To use a Speaker as a Mike

Using this circuit will give a reasonable output signal to drive an

The Speaker can be any size or even two in series. Eg: "A Woolfer and Tweeter" For increased bandwidth!

Bass response is good but will produce an increased response at the speaker resonant frequency!

Reducing the value of the 47 MFd, reduces Low Frequency Response.

Other Transistors can be substiuted in this circuit, but change the 3.3M resistor to make the collector voltage approximately 4 1/2 Volts