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Electret Microphone question

Saville

Saville

Well Known Member
So if you have a NON-ANR headset you still have those electret mikes which have two mike inputs....the one near your lips and the one on the other side.

From what I've read the noise in the headset is reduced by "subtracting" the sound coming in from the forward mike from the sound coming in form the mike near your lips.

Question:

Where is that "subtraction" done? In the mike itself? Or in other electronics inside the headset?

Thanks!
 
I happen to have a new in box David Clark M-7A electret microphone in front of me. I bought two and used the first one to build my own in ear headset (which works pretty well). The instructions/specifications for the microphone don't answer your question directly, but a couple of clues suggest that the microphone itself does the cancelling. There are only 2 leads connecting to the microphone and it requires a DC bias voltage supply.
 
Flying Canuck said:
I happen to have a new in box David Clark M-7A electret microphone in front of me. I bought two and used the first one to build my own in ear headset (which works pretty well). The instructions/specifications for the microphone don't answer your question directly, but a couple of clues suggest that the microphone itself does the cancelling. There are only 2 leads connecting to the microphone and it requires a DC bias voltage supply.
Click to expand...

Yeah that makes sense - why didn't I think of that:

If the two inputs are not subtracted within the mike then you need more wires to carry the two signals into the headset for "subtraction".

Thanks Flyer
 
It is a physical cancellation. Your voice sound pressure is a differential signal against the mic electret diaphragm
 
Saville said:
So if you have a NON-ANR headset you still have those electret mikes which have two mike inputs....the one near your lips and the one on the other side.

From what I've read the noise in the headset is reduced by "subtracting" the sound coming in from the forward mike from the sound coming in form the mike near your lips.

Question:

Where is that "subtraction" done? In the mike itself? Or in other electronics inside the headset?

Thanks!
Click to expand...

The one that I took apart had a diaphragm that was open to both sides. The general environment sound pressure hits both sides equally and voice hits only one side. The "canceling" is not electronic.
 
fl-mike said:
It is a physical cancellation. Your voice sound pressure is a differential signal against the mic electret diaphragm
Click to expand...

Ah I see. Thanks.

Next Question:

Aside from volume and left-right controls, what do the electronics do in a NON-ANR headset? Anything else?
 
Last edited:
Normally, the only electronics in a standard headset is the amplifier for the electret condenser mic. But you would never see it, because it's built into the mic housing. Many of the mics will have a mic gain potentiometer accessible through a hole in the mic housing. That's it; 2 speakers, volume control(s), wire, and the mic assembly.

Charlie
 
rv7charlie said:
Normally, the only electronics in a standard headset is the amplifier for the electret condenser mic. But you would never see it, because it's built into the mic housing. Many of the mics will have a mic gain potentiometer accessible through a hole in the mic housing. That's it; 2 speakers, volume control(s), wire, and the mic assembly.

Charlie
Click to expand...

And that amplifier inside the electret mike is a JFET transistor yes? That's what I'm seeing in circuit diagrams on the web.



I wonder how an electret would work inside a rubber oxygen mask..I can get one that does not have the second input or I could just assume the second input is blocked.
 
It'll almost certainly be fine. It'll sound a little odd because of the mask, but any microphone will sound odd in the mask.

It certainly won't hurt anything, except the long term exposure to higher humidity due to the trapped moisture in your breath may affect looong term reliability. If it were mine, I wouldn't give it a second thought.

Charlie
 
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