How do inline microphone capsules vary the bias voltage?

[jaydnul]

In a standard set of headphones, the inline microphone only has two leads, ground and hot. I took a multi-meter to the microphone input of one of my devices and there was 1.7V DC waiting.

So I'm wondering how such a microphone operates (just that type of mic in general). I searched online for a diagram, but no success. Does it vary the 1.7V DC that's fed into it?

Also, what output voltage are those inline mics usually at?

Thanks

 

[Baluncore]

Maybe this is will help.
http://en.wikipedia.org/wiki/Electret_microphone

 

[jaydnul]

Perfect. Thanks Baluncore!