How do hearing aids work? Are they just blasting what they hear directly into the ear potentially causing more damage?
In: Biology
For starters, I work as an Engineer for one of the largest hearing aid manufacturers in the world, although in the Quality & Regulatory Affairs side of things, so I’m not as well-versed as a member of R&D would be.
I’ll cover the second point first, Power and Super Power hearing aids intended for those who have severe and profound hearing loss can be amplified to the extent where they would cause damage to those without hearing loss or with moderate loss.
As such, any hearing aid should always be programmed by a hearing care professional (audiologists and hearing aid dispensers in the UK) prior to issue, as they ensure that the hearing aid is programmed on safe settings. DO NOT buy hearing aids via mail order or over the internet, as the face-to-face consultation and fine tuning is essential for ensuring safety and maximising performance/troubleshooting.
Effectively, your hearing doesn’t get damaged because the only time a hearing aid should put out potentially damaging volumes is at frequencies where the damage has already been done.
As part of your hearing aid fitting the HCP (Hearing Care Professional) will perform a hearing test, which produces an audiogram detailing your hearing loss at various frequencies, typically up to 8 kHz. This audiogram is then used to determine which hearing aids (if any) are suitable for your hearing loss – typically the less severe your hearing loss, the more options you have as the smaller, custom instruments typically produce less powerful outputs.
If you are getting an off-the-shelf hearing aid, either called a behind-the-ear (BTE) or receiver in-the-ear/canal (RITE/RIC) with no custom ear mould this can be fitted to you the same day as your test, but if a custom hearing aid or mould is chosen there’s usually a 1-3 week turnaround for the aid/mould to be manufactured.
When the finished product is available the HCP will program the device to suit your hearing loss – in broad terms it will amplify frequencies which you don’t hear well and leave frequencies which you can hear un-amplified, which is why another person’s hearing aid won’t work for you. Newer hearing aids also perform frequency transposition, where high frequencies (such as the letter “S”) that patients can’t hear well, or at all, are changed to a lower frequency to allow them to hear it.
In crowded rooms basic hearing aids in a pair will also evaluate the sound that you are hearing to allow you to focus on a single person. This is typically done by determining if both hearing aids are receiving speech at the same volume, as that indicates that you are facing the source of the speech. When this occurs the rear microphones are made quieter to allow you to focus on the person you are facing.
More advanced hearing aids will scan the room hundreds of times per second to allow speech from all around you to be cleaned up and give a more realistic experience in a crowded room.
On top of that you have bluetooth functionality, connectivity to phones, TVs, mobiles, FM adapters (primarily in schools), but they don’t have any real effect on the basic functionality of the aid.
Please note, this is a very simple take on a really complicated subject, so there may be sections which aren’t 100% correct, but are worded in a way to make it easy to understand.
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