SparkFun COM-08635 Electret Microphone
An Electret Condenser Microphone is a type of transducer that is used to detect or measure sound signals. It is used in noise detectors and sound recorders etc. It is essentially a parallel plate capacitor in which one plate is fixed and the other is movable (diaphragm) with a very small gap between them. When a sound wave strikes the diaphragm, it starts moving which changes the capacitance of the capacitor and causes a variable current to flow. This variable current is then filtered and processed to get the sound you want to record.
Also available all mounted with supporting circuitry on a breakout board, to easily add it to your project
Since the datasheet isnt super clear, this polarity of microphone is important (it matters which way around you wire it). Think of it like an electrolytic capacitor – you measuring the change in capacitance when the mic detects sound
If you look at the back of the microphone you will see 2 pins. One of them looks like it is not connected to anything – that is the signal output pin. The other pin has 3 connections coming out connecting that pin to the metal case, that’s the ground.