A condenser microphone uses a charged capacitor whose capacitance varies with diaphragm movement

A condenser (capacitor) microphone consists of a thin conductive diaphragm spaced close to a fixed backplate. The two form a capacitor. A polarizing voltage (either from phantom power or a permanent electret charge) is applied. When sound pressure moves the diaphragm, the capacitance changes, which with fixed charge produces a varying voltage. A high-impedance FET amplifier (built into the mic capsule) converts this to a low-impedance output. Condensers have very low diaphragm mass, giving excellent transient response and extended high-frequency response. They require power (phantom power for most professional condensers; battery for some). Electret condensers have a permanently charged polymer foil eliminating the need for an external polarizing voltage.

Examples

An AKG C414 condenser mic requires 48V phantom power from the console. Its lightweight diaphragm captures cymbal transients and ‘air’ frequencies above 12 kHz that a dynamic mic might miss.

Assessment

A condenser mic is accidentally connected to a console channel with phantom power switched off. What will happen? Why do ribbon mics need similar phantom power precautions?