” It didn’t shout it in English but in electronics as a squeal.

In hearing aids, feedback happens on a smaller scale when sound leaks from the receiver, the speaker, back to the microphone, the microphone will continuously re-amplify the sound. This creates a feedback loop, which manifests as a high-pitched, unwanted squeal or “whistle.”

Sound leaks back to the microphone when the hearing aid is loosened. This can happen any time a person chews, talks, puts on a hat or combs their hair.

Loose hearing aids may also be the result of poor fitting, the fault of the professional.

Vents can also cause feedback issues. Vents are holes drilled into hearing aids that air in, a voice to sound normal, but also allows amplified sound to escape the ear canal. Vents help avoid the “occlusion effect,” an acoustic phenomenon that increases the volume perception of a person’s own voice due to sound trapped between the hearing aid and the eardrum. Without proper venting, the hearing aid wearer tends to hear their voice through their nasal cavity like plugging your ears with your fingers and talking. Try it. That’s occlusion.

Digital signal processing is now permitting us to reach our amplification goals without the limitations imposed by acoustic feedback.

Early feedback suppression systems worked by reducing the degree of amplification at the feedback frequencies. The hearing aid would “notch out” the offending frequency by markedly reducing the gain around that point.

While both methods worked, in that more hearing aid gain was possible before the squealing point was reached, the consequence was less audibility at frequency locations where the person may have required more. Feedback was managed, but at the expense of understanding what was said.

An optimal feedback cancellation or suppression circuit will reduce acoustic feedback without any undesirable modifications of the hearing aid’s frequency response. Most manufacturers now include this capability in their hearing aids. While each company has its own proprietary software method, they all apparently have this one feature in common.

Generally, feedback cancellation circuits continually monitor the output of the hearing aid to determine whether some portion of the amplified signal contains elements that have the acoustic characteristics of acoustic feedback. This attribute of the circuit jumps into action when it immediately recognizes a sound it just heard. As the sound, the feedback, begins to repeat, the feedback circuit first determines the electronic characteristics of the feedback signal and then generates signals of opposite wave phase attributes that will cancel (or markedly reduce) that feedback.

Current hearing aid feedback technology uses advanced digital signal processing for real-time cancellation via phase inversion and notch filtering, adaptive algorithms that memorize environments and even biometric sensors for personalized adjustments, virtually eliminating annoying whistles and allowing for higher, clearer amplification. These systems differentiate true feedback from other sounds and constantly monitor feedback loops, creating an inverse sound wave or reducing gain at specific frequencies to cancel the noise instantly, ensuring a more natural listening experience. Sound complicated? It is fascinating technology inside a tiny micro processing chip in the hearing aid.

The simple thing to remember is that feedback is not the problem it used to be for the patient who wears hearing aids.

Hearing care is health care. If you have symptoms of hearing loss let a professional help you find out why. The hearing professional will help you sort out the technology level to meet your need and your budget, and answer your hearing needs questions. This could really be your year to hear better.

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Jeffrey L. Bayliff, NBC-HIS, is owner of Hear the Birds Hearing Aid Center in Lock Haven.