Specifications

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circular. This can be advantageous, since one omnidirectional microphone
can be used to pick up voices from several directions, as long as each
person talking is approximately the same loudness and the same distance
from the microphone. The handheld microphones used by news reporters
are usually omnidirectional, allowing the reporter and interviewee to be
picked up by one microphone held between them. It is important to note
that omnidirectional microphones do not suffer from the bass boost
proximity effect mentioned earlier.
There are some drawbacks to consider when using omnidirectional mics,
however. First, since they pick up sounds equally well from all directions,
they may pick up undesired background noises (doors slamming, traffic,
etc.) as well as the desired source. Second, they tend to pick up greater
amounts of room reverberation when used in rooms that have hard-surfaced
walls and floors. This can sometimes result in a diffuse, hollow, “inside a
barrel” sound. This effect may be minimized by moving the microphone
closer to the source and turning down the input level control at the mixer to
compensate. A third drawback to omnidirectional mics is that, when fed
through a loudspeaker system for sound reinforcement, they tend to
produce feedback easily. (We’ll discuss feedback and room reverberation in
more detail in the Troubleshooting section.)
Unidirectional — A unidirectional
microphone rejects sound coming
from behind the mic while still picking up sound from the front. For this
reason, unidirectional microphones pick up less room reverberation and are
less susceptible to feedback when used with loudspeaker systems. There
are different kinds of mics that fall into this category, each one having a
slightly different polar pattern and its own set of advantages and
disadvantages.
By far the most common type of unidirectional microphone is the cardioid
,
so named because its polar pattern resembles a heart-shaped figure. Most
cardioid mics will pick up less than half as much sound from the sides as
from the front, and less than one tenth as much sound from the rear as from
the front. So, the cardioid mic tends to pick up more of the desired sound
and less of the undesired sound.
Other unidirectional types such as the supercardioid and hypercardioid
have progressively greater rejection of sounds from the sides, but pick up
more sound from the rear. Using these more directional patterns requires
that the talker be more careful about staying directly “on mike” and not
straying off to the sides, where the mic’s sensitivity drops off rapidly.
Most types of microphones are available in both omnidirectional and
unidirectional versions. Lavalier microphones are usually omnidirectional,
although unidirectional models are becoming popular. The shotgun
microphone is by definition extremely directional.