Justification of standardized level differences in rating of airborne sound insulation between dwellings

It has long been recognized that single-number quantities R′w, DnT,w or Dn,w result in different conclusions in objective rating of airborne sound insulation between dwellings. The difference between the values of these single-number quantities (SNQ), however, does not prove which of them describes the sound transmission between rooms most correctly. The main object of this article was to study which SNQ correspond best with transmitted living sound levels in buildings when reverberation time, volume of receiving room and sound insulation are taken into account. Data of 100 field measurements of airborne sound insulation were collected as well as 207 reverberation times of furnished rooms. The transmitted sound levels of living sounds were evaluated on the basis of known living sound spectra and measured level differences D. The results show that the SNQs standardized to reference reverberation time of 0.5 s lead in all cases to best correlation between the SNQs and the sound levels of transmitted living sounds. It was also checked whether the rating by DnT,w would lead to higher transmitted sound levels of living sounds in larger rooms, but this was not detected. The use of DnT,w makes rooms of different volumes equal in regard to required sound insulation between them. It is thus justified to replace R′w with DnT,w as the SNQ for rating the airborne sound insulation. Widening the frequency range down to 50 Hz or up to 5000 Hz did not give noteworthy improvement in the correlation.