I was building a simple sound meter using an electet mic, audio amp, and a LM339. I purchased the mics years ago so I don't remember any of the specifications about them. I measure the resistance of the mic between the two leads and it appears to have an internal resistance of 1Kohm. I may be wrong, but I thought, to select the desired voltage for the mic, I could treat the mic as a resistor and set it up like a voltage divider. With 1K of resistance in the mic and a 5Vdc power supply, if I wanted 1V I would need a 4K resistor ((1K/[1K+4K])*5V). I measured at the node where the mic, resistor, and capacitor meet. This doesn't seem to work properly and I needed to resort to trial and error with a multimeter. Currently I'm using a 15k resistor which should only allow 0.3V at that node if my calculations are correct ((1K/[1K+15K])*5V). Am I wrong in my assumption that I could treat the mic as a resistor in this circuit? If my logic is wrong, how do I go about selecting the proper resistor to supply the proper voltage if this doesn't act like a standard voltage divider?
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