a. Pressure-Operated Microphones. Pressure-operated microphones include carbon, crystal,
dynamic, and condenser (capacitor) microphones. In a pressure-operated type microphone, the electrical
output results from the motion of a conductor, usually a small coil moving back and forth, which moves
with the varying sound pressures in a magnetic field. In a pressure-operated microphone, sound waves
strike only one side of the diaphragm.
b. Velocity Microphone. The velocity, or ribbon microphone, uses the moving conductor
principle. A ribbon is suspended so that it vibrates freely in a magnetic field. In this case, the ribbon is
the diaphragm, since it is not housed in any closed type of case and is exposed to the air on both sides.
Sound waves strike the sides of the ribbon. The output is proportional to instantaneous sound pressure
from the velocity component of the sound wave.
3.
Primary Microphone Characteristics. All microphones share common characteristics called
"primary microphone characteristics." These consist of frequency response, sensitivity, directivity,
impedance values, noise and distortion.
a. Frequency Response. The frequency response is the part of the audio spectrum that the
microphone picks up.
b. Sensitivity. A microphone's sensitivity determines its ability to pick up various sounds.
Sensitivity, measured in decibels, starts from the input of a signal to the output of a signal for a given
pressure at the diaphragm.
c. Directivity. All microphones do not pick up sound equally from all directions. The
directivity or pickup pattern of a microphone tells how to position a sound source at the microphone for
optimum sound pickup. Four types of pickup patterns describe a microphone's directionality. They are:
(1) The Omnidirectional Pickup Pattern. Microphones with this pattern configuration accept
sound equally from any direction without loss of characteristics. There are no variations of this pattern
(fig 2-21).
Figure 2-21. Omnidirectional pickup pattern
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