Behind The Mixer

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PHANTOM POWER

Phantom power (labeled as +48 V on most audio equipment) is a method that sends DC voltage through microphone cables. It is best known as a power source for condenser microphones, though many active DI (direct input) boxes also use it.

Phantom power supplies are often built into mixing desks, microphone preamplifiers and similar equipment. In addition to powering the circuitry of a microphone, in traditional (DC-polarized) condenser microphones the phantom powering directly or indirectly supplies the voltage used for polarizing the microphone’s transducer element ("capsule").

Polarizing the microphone’s transducer WHAT?  What’s a Capsule?

Condenser microphones 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 diaphram.

Take a standard grocery store tub of whip cream.  Empty it and then cover it tightly in saran-wrap.  Now if you press down on the saran wrap, you are decreasing the potential energy because there is less space inside.  If you pull up on the top of the saran-wrap in the middle you are increasing the potential energy because there is more room.

The variation between the spacing (the increasing and decreasing pressures) produces the electrical signal which represents the sound detected by the condenser microphone. 

Sound To Energy

Microphones have transducers, either dynamic or condenser types (hence dynamic or condenser microphones).  A transducer changes energy from one form into another, in this case, acoustic energy into electrical energy.

Back to That Old Phantom Magic

A condenser microphone needs some means for maintaining the electrical charge / polarizing voltage.  Creating the charge on the capsule of condenser microphones can be accomplished by battery, phantom powering, and by using fixed charge materials in manufacturing.

In the case of phantom powering, the voltage supplied through the microphone cable, such as by a mixer equipped with phantom power, 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 ground.

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

Phantom power can be thought of as just the right about of power where you need it.  In some sound board mixers, multiple phantom power buttons can be present for different channels.  For example, a button for channels 1-8 and one for 9-16.  Knowing what microphones require it, tells you what channels will need it.

Note: condenser microphones that are made with pre-charged metals or are battery charged may be damaged if used in conjunction with phantom power so make sure you read the instructions with the microphone.

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  2. Hi Chris. I wonder if you can help me please as I am getting confused?

    Consider an active speaker with just one XLR input and no switch to switch off phantom power.

    If I plug in a microphone the phantom power will power the microphone.

    However if I plug the output of a mixing desk into the same socket of the active speaker, will the active speaker send 48v to the mixing desk and damage it? If so, should I only buy active speakers with additional not mic inputs and/or ones with a phantom power on/off switch?

    Thanks.

    Reply

    • Good question and one I don’t have a straight answer. I would not use one in that setup. I’d make sure I wasn’t sending phantom power to the mixer.

      Reply

  3. I am considering upgrading our older Mackie Onyx Mixer to a Soundcraft Signature 22 MTK. I noticed that the phantom power is one button for every channel. Is that not ideal? Right now I can select individually which instruments need phantom. Any other tips about this board? My sound guys are pretty inexperienced so I think a digital board would be the death of them:) I’m trying to find the best Analog 20ish channel mixer that I can find, any suggestions?

    Reply

    • Phantom power is sending equal voltage on both pin 2 and 3 so even if on where you don’t need it, it’s not likely to damage anything. That’s why you see mixers with phantom power buttons for groups of channels. The Soundcraft line would be a good one.

      Reply

  7. Can phantom power damage a passive DI box? The Rolls db25 at one of our church keyboards began making buzzing noise when the keyboard is turned off. When checking the system I found the phantom power was on. I turned it off but the problem persisted. I replace the Rolls with a Livewire Direct Box and the problem was resolved. This is the second Rolls that has failed in the past month. Both times I found the phantom power was on for the passive DI box.

    Reply

  8. I know you need phantom power for condensor mics (for my congas) and mostly all big boards provide it. My question is, if i get a mixer with phantom power (for on stage), but the main sound board at engineer does not have phantom power. Can i turn on my phantom power from my mixer feeding to the engineers board and will it work even though engineer does not have his own phantom power? The reason i am asking is, I’m afraid if engineer does not have phantom on his board, then im not going to be able to be heard unless my phantom will work from my mixer still going to his board. Also, say we play a show where they do not have any phantom power (board is smaller) if this works in either direction i will never have to worry about where i play, either engineer has it or i have it? Thank you so very much for kindly answering this. Im afraid to make this big investment with it only working one way. Please respond to my email only, thank you

    Reply

  9. “condenser microphones that are made with pre-charged metals or are battery charged may be damaged if used in conjunction with phantom power so make sure you read the instructions with the microphone.”
    What kind of damage?

    Reply

  10. i have a question
    for a mixer with a phantom power supply, is the phantom power (+48v supply) only present in the xlr input? is it not present with the PL input also?

    Reply

  11. Question, at my church we have a mic that I believe needs phantom power, i hink its a drum mic. we have no instructions for the mic. Phantom power would be applied at the mixing console. Is there a possibility of damaging the other mics and instruments if we press that button for only the one mic?

    Reply

      • What about other gear in the board…acoustic electric, digital piano, keyboards? Could Phantom Power damage those? They are all on passive DI boxes right now because I wasn’t sure how Phantom Power would affect them. Thanks!

        Reply

  12. Regarding the whipped cream tub analogy: When you press down on the saran wrap, you are doing work, and thus increasing the potential energy. Similarly, when you pull up on the saran wrap, you also do work, and increase the potential energy. Potential energy is the lowest when the saran wrap is flat. Just like a spring. You can pull or push on the spring, and in both cases, the potential energy increases. Release the spring and it returns to its lowest potential energy state, which is its normal un-deformed length. Same in a microphone. The compression and expansion of the diaphram each will produce a different voltage polarity, giving rise to an AC signal, but the negative peak and the positive peak both represent high potential energy states.

    Reply