microphone is divided into omnidirectional and unidirectional according
to the direction.
Imagining that a microphone
is set in the center of a sphere, and the sound is generated on
the surface of the sphere. Because the sound waves are diffused
and diffractive, the SPL which the omnidirectional microphone receives
from different angles (in the same distances) should be the same
Depending on the different
designs, a unidirectional microphone can receive the sound from
some particular angles, but none of the sound is from the back of
the sound receiving holes, the sensitivity might be at least 12dB
difference between 0 degree (the front) and 180 degree (the back).
For example, the wide-angle unidirectional microphone can be used
in a conference to receive the human voice; and the narrow-angle
one may be used outdoors to get the sound of wild animals.
Besides, there is another
type of microphone, noise canceling microphone, the low frequency
response is the characteristic of it which related to the distance.
The low frequency will be reduced at the further distance; it is
usually noted in the graph with two frequency response curves at
1 cm and 50 cm in the specification. The frequencies of the noise
are usually low, such as the movement of cars or the sound of the