How a microphone works
Microphones are transducers, devices that change information
from one form to another. They detect sound information as air
pressure patterns, which they interpret and "translate" into
electric current patterns. The accuracy of this transformation
provides a better or worse sound. Magneto dynamic microphones
have a thin metallic surface (like a diaphragm) and a coiled
metal wire attached to it. When the coil is in motion, due to
the magnetic field surrounding the coil, current flow is
facilitated. The amount of current is determined by the
frequency and speed of the motion of the diaphragm, caused by
the incoming air patterns. These groups of microphones are known
as velocity sensitive devices. Here are some of the most
important characteristics involved in making the microphone work:
The microphone sensitivity
This measures the amount of electrical output that is produced
by a particular sound. Low and short sounds cannot be recorded
unless the sensitivity levels are high enough to capture them.
Quiet sounds and musical instruments require higher sensitivity
microphones. Otherwise you have to increase microphone gain
levels and the sound receives a certain amount of distorting
noise.
Microphone overload
When loud sounds overdrive a microphone, a sound distortion will
be noticed. With dynamic microphones, the magnetic field loses
contact with the coil and the diaphragm may be permanently
damaged if loud sounds are consistently recorded. If the
microphone is placed to close to a musical instrument, for
example, overload is likely to happen
Distortion characteristics
The amount of noise distortion varies from one microphone to
another, even when they are the exact same model produced by the
same manufacturer. The level of distortion depends on the
precision of the alignment and arrangement of the diaphragm.
Although a completely linear diaphragm is unlikely to be found,
the best thing is to choose a low distortion and, if possible,
one that complements the sound and style of your recordings.
Frequency response
Flat frequency responses are the most accurate and produce the
best sound quality. Modern microphones offer very high quality
levels for front emitted noises.
Microphone noise
The electrical currents produced by the microphone are very low,
since they need to be sensitive enough to capture all the sound
fluctuations. In order to make this weak electrical impulse
readable by any electronic equipment (such as recording devices)
it has to be amplified. This means that the noise emitted by the
electrical current will also get amplified. While this was a
problem with older microphones, modern ones are essentially
noise free.