Why is this important?

• The sound power level enables a comparable assessment of noise emissions from different devices.
• It is therefore part of safety at work

Wikipedia:

The sound power level objectively describes the sound emission from a sound source, i.e. without depending on the distance between the source and the listener or the audible conditions of the room in which the source is located.

Numerically, the sound power level corresponds to the sound pressure level that would be measured on a sphere with a surface area of one square metre, if the sound source were a point located at the centre of that sphere.

Sound power is the cause; the perception (of sound pressure) corresponds to the effect.

This is directly comparable to the electrical power of a light source: the power of a 60-watt incandescent bulb does not change when viewed from a greater distance, or when it is shining in a bright room rather than a dark one. A sound source initially emits only direct sound. If the source is located indoors, some of the sound is absorbed by the walls. The unabsorbed portion is reflected and contributes to the listening experience. The proportion of sound that is absorbed is indicated by the room’s equivalent absorption area.

[Wikipedia / Further explanation: de.wikipedia.org/wiki/Schallleistung]

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