c. The capacitor microphone requires an external power source and is adversely affected by
high or changing humidity.
d. The output voltage is small; therefore, amplification is required, and the leads must be kept
very short to avoid picking up stray field noise. New developments with solidstate amplifier built into
the microphone housing have changed this situation.
Microphone Characteristics. The characteristics of the various microphones are summarized in
Figure 2-5 which lists the various major types of microphones, together with their output level in dB and
their frequency range in hertz. From Figure 2-5, you can see that from the standpoint of output level the
carbon type is best and from the standpoint of frequency range the velocity type is best.
Figure 2-5. Comparison of microphones
Learning Event 2:
DESCRIBE AND IDENTIFY THE ADJUSTMENTS AND MAINTENANCE REQUIRED FOR
PROPER MICROPHONE OPERATION
Microphone adjustments. It should be said that most of the difficulties with microphones are
caused by misuse or careless handling. Nevertheless, let us mention a few adjustments that can be made
on a microphone. The polydirectional microphone may be any of the basic types which have an
adjustable aperture. When the aperture is fully open, the microphone has a bidirectional pattern; when
the aperture is closed, the microphone is nondirectional. At shutter settings between the open and closed
positions, the microphone is unidirectional. Some microphones are designed with blast filters which are
adjustable and require settings commensurate with the operating conditions.