If you wear hearing aids you must have noticed the little white, transparent, or dark small pieces of silicon at the end of the tube or the wire. They called hearing aid domes. But what do they do, and why are they different in size and shape? Do they need maintenance? Can you change them yourself? Read through this article to build a base of knowledge about hearing aid domes.
To understand the hearing aid domes and their function you need to learn a little bit about the severity of hearing loss first.
What is an audiogram and how to read one?
If you have ever visited a hearing care practice to do a hearing test you know what an audiogram is. The audiogram is the first outcome of the hearing test. The audiogram chart shows the hearing threshold of your left and right ear, meaning the quietest sound that your left and right ear can detect. Usually, the threshold is shown in decibels (dB) over a 250 to 8,000 Hz range of frequencies to understand your hearing thresholds over low, mid and high frequencies.
As you see the below chart the result for the right ear is colour coded in red and the one for the left ear in blue.
What is the severity level of my hearing loss?
In the audiology world, any hearing threshold between zero and 20 dB means the patient has no hearing loss. Although the patient may still have a deficiency in speech recognition if all the test points are recorded lower than 20 dB it shows that the outer, middle and inner ears of the patient can detect very quiet sounds perfectly.
As shown in the above chart, hearing loss recorded between 20 to 40 dB is classified as Mild Hearing Loss. The severity levels are as per the following:
Zero to 20 dB: No hearing loss
20 to 40 dB: Mild hearing loss
40 to 70 dB: Moderate hearing loss
70 to 90 dB: Severe hearing loss
90 dB and higher: Profound hearing loss
Can I have different hearing loss in different frequencies?
Absolutely. In fact, most people with hearing loss have different thresholds in different frequencies. Very rarely does a patient has the very same thresholds over all frequencies. The hearing loss recorded in the above chart is called Mild-to-Severe Sloping hearing loss. As you see the hearing thresholds of the patient over low frequencies (250 to 500 Hz) are at around 20 dB baseline. Also, the patient's hearing thresholds over the mid frequencies (500 to 2000 Hz) range are at a mild hearing loss. Only when we get to high frequencies (2000 to 8000 Hz) the severity level of the hearing loss drops to Moderate and Severe. This audiogram demonstrates a typical case of deterioration of the human auditory system due to ageing (or presbyacusis).
How the audiologist chooses the size and shape of the hearing aid dome?
The information from the audiogram of the patient is the main input on how the audiologist chose the type of hearing aid and the choice of domes. The size of the dome is mainly dictated by the size of the ear canal of the patient. For patients who have no hearing loss in the low to mid frequencies, the audiologist might pick open domes to allow natural sound to pass through the dome and only the frequencies that are hard to hear by the patient (e.g. high frequencies in this case) to be amplified. Such fitting is called Open-Fitting.
As the hearing loss in the low and mid frequencies deepens the audiologist would progress from Open dome to Tulip, and then Vented-Close domes. When the hearing thresholds at low frequencies are at about 40-50 dB and higher the choice might step up to Double Dome (also called Power Dome). In such an extreme case the dome blocks off the ear canal of the patient and stops any natural sound to pass through (to be heard), instead, all sound shall be processed/amplified over the full spectrum of the hearing frequencies.
Can I change my hearing aid domes myself?
The short answer is no. Most of the hearing aid providers offer long-term warranties and services (HearingNow offers 4 years warranty on all our hearing aids). You might be eligible for a free hearing test and replacement of your hearing domes. Replacement of the domes might come naturally as part of your annual hearing test with your audiologist. If your hearing thresholds have deteriorated the domes may be required to be replaced by the next step anyway. So best to consult with your audiologist if you have any problem with your hearing aid domes.
What if my domes make my ears itchy?
The shape and size of the hearing aid domes are critical not only in the acoustics and quality of the hearing but in the comfort and retention of the hearing aids. Wrong-size domes might give you an earache. If domes are too small for your ears they will feel too loose and the retention of the hearing aids would not be perfect (see this post on hearing aid retention). If you feel the domes in your ear are too big, or too small, don't stay in your ear canal, or make you feel itchy in the ears then contact your audiologist for a revisit of your hearing aid domes.
Do I need to clean up my hearing domes? How?
The domes are usually made of silicon. They are durable and don't need replacement sooner than 9-12 months. If you noticed that they are brittle or dry and not flexible anymore then contact your hearing care provider for a replacement. Other than that you need to clean them daily. Yes, daily, for two reasons; a. to stop any ear wax to go through the dome and block the receiver (the piece that the amplified sound comes out of it in RIC hearing aids) or the thin tube in the case of BTE hearing aids), and b. to make sure that it is clean from any bacteria so you don't get an ear infection. An anti-bacterial wipe would do a great job of cleaning the domes. Best done before you put your hearing aids on in the morning.
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