scope:

This standard specifies a method by which the frequency dependent values of the sound absorption coefficient can be converted into a single number. Before this is done the one-third octave band values of the sound absorption coefficient measured according to ISO 354 are converted into octave bands. In addition, in Annex B, which is informative, a classification method, based on these single numbers is given. The single number rating of this standard can be used to formulate requirements and to describe acoustical properties of sound absorbing products to be used for routine applications in normal offices, corridors, class rooms, hospitals etc. The rating is not appropriate when the products are to be used in qualified environments requiring careful acoustical design by expertise. In such cases only complete soundabsorption data as a function of frequency are satisfactory. The standard is not applicable unless the applications cover the whole frequency range of the reference curve. If only a part of this range is of interest it may be more appropriate to look for products with a good sound absorption within this range only. The shape indicators described in this standard give some guidance in identifying such products which may have a relatively low single number but a much higher potential if a more restricted frequency range is judged from the complete sound absorption curve. As the rating curve in this standard is limited downwards to the 250 Hz octave band the rating is not appropriate below this frequency. If such low frequencies are of interest reference must be made to the complete sound absorption curve.