Talking Hearing Loss

Feedback!! Hearing aid users know it well. It can vary in sound from the occasional chirp to a persistent whistle. Usually it’s those around us who make us aware of that ‘god awful whistle’ coming from our hearing aids. Many times we will see our hearing specialists to try and get rid of that chirping sound.

As an audiometrist, I often see clients with feedback problems. Most of the time, they perceive the feedback as a sign that the hearing aid is broken, generally not working correctly or purely inferior in quality.

A client told me the other day “My friend spent $X,XXX on her hearing aids and they never whistle!!” As it turns out, this friend only had a mild hearing loss so her hearing aids did not need to provide a high level of amplification. Feedback is going to be rare in this situation.

Another comment I often hear goes along the lines of, “My grandfather wore hearing aids and they always whistled. It drove us nuts!”  Hearing loss can be quite severe in the elderly, especially in the higher frequency range. This often requires use of higher powered hearing aids which can boost sounds to quite loud levels and require custom ear molds to try and contain the sound within the ear canal. Even the smallest amount of sound leaking out of the ear can cause feedback.

So what is feedback and what can you do about it??

Feedback is something that can occur in any hearing aid regardless of it’s cost, however advances in the digital sound processing of hearing aids have reduced the instances of feedback occurring.

Many times, the cause of feedback is not the actual hearing aid but some other factor. As a child, I used to find it fascinating that if I held a microphone close to the speaker it was connected to I could produce a squealing sound. Varying the distance between the microphone and the speaker would produce different types of squeals. While it drove my parents crazy, what I was toying with was a concept known as acoustic feedback.

Acoustic feedback occurs when an amplifier has its microphone close to its output speaker and sound is amplified over and over again around the feedback loop. In a hearing aid this gives rise to a high-pitched whistle because the feedback loop is so small.

Nearly every hearing aid will create feedback when something is placed next to the microphone.

One way to almost guarantee to make your hearing aid whistle is to cup your hand over it.

If your hearing has been properly fitted however, it should not whistle during ordinary wear when there is nothing near the microphone.

Some of the most common reasons for persistent whistling of a hearing aid are:

• hearing aids that are not seated properly in the ear.
• loose-fitting hearing aids.
• Poorly fitting earmold
• blockage in the ear canal such as earwax.
• excessive jaw movement with chewing, smiling

Basically any time there are gaps between the hearing aid 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.

Advances in Digital Sound Processing

Today, most hearing aids have features built into their circuitry that reduce feedback. These systems quickly detect the feedback and eliminate it before it becomes audible to you or others nearby. Most hearing aid manufacturers include basic feedback reduction into even their basic hearing aids, but more sophisticated, high-end products may have more advanced feedback reduction systems.

Because acoustic properties of a feedback loop change if you put your hand or a hat or another object close to the hearing aid, an advanced feedback canceller needs to be adaptive to prevent whistling quickly when conditions change. This is especially important for open-ear devices that have an open path for sound between the output and the input of the hearing aid.

If you are thinking about hearing aids but feedback is a concern for you, ask your Hearing Care Professional about hearing aids and settings that most effectively control it. If you already wear hearing aids and have trouble with whistling, visit your Hearing Specialist. They can determine the cause of the feedback and make adjustments to correct it.