How do I check my Electret mic?
Electret mics have a built-in FET as an "amplifier" which requires power.


get a power supply, say 5V
connect GND to the - of the mic
connect 5V to a 22k resistor, the other side of the resistor goes to the mic
connect your oscilloscope between GND and the + pin of the mic
start whistling, alter two frequencies
change input sensitivity on the scope, you shall see a signal in millivolts range
and you will see nice sine waves as you're whistling.


Basically this is what you do (without the output capacitor, which cuts the DC power from the output):

http://i0.wp.com/www.scienceprog.com/wp-content/uploads/2014/01/Electret_condenser_microphone_schematic.jpg?resize=300%2C208