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Comment by 40four | Hacker News Reader

I'm not sure I understand how hearing aids work. I think they pick up sound and amplify it for the user, giving them the ability to adjust the volume.

I remember seeing my grandmother's aids. They had a little knob on the side to adjust the volume, and if she turned one to high they would produce an ear piercing loud 'shriek' for eveyone in the room.

This was years ago, I'm sure the technology has progressed since then. But now that I really think about it, how does a device like that just not accelerate hearing loss.

We know we're not supposed to listen to earbuds/ headphones too loud, or risk ear damage. Seems like hearing aids are a kind of earbud that amplify external sound.

Seems like a high risk of folks blasting the volume, and damaging already poor hearing even further. Or a least a sure path to a nice case of tinitus over time.

What am I missing?

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The most common type of hearing loss is age related hearing loss. This type of hearing loss makes it difficult to hear high frequencies. The main thing a hearing aid does is compensate for this by adjusting the volume of high frequencies. But here's what you're missing - The key is to amplify at low volumes and reduce at high volumes, AKA dynamic range compression [2]. This allows people to hear better at low volumes but not blast their ears at high volumes.

FYI - The ear piercing shriek you heard was from poor feedback cancellation on the hearing aid. Hearing aids have a microphone and speaker so feedback is common and a nightmare.

Also, I'm the founder of AudioFocus (YC S19)

[1] http://www.hearingresearch.org/ross/hearing_loss/the_audiogr... [2] http://openaudio.blogspot.com/2017/01/the-need-for-dynamic-r...

Great, thanks for the explanation.

I have a set of the modern-but-cheap NHS hearing aids.

The diagnostic process for getting them involves playing a set of random quiet tones, and you press a button whenever you hear one (and not when you don't). This produces a hearing profile showing how much hearing loss you are experiencing and at which frequencies. Usually the higher ones. If the profile is bad enough and you are given the hearing aids, the profile is downloaded into them and used as a parametric equaliser.

The amplification is not user-controllable, so you can't set it to dangerous levels.

There is also feedback cancellation - there may be a small shriek on power-on (along with the cheerful bootup chime), but it detects this and mutes that frequency.

They aren't magic, but they do make it much easier to understand speech, especially consonants and 's' sounds with high frequency components. Also little things like being able to hear my oven timer's high pitched beep when not in the kitchen.

There is a latency on the amplification and filtering. The ear adapts but I can occasionally notice it.

Battery life is about a week from non-rechargeable zinc-air batteries, £10 for 60 from Amazon or free on the NHS if you can be bothered to go to them.

Do you have a link to the device that you're talking about?

They're "Unitron Yuu M 312 N", didn't find a great link on initial googling.

The Yuu is an older Unitron model: https://www.audiologyonline.com/releases/unitron-hearing-int...

Often subsidized hearing providers will be given low-cost older hearing aids from manufactures.

Thanks for the details! I didn't think about latency time for the device to process the sound, but that makes sense.

If we're talking about damage to the cochlea:

- We don't really care if we further damage the hair cells that don't work.

- Outer hair cells amplify sounds. If they don't work, well, gotta amplify them some other way.

- A phenomenon called "recruitment" can cause loud sounds to be more painful for those with hearing loss. So you may not be able to amplify everything.

Hearing aids are a bit more sophisticated than an amplifier; they also act as an equalizer, compressor, feedback cancellation, and a bunch of other features of dubious benefit.

Interesting, sounds like a lot of tech is packed into these tiny devices!

We do care and take great pains to prevent further damage to the hearing systems. All hearing aids will have a MPO (maximum power output) setting. All hearing tests (should)include a test to determine the maximum threshold of volume level.

Only in cases of sever to profound will a hearing device be programmed to exceed a safe normal hearing level.

Outer (inner actually) hair cells receive an input and there movement sends an electrical signal down the auditory nerve. In cases of hearing damage these hair cells are not as receptive and require a stronger "push" to move.

Dubious (in your opinion) or not, the other features are designed to improve the understanding of speech especially in noisy situations.

=============== Hearing aids cost a lot of money. no question. But they are not just devices pulled from the shelf and stuck in your ear. They require both initial settings (derived from hearing exams) and frequent follow ups as the user adjusts.

What you're missing, in short, is filtration and delivery.

Most hearing aids don't deliver sound directly to the damaged ear canal, but also utilise other sound delivery mechanisms. Like induction. This can help prevent damaging the ear internals further.

They also rarely deliver a 1:1 version of the sound in the world around us, because a damaged ear drum already distorts the sound it receives. There is no need to make it harder for the brain to filter out background noise. These filters can be simple - a dial switch on the device, or they can be complex - adaptive filtering based on the current environment. The filter complexity and effectiveness is usually reflected in the price, but as software gets better and hardware more powerful things are slowly shifting towards a better median.

The higher-end hearing aids can also be tweaked by the specialists involved to avoid frequencies that can further damage the ear, but that tends to be on a case-by-case basis and is difficult to tune correctly for an individual.

But you're right - if the hearing aid isn't tuned correctly, or the individual regularly just turns it all the way up, it can lead to further loss. Which is why many doctors have regular appointments to check the device is in a safe range.

The bad habit of the user, turning the device up, can usually be prevented by better sound filtration. They're turning it up because they can't hear something they're trying to focus on, making it easier to focus at lower volumes can curb the habit.

> Most hearing aids don't deliver sound directly to the damaged ear canal, but also utilise other sound delivery mechanisms. Like induction.

I don't think this is correct. All hearing aids do work this way, and I also don't know of any way that (electromagnetic?) induction could be used to deliver sound.

In a person with hearing loss, not all frequencies are affected equally. Hearing aids can compensate by

1. Amplifying the affected frequencies (this is by far the most common approach) or

2. Compressing and pitch shifting the sound to a range that the user has better hearing.

> [electromagnetic] induction

Maybe they meant [bone] conduction?

When I studied at Uni, some lecture halls had induction, where the sound recorded by the microphone would be transmitted via an inductive system throughout the entire room and compatible hearing aids would be able to use that sound instead of having to boost the audio from the speakers throughout the hall.

That is input via induction (there is also FM and BT transmitters)

The GP was referring to induction output - of which comprises a minority of hearing devices.

It's much more than just a volume problem. This article describes it: https://medium.com/@AMP/cant-you-just-turn-up-the-volume-4ec...

I can ear the compressed track far far better than the uncompressed one. Should I consult a doctor ?

Disclaimer: Absolute layman here, but afaict they just mixed the low volume parts higher, so of course you can hear them better. Unless you can't hear those parts at all in the uncompressed version, I see no reason to worry.

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