A condenser capsule is constructed similarly. It consists of a thin membrane in close proximity to a solid metal plate. The membrane or diaphragm, as it is often called, must be electrically conductive, at least on its surface. The most common material is gold-sputtered mylar, but some (mostly older) models employ an extremely thin metal foil.

 

When sound waves hit the diaphragm, it moves back and forth relative to the solid backplate. In other words, the distance between the two capacitor plates changes. As a result, the capacitance changes to the rhythm of the sound waves. Voilà, we have converted sound into an electrical signal.

 

The capsule signal itself, however, is much too “fragile” to be connected to other pieces of gear. The condenser capsule’s output voltage is actually quite high, but it produces almost no current, because so little energy is stored in this small capacitor. It requires what is called an “impedance converter”, a circuit that buffers between the capsule and the outside world. The impedance converter makes the signal more “sturdy” by making more signal current available.

 

Condenser microphones therefore require external power. This could be inconvenient in the old days, but today just about any microphone input offers P48 phantom power – a Neumann invention, which has become the international standard (see box “Powering Condenser Microphones”).

A voltage is required across the capacitor for this to work. This voltage is supplied either by a battery in the mic or by external phantom power.