Acoustic amplifier for those who hear differently

I found a similar topic, there the silencing was with the help of felt: https://www.elektroda.pl/rtvforum/topic3745043.html

What if I had two regular microphones and one inside the case, this one should pick up mainly surface noise and crackle, something that would need to be subtracted from the signal from the microphone that is in contact with the air outside the case?

TechEkspert wrote:

And if you had two regular microphones and one inside the enclosure, this one should pick up mostly surface noise and crackle, something that would need to be subtracted from the signal from the microphone that is in contact with the air outside the enclosure?

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This is what I did, but the effect was poor. Maybe I was isolating the other microphone too poorly? But I've done trials with several different insulations, although the felt was not tried.

It probably sounds funny... Maybe try hanging the microphone on thin rubber bands. It would then hang almost 'in the air'.

The best effect would be to cover the case with something soft that does not "hum" when touched, foam rubber, velvet. In addition, stick the microphone into the case, because placing it inside causes it to collect everything that appears inside, something like a shell put to the ear, which you can hear in it.

The housing creates a resonance box and the microphone picks this up from the inside.
The easiest way is to expose the microphone to the outside, wrap it in a sponge or other damping material.

In the analogue omig, the microphone just hung from rubber bands and was connected by thin wires to the board.

In many old models of "mobile phones", the microphone was mounted in a rubber band with an acoustic channel of a few millimetres connecting the microphone to a hole in the casing. Thanks to this design, sounds from inside the phone were not picked up.
I do not have at hand specific models of class AB or class D amplifiers used in small BT loudspeakers or BT headphones, but many of them have a DC volume control, which makes it easy to make a simple ARW, and in the feedback you can give a corrective element boosting frequencies of 0.8-1 kHz to improve the intelligibility of speech and at the same time cut the hum and noise.

Hearing is a much more complex sensory phenomenon than one would think. Sometimes someone responds well through the nervous system to an auditory stimulus, but fails to recognise it, to process it. There are also situations where a person hears badly, then gets rid of the infection as the pus comes off the ear canal and suddenly the person hears one big scream. Children in particular have this problem. These issues are dealt with by ENT and speech therapists.
If the device works OK and resembles a factory solution, that is a big plus here. It's certainly healthier than the horribly coupling headphones of the 1990s, where the microphone was covered up and there was a big squeal. A severely deaf person couldn't even hear it. I slowly need such an eye aid. It is no longer possible to read 4pc fonts in the morning reading is also a curiosity. At first I thought it was a headphone amplifier for audiophiles because I misunderstood the title.

For audiophiles it would have gold transistors.😉

yego666 - what 3D printer are you using?

bratHanki wrote:

For audiophiles it would have gold transistors

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I have a Czechoslovakian KD502 purchased for a Class A amplifier with beautifully gold plated legs, just how do I solder them so as not to cover the gold?

acctr wrote:

bratHanki wrote:

For audiophiles this would have gold transistors

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I have a Czechoslovakian KD502 purchased for a Class A amplifier with beautifully gold plated legs, just how to solder them so as not to cover that gold?

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There are special bronze-based jeweller's solder alloys that give a golden colour.

There are also special gold-plated tin pins and that would probably be best. 😆
I have a couple of matched KD pairs from the old days. I also have 2N3055 in identical cans from Fairchild and Toshiba in plain tin with pink lettering. The 3055 and KD were also paired with pnp BDX18 from Tungsram.

phanick wrote:

yego666 - what 3D printer are you using?

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I've been using a TronXY x5sa pro for almost 2 years now.
It is nothing extraordinary, but for my purposes it is completely sufficient.
I usually use PLA and print at 60/70mm except for the first layer of course.
For now I am using Marlin but I am carrying the intention to switch to Kliper.
I have not had any serious problems with the printer or Marlin. I have modded Marlin for myself and added some factory disabled options and it's not too bad.
I don't plan to buy anything better for now. CoreXY in this implementation satisfies me.

@yego666 I'll come back for a moment. With a 3D printer and a knack for working on it, you could have made this deaf ear just in an eyeglass frame and not in a big box - a pendant with acoustic resonances in the corners. At least I would have done that.

Well I could have squeezed it into glasses, only my mum doesn't wear or like any pings, hence the choice.
And I also have a whole mine of smd components, so I could probably fit this even in glasses, but maybe someone else will implement your idea.
There is another issue with 3Ð printing. Not everything can be printed nicely, especially on, say, mid-range hardware, even with support.

Coming back to the topic again, I noticed one problem caused by the regular use of such an amplifier.
My mother recently had to spend a week in hospital.
This gave her the opportunity to use the amplifier regularly.
This has led to her participating in conversations with her co-workers again, and consequently also with her household members after her return home.
I am very pleased about this, as the emotional state previously caused by the "social exclusion" situation has improved.
Now Mum is very keen to speak and hear what is going on around her, but there has been a side effect that I did not expect.
As a result of her hearing aids, she is able to hear both her surroundings and herself better, which has meant that we now have difficulty hearing what she is saying to us.
Since she can hear herself well, she lowers her voice in the belief that others can hear her well too.

