Tech Tip:For the Love o' Mics: Part 1: Microphone Types/Dynamic Mics/Microphone Patterns
Microphones, as you may have noticed, come in a lot of shapes and sizes. For every type of mic there's a set of requirements, specs and applications to understand, so we've got a bit of sorting out to do. It's always nice to get a good tip on a particular mic for a particular application, but it really helps to know the how's and why's of microphone mechanics. This knowledge will help you make informed choices when it comes to selecting among microphone makes and models.
The main types of mics are dynamic, condenser, ribbon, and crystal, with variations available on each theme. The names describe the sound pickup method; that is, how air pressure fluctuations (sounds) are translated into the electrical signals sent along to your mixer, tape machine or DAW.
Microphones also differ by pickup pattern. The mic's response to sound depends on which direction the sound is coming from. Some patterns are very directional, like the zoom lense on a camera, while others pick up sound coming from many directions, like a wide-angle lens.
DYNAMIC MICS: All-purpose toolkits
Dynamic mics are generally cheaper and more commonly used than other types. They are tough and reliable, largely due to their simple construction. The trusty Shure SM57 and SM58 are classic examples. A thin, convex piece of mylar plastic stretches across the mic's diaphragm, which is attached to a coil of wire sitting in a magnetic field. When vibrating air (again, that's all sound is) moves the diaphragm, an electric current is generated in the coil. The coil is in turn connected to the mic cable and - presto! - signal is sent to your console. See Figure 1.
Dynamic mikes are tough, cheap, and can be used close up on very loud instruments without crapping out or blowing up. They sound acceptable, at the very least, on a wide range of instruments. For these reasons they are very popular in home studios, and they're always available in top-notch commercial studios as well. A friend of mine used an SM57 to hammer a 16d common nail into a 2x4 and the mic was fine afterwards,so, yeah, it's a toolkit!
Dynamic mics almost always have a cardioid, or unidirectional, pattern, which means they are very sensitive to sounds that are directly in front of them and hardly sensitive at all to sounds behind them. Figure 2 shows a cardioid mic with its pattern drawn around it. The mic is most sensitive to areas where the pattern line is farthest from the diaphragm. This directionality is also shown with fatter arrows for high sensitivity and thinner arrows for lower sensitivity.
As shown above, a pattern is the map of the microphone's directional sensitivity. The possible patterns are cardioid (unidirectional), figure-eight and omnidirectional.
There is another variant of the cardioid mic called hyper-cardioid, which is much less sensitive to sound coming from the sides of the mic. Hyper-cardioids are the zoom lenses of microphones, and they're very useful - but watch out, it also listens to some of what's coming from directly behind it.
Figure 3 shows the three basic patterns plus hyper-cardioid. The omni pattern (short for omnidirectional) has equal sensitivity from all directions, while the figure-eight pattern is most sensitive to sounds from mic's front and back. There is often a drawing of the pattern right on the microphone.