Microphone Polar Patterns and Positioning

One of the ways we classify microphones is by what are called polar patterns. Any given microphone can cover a certain amount of area around it. Sounds that make it to that area are the ones that are captured by the microphone. That area is called the polar pattern. And as you may have already guessed by now, more than one pattern exist.

Omnidirectional

This type accepts sound equally from all directions. As such, it must typically be closer to sources in order to pick up more direct sound and less reverberation. It is the simplest of constructions and is found in small microphones, such as lavalieres.

Omnis are used when:

  • Where the source-to-microphone distance is small, so that the fact that it is nondirectional does not cause a severe disadvantage.
  • Where the source is a talker and the microphone can be very close, right in front of the talker, for two reasons: this type demonstrates less susceptibility to popping and no bass boost from close use.
  • Where wind is a significant problem.
  • Where you must because of the requirement for small size, such as lavaliere use and for planting hidden microphones, where the size must be kept small. • Using multiple spaced omnis is one type of stereophonic recording that may be particularly useful with certain large-scale effects (e.g., a train going past the microphones)

Bidirectional

This type prefers sound from the front and back but nulls out sound from the side. Its main use in film and video sound is in making the side-facing component of single-point stereo microphones. Random sound energy like reverberation originating from all angles is attenuated to a factor of one-third of the level of on-axis sound.

Cardioid

This type has a broad frontal acceptance and a null at 180 degrees from its principal direction. Although this polar pattern is probably the most often found among directional mics in the world, film and video boom mics are usually more directional, such as the following types. Like a bidirectional mic, random sound is picked up at about one-third the level of on-axis sound. There is also a subcardioid available in some types, with its polar pattern between that of an omnidirectional mic and a cardioid. • Hypercardioid/supercardioid – These types have a little narrower frontal acceptance than a cardioid, being somewhat more attenuated at 90 degrees than a cardioid, and they have a null in the shape of the surface of a cone, at an angle from the front of 110 degrees or 126 degrees. There is a small rear lobe of sensitivity. These are the most directional types of simple microphones, with random sound being picked up at a level about one-quarter that of on-axis sound. Because the null is off the rear axis, these types can be put on a boom and aimed at the actor, while the null is aimed at the camera, and not be in the field of view of the camera.

Cardioids are used when:

  • Where you can differentiate the sound field into desired sound coming from one direction and undesired from 180 degrees away from the desired, such as placing a microphone near a talker on a street and pointing the mic at the talker and its back side at the street.
  • However, note that cardioids, which in the wide world are the most common directional microphone, are not as widely used in filmmaking as in music recording or public address systems, because hypercardioid and supercardioid mics are more directional, and thus discriminate against noise and reverberation better than cardioids. Use hypercardioid or supercardioids:
  • Where you want to discriminate the most against reverberation in a mic having a relatively small body.
  • Where the source of noise can be placed in a null in the range of 110 degrees to 126 degrees from the front, and the desired source on axis, such as on a boom capturing an actor on-mic and placing the camera in the null (typically more important with film cameras than video ones)
  • These considerations lead to the selection of these types for boom microphone use.
  • This is probably the most often used boom microphone.

To view illustrations of these polar patterns, visit this Web page, or this one.

You can also watch the video below to study how to work with these patterns in lieu of how you can do mic positioning:

Also, take note that some microphones, such as modern field recorders have multiple elements that allow for different polar patterns to be used.

References:

Henshall, M. (2015). Microphone directionality & polar pattern basics. Retrieved from http://shureblog.co.uk/microphone-directionality-polar-pattern-basics/#.Vqn_4yp96Uk.

Media College. (n.d.). Directional Properties. Retrieved from http://www.mediacollege.com/audio/microphones/directional-characteristics.html.

Shure. (n.d.). Microphones: Polar pattern / Directionality. Retrieved from http://www.shure.co.uk/support_download/educational_content/microphones-basics/microphone_polar_patterns.

Stearns, L. (2014). Microphone polar patterns. Retrieved from https://youtu.be/FIetk685cuc.