A system is introduced with the purpose of simplifying the basic standard ISO 717-1 for rating of sound insulation in buildings and of building elements. The core idea is that the whole rating procedure can be accomplished by using only two basic weighted sound reduction indices. The difference between these indices plays an important role, because all other indices defined in ISO-717-1 that depend on the incident spectrum can be approximated using one of the basic indices and the defined difference only.
The system is based on so-called spectrum indices defined as a C- and A-weighted level difference of the spectrum considered. Sound insulations have been found to exist that are unequivocal functions of spectrum index. General representations for such sound insulations are introduced, and they are shown to be very effective for estimating a weighted sound reduction index for any spectrum. A given collection of spectra is shown to give accurate results.
The basic rating mechanisms to be used in requirements and for rating of sound insulation of building elements are based on the new indices and the defined difference. The rating for octave band measurements is based on reference curve methods also in the case of incident traffic noise spectra. The estimation procedure introduced in the study also has applications for estimating A-weighted sound pressure levels when hearing protectors are worn.