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Basic Microphone principals:

A microphone is a transducer, a device that changes information from one form to another. Sound information are represented as patterns of air pressure; the microphone changes this information into corresponding patterns of electric current.

A variety of techniques can be used in building microphones. The two most commonly encountered in recording studios are the dynamic and the  condenser designs.

DYNAMIC :

In the dynamic, microphone, sound waves cause movement of a thin diaphragm and its’ attached coil of wire. A magnet produces a magnetic field around the coil, and the motion of the coil within this field causes current to flow.  It is important to remember that current is produced by the motion of the diaphragm, and that the amount of current is determined by the speed of that motion. This kind of microphone is also known as a velocity microphone.

CONDENSER:

In a condenser microphone, the diaphragm is mounted close to, but not touching, a rigid plate.  A D.C. voltage source is connected to both the diaphragm and the plate, which produces an electrical  charge, between them.  This distance to the plate changes as the diaphragm moves in response to sound. When the distance changes, current flows in the wire. The amount of current is essentially proportional to the displacement of the diaphragm, and is so small that it must be electrically amplified before it leaves the microphone.

ELECTRET:

A common variation of this design uses a material with a permanently imprinted charge for the diaphragm. Such a material is called an electret and is usually a kind of plastic.  Plastic is a good material for making diaphragms since it can be dependably produced to exact specifications. (Some popular dynamic microphones also use plastic diaphragms.) The major disadvantage of electrets is that they may lose their charge after a few years and cease to work.

COMPARISON:

There is no inherent advantage in fidelity of one type of microphone over another. Condenser types require batteries or power from the mixing console to operate, dynamics require shielding from stray magnetic fields, which makes them a bit heavier. The most important factor in choosing a microphone is how it sounds in the required application. The following issues must be considered:

SENSITIVITY:

This is a measure of how much electrical output is produced by a given sound or, amount of air pressure applied.

FREQUENCY RESPONSE:

A flat frequency response is the main goal of microphone selection for Voice Over work. Most of the  professional microphones available today are reasonably flat, at least for voice work.

MICROPHONE PICK UP AREA PATTERNS:

Omnidirectional

Cardioid

Super cardioid

RECOMMENDATIONS:

What is the “BEST Microphone”?  Depends upon your needs/usage
For Voice Over work the better microphone is one with as flat a frequency response as is possible within the range of your Voice.
A Cardioid pattern is prefferable, as can be seen from the diagrams above the Cardioid microphone has minimum pickup from the rear therefore minimizing noise from the back of the microphone. A very good place to look up microphone specifications is http://www.microphone-data.com/default.asp This is a free site with Spec. Sheets on microphones.