Answer

Condenser microphones require a polarizing voltage and power for their built in amplifiers. Sometimes provision is made to supply this voltage directly though the microphone cable. The procedure is called phantom powering. Most commonly 48 VDC is supplied by mixing consoles, though 24V supplies are widely used. Phantom powered microphones can operate on a range of voltages from 1.5 or 9 volts, up to 50 volts.

In a phantom power system the polarizing supply voltage is placed on both signal lines in a balanced connection, with the same polarity on each line. Dynamic microphones connected in a balanced system with a phantom power input are then protected from damage, theoretically, since the system results in a net zero DC potential across the coil. A dynamic microphone connected unbalanced to a phantom power input may however be destroyed.

It is important to be aware whether a mixing console input is wired for phantom power. Most such inputs provide a switch to disable the phantom power when it is not needed. Always be sure that this switch is set to off when dynamics or electret condensers with internal batteries are connected to the input.