Do dynamic mics need phantom power?


On your audio interface or mixer, you may have noticed a button labeled ‘phantom power’ (or perhaps ‘48v’). This might seem quite mysterious if you don’t know what it is.

After realizing phantom power is needed in order for some microphones to work, many people ask the question, do dynamic mics need phantom power?

Well, the answer is no, dynamic mics do not need phantom power because they do not contain active circuitry. Applying phantom power to a dynamic microphone will not do anything or cause any damage to the equipment.

In the rest of the article, I will explain why this is in more detail and also answer a few other related questions along the way.

What is phantom power?

Phantom power is a term used to refer to a direct current (DC) which is sent down a microphone cable in order to activate active electronic circuitry (if the microphone contains it).

Direct current (DC) simply refers to the flow of electrons along the wire. They flow directly in a single direction. This is different from an alternating current where electrons switch direction along the wire.

This current is used within certain types of microphone to apply a charge to a small metal plate which will make the diaphragm move, making the microphone work.

What type of microphones DO require phantom power?

Answer: Condenser Microphones

A condenser microphone contains a ‘diaphragm’ which is a thin piece of metal (or sometimes plastic), behind which lies another piece of metal referred to as the ‘backplate’.

1) Sound Waves 2) Diaphragm 3) Back Plate 4) Battery 5) Resistor 6) Audio Signal (Image: Wikicommons 3.0)

The phantom power is applied to these pieces of metal, creating a static charge between them. When a soundwave (perhaps from your voice or a guitar) hits the diaphragm it causes in to move backward and forwards. This movement generates a voltage that can be read as an audio signal by whatever device you have the microphone plugged into.

The phantom power can also be used to power other active circuitry within a condenser mic such as a pre-amplifier. This amplifies the tiny electronic signal produced by the delicate diaphragm to ensure it can make it down the cable to your amp, mixer or interface.

So all condenser mics need some phantom power to work. The amount of phantom power required can vary from as little as 9 up to 48 volts.

This power can come from various sources. This could be a battery within the microphone itself, or in many cases it comes from your audio interface or mixer. It can usually be turned on and off with a switch such as the one shown below.

Why don’t dynamic microphones need phantom power?

Dynamic microphones are designed for a different purpose to condenser microphones.

1) incoming sound 2) diaphragm 3) coil 4) permanent magnet 5) resulting signal (Image: wiki commons CC3.0)

They are less delicate in their design and therefore can withstand louder noises and more ‘rough-use’ than a condenser mic. This makes them more favorable as microphones for live performance.

This ruggedness is due to a cruder design. When sound waves hit the diaphragm they cause it to move in the same way as in a condenser microphone but this is simply attached to a metal coil that is suspended between two magnets.

The coil moves up and down between the magnets generating a current which is sent to the amplifier or other device.

This simpler design does not require a charge to be generated between the backplate and the diaphragm and therefore no phantom power is required to make it work.

For a more in-depth article on the difference between dynamic and condenser microphones click here.

Do dynamic microphones need any sort of power?

Nope. Not only do dynamic mics not need phantom power, they don’t need any power to work.

This is due to the design I mentioned above. The sound waves from your voice or instrument move the diaphragm which moves the coil between the magnets in the microphone. That is enough to create a signal.

Of course, this signal is tiny and not audible and this is why you still need to plug the microphone into an amplifier or a PA system or an audio interface.

So technically you need power for those systems, but no power is needed within the microphone body itself.

Will phantom power damage a dynamic microphone?

Whilst dynamic microphones don’t require phantom power to operate, this does not mean phantom power will damage them.

It is only natural to think that running power into something that doesn’t need it will probably break it. But most dynamic mics, particularly modern ones are designed to be able to accept phantom power and simply not use it.

To give a little more detail of why it is fine, it is due to the fact most microphones use balanced XLR cables.

On your standard microphone XLR cable, when phantom power is applied at the standard 48V, the power is equal on pin 2 and pin 3 of the connector, 48v on pin 2 and 48v on pin 3. Pin 1 in the ground. For voltage to start flowing there needs to be a difference between the two values. Because these voltages are identical phantom power will not effect a dynamic mic.

For extra peace of mind you can always check the manufacturer’s details, particularly for older models. But I’d be surprised if they advised against phantom power.

How do I know if my mic needs phantom power?

Well, the simplest way would be to verify whether your microphone is a condenser type or another type such as dynamic or ribbon. If it is a condenser microphone it will need phantom power, if it is a different type of microphone it will not.

A second way you could test is to simply plug it into a standard amplifier or PA which does not have phantom power and turn it on. If you don’t hear anything you either need phantom power, or your microphone is broken.

Do microphones that require phantom power sound better?

Condenser microphones and dynamic microphones both have pros and cons and are better suited to different applications.

A condenser microphone that does require phantom power is more delicate in its design. The diaphragm is very thin and so can detect very small changes in frequency. So when you are recording an instrument and you want to get an accurate representation of the sound; condenser microphones are usually the top choice.

This is particularly true for acoustic guitar or vocals where you will probably want to capture all the frequencies as accurately as possible.

Dynamic microphones are still very useful though. They are often cheaper and much more robust. This means you may not get quite the clarity and accuracy of sound, but they will last longer and can withstand life on tour much better. Being thrown into bags or dropped on stage. Despite these things still not being recommended, the design of a dynamic mic will allow you to be a bit more heavy-handed.

Condenser microphones, being so delicate in their design, are much more likely to get damaged and so this is why you tend to see them more in a studio setting than on then live stage.

Testing a dynamic microphone with phantom power

Because I love to go above and beyond for my readers. I have decided to do a test.

I’ve plugged my Shure SM58 dynamic microphone into my audio interface and pressed the mysterious ‘phantom power’ button (you can see it glowing a mysterious red in the photo below). It is actually marked as ’48v’ on my Focusrite interface.

I’ll be honest, even knowing how all the circuitry works I still tensed a little bit when I pressed the button… as if the microphone was about to explode in my hand.

I can confirm that the sound was exactly the same after pressing the phantom power button as it was before. There was a slight click as I pressed it and the meter went red. But it didn’t cause any damage to the microphone or sound. The balanced XLR cable ensured the power passed through without affecting the SM58 in any way.

Concluding Remarks

So there you have it! You can work a dynamic microphone perfectly fine without the need for phantom power.

All the crude, yet clever, technology needs to work is the vibrations caused by your voice or an instrument to work.

And remember, as scary as it sounds, you can run phantom power through a dynamic microphone without causing any damage.

Rob Wreglesworth

Rob has come to terms with the fact he will probably never be a famous rock star....but that hasn't stopped him from writing and recording music in his home studio. Rob has over 15 years experience of recording music at home.

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