Now I guess I will have to make a few more copies of the amplifier for all the household members so that everyone can hear each other well .

A paradox has arisen... The hard of hearing hears better than those who hear better than him .
And how have you dealt with the 'murmuring' of the enclosure?

You could say "Grandma's Paradox" as she also has a grandson .
The background noise and crackle turned out to be relatively unobtrusive when I turned the gain up a bit.
Now, apart from this paradox, everything works as it should.

yego666 wrote:

Now I think I'm going to have to make a few more copies of the amplifier for everyone in the house so they can all hear each other properly

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No, you need to make an anti-local circuit, meaning an extra microphone on top of the box that will catch what Mum is saying and a differential amp that will subtract this from the microphone at the front, then she won't be heard as much and will speak louder.

I will wait a little longer with this.
Maybe this paradox can be resolved through goodwill negotiations.
Time will tell .

Janusz_kk wrote:

yego666 wrote:

Now I think I'm going to have to make a few more copies of the amplifier for everyone in the house so they can all hear each other properly

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No, you need to make an anti-local arrangement, that is, on top of the box an extra microphone which will catch what Mum is saying and a differential amp which will subtract this from the microphone at the front, then she won't be heard as much and will speak louder.

Wouldn't it be better to add the simplest dynamics compressor? Take the output signal, rectify it and control it with an input signal divider composed of a resistor and a transistor? You could also vary the voltage supplying the electret microphone.
Instead of transistors, I suggest using an LM4871 or 8002 .

Maybe I'll change something in a while if persuasion doesn't work.

Just as a quick aside, I'm wondering if in an arrangement like the one below it would work if one ( top ) microphone listened to the environment and the other ( bottom ) to my Mom.
I might still give some resistance to adjust somewhere, but the idea is rather clear I think.

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I don't know if this will do anything because the two microphones will be close to each other so they will practically pick up identical sounds. The anti-local system works well when two different transmissions reach the device, but one of them goes over the wire. In this case, the effect of hearing oneself could be weakened if the microphone was placed on the headband of the headphones, in an additionally attenuated tunnel a few cm long, and not on the neck under the chin.
https://www.amplifon.com/pl/zycie-z-aparatami-sluchowymi/efekt-okluzji

bratHanki wrote:

I don't know if this will do anything because both microphones will be close to each other so they will practically pick up identical sounds.

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After all, I wrote that they have to be on different walls, one on top of the other at the front, meaning they will be at 90st angles to each other. In addition, putting them in foam will isolate them a bit from the case.

Added after 1 [minute]:

yego666 wrote:

Maybe I'll still give some resistance to adjust somewhere, but the idea is rather clear I think.

I'm not sure if such a connection wouldn't work as a combiner. Need to check.

Janusz_kk wrote:

bratHanki wrote:

I don't know if this will do anything because both microphones will be close to each other so they will practically pick up identical sounds.

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After all, I wrote that they have to be on different walls, one on top of the other at the front, meaning they will be at 90st angles to each other. In addition, placing them in foam will isolate them a bit from the case.

"After all I wrote. I know what you wrote but a sound wave is a spherical wave i.e. directionless so it propagates evenly in all directions vertically and horizontally. What you came up with would work for el-magn waves with different polarisations, e.g. ferrite antennas or polarisers set at 90° for optical communications.

bratHanki wrote:

I know what you wrote but a sound wave is a spherical wave
and propagates uniformly in all directions vertically and horizontally.

But the microphone most often does not have this characteristic. So there will be a difference between the two which should be sufficient for attenuation from the other direction.

bratHanki wrote:

I know what you wrote but a sound wave is a spherical wave i.e. directionless so it propagates uniformly in all directions vertically and horizontally.

Huh? What kind of nonsense are you writing? A non-directional sound wave?
A sound wave is an example of a longitudinal wave, which is described by a direction.

If you are standing next to someone talking can you only hear them if you are in front of them or if you are standing next to or even behind them?
It is the same with bluetooth headphones. The microphone is set back a few centimetres from the sound source, i.e. our mouth, and yet it reacts to sound waves and it shouldn't.

bratHanki wrote:

If you are standing next to someone talking can you only hear them when you are facing or when you are standing next to or even behind them?.

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And how are you supposed to hear? only straight ahead? why not sideways? this is anatomy and drawing conclusions about the nature of sound based on it is a bit infantile.
An already better example to analyse is bats, which use ultrasound to target prey. Direction is of considerable importance here for an insect to fall into a bat's mouth.