Transducer = a device that converts one type of energy to another. A microphone converts acoustic energy to electrical energy. A speaker converts electrical energy to acoustical energy. They are both transducers.
good reading Audio Technica Guide to Microphones
Types of microphones
- piezo electric (contact Mic)
other (Stereo, binaural, PZM- pressure zone microphone http://www.crownaudio.com/mics.htm)
- The first type of mic was a Ribbn Microphone. Basically a light wieght ribbon that conducts electricity the is suspened in between two magnets. Older ribbon mics usally have a reduced frequency response.
- A light weight diaphragm is connected to a coil that is suspended between a magnet.
- A very light weight diaphragm is suspended in front of an electrically charged back plate. The two plates basically act as an open air capacitor. As the air pressure changed the distance between the plated the capacitance between the plates also changes.
Condenser microphones need Phantom Power to work.
Our stereo mic: Audio Technica AT825 
The frequency response of a directional microphone changes as it it brought close to a source. The bass response increases.
- Omni-directional - all directions
- Bi-directional (figure 8)- front and back rejects on the side
- Uni-directional - one direction
- Cardioid - one direction with lobe
- Hypercardiod - really one direction with lobe
http://www.mikelights.com/micpolar.htmlALC Microphone Directionality Some pictures
http://www.csun.edu/~record/polar.html Some more Pictures
Stereo Mic Techniques
Spaced Omni's - two spaces Omni mics
XY - Coincident cardioids at 90 degrees
ORTF (Office de Radiodiffusion -- Television Francaise)110 degrees 17cm apart - Near Coincident Pair About.com Microphones Part 1
Dat Heads mic-FAQ.txt