Polar pattern

A polar pattern is the description of a microphone’s sensitivity as a function of the angle from which sound arrives, usually drawn as a circular plot around the capsule. In audio and microphone practice, it is also called the pickup pattern or directivity, and it determines how much of the wanted source and how much of the room, the monitors and other instruments a microphone captures.

The plot shows relative output in decibels, normalized to 0 dB on the main axis. A point 6 dB inside the outer ring means that sound from that direction is reproduced at about half the voltage. Choosing the right pattern is often more important than choosing the microphone type, because it decides rejection, room sound and proximity behavior.

How a microphone acquires its polar pattern

Directivity results from how sound pressure reaches the diaphragm. A pressure capsule is sealed at the back, so it responds only to pressure at one point and is equally sensitive in every direction, which gives an omnidirectional pattern. A pressure-gradient capsule is open on both sides and responds to the difference in pressure between front and back, which gives a figure-8 pattern with deep nulls at the sides.

Most directional microphones combine both principles. Adding an acoustic delay network behind the diaphragm, or mixing the outputs of two capsules, produces the family of first-order patterns. Mathematically, each pattern is a blend of omnidirectional and figure-8 response, written as A + B·cos θ, where the ratio between A and B defines the shape.

Multi-pattern condenser microphones use two back-to-back cardioid diaphragms. Changing the polarization voltage on the rear diaphragm blends their outputs, so a single switch selects omnidirectional, cardioid, figure-8 or intermediate settings. Some modern microphones store both capsule signals and allow the pattern to be chosen after recording.

Common polar patterns and their properties

The first-order patterns differ in where their null points lie and in how strongly they favor on-axis sound. The directivity factor expresses that preference: it compares on-axis pickup with pickup averaged over all directions, which describes how much diffuse room sound is rejected.

The reach figure, sometimes called the distance factor, indicates how much farther a directional microphone can be placed from the source than an omnidirectional one while capturing the same ratio of direct to reverberant sound. Shotgun microphones go beyond first-order patterns by adding an interference tube, which narrows pickup at high frequencies but becomes much less directional at low frequencies.

Polar patterns across frequency and in practice

A published polar plot is an idealization. Real microphones become more directional at high frequencies, because the capsule body and housing obstruct short wavelengths, and directional microphones often become more omnidirectional at low frequencies. Good data sheets therefore show several curves, for example at 125 Hz, 1 kHz and 8 kHz.

Off-axis coloration matters as much as rejection. A microphone with a smooth off-axis response makes bleed from other instruments sound natural, whereas uneven off-axis response turns spill into a harsh or dull coloration that is hard to fix with EQ.

Directional patterns also bring the proximity effect: pressure-gradient capsules boost low frequencies when the source is very close, often by 10 dB or more below about 200 Hz at a few centimeters. Omnidirectional microphones show no proximity effect, which makes them easier to use on moving sources such as lavaliers.

Choosing a polar pattern

The right pattern depends on where the unwanted sound comes from. Aiming the null of the microphone at the strongest interference source is usually more effective than choosing the narrowest pattern available.

Patterns also define stereo techniques. A coincident pair of cardioids forms XY, a cardioid with a sideways figure-8 forms mid-side, and two crossed figure-8 microphones form the Blumlein pair, each with a characteristic image width and room balance.

Misconceptions about polar patterns

Placement errors also undo a good choice. A cupped grille on a handheld microphone blocks the rear ports and turns a cardioid into an almost omnidirectional pickup, which is a frequent cause of stage feedback.

Boundary and nearby surfaces change the pattern as well. A microphone placed close to a wall, a desk or a music stand receives strong reflections from behind or below, which fill in its nulls and add comb-filter coloration. Checking the pattern in the real position, rather than trusting the data sheet, is therefore standard practice for critical placements.

Explained without jargon

A polar pattern is a map of where a microphone listens. Some microphones hear equally well from every side. Others listen mainly to the front and ignore sound from behind, like a person cupping a hand behind one ear.

Picking the right pattern means pointing the deaf side at the noise. That might be a loudspeaker, a drum kit or a noisy street. The voice stays clear and the unwanted sound fades into the background.

A typical use case

A sound engineer runs a small club concert where the singer stands in front of two floor monitors placed at about 45 degrees to each side of the microphone stand. With a cardioid vocal microphone, feedback starts at moderate monitor levels, because the monitors sit at roughly 135 degrees off axis, well away from its 180-degree null, where a cardioid still picks up sound only about 8 dB below its on-axis level.

The engineer switches to a supercardioid microphone and angles the monitors so that they face its rear nulls. Monitor level can now be raised by several decibels before feedback, and the singer hears the mix clearly. A single pattern change solves a problem that EQ alone could not.