Dynamic microphones are among the simplest types of microphones.
They consist of a diaphragm that is attached to a small coil of
wire. This coil of wire is mounted such that it is surrounded by a
magnet. The diaphragm is arranged such that it will move when it is
exposed to sound pressure. This, in turn, moves the coil, creating an
electric current in it, due to the magnet. The current produced is an
electrical representation of the sound that moved the diaphragm.
Dynamic microphones are durable, reasonably inexpensive, and usually
have good sonic characteristics. Their applications in theatre are
numerous; everything from wireless mic transmitters to intercom
systems can use dynamic microphones. They are also especially useful
in situations where a production calls for an actor's
``disembodied'' voice to play a role, as dynamic mics are an excellent
choice for speech and singing. Two common, favorable types of dynamic
microphones are Shure models SM-57 and SM-58. These
durable mics are suited to a wide variety of tasks, and are quite
affordable. The microphone resting on top of the case in figure
6.2 is a Shure SM-58, while the microphone directly
below that is an SM-57.
A variety of microphones in a microphone road case.
Condenser microphones and electret condenser microphones
vary in design considerably from dynamic microphones. A full
dissertation on the operating characteristics of condenser mics will
not be given here; suffice it to say that they use properties of
capacitance to produce a very small signal proportional to the sound
wave entering the microphone. This signal is amplified with a
small transistor amplifier mounted inside of the mic. Because of
this, condenser microphones require some sort of power, either from a
battery or what is known as phantom power (the powering of
microphones remotely from the sound board). Condensers are very
sensitive, and offer excellent sonic capabilities. For this reason,
they can be useful in theatre applications where a sound needs to be
picked up from some distance away from its source. A favorite
condenser microphone for many applications is the Shure model
There are many other methods for converting sound energy to electrical
engergy. Carbon, piezoelectric and ribbon are also common types of
microphones, though less so than dynamic and condenser
types. It is not within the scope of this book to provide an in-depth
description of all types of microphones, so further reading elsewhere is
recommended for those with an interest in the subject.