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How to place the microphone?

How to place the microphone?

Issue Time:2020-08-19
The microphone is the first component in any sound recording or playback system. Its function is to convert acoustic sound waves into corresponding electronic signals. This later signal can be recorded, sent out, amplified or corrected.

However, a microphone cannot effectively distinguish those sounds that are what we need in an environment with strong reflected echoes. At the same time, it is impossible for a microphone to be placed in such an environment to improve the acoustic environment.
What is the critical distance?

In every room, there is such a distance (measured from the position of the lecturer); the intensity of direct speech and the intensity of reflected speech are exactly equal. In terms of acoustics, this distance is named critical distance, which is abbreviated as Dc.
Why is Dc important in deciding where to place the microphone?

If a microphone is placed at or further away from the lecturer's Dc, the speech quality will be poor. This poor sound quality is often described as "reverberation", reverberation, "sound at the bottom of the barrel". This is the lecturer's words that will be difficult to distinguish because the reflected sound overlaps with the speech sound and the speech sound becomes blurred.
Method for determining indoor critical distance

In room acoustic design, determining the critical distance can better place the sound system to achieve better sound effects.

The simplest method is:

Use the audio system to play compressed pop music, start with a speaker (left or right), walk back and forth in the room, but when the sound is the most round and natural, it is easy to find the critical distance. This is repeated, and finally two speakers are used to search in the room to determine the critical distance in the room.
In order to get the best sound effect, how should we use Dc to guide the microphone position?

Generally speaking, an omnidirectional microphone should be placed at a distance of no more than 30% of the critical distance from the lecturer. For example, if the critical distance is 10 feet, then an omnidirectional microphone should be placed 3 feet away from the lecturer.

A unidirectional microphone (cardioid, super cardioid, or shotgun microphone) should not be placed at a distance of no more than 50% of the critical distance from the lecturer. For example, if the critical distance is 10 feet, then a unidirectional microphone should be placed 5 feet away from the lecturer.
What if the microphone must be placed more than 50% of the critical distance?

Use acoustic methods to reduce the reflection in the room. This will increase the critical distance.
Or you can...accept the unqualified sound effect caused by exceeding the critical distance. No other solution.
Important hint

It does not involve the problem of affecting sound clarity due to some unintentional background noise-such as the noise of air conditioners. Even if the microphone is placed less than 50% of the critical distance, a poor speech to noise ratio will still ruin the clarity of the sound. The problem of background noise affecting sound clarity must be solved by eliminating the noise source or by moving the microphone closer to the lecturer.
We could find that the unidirectional microphones (cardioid, super cardioid) are placed farther away, and it is easier to get better sound effects. All Sinbosen microphones are cardioid or super cardioid (no matter if it is limited or wireless)

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