All pressure-gradient microphones present similar concepts and qualities. Obviously, because pressure-gradient pickups can be designed to work as dynamic, condenser, ribbon and electret-condenser microphone systems, the criteria for design is based not upon the microphone's electrical operation per se (although this can be an important factor), but rather upon the physical and acoustic design of the total system and how it responds to the direction of the sound source. Therefore:

1.	sensitivity varies with respect to sound source
2.	variations in sensitivity may be plotted (with respect to front/on-axis sensitivity) on a chart. This is in polar coordinates and is known as the polar response or polar pattern of a microphone
3.	polar patterns are used to evaluate the mic sensitivity with respect to direction and frequency

The graphic at the left shows a moving coil pickup with additional ports that allow sound vibrations which are 180 degrees off-axis to the front of the microphone to influence the motion of the voice coil. Therefore, the pickup pattern would emphasize the on-axis sound and would negate, or de-emphasize sounds originating 180 degrees off-axis.