Design specific trial on Hearing Aid

[MD MUBDIUL HASAN]

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.

Can you show any circuit idea?

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.

In which aspect you are saying 6dB? Kindly give any related documented to understand.

If you want to make a hearing aid then make much more complicated circuit.

Sure, I wish to use ATmega128.

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

Yes, this option remains for MCU coding.

 

[audioguru]

In which aspect you are saying 6dB?

A series capacitor feeding a resistor to ground is a simple single order filter. It is a highpass filter with slope that is only 6dB per octave like your tone controls circuit.
The graph I showed of hearing impairment shows a slope of 12dB per octave for men my age which needs a second-order highpass filter which has two RC networks. You can lookup a Sallen-Key second order highpass filter circuit in Google.

 

[MD MUBDIUL HASAN]

A series capacitor feeding a resistor to ground is a simple single order filter. It is a highpass filter with slope that is only 6dB per octave like your tone controls circuit.
The graph I showed of hearing impairment shows a slope of 12dB per octave for men my age which needs a second-order highpass filter which has two RC networks. You can lookup a Sallen-Key second order highpass filter circuit in Google.

Dear Sir Audioguru,

You might be talking about sweep type AC analysis of the high pass filter, where the word arising "octave", Linear, decade.
Looking at your previous idea, Bxandall circuit is meaningful, I am trying to simulate this idea in Multisim. Using single opamp is good choice, but need to understand how the frequency depended components are working.

 

[audioguru]

I guess you did not lookup the word "octave" which is used in audio to describe two times or half a frequency.
I also guess you did not lookup a Sallen Key second order highpass filter circuit.

I show the circuit which has two RC networks: R1 C1 and R2 C2. Each network causes a rise in frequency response of 6dB per octave like your tone controls circuit but this one rises at 12dB per octave and gives a boost of 40dB from 1kHz to 10kHz like my hearing aids do.

 

[MD MUBDIUL HASAN]

I guess you did not lookup the word "octave" which is used in audio to describe two times or half a frequency.
I also guess you did not lookup a Sallen Key second order highpass filter circuit

Things are clear now what you want to say. Dont you say 33k and 0.1 uF combined RC filter in my design?

I show the circuit which has two RC networks: R1 C1 and R2 C2. Each network causes a rise in frequency response of 6dB per octave like your tone controls circuit but this one rises at 12dB per octave and gives a boost of 40dB from 1kHz to 10kHz like my hearing aids do.

Its a good example for understanding, let us focus on what we can do with Baxandell or wein bridge for particular frequency boost up.

I am trying with this design,

This tone control combines adjustable low and high pass filters.

• If the treble 100k linear pot' is adjusted with the slider all the way to the left, more high frequency signal reaches the inverting input through the 560pF capacitor. Also less high frequency negative feedback reaches the inverting input. This gives treble boost.
  
• If the slider is adjusted to the right, less high frequency input reaches the inverting input and there is more high frequency negative feedback. This causes treble cut.
  
• The bass 100k linear pot works in a similar way but the low frequency signals are affected giving bass cut or boost.

Could you help me to understand this circuit action, I have set bass POT at 0, and treble POT maximum, then I received the following graph,

If it goes wrong with the design, let me know.

 

[audioguru]

Your simulator program gives a wrong frequency response. My image in green correctly shows its graph with the treble control at maximum and the bass control at minimum.

It has only a single RC so it boosts and cuts only 6dB per octave which is OK for tone controls but is not enough boost for a hearing aid.

The design of a lousy 741 opamp is 50 years old so it should never be used for audio because it has a high noise level, distortion and poor high frequency response. Also, it needs a fairly high supply voltage.

 

[audioguru]

Here is the frequency response of the same tone controls made by another person:

 

[MD MUBDIUL HASAN]

Your simulator program gives a wrong frequency response.

Could you kindly share me your simulation setting? How did you calculate the gain ?
Take a look my setting

My image in green correctly shows its graph with the treble control at maximum and the bass control at minimum.

How did you set your graph?

It has only a single RC so it boosts and cuts only 6dB per octave which is OK for tone controls but is not enough boost for a hearing aid.

If not enough, whats your expectation ?

The design of a lousy 741 opamp is 50 years old so it should never be used for audio because it has a high noise level, distortion and poor high frequency response. Also, it needs a fairly high supply voltage.

Can you see those abnormalities in simulation?

 

[audioguru]

I have never used the old Multisim program. I use LTspice like most of us here but I don't have time to simulate your simple tone controls.
The tone controls are a simple RC for bass and another simple RC for treble and one RC produces a simple slope of gain that is 6dB per octave. 6dB is double or half the AC level, octave is double or half the frequency.
If the level at 50Hz is 1V then at 100Hz it is 2V and at 200Hz it is 4V and at 400Hz it is 8V. Then the difference between the level at 50Hz and the level at 400Hz is +18dB like a bass tone control at minimum.
If the level at 2kHz is 1V then at 4kHz it is 2V and at 8kHz it is 4V and at 16kHz it is 8V. Then the difference between the level at 2kHz and the level at 16kHz is +18dB like a treble tone control at maximum.

Here is your simple tone controls with the bass set at minimum:

 

[MD MUBDIUL HASAN]

I have never used the old Multisim program. I use LTspice like most of us here but I don't have time to simulate your simple tone controls.

We cant say, my simulation does not work,take a look now in my result. If I change the POT 100% in bass and treble the total system works.

