Polar patterns on microphones are a great tool for helping you decide what microphone, or what type of microphone, works best for your needs.
We can tell “how” a microphone picks up sound by its polar pattern; thus, microphone polar patterns tell us about the microphone’s sensitivity to sound waves coming in from different angles and directions. More specifically, the space surrounding the microphone and can be thought of as the microphone’s polar pattern, or how the microphone itself hears or the pattern in which it picks up sound.
Microphone Polar Patterns
The three fundamental microphone polar patterns are omnidirectional, figure-8, and cardioid. Figure-8 is bi-directional, so the way these microphone polar patterns progress is sequential and logical, as explained in the next paragraph.
The entire area surrounding is sensitive to sound equally with omnidirectional polar patterns, the sides are ignored with the front and back being equally sensitive to sound when you have a figure-8 polar pattern, and with a cardioid polar pattern, the front is sensitive and the back is ignored, with the sides being less sensitive than the front.
The cardioid microphone polar pattern was the last one “born”, out of a combination of both omnidirectional and figure-8 polar patterns, with their positive signals being twice as strong in the front, and the rear having a clearer and sharper directional sound, with the figure-8’s negative signal canceling out the positive signal of the omnidirectional polar pattern.
There are also multi-pattern microphones that allow you to switch between different microphone polar patterns (as well as two narrower forms of cardioid called the super-cardioid and hyper-cardioid, with small and larger bulbs of sensitivity in the rear, respectively).
Our understanding of how cardioid came to be is what will help us understand multi-pattern microphones as well. Two back-to-back cardioids are all we need, and simply varying their output helps us to be able to virtually recreate any microphone polar pattern needed.
Both signals in a multi-pattern microphone (being two cardioid capsules) combined make an omnidirectional polar pattern, reversing the polarity of one of both signals gives us a figure-8 polar pattern, and of course, simply using one, with the other offs, results in a cardioid polar pattern. Many popular USB microphones are multi-pattern.
Omnidirectional Polar Pattern
An omnidirectional polar pattern is a perfect circle. While these are very prone to what engineers know as an off-axis spill, this also makes them very useful in very specific situations, owing to their immunity to the low-frequency boost of the proximity effect and lower amounts of self-noise and a wider frequency range as compared to cardioid mics, usually even lower by a full octave.
These specific situations include the A/B technique for recording in stereo, miking drums, or when recording something like an orchestra, grand piano, or any similar wide sound source.
Figure-8 Polar Pattern
The name gives us our understanding of how these bidirectional polar patterns pick up sound: two “circles” of sensitivity in the front and rear, like a figure 8. These are also popular for stereo recordings, as well as with ribbon and large-diaphragm microphones, to record duet or ensure off-axis sounds are fully isolated.
Positioning is key in using figure-8 polar pattern microphones. More isolation is possible with these than with any other polar pattern; this is why they’re popular for recording duets, or with the rear end having acoustic absorption for different instruments being recorded with clarity.
Figure-8 microphones even detect the velocity of sound waves, hence why they’re called velocity microphones, as well as being known as pressure gradient microphones – owing to how it responds to how the diaphragm is open on the front and rear, meaning its response comes from the difference in pressure.
Cardioid Polar Pattern
The cardioid is famous for how well it’s able to discriminate between sounds from the left and right and the rear spaces. This colors the off-axis, however, often with a high-frequency drop-off of sensitivity, being susceptible to the proximity effect just like the figure-8.
However, these are still the most preferred choices for vocals particularly in live performances. These are also used for close-miking untreated rooms with unideal acoustics, and, with the right positioning, these are perfect for miking drums (especially when live or when acoustic) for maximum clarity and isolation.