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External power for mics?

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rick pearl
External power for mics?
on Jul 17, 2008 at 4:42:07 am

Sorry for having to ask this:

1.) How can you determine if a mic needs power to operate?
2.) I want to plug a mic into a mac using an XLR on one end and the computer mic input on the other. Is the idea that it will work though it needs some type of power to make the volume louder? I tried it and it seemed to work. I'm trying to understand why some mics need power.

Thanks.


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Will Salley
Re: External power for mics?
on Jul 17, 2008 at 6:44:49 am

There are basically three types of mics, dynamic, condenser, and ribbon. Ribbon mics are pretty rare and operate similar to a dynamic mic, so I won't describe that type further.

A dynamic mic uses a diaphragm attached to a coil to transfer acoustic (sound) energy to mechanical energy, and finally to electrical energy. The coil moves around a fixed magnet and creates a slight electrical charge. This charge (voltage) is sent by a cable to an amplifier and transfered back to acoustical energy by a loudspeaker.

A condenser mic works by applying a small voltage (requiring a battery or external power) to a coil, which is aligned with another coil attached to the diaphragm. The movement of this second coil causes a change in the voltage flowing through the first coil. This change in voltage is summed with a negative, but equal voltage and then passed on to be amplified.

Because it presents less impedance to the circuit, a condenser is much more sensitive than a dynamic mic. Condenser mics are typically louder than dynamics for this reason as well. If you can hear a mic connected to your Mac through a 1/8" jack, you probably have a dynamic mic - but if it has a battery, it is a condenser. Some condensers get their power from a battery or what is known as "phantom" power, or both. These are known as electret condensers. Most higher-end condenser mics do not have batteries and are called true-condensers.

There is no single way to tell visually if a mic is condenser or dynamic with out removing the windscreen and observing the electronics. Since this is not advisable, look for marking that may indicate that power is required such as "+48". Also, true condensers (with no battery) rarely have on/off switches, although they often have low cut and/or attenuation switches.


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Brian Reynolds
Re: External power for mics?
on Jul 17, 2008 at 9:04:45 am

Here is a web site that gives some more info on powering of microphones.

http://www.epanorama.net/circuits/microphone_powering.html#intro


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Ty Ford
Re: External power for mics?
on Jul 18, 2008 at 1:13:21 am

Hello Rick and welcome to the Cow Audio Forum

The best way to get audio from a mic into your computer is with a Centrance Micport Pro.
I provides Phantom Power if your mic needs it and uses the USB port on the computer.

http://www.centrance.com/products/mp/buy.shtml

The Phantom Power supply powers a small circuit in externally polarized condenser mics that converts the exceedingly high capsule impedance into an impedance that a mic preamp wants to see.

Regards,

Ty Ford




Want better production audio?: Ty Ford's Audio Bootcamp Field Guide






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