Adaptive hearing protection device

DickCappels

Joined Aug 21, 2008
10,153
It sounds as though you are looking for a hearing aid that will switch off its output quickly when the SPL exceeds some limit. This would probably be a relatively easy modification of a modern DSP hearing aid. Do you have a relationship with a hearing aid manufacturer?
 

Thread Starter

jagruti mahajan

Joined Jul 20, 2018
21
It sounds as though you are looking for a hearing aid that will switch off its output quickly when the SPL exceeds some limit. This would probably be a relatively easy modification of a modern DSP hearing aid. Do you have a relationship with a hearing aid manufacturer?
No not exactly with hearing aid manufacturer. According to you it is possible to design this kind of device without DSP?
 

KJ6EAD

Joined Apr 30, 2011
1,581
Peltor active hearing protection devices mute at an SPL of 82 dB. I've often wished I could set a lower threshold, ≈75 dB to eliminate annoying but non-hazardous sounds.
 

BR-549

Joined Sep 22, 2013
4,928
I am certainly no expert.....from what I understand, in adaptive hearing....you sample the ambient noise and determine the frequencies with highest power. Then knock those frequencies down. But this can interfere with wanted frequencies too. Results are mixed.

I think the TS just wants to limit. Maybe I mis-understand.
 

Thread Starter

jagruti mahajan

Joined Jul 20, 2018
21
It sounds as though you are looking for a hearing aid that will switch off its output quickly when the SPL exceeds some limit. This would probably be a relatively easy modification of a modern DSP hearing aid. Do you have a relationship with a hearing aid manufacturer?
Not hearing aid , Hearing protection .
 

Thread Starter

jagruti mahajan

Joined Jul 20, 2018
21
As in most feedback systems based on classical control theory, the basic operation is just to subtract the feedback from a setpoint voltage that corresponds to the desired output. But you will have to worry about scaling the result for your gain adjuster's control input, and might need to worry about having enough dynamic range everywhere. A lot might also depend on exactly what you want the AGC to be able to do.

I am not sure that an analog circuit would necessarily be better. A mostly-digital implementation might be both better and easier to implement, for all I know. But I have only designed purely-analog AGC-type circuits.

To do the subtraction with an analog circuit, you could just use a simple opamp difference amplifier. You can find probably all of the opamp circuits you will need in application notes AN-20 and AN-31, at national.com. (Actually, you might want to use a differential integrator opamp circuit, instead of a plain difference amplifier.)

What frequencies are you going to be dealing with? RF? Audio? I will assume audio.

Your detector will probably just be an envelope detector or an averaging detector. If you need a very fast and accurate correction response (say 200 ms or less for a full-scale error), it can be tricky to get a simple one of those to work well all the way across the extended audio range, or for more than about 2.5 decades of frequency.

You will probably want to use a high-input-impedance opamp buffer or amplifier to pick off the signal to measure and create the feedback. Then, for the detector, you "could" use a series diode followed by a capacitor to ground. That would be a really-basic peak detector. But you will also need a resistance in parallel with the capacitor, to be able to follow downward-going signal envelopes. Adjusting the resistor and capacitor values will define how the detector handles a particular range of signal and envelope frequencies. And instead of a plain diode, you might want to use an "ideal diode" type of opamp circuit, so it can go all the way to zero. And you might want a full-wave rectifier version, so you will also "see" the envelope of the negative half of the signal. After the detector, you'll probably need another opamp buffer or amplifier. And somewhere in the feedback path you might need a low-pass filter, so you don't end up modulating the envelope amplitude with detector artifacts. There might be a lot of time-constants to adjust, to get it right, depending on your application.

If you are at all familiar with spice, I strongly recommend using LTspice (or your favorite spice, but LTspice is free to download from linear.com and is really great) to model and simulate your design. With LTspice you can even have WAV files as inputs and outputs. If you are not familiar with it, maybe now is a good time to learn.

Cheers,

Tom
 

Thread Starter

jagruti mahajan

Joined Jul 20, 2018
21
Hello
I also want to design analog AGC circuit for hearing protection device but I also dont have any idea how to start?
Can you please help me with that .
Thanks.
 

MisterBill2

Joined Jan 23, 2018
18,167
I am trying to imagine even just the specifications of a hearing protection device that would work for an infantry person patrolling through the jungle, where any noise could be an enemy about to kill, and yet somehow protect hearing while firing a military weapon, which are "quite noisy." so my hearing is indeed quite damaged now.
Many protective devices exist, at all levels of price points, and a rational effort to create a product to achieve some goal is to first investigate what already exists. Quite often, if a need for something exists, efforts have been made to fill that need. You might even try a patent search, to avoid the pain of creating a wonderful design only to find that somebody else has already done that and got a patent on it. That does happen.
 

DickCappels

Joined Aug 21, 2008
10,153
@jagruti mahajan , Do you have any specifications that you need to meet, or do you just have to demonstrate some basic functionality.

I also noticed that you posted a hand-written list on another thread. I tried to read it but could not make out what you are trying to do there. Could you please explain it here?
 

dl324

Joined Mar 30, 2015
16,845
I also want to design analog AGC circuit for hearing protection device but I also dont have any idea how to start?
Can you please help me with that .
It sounded like you wanted a circuit to cutout if volume was too loud, now you're talking about AGC. What is it that you really want?

There are many AGC circuits on the internet. You should also be able to find limiters, dynamic range compression, etc.

You can start with this Wikipedia article.
https://en.wikipedia.org/wiki/Automatic_gain_control
 

Reloadron

Joined Jan 15, 2015
7,501
I am trying to imagine even just the specifications of a hearing protection device that would work for an infantry person patrolling through the jungle, where any noise could be an enemy about to kill, and yet somehow protect hearing while firing a military weapon, which are "quite noisy." so my hearing is indeed quite damaged now.
Many protective devices exist, at all levels of price points, and a rational effort to create a product to achieve some goal is to first investigate what already exists. Quite often, if a need for something exists, efforts have been made to fill that need. You might even try a patent search, to avoid the pain of creating a wonderful design only to find that somebody else has already done that and got a patent on it. That does happen.
I have played that game. Back in post #6 I mention what I use today and while they never would have been suited for my military days they work real well for things like gunshots. Time in service followed by time on flight decks over the years, combined with just plain old age took a toll on my hearing. These things work really well in that they can amplify normal sounds around me like conversation and totally clip gun fire on the range. I would think this ability could be built into any of the available hearing aids on the current market. On the firing range it is so nice not to hear the loud gunfire but yet be able to carry on a conversation. During conversation the loud sounds like gunfire are just clipped. You hear the shots but quietized. :)

Ron
 
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