Specifications

Dynamic mic Condenser mic
CHAPTER FOUR
MICROPHONES:
CHARACTERISTICS, SELECTION
The microphone is the first link in the audio chain and
is therefore critical to the overall performance of a sound
system. Improper selection of microphones may prevent
the rest of the system from functioning to its full potential.
Proper selection of microphones depends on an
understanding of basic microphone characteristics and on
a knowledge of the intended application.
To be most effective, a microphone must be
matched both to the desired sound source (a voice, a
musical instrument, etc.) and to the sound system (a PA
system, a tape recorder, etc.) with which it is used. There
are five areas of microphone specifications that must be
considered when selecting a microphone for a particular
application. These are: 1) the operating principle of
the microphone, 2) the frequency response of the
microphone, 3) the directionality of the microphone,
4) the electrical output characteristics of the microphone,
and 5) the physical design of the microphone.
1) Operating Principle: How does the microphone
change sound into an electrical signal?
The operating principle describes the kind of
transducer inside the microphone. A transducer is a
device that changes energy from one form into another, in
this case, acoustic energy into electrical energy. It is the
part of the microphone that actually senses air movement
(sound) and converts it into an electrical signal.
The operating principle determines some of the basic
capabilities of the microphone.
The two most common types are dynamic and
condenser. Although there are other operating principles
used in microphones, such as crystal, carbon, etc., these
are used primarily in radio communications systems or
are only of historical interest. They are almost never
encountered in meeting facility sound applications.
Dynamic microphones employ a diaphragm/voice
coil/magnet assembly which forms a miniature sound-
driven electrical generator. Sound waves travel to
the microphone and strike a thin plastic membrane
(diaphragm) which vibrates in response. A small coil of wire
(voice coil) is attached to the rear of the diaphragm and
vibrates with it. The voice coil itself is surrounded by a
magnetic field created by a small permanent magnet. It is
the motion of the voice coil in this magnetic field which
generates the electrical signal corresponding to the sound
picked up by a dynamic microphone.
Dynamic microphones have relatively simple
construction and therefore are economical and rugged.
They can be manufactured with excellent sound quality
and with good specifications for use in every area of
microphone applications. Dynamics are most widely used
in general sound reinforcement and have many uses in
meeting facility sound systems.
Condenser microphones are based on an electrically-
charged diaphragm/backplate assembly which forms a
sound-sensitive capacitor. Here, sound waves vibrate a
very thin metal or metal-coated-plastic diaphragm. The
diaphragm is mounted just in front of a rigid backplate
which is metal or metal-coated-ceramic. In electrical
terms, this assembly is known as a capacitor (historically
called a condenser) and has the ability to store an
electrical charge or voltage. When the condenser element
is charged, an electric field is created between the
diaphragm and the backplate, proportional to the spacing
between them. It is the variation of this spacing, due to
the motion of the diaphragm relative to the backplate, that
produces the electrical signal corresponding to the sound
picked up by a condenser microphone.
Audio Systems Guide for
MEETING FACILITIES
9