The diaphragm of a condenser microphone is a very thin plastic film, coated on one side with gold or nickel, and mounted very close to a conductive stationary back plate. A polarizing voltage is applied to the diaphragm by an externalÂ powerÂ supply (battery orÂ phantom powerÂ ) or by the charge on an electret material in the diaphragm or on the back plate charging it with a fixed static voltage. Because the diaphragm of the condenser is not loaded down with the mass of a coil, it can respond very quickly to transients. Also, the condenser capsule can be made very small. Condensers generally have excellent sonic characteristics, and are widely used in high-quality professional microphones in sound reinforcement, measurement and recording.