Most of you will have used a dynamic mic at sometime or another -- if it looks like a mesh ball on a stick, then it's almost certainly a dynamic model. In live sound, nearly all the mics used are dynamics, and in the studio, instruments such as drums, electric guitars, and basses may also be recorded using dynamic mics. Dynamic microphones have the advantages of being relatively inexpensive and hard-wearing, and they don't need a power supply or batteries to make them operate. So, how do they work?
A lightweight diaphragm, usually made of plastic film, is attached to a very small coil of wire suspended in the field of a permanent magnet. When a sound causes the diaphragm to vibrate, the whole assembly works as a miniature electricity generator, and a minute electric current is produced. Because the electrical output is so very small, it has to be amplified using a mic preamp before it is large enough to be useful.
Given the stated advantages of dynamic mics, why bother with any of the other, more expensive types? The weakness of the dynamic mic lies in the fact that the sound energy has to move both the mic diaphragm and the wire coil attached to it. The mass of the coil adds to the inertia of the diaphragm assembly, which in turn restricts the frequency response of the microphone. In practical terms, the outcome is that dynamic microphones fail to reproduce very high frequencies
accurately. In some applications, this isn't too serious, but if you're working with an instrument where a lot of tonal detail is contained in the upper harmonics, a dynamic mic is unlikely to bring out the best in that instrument.
Another side-effect of the finite mass of the diaphragm/coil assembly is that the dynamic microphone is not particularly efficient -- a lot of amplification has to be used to make the signal usefully large, and the more gain you use, the more noise you add to the signal. In the studio where the mic is used very close to the sound source, this lack of efficiency is not a major problem, but if you're trying to capture a quiet or very distant sound, then a dynamic mic isn't likely to produce good results.
To summarise; dynamic microphones are most effective when working with relatively loud sound sources that don't contain a lot of very high-frequency detail. They're also tough as old boots, which makes them good for live work, or for any application within six feet of a drummer!
Another type of dynamic microphone is the ribbon microphone, but these are only used in fairly esoteric recording applications by engineers who appreciate the subtleties of the ribbon sound. These mics are comprised of a thin metal ribbon suspended in a magnetic field, and when sound energy is encountered, the electrical signal generated is induced in the ribbon itself rather than in a voice coil. The main advantage of ribbon microphones is their smooth, detailed sound; the disadvantages are their higher cost and the fact that they are more fragile than conventional dynamic mics.
DYNAMIC MICROPHONES
GET TO KNOW MIC
Microphones are the heart and soul of the studio, so why not know your microphones?