Sound absorber classes / Sound absorption coefficient

The sound absorption coefficient α indicates how large the absorbed portion of the total incident sound is. α = 0 means that there is no absorption, the entire incident sound is reflected. At α = 0.5, 50% of the sound energy is absorbed and 50% is reflected. At α = 1, all incident sound is absorbed.

Depending on the weighted sound absorption coefficient acoustic panels achieve, they are assigned to one of the absorber classes A, B, C, D or E. This is done according to a procedure defined in DIN EN 11654 (“Sound absorption for use in buildings”).

It is important to note that the highest absorption capacity (class A) does not mean that this is the “best” class. Rather, depending on the acoustic conditions in rooms, each absorber class has its specific area of application or its justification. This is because the materials of the various absorber classes supplement the sound absorption already present in rooms in a frequency-dependent manner. The type and extent to which this is necessary depends on the type of use of a room. However, because balanced room acoustics also require the reflection of sound waves, sound-reflecting acoustic panels are produced which are described as unclassified.

A: 0.90 … 1.00 αw (weighted sound absorption coefficient)

B: 0,80 … 0,85 αw

C: 0,60 … 0,75 αw

D: 0.30 … 0.55 αw

E: 0.15 … 0.25 αw

not classified: 0.00 … 0.10 αw

Common mistake:

“Only class A absorbers work best” (wrong)

Contrary to widespread opinion, absorber classes A, B, C and D do not convey any weighting of quality in the sense of a school grade. The class is merely a categorization to show the absorption in different frequency ranges. It is descriptive and not evaluative. Class C is sufficient for most rooms.