1) DYNAMIC microphones are quite simple.  The air pressure changes produced by
   speaking into the microphone move a membrane which is attached to a tiny
   copper wire coil, which is suspended over a permanent magnet.  The coil
   moving back and forth over the magnet produces a small voltage, which is
   the audio signal.  No external power or batteries are required. 

2) ELECTRET CONDENSER microphones work by placing a small metal diaphragm
   close to an electrically-charged plate.  When you speak into the
   microphone, the metal diaphragm moves back and forth within the electrical
   field of this charged plate.  A tiny signal then appears at the output of
   the microphone.  This tiny signal needs to be further amplified in order 
   to work with a standard microphone input.  Both the microphone itself and 
   the pre-amplifier need power sources.  These can be provided by a battery 
   or by another external power source. 

3) UNIDIRECTIONAL, or "CARDIOID" microphones only pick up sound from in front,
   while rejecting sounds from the back and sides.  The microphone is then
   said to have a "cardioid" polar pattern. The pattern is heart shaped 
   (hence the name - cardiod). Point a cardioid microphone at your mouth and 
   it "ignores" any sounds coming from behind the Mic. This makes it possible 
   to sing into it without picking up much from monitors or an audience.

4) OMNIDIRECTIONAL microphones pick up sounds equally from all directions. 
   Such microphones are good at picking up multiple sound sources and room 
   ambience.  Omnidirectional microphones are undesirable for use with 
   voice recognition packages, as environmental noise will "confuse" the
   software.

CONDENSER vs. DYNAMIC: 
The condenser mic converts sound waves into an audio signal via a condenser
(which must be electrically powered). A dynamic mic does the same thing with
a mechanical diaphragm (no power needed). Dynamic mics can take more abuse,
but the condenser mic will give a better sound. Use a dynamic for live music
or recording heavy stuff (distorted guitars). Use a condenser for recording
voice or instruments such as acoustic guitar, piano, etc.


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