Understanding directionality on a microphone

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Whether you are looking for a vocal microphone for the stage or a condenser microphone for the studio, you will always come across these recurring terms: directivity, recording area or polar pattern. Polar pattern is a main characteristic of the microphone and represents the angle of action. Most microphones have a cardioid or omnidirectional pattern. In this article we will briefly describe this feature and explain why directivity is so important when choosing a microphone.

Recording a good sound effect, a beautiful ambience or a musical instrument requires choosing the right microphone. Indeed, the success of a sound recording depends on the choice of the type of microphone used and behind that on the choice of the directionality of this microphone.

Directionality refers to the direction and limits of a microphone’s sensitivity in space. Not all microphones pick up sounds in the same way, some pick up all surrounding sounds in front of, behind, or to the side of the microphone, others pick up only the sound sources in front of the microphone, and still others specialize in picking up distant sounds. The directionality of a microphone is therefore the area, of different size and shape, within which the sound sources must be located to be picked up.
The main microphone polar patterns are omnidirectional, cardioid, hypercardioid, supercardioid (cannon) and bi-directional (figure 8). Each of these polar patterns is represented by a polar diagram showing the pickup area of the microphone.


The different types of directionality

There are different types of polar patterns. In this article we will explain the most common directionalities: omnidirectional, unidirectional (cardioid, supercardioid and hypercardioid) and bidirectional (figure 8). See the picture below for a diagram illustrating them.

👉 Omnidirectional

Omnidirectional microphones (directionality 1 in the picture) pick up sound from all directions. Therefore, these microphones cannot be pointed in a certain direction.

Small-diaphragm condenser microphones are also available in an omnidirectional version and some of them have an interchangeable capsule.

Some large-diaphragm condenser microphones have a switchable pickup pattern and allow you to select omnidirectional mode. Tie microphones and broadcast microphones are often omnidirectional and allow the speaker to speak in either direction.

Neumann KM 183

Omnidirectional microphones pick up all sounds within a 360° sphere. In other words, they pick up all the sounds surrounding the microphone without favoring any particular source. These microphones are best used for recording ambience or choirs. They will give you wide, deep and above all very rich and realistic ambiences. Their strength is also their weakness. Since omnidirectional microphones record sounds coming from all directions, they are also more likely to pick up “parasitic” sounds such as the noise of cars passing on a road located a few hundred meters behind the microphone. Their use is therefore often difficult because it requires being in an environment that is relatively free of extraneous sound. Examples of omnidirectional microphones: Neumann KM183; Schoeps CCM 2 omnidirectional.

👉 Cardioid

Rode NT-4

Cardioid microphones (directional pattern 2 in the picture) only pick up sound from the front of the diaphragm and are not very sensitive to background noise and reflections from space. Most microphones have a cardioid pickup pattern or a variation of this pattern.

Cardioid microphones are unidirectional microphones that favor the pickup of sound sources located in front of the microphone. They have the particularity of rejecting, i to say not picking up, sound sources located behind the microphone and to a lesser extent sounds from the side.

Their pickup zone is shaped like a heart. The sounds captured are less realistic than those captured with an omnidirectional microphone since part of the sound environment is rejected, but they are both closer and “cleaner” (less extraneous noise or reverberation). For example, they can easily avoid the noise of the road behind the microphone, provided that the noise is not too loud. Cardioid microphones are therefore quite versatile and are among the most commonly used for recording soundscapes, sound effects, but also voices or solo instruments. Examples of cardioid microphones: Rode NT4 and NT5; AKG D112 and C415B.

👉 Supercardioid and hypercardioid

Supercardioid is a variant of the cardioid pattern. Compared to cardioid microphones, supercardioid microphones are more directional.

Sound from the rear is recorded but not as loud as sound from the front of the diaphragm. Hypercardioid microphones (pattern 4 in the picture) are even more directional and resemble bidirectional microphones. Cardioid, supercardioid and hypercardioid microphones belong to the family of unidirectional microphones. Especially dynamic vocal microphones have a supercardioid or hypercardioid pickup pattern.

With an even narrower front lobe than the hypercardioid pattern, the ultracardioid pattern really focuses the pickup on one element while isolating it from the rest of the environment. Often perched above the actors’ heads, ultracardioid microphones (also called cannon microphones) are used extensively for recording film dialogue.

