When to Use Phantom Power

Ah, our good old friend, phantom power. You may have heard this term being tossed around here and there when reading about microphones and audio interfaces. But if you’ve found yourself here, you’re definitely wondering when to use phantom power. Don’t worry we have you covered!

What Is Phantom Power?

In order to know when to use it, it’s important to know what it is first, and a little bit about how condenser microphones work. Condenser mics contain active circuitry, meaning the circuit has components that supply energy. Phantom power is the +48 V DC electrical power that is used to power the active circuitry of the microphone.

Condenser Microphone Principle of Operation

Microphones turn sound, which is pressure oscillations in the air, into an electrical signal by varying the electrical capacitance between two components. The part of the mic that does this is called the capsule. The capsule is further broken down into these two main components – the backplate and the diaphragm. The two work together to transform sound into electrical energy.

The diaphragm is an extremely thin, circular, electrically conductive wafer. Usually, it’s made of gold-sputtered Mylar. In the process of sputtering, gold atoms are sprayed onto the Mylar to create a very thin layer. Gold provides the conductivity needed, and the Mylar beneath is flexible and able to move as the sound waves pass over it.

The backplate is a thicker plate of metal that sits in close proximity to the diaphragm. The backplate needs to be charged with electrical power in order to create capacitance between it and the diaphragm. This is where phantom power comes into play. The backplate needs power for capacitance to exist.

The equation for capacitance is:

C = capacitance
A = area of overlap between the diaphragm and backplate
ε = electric constant
d = distance between the diaphragm and backplate

As the diaphragm vibrates in relation to the backplate, it changes the distance between the two, and therefore the capacitance of the circuit. As capacitance changes, so does the voltage and current in the circuit.

  1. Sound waves
  2. Diaphragm
  3. Backplate
  4. Phantom power supply
  5. Resistor
  6. Differential voltage out

Conclusion

So, long story short, we should use phantom power whenever we’re using a condenser microphone. Most modern audio interfaces have phantom power circuitry built in, so there’s no need to buy a separate power supply.

Phantom power will be sent through pins 2 and 3 of the balanced XLR cable that you use to connect your microphone to your audio interface. All you need to do is make sure your phantom power is switched on. You should always switch it on after connecting your mic, and turn it off before you disconnect your mic. Failing to do so could damage your equipment.

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