CONDENSER MICROPHONES
A condensor microphone has a capacitor consisting of a pair of metal plates separated by an insulating material called a dielectric: One of its plates is free to move in response to changes in sound pressure. The sensitivity of the microphone is related to its polarizing voltage and distance of separation between these plates.

Key design equations for this type of microphone are: Thus, the sensitivity depends on the polarizing voltage, V_cc, which explains why many microphones operate at large voltages (often 100V or more).