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Sound absorption classes

The absorption diagrams in this publication show the practical sound absorption coefficient, αp in accordance with the international standard EN ISO 11654. The same standard defines the sound absorption single value, αw, and the sound absorption classes, which are provided for the products in this publication.

Functional demands Acoustics  

1. Absorption class A

2. Absorption class B

3. Absorption class C

4. Absorption class D



5. Absorption class E

6. Unclassified

7. Frequency Hz

8. αp Practical absorption coefficient


The absorption classes are designated A-E, where absorption class A has the highest sound absorption. A specified overall dept of system (o.d.s) must always be stated for a given absorption class.

The ASTM standard C 423 specifies two different single values, the NRC (Noise Reduction Coefficient) and the SAA (Sound Absorption Average). Both values are calculated as an average over the frequency ranges (250-2000 Hz and 200-2500 Hz respectively).


1. Room surface
2. Overall depth of system (o.d.s.)
3. Sound absorber


All types of sound absorption values and curves must be accompanied by a figure which gives the overall depth of mounting (o.d.s.). Sound absorption figures without corresponding o.d.s. are inconclusive and cannot be used for comparison.

NOTE The stated absorption coefficients as well as the fire properties will deteriorate in the case of repainting.


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