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  • Writer's pictureDavid Engelman

How Do Hearing Aids Work?

Updated: Jan 22

Soundwaves, such as those being amplified by a hearing aid.

There are unfortunately a lot of misconceptions about what exactly hearing aids are and how they work. Hearing aids are very complex, high-tech instruments, and many audiology patients are surprised to discover that they are not just simple devices that make things “louder”. While this article won’t serve as an overly technical description of the engineering that goes into a hearing aid, I thought it would be useful to present a basic overview of how hearing aids operate, and how they are programmed.

Hearing Aid Bits and Pieces

Parts of a hearing aid.

Before delving into what hearing aids do and how they do it, it is important to learn some of the basic components of a hearing aid. All hearing aids operate with a few key parts for them to work. This involves a 1) battery, to supply power to the hearing aid, 2) a microphone to collect the sound in the environment, 3) an amplifier that, not surprisingly, amplifies the sound, and then finally 4) a receiver, which is essentially the “speaker” of the hearing aid, where the sound exits the device and into the ears.

Amplification and Digitisation of the Sound

Circuit board, such as what may be found in a hearing aid.

Nowadays, almost all hearing aids work digitally (this includes hearing aids fitted under the NHS), where the amplifier in the hearing aid digitises the analogue soundwaves entering the device. Consequently, the digital amplifier can then manipulate the sound that enters the ear canal, in a way that is beneficial for the hearing aid wearer. This is done via signal processing algorithms that can determine if the sound is for example, background noise, music, or conversation. The amplifier can then, essentially, amplify more of the “desired” sound rather than the “undesired” sound. Suppose you are dining in a restaurant, and having a conversation with your spouse sitting across from you, the hearing aids will focus more on what your spouse is saying, and less on the surrounding, distracting background noises. Hearing aids that are technologically more advanced will usually do a better job of this than more basic hearing aids. Hearing aids, however, will not eliminate background noise entirely, as this would not give you a normal perception of sound.

It is better, then, to think of hearing aids as tiny computers on your ears. While the hearing aids are switched on, they are constantly working and analysing the sounds around you, and making split second decisions about how to the process these sounds. Many people do well with their hearing aids operating at their default settings, but changes and adjustments can also be made by your audiologist based on the feedback you provide to them at your follow-up appointments. For example, if you find background noise continues to be overpowering, an adjustment can usually be made to help relieve you from this to an extent. Many hearing aids can also be paired up to your smartphone via an app, which will allow you to make some basic adjustments yourself, to your own preferences. It is important though, that you wear your hearing aids as consistently as possible, as the brain also needs to take time to adapt to all the new sounds that it will be hearing. While the hearing aids do a lot of processing and manipulation of the sound, the brain still needs to process everything on its end—as if the soundwaves are going from one computer (the hearing aid) to the next (your brain)!

Hearing Aid Prescription

Woman in a healthcare consultation, such as when being prescribed hearing aids.

Hearing aids are also not fitted with a “one size fits all” approach. Rather, they are prescribed and programmed to your hearing loss, considering its degree of severity, and what parts of the ear may be affected. Someone with a mild hearing loss, for example, will obviously require less amplification than someone with a more severe hearing loss. Furthermore, the degree of severity of hearing loss will typically differ based on different frequencies (essentially the “pitch”) of sound. Someone may have only a mild degree of hearing loss for low frequency sounds, but a severe degree of hearing loss in the high frequencies. At your hearing aid fitting appointment, your hearing aids will be programmed digitally by your audiologist to reflect these differences, which is what creates the hearing aid prescription.

There are also different formulas that can be used to write the hearing aid prescription, which will alter how the hearing aid performs and sounds. Typically, a different formula is often used for children than for adults, and for people who have a longstanding history of hearing aid use versus people who may be getting hearing aids for the first time. An audiologist will usually determine which formula will work best for you based on several factors, such as your age, and the case history that you presented with at your hearing assessment. Sometimes, however, the audiologist may choose to change the formula to see if you prefer one over the other. The goal is to ultimately provide you with a relatively normal perception of loudness. In other words, loud sounds should sound loud with your hearing aids on, and soft sounds should sound soft. These settings can be verified by performing a series of tests referred to as “real ear measurements” or “REM”. I describe this procedure and other aspects of the hearing aid fitting appointment in another article that can be found here.

Hearing Amplifiers and Similar Devices

Headphones, such as those that may be used as a hearing amplifier.

A caveat, to all of the above, are devices referred to as personal sound amplification products (PSAPs). These are more simple devices, that do indeed tend to work by just making everything louder and are not prescribed to a specific degree or type of hearing loss. Occasionally, these devices are falsely marketed as hearing aids, and will be designed to look like a typical hearing aid, but it is important to recognise that they work quite differently from audiologically fitted hearing aids. Some people may find these devices helpful to an extent, especially if their hearing loss is really impacting their everyday conversations. PSAPs sometimes fall under the broader category of assistive listening devices, or ALDs. ALDs are devices that work either independently of a hearing aid, or together with a hearing aid (as an accessory) and can help with things like day-to-day communication, watching TV, talking on the telephone, etc. An excellent example where the use of a PSAP may be warranted, is when a patient is struggling with their hearing, and are waiting to be fitted with hearing aids on the NHS. These devices can really help provide some relief in the interim. The equipment will usually be referred to as a “personal listener” and will consist of a set of headphones to be worn over the ears, that attaches to a microphone that people can speak into. Personal listeners can often be provided to you on loan by your NHS audiology department, until you receive your hearing aids.

I hope that the above information provides a bit of clarification on how hearing aids work and demonstrates that hearing aids are not simply amplifying all sounds without any rhyme or reason. If you'd like to learn more about the kind of hearing care we provide for our patients at Finchley Hearing, please explore our website and feel free to get in touch with any questions.

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