The average sound pressure level in the room (L)

Professional Definition

This is the averaged value of the sound pressure level in the reverberation field of the room over time and space. This value depends on the sound power level of the source (LW) and the acoustic absorption of the room (A).

Mathematically, this relationship (for the reverberation field) is described by the formula: L = LW - 10 log(A) + 6 dB (approximately for standard conditions). This means that the sound pressure level (what we hear/measure with a microphone) is directly related to the energy emitted by the source, reduced by the ability of the room to absorb that energy.

Acoustics in Simple Words

This can be compared to heating a room. A radiator has its constant power (the equivalent of the acoustic power of the source LW). However, the temperature you actually feel in the room (the equivalent of the average pressure level L) depends on how airtight the windows are and how large the room is (the equivalent of the acoustic absorption A). In a small, well-insulated room, the same radiator will create a “sauna” (loud noise), while in a large hall with open windows, you will barely feel it (less noise), even though the radiator operates the same way.

Summary

The average sound pressure level is the resultant loudness in a given interior. It is a key parameter in designing the acoustics of industrial and office interiors, showing how much acoustic adaptation (increased absorption) can reduce actual noise levels.