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What is Phantom Power?

You may have noticed the phantom power switches on your audio console, either one per channel, or in the case of smaller and less expensive consoles, perhaps one for a group of channels.

I thought I’d change gears and talk about some of the details of professional audio that you may have heard of, but perhaps you don’t have a full understanding of.

I’m going to start today with phantom power.

You may have noticed the phantom power switches on your audio console, either one per channel, or in the case of smaller and less expensive consoles, perhaps one for a group of channels.

This isn’t a button you press if you feel you need more Holy Spirit presence in your worship; instead, it has to do with enabling certain types of microphones and devices to work by providing power through the microphone cable.

There are two primary types of microphones that are used in professional audio: dynamic microphones and condenser microphones.

A dynamic mic uses a magnet moving through a coil of wire to produce a reasonably strong audio signal all by itself.

A condenser microphone, however, uses two electrically charged plates that vary in distance between each other in response to sound waves, and generates a very weak electrical signal. This signal then needs to be amplified before it leaves the microphone in order to be usable by the audio console. This amplification circuitry requires a power source to work. And that’s where phantom power comes in.

By the time that phantom power was introduced in professional audio systems, microphone cabling was already standardized, so a way of delivering phantom power to microphones was needed that would work with existing cabling and microphone designs and not damage microphones that don’t use phantom power.

Professional microphone cabling, referred to as balanced cables, use positive and negative signal wires and a shield that surrounds the two wires. 48 volts is applied to both the positive and negative signal wires, which effectively cancels out at the microphone from an audio signal perspective as it’s applied equally to both sides of the signal, and the ground of the power supply is connected to the shield of the mic cable. This allows a microphone that needs it to use the power between one of the signal pins and the shield, without effecting the actual audio signal itself.

Besides condenser microphones, other devices may also make use of phantom power.

Some direct boxes (used to convert an unbalanced audio signal to a balanced audio signal) are “active” direct boxes and require power. Usually they have options for either a battery, external local power supply, or the ability to get its power from phantom power.

TAGS: Audio
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