Quick answer....
The type of mic normally fits into two categories, those which create a small current when the diaphram moves, these are known as dynamic mics and those which change a voltage moving through the mic, often called condenser mics. The condenser can have a part of the diaphram magnetised permenently, called an electret or permenantly polarized, or can be charged when the mic is powered up. Permenantly charged (electret) mics tend to be cheaper but the charge can weaken over years (but don't panic, it takes at least twenty years before the effect gets noticable!).
Mics also have different directional capabilities. A mic which "hears" everything in front, to the side, at the back, in fact from all directions is called an "omnidirectional" mic. Microphones which hear from the front, sides and hardly at all from the back, a sort-of heart shaped response, are called cardiod.
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...The diffrence is amazing.
Linear Mode
