Microphone Directionality: Omni-directional Cardioid, etc

Microphone directional pattern can have a major impact on its performance and hence the way it is used.

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Every microphone has its own directional pattern. This is known as the microphone directionality.

Some microphones pick up sounds equally in all directions, whereas others pick up sounds better in one direction than another – they are more sensitive in one direction than another.

There are different names for the different types of microphone directionality and their directional patters. Cardioid, omnidirectional, hypercardioid, supercardioid and others. These describe the directional patterns and using these terms it is easy to select the required form of directivity.

Omni-directional

As the name implies microphones with this type of directionality from all directions. Omni-directional microphone directivity is useful in many applications where it is necessary to pick up sounds from all directions. Some applications may include instances where an interviewer is interviewing someone for broadcast radio, a video interview, etc. As the sound will be moving from one person to another and it is often not possible to get the microphone pointing in the right direction instantly, an omnidirectional microphone is useful here. Another application is for Lavaliere microphones worn on the clothes. These are good at picking up sounds as the person moves, but by their very nature it is not possible to control the direction from which the sounds come and therefore an omnidirectional microphone directionality is needed.

The downside to omnidirectional microphone directionality is that many other extraneous sounds are picked up. In interviews this will lead to an increase in background noise, and for sound support and PA applications it enhances the possibility of acoustic feedback.

Cardioid microphone directionality

The other main type of microphone directionality is known as a cardioid response.

The cardioid response resembles that of a heart – hence the name. It has a much greater response towards the front of the microphone and less at the sides and back.

The change of response with the angle of incidence θ can be expressed by the equation:

Response = \frac{1 + \cos θ}{2}

The cardioid form of microphone directionality is excellent for many applications. It reduces the extraneous noise that can come from any direction and for PA and other live music events it reduces the possibility of acoustic feedback.

As a result of its application, the cardioid directionality is by far the most popular as it enables high levels of audio performance to be achieved in many instances.

Hypercardioid / Supercardioid

This form of microphone directionality is an enhanced version of the cardioid response.

For the supercardioid response the microphone has a narrower forward lobe, and rather than having the null at the back, there is a reverse lobe with two side null points.

This form of microphone directionality is useful where additional directional selectivity is needed, possibly where the microphone is placed a little further away from the audio source and where additional noise reduction is needed.

Other microphone directionality patterns

There are many other forms of microphone directionality pattern that can be obtained. Gun, figure of eight and others. However the three mentioned above are the most widely used.