The only way to obtain the absorption coefficient of a material is through a test. The tests to obtain the absorption coefficient of any material are carried out in accordance with the specifications established in the international standard ISO 354. This standard establishes the test methodology to obtain the absorption coefficient of a material, indicating the degree to which it can reduce the existing reverberation in the room where is going to be installed.
The absorption coefficient tests of this norm are carried out in standardised reverberation chambers. These chambers are closed rooms with high reverberation -reverberation times greater than 10 seconds- in which the reverberation time of the empty room is first measured using an omnidirectional loudspeaker to emit the noise and, subsequently, the reverberation time is measured with the curtains installed inside the room. From the results of both situations, the curtain absorption coefficient -the noise absorbed by the curtains- is obtained.
In addition, to ensure that the measurements are reliable, the curtains tested must be between 10 and 12 m2 in size.