Comments on “Subjective and Objective Rating of Airborne Sound Insulation – Living Sounds [Acta Acustica united with Acustica 100 (2014) 848–863]”

In the paper [1], the researchers working with the revision of the single number quantities (SNQs) for sound insulation in the present ISO standard 717 claim that the applied SNQs must be based on scientific evidence. They also express disappointment in the poor adequacy of the literature concerning SNQs. The aim of the comments is to refer to and review some papers which the researchers have not taken into account in their work. The two basic SNQs are the reference curve method and the sound pressure level difference method. Some known properties of the methods are reviewed, but also some new ideas are presented. The sound pressure level difference method does not necessarily work well due to an overly strong spectral dependence. On the other hand, the reference curve method seems to be better, being based more on the arithmetic mean of the sound reduction indices. The requirement concerning the arithmetic mean is a consequence of loudness. Finally, the comments imply that the reference curve method is worth preserving.