Condenser microphones require a power supply to operate because they rely on a polarized capacitor element to convert sound waves into electrical signals. The capacitor in a condenser microphone consists of a thin diaphragm (usually made of metal-coated plastic) that is placed close to a backplate. When sound waves strike the diaphragm, it vibrates, causing the distance between the diaphragm and the backplate to change. This variation in distance changes the capacitance of the capacitor, resulting in an electrical signal that represents the audio waveform.

To maintain the diaphragm’s polarization and enable it to respond to sound waves, an external power supply is required. The power supply provides a constant voltage across the capacitor, keeping one side of the capacitor charged while allowing the other side to fluctuate with the sound waves. This voltage polarization is essential for the microphone to function properly and produce accurate audio signals.

The term “phantom power” or “ghost power supply” is used to describe this type of power supply because it operates discreetly and is hidden within the same audio cable that carries the audio signal. In most professional audio setups, condenser microphones are connected using balanced audio cables (usually XLR cables). These cables have three pins: one for the positive audio signal, one for the negative audio signal, and one for the phantom power supply. When you connect a condenser microphone to an audio interface or a mixing console that provides phantom power, the microphone receives its operating voltage through this third pin, often without the need for any separate power cables or batteries.

Phantom power is usually standardized at either 48 volts or 24 volts and is a common feature in most professional audio equipment. This convenience of combining audio and power in a single cable makes phantom power a practical and widely used solution for powering condenser microphones without adding extra clutter or complexity to audio setups.