Larson Davis SoundTrack LxT, Руководство пользователя

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LxT Manual Glossary and Formulas
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Guidelines :
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
vibration, particularly in direction at right angles to the plane
of the diaphragm.
4. Keep microphones away from strong electrical fields.
A microphone measures force, not pressure. We would like a
microphone to measure sound pressure (force per unit area)
instead of sound force. If the pressure is applied uniformly
over the microphone diaphragm a simple constant (the
diaphragm area) relates the two, but if the pressure varies
across the diaphragm the relationship is more complex. For
example, if a negative pressure is applied on one-half the
diaphragm and an equal positive pressure is applied to the
other half, the net force is zero and essentially no motion of
the diaphragm occurs. This occurs at high frequencies and
for specific orientations of the microphone.
Rules :
1. Do not use a microphone at frequencies higher than
specified by the manufacturer; to increase the frequency
response choose smaller microphones.
2. Choose a microphone for free field or random incidence
to minimize the influence of orientation.
A microphone influences the sound being measured. The
microphone measures very small forces, low level sound can
be about one-billionth of a PSI.
Every measurement instrument changes the thing being
measured, and for very small forces that effect can be
significant. When sound impinges directly on a microphone
the incident wave must be reflected since it cannot pass
through the microphone. This results in the extra force
required to reflect the sound and a microphone output that is
higher than would exist if the microphone were not there.
This is more important at high frequencies and when the
microphone is facing the sound source.