Sound arrives at the microphone from all directions. However, a microphone might not be equally sensitive to sound from all directions. If it is, it is called an ”omni-directional“ microphone. Very common are microphones, that are sensitive for sound coming from the front, while sound from behind is (almost) blocked. Those microphones are called ”Cardioids“, because the graph, that shows the sensitivity as a function of the angle of the incoming sound looks a bit like a heart (heart is Kardía in the Greek language).
Imagine you look at the microphone down from above. Then you can draw a graph that shows the sensitivity of the microphone in each angle. If the graph is close to the center, the sensitivity is low. If it is far away, the sensitivity is high. The bottom direction stands for sound from behind, the top direction for sound from the front. The whole thing is called ”Polar Pattern“.
There are very typical patterns:
Omnis: equally sensitive in all directions.
Cardioids: Highest sensitivity in the front, blocking sound from the back, attenuating sound from the sides.
Wide Cardioids: Highest sensitivity in the front, attenuating sound from the rear, but not completely. Sound from the sides is attenuated less then Cardioids do.
Super Cardioids: Highest sensitivity in the front, blocking sound back left and back right, attenuating sound from the rear. Sound from the sides is more attenuated than Cardioids do.
Figure of Eight: Equally sensitive in front and back, blocking sound from the sides.
A dashed graph means that the sound is captured with inverted phase.
You can try out those patterns here: move the slider to change the pattern and press ”Start“ for an auralization: a bell will circle around the virtual microphone and you will hear, that it's volume changes depending on its position. Although one single microphone cannot capture stereo sound, the auralization here is made in stereo to make it more instructive (you will notice, when the sound comes from the sides).
Start Auralization
Adjust Polar Pattern
The simulation here is very theoretical. The pattern of real life microphones usually depend on the frequency of the incoming sound. For instance common omni microphones are attenuating higher frequencies in the rear. Cardioids are not fully blocking rear sound, especially lower frequencies. Vendors are publishing the polar patterns of their microphones in the way that they show the graphs for different frequencies. Especially for Stereo setups high quality microphones with a pattern that is mostly the same for all frequencies are advisable, as otherwise the stereo image becomes frequency dependet. More about that in the Polar Patterns Calculator
Omnidirectional microphones at one end, figure of 8 as most directional pattern at the other end represent also opponent tonal characteristics. Omni directional microphones usually have a very flat frequency response down to very low frequencies like 20Hz or even 10 Hz and no proximity effect. The more directional the pattern, the stronger the proximitiy effect and the less bass response.
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