(This is the first of a series of articles I plan on writing on various aspects of live sound, audio, recording, mixing, etc. If people express any interest, I will be motivated to continue. If nobody cares, I’ll just assume that nobody cares and forget about it. -Al)
The first link in the audio chain is the microphone. A microphone converts air motion into electrical waves which (hopefully) correspond to the air motion (sound). There are several techniques used, and these define the basic microphone types: Dynamic, Condenser, and Ribbon.
A Dynamic Mic is rather like the opposite of a speaker. There is a moving diaphragm which is connected to a coil of wire. The coil sits encased in a magnetic field. When air movement (sound waves) cause the diaphram/coil assembly to move, the motion of the coil in the magnetic gap creates a small electric signal. This is the most durable type of microphone, and typically the cheapest. These may have any “pickup pattern,” which I will go into later. The quality of these microphones varies more than any of the other types – from really really good, to absolute crap.
A Condenser Mic has two charged metalized plates separated by an air gap. The two plates are charged with a DC voltage (either via ‘phantom power‘ or by use of a battery in the mic itself). Air movement causes one of the plates to move, which, varying the distances between charged metal plates, creates a small electrical voltage. These mics tend toward the more expensive and higher quality. These too may have any pickup pattern, and in fact, since they may also have multiple diaphragms and elaborate electronics built-in, may have multiple pickup patterns. They are more fragile than dynamic mics, are more susceptible to environmental factors (temperature, humidity, etc), and require a power source (phantom or battery).
A Ribbon mic has a very small metalized ribbon suspended between to points, one of which is a transducer (converts motion to electricity). Air movement (sound) moves the ribbon, which transfers the motion to the transducer, producing a small electrical signal. The ribbon typically has a very small mass, and thus has a fast transient attack, which translates into “airiness” or “transparency.”
Dynamic mics –
Advantages: cheap(er), very durable, require no power supply
Disadvantages: Poor transient response (due to relatively high diaphragm mass)
Examples: Shure SM57/58, Sennheiser MD421, Beyer M400, EV RE-20
Condenser mics –
Advantages: Excellent frequency response, low noise (high S/N ratio), Multiple patterns available in the same mic (switchable)
Disadvantages: Not as durable, require power supply (batteries or phantom power)
Examples: Neumann U87 and KM84, AKG C451 and C414
Ribbon mics –
Advantages: low handling noise, good frequency response, good transient response
Disadvantages: Not as durable, sensitive to excessive SPL (volume)
Examples: (I can only think of two) Beyer M500, RCA 77