Capacitor/condenser microphones require a power supply, commonly provided from mic inputs as phantom power, but give a high-quality sound signal and are now the preferred choice in laboratory and studio recording applications.
phantom power is a widely-used method for supplying current to devices over signalling cables, especially audio. This is most often used for condenser microphones, and occasionally microphones of other types.
Phantom power supplies are often built into mixing desks, microphone preamplifiers and similar equipment. Many active DI boxes also use it. In addition to powering the circuitry of a microphone, in traditional (DC-polarized) condenser microphones the phantom powering directly or indirectly supplies the voltage used for polarizing the microphone's transducer element ("capsule").
Phantom powering consists of direct current applied equally through the two signal lines of a balanced audio connector (in modern equipment, usually an XLR connector). The supply voltage is referenced to the ground pin of the connector (= pin 1 of an XLR), which normally is connected to the cable shield and/or a ground wire in the cable. Thus the same type of balanced, shielded microphone cable which studios already used for dynamic microphones could also be used for condenser microphones — in contrast to vacuum-tube microphones, which had required special, multi-conductor cables of various kinds.
It is called "phantom" powering because the supply voltage is effectively invisible to any balanced microphones (though it is likely to cause issues if adaptors that connect one side of the input to ground or equipment other than microphones is connected) which do not happen to use it. (A balanced signal consists only of the differences in voltage between two signal lines; phantom powering places the same DC voltage on both signal lines of a balanced connection.) This is in marked contrast to another, slightly earlier method of powering known as "parallel powering" or "T-powering" (from the German term Tonaderspeisung), in which DC was overlaid directly onto the signal in differential mode. Connecting a dynamic microphone (especially a ribbon microphone) to an input that had parallel powering enabled could very well damage the microphone severely, but this is not normally so with phantom powering unless the cables are defective or wired incorrectly. In 1966, Neumann company of Berlin, Germany, presented a new series of transistorized microphones to Norwegian Radio. For compatibility reasons, Norwegian Radio requested for phantom power operation. Due to the limited daylight hours during winter months, the studios used an auxiliary lighting system fed by a central 48 volts power supply. This was therefore the voltage used for powering those mics and is the origin of 48V Phantom Power. This was later standardized in DIN 45596. The prevailing IEC standard defines 48 volt and 12 volt phantom powering; a 24 volt version of phantom powering was included in the DIN standard for several years, but was never widely adopted by equipment manufacturers. The signal conductors are positive, both fed through resistors of equal value (for 48 volt phantom powering the standard value is 6.81 kΩ), and the shield is ground. (In an earlier system used mainly in France, the positive side of the 9–12 volt supply was grounded and the phantom supply voltage was negative.)
Many desks have a switch for turning phantom power off or on. On some top of the line equipment this can be done individually by channel, more commonly all channels are either off or on at once. If it is desired to disconnect phantom power from one channel only, this can be done by using a 1:1 isolation transformer or blocking capacitors.
