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Design specific trial on Hearing Aid

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by MD MUBDIUL HASAN, Dec 3, 2017.

  1. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    Hello Sir,
    I have been posted this idea in another group,http://www.eevblog.com/forum/projects/a-hearing-aid-amplifier/ ;)
    Many of them suggested many idea, but let me start it again for particular design,
    Hearing_aid_old.PNG


    It looks clear, I have been trying

    1. Treble and Bass control by frequency selecting gain, considering High, low and mid frequency gain through frequency selector.
    2. Tried to boost and buck the gain of the amplifier.
    3. Assume all OPAMPS are 741.

    Suggest me a good design, where we can development more.:happy:
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Get rid of the '741s
     
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  3. AnalogKid

    AnalogKid Well-Known Member

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    You have given zero information about what you want the circuit to achieve.
    What is the overall gain in the mid-band (all tond controls set to flat)?
    What is the frequency bandwidth?
    What are the tone controls for?
    What effect do you want them to have (max/min cut and boost)?
    What is the input?
    What does the output drive?
    What is the power source?

    ak
     
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  4. dave

    Dave New Member

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  5. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    Thank you for your interest here. I want to go along with you here.

    In mid frequency band the gain should be 17dB to -15dB. According to this design, as audio signal is fed by single input, so all frequency signal from the air will be chosen by selector, must be flat for minimum frequency gain.
    As far as I remember, 200Hz to 8kHz, we have used signal generator.
    Bass control, Mid frequency control and treble control.
    I think, all pots are used to maximize the gain at particular frequencies.
    Microphone.
    Ear phone.
    +9V and -9v battery or external power module.

    I think, this figure will give you some idea what I want to do.


    hearing_aid_graph.png



    ak[/QUOTE]
     
    Last edited: Dec 4, 2017
  6. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    Thank you sir to participate here, could you suggest anything else, people says LM324 is also useless.
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Almost all old people have high frequency hearing loss. I got tested (for free) and the result is perfectly normal for my age then (I was 69) and 8kHz had a loss of about -40dB but low frequencies were fine. Some people who went to war or played with guns and noisy machines have hearing loss for most frequencies.

    Each of my hearing aids operate for 1 or two weeks with a tiny 1.45V zinc-air battery cell. Each hearing aid communicates wirelessly for setting modes and for programming the response and with each other.

    My hearing aids have a noise reduction mode that emphasises voice frequencies but cuts gain (then reduces noise) when there is noise but no voices. There is a level limiter that reduces very loud sounds down to normal but with no distortion. I have a mode where the gain is much higher than normal so that they are very sensitive to distant or weak sounds. I have a mode that mutes them when dogs are barking, babies are crying or a motorcycle with no muffler blasts past. Of course they have a music mode where the sounds are high fidelity.

    Your maximum boost of only 17dB is not enough to fix my 40dB loss.

    The opamps you selected are 50 years old and are too noisy (hiss) for audio. The 741 opamps need a pretty high supply voltage and the LM324 opamps produce noise and crossover distortion. You need modern audio opamps for this project.
     

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  8. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    Dear Sir Audioguru,

    Thank you to participate here again. I got to know about this post from you a lot in EEV forum!
    Your graph is nicely presents what we can do to set the gain for different aged people.

    As a hearing loss person, your case is critical as I heard before.
    My intention is to make a suitable one first that is more general, so I will be happy if you talk more about your circuit.
    Let me know how you manage the circuit for " noise reduction mode that emphasises voice frequencies but cuts gain (then reduces noise)".

    Particular design concept is appreciable.

    Regards
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

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    My hearing aids make my hearing young and normal again and I forget I am wearing them until I switch them to a different mode.

    I did not design my hearing aids. If I designed them then they would be analog, huge, heavy and would have only one mode.
    My hearing aids are designed and made by Phonak of Switzerland. They use DSP digital circuits, not analog. I think Bluetooth is used for their communication.

    For your circuit to emphasise voice frequencies then use a suitable bandpass filter. But the DSP used in my hearing aids probably also senses the cadence of speech so that it does not react to noises in the speech frequency bandpass. If speech is detected then the gain is normal. With no speech then the gain slowly ramps down which reduces noise. If speech is detected then the gain quickly ramps up.

    My hearing aids also reduce noise by sensing and controlling speech direction: front left, front right, rear left and rear right then turn on one or two microphones aimed at the speech direction. The other microphones exposed to background noise are turned off.

    When I put a telephone to one ear then I hear the telephone sounds in both my hearing aids because it detects the magnet in the phone and picks up the telephone sounds then transmits them wirelessly to the other hearing aid in the other ear.

    Low battery? Yes, each hearing aid senses a low battery and gives a warning half an hour before it stops working.
     
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  10. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    I have tinnitus at 2600 Hz. There is a dip at precisely that frequency. I don;t have a hearing aid, but the amount of 2600 Hz changes with who knows, probably stress. Certain people I have trouble understanding and I'm sure it's the pitch of their voice.

    I would guess that a hearing aid should employ a DSP to fix all of the frequencies.

    Hearing aids are likely to use class D amplification. My guess.

    Loose the 741's.
     
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    For the tiny batteries to last for one or two weeks then the output amplifiers must be efficient class-D.
     
