D-12 824 Reference Manual 11/3/00
Capacitor
(Condenser): A microphone that uses the motion
of a thin diaphragm caused by the sound to change the
capacitance of an electrical circuit and thereby to create a
signal. For high sensitivity, this device has a voltage applied
across the diaphragm from an internal source.
Electret:
A microphone that uses the motion of a thin dia-
phragm caused by the sound to change the capacitance of an
electrical circuit and thereby to create a signal. The voltage
across the diaphragm is caused by the charge embedded in
the electret material so no internal source is needed.
Microphone - Uses
: The frequency response of micro-
phones can be adjusted to be used in specific applications.
Among those used are:
Frontal incidence (Free Field):
The microphone has been
adjusted to have an essentially flat frequency response when
in a space relatively free of reflections and when pointed at
the source of the sound.
Random incidence:
The microphone has been adjusted to
have an essentially flat frequency response for sound waves
impinging on the microphone from all directions.
Pressure:
The microphone has not been adjusted to have an
essentially flat frequency response for sound waves imping-
ing on the microphone from all directions.
What a microphone measures
:
A microphone detects more
than just sound
. The motion of a microphone diaphragm is
in
Microphone Guidelines
, cont.response to a force acting on
it. The force can be caused by a number of sources only one
of which are we interested: sound. Non-sound forces are: (1)
direct physical contact such as that with a finger or a rain-
drop; (2) those caused by the movement of air over the dia-
phragm such as environmental wind or blowing; (3) those
caused by vibration of the microphone housing; and (4)
those caused by strong electrostatic fields.
Rules
:
1. Do not permit any solid or liquid to touch the microphone
diaphragm. Keep a protective grid over the diaphragm.
2. Do not blow on a microphone and use a wind screen over
the microphone to reduce the effect of wind noise.
3. Mount microphones so their body is not subject to vibra-
tion, particularly in direction at right angles to the plane of
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