Capacitor Microphone - Also known as a \'condenser microphone\'. This is a specific form of electrostatic microphone which operates on the principle of measuring the change in electrical voltage across a capacitor. The capacitor is formed from two metal electrodes, one fixed (the back-plate) and the other a thin conductive membrane that flexes in response to sound pressure. (See also Back Electret, and RF Capacitor Microphone.)