1) What is phantom power?
To know what phantom power is, you need to understand how condenser microphones work. Condensers work on the principle of variable capacitance. In Britain, they are actually called “capacitor microphones.” Sound waves vibrate a diaphragm (usually gold-sputtered mylar) that is stretched in front of a metal plate (called the backplate). As the diaphragm vibrates, the distance between the diaphragm and the backplate changes, which changes the capacitance.

Those tiny electrical variations which must be amplified before they leave the mic so there’s an internal preamp inside the mic. The phantom power provides the voltage to charge the diaphragm and also powers the preamp inside the mic.

This amplification method is what’s known as phantom power.

2) Why do I need phantom power?
Phantom power, commonly designated as +48V or P48, was designed to power microphones without using bulky external power supplies such as the ones required for tube microphones. It’s a way of sending the DC electrical current required through a balanced XLR cable. We need that voltage to power the diaphragm and the mic’s internal amp. When phantom power is turned on, DC current is sent through the XLR cable and delivers the voltage necessary to power the microphone. It’s most widely used as a power source for condenser microphones, which have active electronics. In addition, true condenser microphones (as opposed to electret) require a voltage for polarizing the microphone’s transducer element, and phantom power provides a voltage for both of these purposes.