Analogue Active Noise Cancellation Headphones

[BradtheRad]

this is how ANC headphones work
what you ll suggest me now ?

I looked at the article. It says the mic goes inside the ear cup.

It will be close to the speaker. Seems to me that feedback troubles (squealing) could arise, unless you experiment with mic positions, in order to find just the right spot where you do not get feedback.

On the other hand, by putting the mic on the outside, it picks up a sound spectrum which is different from what your ears hear inside the ear cup. However you will not get feedback problems.

I don't know which will be easier to deal with, a mic inside the ear cup, or outside.

I do not know of a reason which would make it necessary to use 2 mics at an earpiece.

 

[fadverd]

hi !
how can i compare my designed headset with market available headphones quantitatively??
and able to say that how much much noise in attenuated in dBs with and with ANC circuit?

 

[BradtheRad]

how can i compare my designed headset with market available headphones quantitatively??
and able to say that how much much noise in attenuated in dBs with and with ANC circuit?

This is done by duplicating the listening environment of the human ear.
a) Place a microphone inside the earcup at the same spot where your ear would be,
b) seal the opening as though your head were against it.

Measure what the mic picks up in various conditions of ambient (room) noise, versus music.
You want to test low and high frequencies, at low and high volume.
Compare results with the ANC working, versus without it.

Ideally you would construct a duplicate of the ear (outer and inner parts), and place the mic 1/2 inch inside the ear canal. This will not be easy, of course.

 

[fadverd]

This is done by duplicating the listening environment of the human ear.
a) Place a microphone inside the earcup at the same spot where your ear would be,
b) seal the opening as though your head were against it.

Measure what the mic picks up in various conditions of ambient (room) noise, versus music.
You want to test low and high frequencies, at low and high volume.
Compare results with the ANC working, versus without it.

Ideally you would construct a duplicate of the ear (outer and inner parts), and place the mic 1/2 inch inside the ear canal. This will not be easy, of course.

which type of microphone i should use to pick this ambient noise for my designed headset (ANC headset)??
i think it should be as sensitive as possible
what you will suggest??

- - - Updated - - -

This is done by duplicating the listening environment of the human ear.
a) Place a microphone inside the earcup at the same spot where your ear would be,
b) seal the opening as though your head were against it.

Measure what the mic picks up in various conditions of ambient (room) noise, versus music.
You want to test low and high frequencies, at low and high volume.
Compare results with the ANC working, versus without it.

Ideally you would construct a duplicate of the ear (outer and inner parts), and place the mic 1/2 inch inside the ear canal. This will not be easy, of course.

which type of microphone i should use to pick this ambient noise for my designed headset (ANC headset)??
i think it should be as sensitive as possible
what you will suggest??

 

[BradtheRad]

which type of microphone i should use to pick this ambient noise for my designed headset (ANC headset)??
i think it should be as sensitive as possible
what you will suggest??

Electret mics are small and inexpensive, and have a wide frequency range. (You might see this type sold for use on computer motherboards.)

An electret requires a power supply. It draws miniscule current.

It also needs amplification. A single op amp can do the job.

 

[fadverd]

Electret mics are small and inexpensive, and have a wide frequency range. (You might see this type sold for use on computer motherboards.)

An electret requires a power supply. It draws miniscule current.

It also needs amplification. A single op amp can do the job.

how can i give input signal to this micro phone ?
i mean i have used this micro phone, but i could't get require signal on oscilloscope..

 

[BradtheRad]

how can i give input signal to this micro phone ?
i mean i have used this micro phone, but i could't get require signal on oscilloscope..

If this is in simulation, I guess you'll have to simulate an audio signal (however that is done). Or as a substitute, use an AC sine wave with amplitude 10 mV.

I have only used real microphones.

 

[fadverd]

If this is in simulation, I guess you'll have to simulate an audio signal (however that is done). Or as a substitute, use an AC sine wave with amplitude 10 mV.

I have only used real microphones.

no..
i am using real electret microphones..which is not picking noise or any signal..
so what i do ?
at what voltage should i operate this micro phone?

- - - Updated - - -

why active noise cancellation is more effective at Lower Frequencies ??
and secondly how it fulfills the claim that it provides Adaption to Noise ?

- - - Updated - - -

why active noise cancellation is more effective at Lower Frequencies ??
and secondly how it fulfills the claim that it provides Adaption to Noise ?

 

[BradtheRad]

no..
i am using real electret microphones..which is not picking noise or any signal..
so what i do ?

How many wires does the mic have? Two or three? This makes a difference how to hook it up. Typical circuits involve a high-ohm resistor to the positive supply, and a capacitor in series with the input. You can try an internet search. Or a search on electret at this message board.

at what voltage should i operate this micro phone?

Whatever is the loudest sound you will expose the mic to, it will generate a certain amplitude of signal. The power supply must be sufficient voltage to create that amplitude of signal, in order that you do not get clipping.

In this development stage, the mic can get the same power supply as the op amps.

why active noise cancellation is more effective at Lower Frequencies ??
and secondly how it fulfills the claim that it provides Adaption to Noise ?

The higher frequencies are more unpredictable and more variable, as to how they will be affected by the muffling effect of the ear cup, or the frequency response of the pickup mic versus that of the earphone.

As you experiment, you will discover what volume setting is best for noise-cancelling, and what frequency range it operates in, etc.

It will be very difficult to make the circuit adapt to the noise automatically.

 

[phongphanp]

Fadverd, You can try limit noise by small signal models in each piece , study circuit theory for this(the black block method).

 

[fadverd]

how noise power affects the performnace of active noise cancellation ??

what would be response of active noise cancellation with increase and decrease of noise power ?

 

[ArNvC]

how noise power affects the performnace of active noise cancellation ??

what would be response of active noise cancellation with increase and decrease of noise power ?

Hi,

Remember one thing, Active noise-canceling headphones - their very structure creates a barrier that blocks high-frequency sound waves. They also add an extra level of noise reduction by actively erasing lower-frequency sound waves. They actually create their own sound waves that mimic the incoming noise in every respect except one: the headphone's sound waves are 180 degrees out-of-phase with the noise waves.

So every time there is increase in noise (or decrease), the ANC system will generate a counter-acting wave which will decease the effect of the noise...as simple as that, pretty much similar to a closed loop system. :wink:

Thank u...

 

[ArNvC]

Importantly, there isn't any noise-cancelling headphones capable of eliminating all noise in your surroundings. You will always hear some noise regardless of which noise-cancelling headphones you use especially analog ANC which will invariably work on same bandwidth all the time. Modern digital ANC use DSP chips which work adapting to different noise environments.:|

Adding to the above point, of course there is some limitation on the amount of active noise cancellation, generally, in army defense (especially the heavy tanks) the present hearing protectors are generally unable to attenuate sufficiently the high-level noise (about hundreds of decibels) and to allow exposure durations in excess of a few tens of minutes. In these conditions, new hearing protectors or with Active Noise Reduction techniques and/or double hearing protection (earplugs and earmuff) can be effective.

 

[phongphanp]

Digital part is rather hard to setup equipments, But it's easy to edit/maintain.