  12. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    I have little knowledge on DSP, can you show me any documents of it? They published any circuits or diagram ?

    Your theory is understandable, but without patent its difficuilt.

    Yes, you told me last year also, can you post a similar circuit of noise remover to understand the phenomena you are talking about?



    Yes, I am working in my company with a similar application energy management IC can do it while getting controlling signal from MCU and USB power!
     
  13. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I think your "hearing aid" will be just an ordinary old preamp with tone controls for an audio system.
    Why does it have a notch filter?
    Do it like this, I have a parts list if you want it:
     

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  14. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Look at this search tool. Find modern low-voltage, micropower, rail-to-rail opamps for battery-powered applications...
     
  15. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I think the opamps must be designed for audio applications and have low noise and have enough gain at the highest audio frequency. Some or most rail-to-rail opamps produce too much noise for audio circuits or use such a low supply current that they have poor gain at high audio frequencies.
     
  16. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    Nice feedback indeed.
    Lets talk about more on notch filter.
    Lets make difference among the 2 circuits where you have proposed wein bridge notch filer.
    My one has more component than you and inverting and non inverting inputs of opamps are variable in action. As far as I remember, I used this design both side (-Ve and +Ve gain).
    Your one is fixed one, mid frequency gain cant be change ?
     
    Last edited: Dec 5, 2017
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Since the Baxandall tone controls circuit I posted is the standard of the audio industry, I was surprised that you have a mid-frequency tone controls circuit using a Wien Bridge. Usually a Wien Bridge circuit is used for an oscillator but the notch filter I found is closer to your circuit so I posted it to show you how similar it is.
    Why didn't you use the standard Baxandall tone controls circuit that is used in almost all audio equipment?

    I hope that your tone controls are planned to be enclosed so that the user cannot wrongly adjust them.

    Your tone controls have parts to boost the frequencies and other parts to cut the frequencies. Are there any people with hearing problems that need frequencies cut because their hearing is "too sensitive" to those frequencies? I doubt it so half the parts that cut frequencies in your tone controls are not needed.

    Did you notice that the standard Baxandall tone controls circuit I posted uses the same single opamp to do it but your circuit uses 3 opamps to do the same thing?
     
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  18. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    wein_bridge_notch_filter.jpg

    The components of a Wien bridge may be chosen and adjusted to make it balanced at a given frequency. When a Wien bridge is balanced, the reactive effects of the capacitors in the circuit cancel each other out, leaving nodes A and B at the same potential. Note that this balancing of the bridge occurs only at a single frequency.

    The circuit in is just a Wien Bridge fed into a difference amplifier. If the frequency of the input signal Vin is equal to the frequency to which the Wien bridge is tuned when it is balanced, then the voltage levels at A and B become equal. This causes both inputs of the op-amp to be at the same voltage level, resulting in zero output voltage. Thus, in effect, this circuit acts as a notch filter, since it does not let an input signal whose frequency is equal to the notch frequency to pass to the output.


    Its also a reasonable idea, but since all frequency dependent resistor and capacitors are connected on a single OPAMP paths, then I think noise could be amplified and I am not sure how the buck action can be done!

    I wish to do, but needs a comparative analysis which design is best suited.

    Let me understand what you are saying, for sure I am looking at the "too sensitive" parts. Can you explain more detail which part of my circuit is not necessary, dont you mean negative gain ?

    Yes, its a good point, but need to compare.
     
  19. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Tone controls like you show are used to vary the uneven frequency response of poor quality speakers. The speakers have frequencies that have too much output level and other frequencies that do not have enough output level. But hearing impairment does not need any frequencies reduced in level, it needs only certain frequencies boosted, usually only high frequencies as shown on the hearing graph I posted.

    If you want an odd Wien Bridge circuit instead of a standard Baxandall tone controls circuit then use the Wien Bridge.

    If you want ordinary boost and cut tone controls then do it or remove the parts that cut frequency levels.

    If you want many opamps instead of one opamp then use as many opamps as you want.
     
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  20. MD MUBDIUL HASAN

    MD MUBDIUL HASAN Member

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    Well said sir. I did not review your graph after I made this circuit, I started in 2009. If you feel that frequency response does not meet the goal, kindly explain more on it. I had been analyse the Baxandall tone control circuit, http://www.learnabout-electronics.org/Amplifiers/amplifiers42.php. If you suggest me , I will go with it more. I saw the effect here,http://makearadio.com/tech/tone.htm



    Yes, let me read the mathematical condition both of it.

    Suggest any example.

    Lets accept just one op amp.
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The hearing graph I posted shows a loss of high frequencies of 12dB per octave for men at 55 to 65 years old.
    12dB per octave is made with a second order highpass filter and the hearing cutoff frequency changes with age.

    Your tone controls circuit is a single order filter that produces only 6dB per octave and does not have an adjustable cutoff frequency. 6dB per octave is a small hearing impairment experienced by men 35 to 45 years old and they will not bother with a hearing aid for such a small amount.

    If you want to make a hearing aid then make much more complicated circuit.
    If you want to make or copy a simple tone controls circuit then don't call it a hearing aid circuit.

    You are making an analog circuit. Modern digital hearing aids have not used analog circuits for many years.
     

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