The tone controls are a simple RC for bass and another simple RC for treble and one RC produces a simple slope of gain that is 6dB per octave. 6dB is double or half the AC level, octave is double or half the frequency.

This theory I want to learn more, and its easy always.

If the level at 50Hz is 1V then at 100Hz it is 2V and at 200Hz it is 4V and at 400Hz it is 8V. Then the difference between the level at 50Hz and the level at 400Hz is +18dB like a bass tone control at minimum.
If the level at 2kHz is 1V then at 4kHz it is 2V and at 8kHz it is 4V and at 16kHz it is 8V. Then the difference between the level at 2kHz and the level at 16kHz is +18dB like a treble tone control at maximum.

How do you fed input on your circuit? I have used a signal generator, hence I am using 3kz with 1V vp(amplitude). How do you change your frequency?

Here is your simple tone controls with the base set at minimum:

Well done. What do you expect at this setting?
Unity gain on negative feedback? What will be the shape of this curve?

 

[audioguru]

I put your tone controls circuit in LTspice simulator program with the bass control at minimum and the treble control at maximum. Its slopes do very little, only 3.75dB per octave, not the 6dB per octave that I expected. My hearing aids produce 12dB per octave.

 

[MD MUBDIUL HASAN]

I put your tone controls circuit in LTspice simulator program with the bass control at minimum and the treble control at maximum. Its slopes do very little, only 3.75dB per octave, not the 6dB per octave that I expected. My hearing aids produce 12dB per octave.

Thank you sir.
Lets accept you design, you might be calculate things in actual angle.
The simulation I have posted later is also meaningful.

Let me work with your design in LTspice, as my design cant work like 6dB per octave.

 

[gary350]

I have had a hearing problem for 35 years I think form too many ear infections. Base & Treble is not good enough for a hearing aid you need a tone controls for every 1KHz frequency range. Equalizer is what we called it 40 years ago not sure that is what it is called now. First stage amplifier output goes to the equalizer then 2nd stage amplifier goes to the ear phone. I put a gain control on both amplifier stages. First amplification is for very sensitive sounds like a pin drop on the floor, wind blowing threw the trees, birds in the trees, water dripping in the sinks at the other end of the house 50 ft away, mosquito buzzing near your head. Second stage amplification if volume to the ear phones. Most sounds in the 2K to 5K are voice. I have trouble hearing people talk with a high Hz voice some women I see there lips move but I hear nothing. Equalizer needs to turn up the HZs that I can not hear. I have to get my ears tested so I have the graph to use to set all the frequency ranges. I have been using a ceramic mic it seems to work best so far there may be something better but don't know yet what it is. Hearing aid needs a quick change control switch for, high, medium, low amplifications. If sounds change like walking into a noisy restaurant click the switch to reduce amplification.

 

[MD MUBDIUL HASAN]

I have had a hearing problem for 35 years I think form too many ear infections. Base & Treble is not good enough for a hearing aid you need a tone controls for every 1KHz frequency range. Equalizer is what we called it 40 years ago not sure that is what it is called now. First stage amplifier output goes to the equalizer then 2nd stage amplifier goes to the ear phone. I put a gain control on both amplifier stages. First amplification is for very sensitive sounds like a pin drop on the floor, wind blowing threw the trees, birds in the trees, water dripping in the sinks at the other end of the house 50 ft away, mosquito buzzing near your head. Second stage amplification if volume to the ear phones. Most sounds in the 2K to 5K are voice. I have trouble hearing people talk with a high Hz voice some women I see there lips move but I hear nothing. Equalizer needs to turn up the HZs that I can not hear. I have to get my ears tested so I have the graph to use to set all the frequency ranges. I have been using a ceramic mic it seems to work best so far there may be something better but don't know yet what it is. Hearing aid needs a quick change control switch for, high, medium, low amplifications. If sounds change like walking into a noisy restaurant click the switch to reduce amplification.

I will be glad to you if you post a similar circuit according to your explanation.

 

[audioguru]

An equalizer is used to flatten the peaks and valleys in the frequency response of a speaker system, not for hearing aids today but maybe they were used 40 years ago. Look in Google for Third Octave Equalizer Circuit. A simpler equalizer is Octave Bands and an even simpler equalizer is low, mid and high frequency tone controls.

A hearing aid needs more range of levels than an equalizer for a speaker system and probably does not need to reduce the levels of any frequencies.
My hearing aids show a graph of their frequency response at octaves. 31Hz, 63Hz and 125Hz have no boost. 250 Hz has 2dB of boost and 500Hz has 8dB of boost. 1kHz has 15dB of boost and 2kHz has 30dB of boost. 4khz and 8kHz have 40dB of boost and 16kHz has 45dB of boost all in the Music mode. The automatic mode cuts high frequency boost for noise reduction when there are no voice sounds.

Electret microphones or very small MEMS microphones are used in hearing aids today, not antique ceramic mics. https://www.analog.com/en/analog-dialogue/articles/mems-microphones-future-for-hearing-aids.html

 

[MD MUBDIUL HASAN]

An equalizer is used to flatten the peaks and valleys in the frequency response of a speaker system, not for hearing aids today but maybe they were used 40 years ago. Look in Google for Third Octave Equalizer Circuit. A simpler equalizer is Octave Bands and an even simpler equalizer is low, mid and high frequency tone controls.

Let me stay in previous idea, after that we will move here.

Electret microphones or very small MEMS microphones are used in hearing aids today.]

I have been used this kind of MEMS microphone while developing a USB audio hub.