The directivity characteristics of a microphone or speaker are generally shown using a polar pattern diagram. This is basically a two-dimensional slice through the center of a 3-dimensional structure, along the axis of the microphone.
The curve in this diagram shows the relative signal level as a function of its angular direction from the center of, in this case, the microphone capsule. The levels are evenly-spaced concentric circles around the center point. The front of the capsule is at 0 degrees, shown as the 0 dB point for this microphone. At the rear of the capsule, 180 degrees, the signal level generated by the microphone is about -11 dB. At 60 degrees and 300 degrees, the sensitivity is -3 dB. The nulls are at 122 degrees and 238 degrees.
The diagrams below show the polar patterns for 5 types of microphones.
Notice the following features:
This type is often used to mic two instruments in close proximity to one another.