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Microphone Manual
Omnidirectional
Omnidirectional mics are pressure-operated devices, which means they respond directly to
changes in air pressure. They are equally sensitive in all directions and do not exhibit the
proximity bass boost effect inherent in pressure-gradient microphones. Omnidirectional
microphones sound very “natural” and are used where there is a need to capture the sound of a
room’s acoustics or where there are several musicians or singers performing together. Spaced
omni microphones are often used for the stereo recording of choirs and ensembles.
Figure-of-Eight
Also a pressure gradient (directional) microphone, the figure-of-eight pattern is produced by a
diaphragm open to the air on both sides and gets its name because its polar pattern looks like
two identically sized circles in contact with each other. Sound arriving from the side reaches
both sides of the diaphragm at the same time, which results in the air pressure on both sides
of the diaphragm being equal, so there’s no movement of the diaphragm and consequently no
electrical output. Conversely, on-axis sounds produce the maximum pressure differential and
hence the maximum output. Figure-of-eight microphones are used in specialist stereo recording
applications and also where it is useful to have a high degree of rejection from 90 degree off-axis
sound.
Care and Maintenance
Though capacitor microphones are now far more rugged than in the era of the so-called ‘classic’ models,
care must still be taken with all capacitor models to avoid damp conditions, humidity or excessive
dust and cigarette smoke. Microphones brought into a warm studio from a cold vehicle, for example,
may suffer condensation on the diaphragm and circuitry, which will compromise the performance of
the microphone until it has completely dried out. It is also important not to subject the microphone to
excessive shocks, such as dropping it onto a hard surface.
Microphones may cleaned using a damp cloth but solvents or thinners should not be used. It is also
important not to use contact cleaners or other aerosols close to the capsule as this may impair
operation.
Mic cables and connectors should be checked regularly for damage. If the cable connecting a tube
microphone to its power supply is damaged, contact your local service agency for a replacement and
under no circumstances attempt to use a cable of a different type as this could damage the microphone
circuitry and/or power supply, and also risk electric shock.
Never run a tube microphone power supply with the ground disconnected as this presents the risk of
electric shock. Do not open the microphone case or the power supply case when the power supply is
connected to the mains supply as there are potentially lethal voltages inside.
If a capacitor microphone produces intermittent noise or spluttering sounds, it is probably suffering
from condensation and should be dried out in a warm place before further use. Do not attempt to
service a microphone yourself other than to change a tube as this will void the warranty and may
cause serious damage. These considerations apply to all capacitor microphones.
sE Electronics Microphone Manual