Cardioid microphone

The most common type of unidirectional microphone; pickup pattern resembles a heart-shaped figure.
1440px Us664a Microphone

The most common unidirectional microphone is a cardioid microphone, so named because the sensitivity pattern is "heart-shaped", i.e. a cardioid. The cardioid family of microphones is commonly used as vocal or speech microphones since they are good at rejecting sounds from other directions. In three dimensions, the cardioid is shaped like an apple centered around the microphone, which is the "stem" of the apple. The cardioid response reduces pickup from the side and rear, helping to avoid feedback from the monitors. Since these directional transducer microphones achieve their patterns by sensing pressure gradient, putting them very close to the sound source (at distances of a few centimeters) results in a bass boost due to the increased gradient. This is known as the proximity effect. The SM58 has been the most commonly used microphone for live vocals for more than 50 years demonstrating the importance and popularity of cardioid mics.

The cardioid is effectively a superposition of an omnidirectional (pressure) and a figure-8 (pressure gradient) microphone; for sound waves coming from the back, the negative signal from the figure-8 cancels the positive signal from the omnidirectional element, whereas, for sound waves coming from the front, the two add to each other.

By combining the two components in different ratios, any pattern between Omni and figure-8 can be achieved, which comprise the first-order cardioid family.

Common shapes include:

  • A hyper-cardioid microphone is similar to cardioid, but with a slightly larger figure-8 contribution, leading to a tighter area of front sensitivity and a smaller lobe of rear sensitivity. It is produced by combining the two components in a 3:1 ratio, producing nulls at 109.5°. This ratio maximizes the directivity factor (or directivity index).
  • A super-cardioid microphone is similar to a hyper-cardioid, except there is more front pickup and less rear pickup. It is produced with about a 5:3 ratio, with nulls at 126.9°. This ratio maximizes the front-back ratio; the energy ratio between front and rear radiation.
  • The sub-cardioid microphone has no null points. It is produced with about 7:3 ratio with 3–10 dB level between the front and back pickup.

Key Terms

cardioid microphone
common unidirectional microphone
pressure gradient
sensitivity pattern
sound waves

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Cardioid microphone
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Sources & Credits

Last modified on September 5 2019
Content adapted from Wikipedia
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