Sennheiser MKH 416

They also allow the recording of point sources in an isolated way. Beware, however, of the strong decay when the source moves away from the relatively narrow pickup zone. These microphones can also capture distant sound sources, a bit like a photo zoom. They are therefore very useful in documentary sound recording, especially for wildlife. Example of shotgun microphones: Rode NTG2 and NTG3; AKG CK69ULS; Sennheiser MKH-416 and MKH-70.

The hypercardioid pattern is very similar to the cardioid pattern, but with a narrower lobe at the front and a small pickup area at the back of the microphone. Hypercardioid microphones therefore have the characteristic of rejecting a large part of the sound sources coming from the rear and sides. They are very useful for sound effects and sound effects recording because they allow you to easily isolate the sound of an object or a particular source.

👉 Bidirectional (figure in 8)

Shure KSM44

Bi-directional or figure-8 microphones (directionality 5 in the picture) pick up sound from the front as well as from the back. They are insensitive to sound coming from the sides (90 degrees).

Tous les micros à ruban disposent d’une directivité figure en 8. Certains micros à condensateur large membrane sont dotés d’une directivité commutable et vous permettent de sélectionner le mode figure en 8.

This type of microphone has two identical pickup zones at the front and back of the microphone. This directionality makes it possible to record both sound sources of an interview or duet simultaneously without movement. A bi-directional microphone is one of the necessary elements for recording in M/S processing. Many ribbon microphones are bi-directional. Example of bi-directional microphones (among others): Apex 205 (ribbon microphone); Shure KSM44; Rode NT3000.

Demonstration schematic of the different directivities

The technology

In the heyday of microphone technology, only two polar patterns existed: omnidirectional and figure-8. Originally called “pressure” microphones, omnidirectional microphones had a diaphragm that measured the sound pressure at a single point in space. Devoid of any directional information, they offered equal sound sensitivity in all directions. Figure-of-eight mics, commonly referred to as “pressure gradient” mics, measured the pressure differences between the two sides of an open diaphragm. As a result, the front and back areas were very sensitive, but the sides remained almost muted. Here’s what happens: in front, the positive signals mix and gain twice the power. At the sides, the signal from the omnidirectional microphone remains the same. At the back, the negative signal from the figure-of-eight mic cancels out the positive signal from the omnidirectional mic. Someone once discovered that mixing the signals from the omnidirectional and figure-of-eight microphones produces what we know today as a cardioid pattern.

Examples of situations according to the mode of directivity

Below are some examples to illustrate the different polar patterns. Since every situation is different, it is very important to listen carefully, research and experiment to find the best microphone for your application.

Chœur : omnidirectionnel (2x)

If you want to record a choir, you have to realize that the sound comes from a rather large area. Placing two omnidirectional microphones on both sides of the conductor will give the most homogeneous sound possible. If the choristers are placed next to each other and not on platforms, it is possible that the choristers in the front row absorb the choristers in the other rows to some extent.

To solve this problem, the microphones are often placed higher up so that they can pick up all the voices.

Snare drum: cardioid

The barrels of a drum set are placed close together. To prevent the snare drum microphone from picking up the sound produced by the hi-hat, you can use a cardioid microphone. Once the cardioid is pointed in the right direction (towards the snare drum), you can make good quality recordings. A cardioid microphone picks up mostly the sound coming from the front and is almost insensitive to sounds coming from the back (hi-hat).

Live singing: supercardioid

In a live performance, it is very important that the vocal mic picks up primarily your voice and not the sound produced by the other instruments on stage. If you are singing in a band, a supercardioid mic would be the best choice. Since the supercardioid also picks up sound from the rear, be sure not to place the monitor directly behind the microphone.

Singing + guitar : figure in 8 (2x)

Do you want to record a singer-songwriter and capture vocals and guitar separately?

In that case, it’s worth experimenting with two figure-of-eight mics. Since a figure-of-eight microphone is almost insensitive to sounds from the sides, top and bottom, you can place it right in front of the singer’s mouth. This way, it picks up only the voice and not the guitar. Point it slightly upward for best results. The other mic is placed near the guitar. By pointing this one down a little, you can get the most out of the microphone’s potential.

Conclusion

Some microphones can respond to different polar patterns. The AKG C414, for example, can be switched between the different polar patterns at the push of a button. Other microphones (Rode NT4 and NT5; Oktava MC-012) offer interchangeable capsules.

There are no fixed rules for choosing and using microphones, just basic principles that can be transcended for creative purposes.

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