This is a template for articles and pages. In the first paragraph of the text, the term can be explained as concisely and precisely as possible. Ex: "Critical distance is, in acoustics, the distance at which the sound pressure level of the direct sound D and the reverberant sound R are equal when dealing with a directional source." or Ex: "In a reverberant space, the sound perceived by a listener is a combination of direct and reverberant sound. The ratio of direct sound is dependent on the distance between the source and the listener, and upon the reverberation time in [the room]. At a certain distance the two will be equal. This is called the "critical distance."
When a speaker speaks in an enclosed space, e.g. a church, the speech is reflected again and again on the floor, walls and ceiling (reverberation) until it has decayed after a few seconds. As a result, the entire room is filled with a sound field, i.e. at every point in the room the amplitudes of all possible reflections add up, e.g. the third reflection of a sound spoken 20 milliseconds ago, perhaps the tenth reflection of a 100 millisecond old sound, etc.
This room sound field is quasi-static and approximately equally loud at every location in the church, since the reflections come from all sides. A distinction is made between direct field (free field) and diffuse field.
The direct sound from the speaker, i.e. the sound that reaches the listener directly without reflection, is louder the closer the listener is to the speaker. The 1/r distance law for linear sound field quantities applies here for the sound pressure decrease. Very close to the speaker, the speaker can be understood well and the reverberation is hardly perceptible; further away, the voice is increasingly lost in the reverberation. In between, there is a distance (a distance) at which the room sound R (early reflections and reverberation) has the same magnitude as the direct sound D; this distance is the reverberation radius.
E \underset{Einstein}{=} m \cdot c^2 \underset{Pythagoras}{=} m \cdot (a^2 + b^2)
Calculators
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Best Practise
When recording large groups of instruments, e.g. orchestras, the distance of the main microphones to the sound body is approximately that of the reverb radius. To obtain a suitable volume ratio between different instrument groups, e.g. 1st violins and percussionists, the height of the main microphones can be varied.
In sound studio rooms where musical material is to be evaluated, reverberation times are deliberately kept short. This has the advantage, apart from the better evaluability of short reverbs on the recording, that the reverberation radius becomes larger. This can lead to, and it is advantageous if the monitoring position is within the reverberation radius of the monitoring monitors. This allows the recording, not the room, to be sonically evaluated.
