A microphone can pick up sounds from all directions or just one direction depending on its technical structure.
This sensitivity to sound from one or more directions is called Directionality.
There are 3 main types of directional microphones –
Omnidirectional Microphones
Unidirectional Microphones
Bidirectional Microphones
Omnidirectional Microphones
These directional microphones pick up sounds from all directions and are generally used only when there are multiple speakers involved in a recording (as would be in the case of a meeting or focus group).
These microphones are not recommended for recording single speakers because they capture sounds from all directions, capturing a lot of unwanted ambient sounds like shifting chairs, doors opening, side conversations, etc.
When using an omnidirectional microphone in an indoors setting, choose a quiet room and lay down some ground rules for the participants.
When outdoors, the microphone should be placed as close to the speakers as possible.
Unidirectional Microphones
These directional microphones pick up sounds from the direction they’re facing.
There are 2 major types of unidirectional microphones –
Shotgun Microphones
Shotgun microphones are best for outdoor recordings because they have a very narrow ‘angle of acceptance’ or ‘pickup pattern’ or simply put, the area from which they pick up sound.
This means they can pick up the particular sound they’re directly towards and reject all other surrounding noise to produce a very clear recording.
Long shotgun microphones provide the highest level of directionality and pick up sound from only the person/object that they’re pointed at. This leads to a very high quality of recording and makes them ideal for noisy locations.
The downside of using these microphones is that since they’re very long (and often used with a boom), they normally need a second person to operate.
Also, the microphone must consistently be pointed directly towards the speaker – any movement away from the speaker will result in an interruption of the flow of sound to the microphone and thereby impact the recording.
Short shotgun microphones are, well, shorter. Their properties are similar to the long shotgun microphones, the only difference lying in their slightly wider ‘angle of acceptance’.
They are more portable as well; this makes them the microphones of choice for outdoor recordings that require a degree of mobility – such as street interviews.
Shotgun microphones are especially useful when the speaker is not close to the microphone.
The more the distance between the speaker and the microphone, the more directional the microphone needs to be.
Cardioid Microphones
The directional microphones most commonly used for recording speech are cardioid microphones. This is because the microphones are directional like shotgun microphones yet offer flexibility in terms of the ‘angle of acceptance’ as well as size and portability.
They pick up sound mainly from the direction that they’re pointed in, some amount of sound from the far sides of the microphone, and very little sound from behind the microphone.
Since they’re unidirectional, they eliminate a lot of surrounding noise and produce high quality recordings.
Bidirectional Microphones
As the name suggests, these directional microphones pick up sounds from two opposite directions and reject sound from other sides.
Also known as figure-of-eight microphones, these microphones are useful for recording two-person interviews where two people are seated on the opposite sides of a table.
Bidirectional microphones are not very commonly used because of their limited application.
Some directional microphones come with multiple options that allow users to switch from let’s say cardioid to omnidirectional mode when required.
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