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Church Sound: The Basics Of Phantom Power

Answering the difficult questions... What does this button do? Why isn't this mic working? Where did that pop come from?

By Chris Huff January 11, 2018

Image courtesy of Yamaha
This article is provided by Behind The Mixer.

Is the phantom power on? It’s a question often asked when a condenser microphone isn’t sending a strong signal, but what does it mean? What is this phantom power and why is it necessary?

Phantom power is a method of sending DC voltage (48V) from a mixer, through a balanced cable, to a condenser microphone. Some say it’s called phantom power because there’s no obvious external power supply. These same cables will also be used to pass the audio back from the microphone. Imagine it as two-way traffic along the same road.

Phantom power should be assigned to only the channels that need it. However, in some mixers, phantom power is assigned to a group of channels, such as 1-8, 8-16, etc. The good news is it will not damage dynamic microphones. Some say this is why it’s called phantom power as it’s invisible to microphones that don’t need it.

The reason it’s harmless to dynamic microphones is the voltage supplied through the cable is equal on Pin 2 and Pin 3 of a typical balanced, XLR-type connector. For example, a 48-volt phantom source would have Pin 2 at 48 VDC and Pin 3 at 48 VDC, both with respect to Pin 1 which is the ground.

Because the voltage is the same on Pin 2 and Pin 3, no current will flow across since there’s no voltage difference across the output. In fact, phantom power supplies have current limiting which prevents damage to a dynamic microphone even if it is shorted or miswired.

WHY does a condenser microphone require phantom power when other microphones do not?

Condenser microphones, like the Shure SM81 and the Sennhesier e865, are based on an electrically-charged diaphragm/backplate assembly which forms a sound-sensitive capacitor (capsule). This capsule stores an electrical charge. When the element is charged, an electrical field is created in proportional size to the distance between the backplate and the diaphragm.

When sound hits the capsule, the variation between the space produces an electrical signal which represents the sound detected. A transducer changes this energy from one form into another, in this case, acoustic energy into electrical energy.

Many modern condenser microphones use this type of mixer-provided phantom power. However, they can also be powered by an onboard battery or an exterior power supply like with the Mojave Audio MA-300. In some cases, they can have fixed charge materials produced in the manufacturing process. Never apply mixer-driver phantom power to a condenser microphone that’s already using one of these other power sources.

As a side note, mixers will provide phantom power at 48 volts but the ANSI standard (IEC 61938) allows for 12, 24, and 48 volts which other equipment might provide, such as with an acoustic guitar preamp.

Also, be aware of Bias power, also known as plug-in power. Bias power can be used by internal guitar mics and wireless systems. It uses a two-wire system, unlike the balanced XLR three-wire system. Around 5 to 9 volts are applied directly to the microphone’s single hot wire. This is not the same as phantom power which sends power down two lines. The two cannot be interchanged.

Phantom power is the right amount of power where needed. Know what microphones require it and you’ll never have someone ask you, “Is the phantom power on?”

As a final warning, when your musicians use an in-ear monitoring system, make sure any required phantom is turned on before they put in their in-ears. If you do need to engage the phantom power, make sure they take their in-ears out because a loud pop can be heard in the system.

 


About Chris

Chris Huff
Chris Huff

Writer/Teacher/Author, BehindTheMixer.com
 
Chris Huff is a long-time practitioner of church sound and writes at Behind The Mixer, covering topics ranging from audio fundamentals to dealing with musicians – and everything in between.
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