Is this correct:
"I have no direct experience but a change in the position of the diaphragm will certainly change the impedance of the coil which will affect both its Q and resonant frequency. A nearby transmitter may well have a detectable audio modulation of its frequency or power. That is after all how a metal detector works!"
Forget it EricaS, for three reasons:
1. Piezo elements make very poor microphones because when mounted they only work over a very narrow audio range, that of the tones used for ringing.
Somebody can shine an invisible infrared beam onto your window or through it onto the glass on a photo on your wall that is vibrated by your voice and the glass reflects the modulated infrared to a receiver.
" They are really poor microphones.
Frank
Your audio clip is intelligible speech.
If you measure the size of your piezo beeper, you'll get an idea what wavelength could resonate inside the piezo beeper. It will be a very short wavelength, which means a very high frequency.
Can you bring in an rf meter tuned to that wavelength (or 1/2 or 1/4)?
I suppose the cavity in the beeper must be lined partially with metal, in order to reflect rf back to the transmitter.
Can you examine the beeper, to look inside for a metal lining?
ALL They make terrible micrphones, the plastic cavity around them and diameter of the outlet hole is designed to make them resonant at ringer frequency. If you remove the plastic casing they WILL work as a crude microphone but the ringer volume would be almost non-existent.
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