Are single number ratings for sound insulation requirements still up-to-date?

In general, soundproofing requirements are given in form of a single number rating. Individual values are therefore singular, i.e. precise, so that no uncertainties are taken into account when checking the quality by measurement or calculation. A better description of the quality of sound insulation would be the formation of classes. In Europe requirements are mainly expressed as a weighted apparent sound reduction index R'w, or by specifying a certain weighted standard sound level difference DnT,w. Both quantities describe a quality that is not necessarily equivalent. The numerical comparison of the requirements is therefore not or only approximately possible. In light of this consideration requirements should be given therefore by classes. In this paper, the difference between a single number rating and a class rating is discussed.