Optimized reference spectrum for rating airborne sound insulation in buildings against neighbor sounds

The aim of the study was to define a new single-number-quantity (SNQ) for airborne sound insulation which predicts best the subjective annoyance experienced from neighbor noise. Our study utilized the data of a recent laboratory experiment focusing on annoyance and loudness of neighbor sounds Hongisto et al.[Subjective and Objective Rating of Airborne Sound Insulation - Living Sounds, Acta Acustica United with Acustica, Vol 100 (2014)]. The experiment involved several different living noises, wall constructions, and 59 subjects, thus forming a data basis solid enough for defining a new SNQ. The shape of the optimal reference spectrum was sought through optimization by formulating the problem as a nonlinear optimization problem with constraints, and solving it numerically. The new reference spectra were determined for each type of living noise separately, and for living noises in general. The new SNQs, which were based on the optimized reference spectra, associated much better with the subjective data than the existing SNQs from ISO 717-1:1996 and ASTM 413 (1999). A suggestion for a reference spectrum for normal living activities is given at the frequency range of 50 - 5000 Hz. Low frequencies are substantially less emphasized by the suggested spectrum compared with the existing SNQs.