Recording Handbook - Hol.gr

MICROPHONE PATTERNS
These are polar graphs of the output produced vs. the angle of the sound source. The output is represented
by the radius of the curve at the incident angle.
Omni
The simplest mic design will pick up all sound, regardless of its point of origin, and is thus known as an
omnidirectional microphone. They are very easy to use and generally have good to outstanding frequency
response. To see how these patterns are produced, here's a sidebar on directioal microphones.
Bi-directional
It is not very difficult to produce a pickup pattern that accepts sound striking the front or rear of the
diaphragm, but does not respond to sound from the sides. This is the way any diaphragm will behave if
sound can strike the front and back equally. The rejection of undesired sound is the best achievable with
any design, but the fact that the mic accepts sound from both ends makes it difficult to use in many
situations. Most often it is placed above an instrument. Frequency response is just as good as an omni, at
least for sounds that are not too close to the microphone.
Cardioid
This pattern is popular for sound reinforcement or recording concerts where audience noise is a possible
problem. The concept is great, a mic that picks up sounds it is pointed at. The reality is different. The first
problem is that sounds from the back are not completely rejected, but merely reduced about 10-30 dB.
This can surprise careless users. The second problem, and a severe one, is that the actual shape of the
pickup pattern varies with frequency. For low frequencies, this is an omnidirectional microphone. A mic
that is directional in the range of bass instruments will be fairly large and expensive. Furthermore, the
frequency response for signals arriving from the back and sides will be uneven; this adds an undesired
coloration to instruments at the edge of a large ensemble, or to the reverberation of the concert hall.
A third effect, which may be a problem or may be a desired feature, is that the microphone will emphasize
the low frequency components of any source that is very close to the diaphragm. This is known as the
"proximity effect", and many singers and radio announcers rely on it to add "chest" to a basically light
voice. Close, in this context, is related to the size of the microphone, so the nice large mics with even back
and side frequency response exhibit the strongest presence effect. Most cardioid mics have a built in
lowcut filter switch to compensate for proximity. Missetting that switch can cause hilarious results.
Bidirectional mics also exhibit this phenomenon.
Tighter Patterns
It is posible to exaggerate the directionality of cardioid type microphones, if you don't mind exaggerating
some of the problems. The Hypercardioid pattern is very popular, as it gives a better overall rejection and
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