The microphone is the first link in the audio chain and is therefore critical to the overall performance of a sound system.
Proper selection of microphones depends on an understanding their basic microphone characteristics and on a knowledge of the intended application.
To be most effective, a microphone must be matched both to the desired sound source (voice, musical instrument, etc.) and to the sound system (PA system, tape recorder, etc.) with which it is used.
How does the mic change sound into an electrical signal? The operating principle describes the type of transducer inside the mic.
A transducer is a device that changes energy from one form into another, in this case, acoustic energy into electrical energy. It’s the part of the microphone that actually picks up sound and converts it into an electrical signal.
The operating principle determines some of the basic capabilities of a mic. The two most common types are dynamic and condenser.
Although there are other operating principles used in mics (such as ribbon, crystal, carbon, etc.) these are used primarily in communications systems or are of historical interest only. They are rarely encountered in church sound applications.
Dynamic mics employ a diaphragm/voice coil/magnet assembly that forms a miniature sound-driven electrical generator. Sound waves strike a thin plastic membrane (diaphragm), which vibrates in response.
A small coil of wire (voice coil) is attached to the rear of the diaphragm and vibrates with it.
The voice coil itself is surrounded by a magnetic field created by a small permanent magnet. It is the motion of the voice coil in this magnetic field which generates the electrical signal corresponding to the sound picked up by a dynamic mic.
Dynamic mics are the type most widely used in general sound reinforcement, including churches.
They offer a relatively simple construction and are therefore economical and rugged, and they can provide excellent sound quality as well as good specifications in all areas of performance. In particular, they can handle extremely high sound levels: it’s almost impossible to overload a dynamic mic.
Condenser mics are based on an electrically charged diaphragm/backplate assembly which forms a sound-sensitive capacitor.
Here, sound waves vibrate a very thin metal or metal-coated-plastic diaphragm. The diaphragm is mounted just in front of a rigid “backplate” (metal or metal-coated ceramic).
In electrical terms, this assembly or element is known as a capacitor (historically called a “condenser”), which has the ability to store a charge or voltage.
When the element is charged, an electric field is created between the diaphragm and the backplate, proportional to the spacing between them.
It is the variation of this spacing, due to the motion of the diaphragm relative to the backplate that produces the electrical signal corresponding to the sound picked up by a condenser microphone.