Airborne sound insulation in terms of a loudness model

Abstract

One of the main goals of building acoustics is the prediction of airborne sound insulation between rooms to determine the quality of sound protection. In many practical cases, however, the objective measures of the airborne sound insulation using procedures in standards are not in agreement with the subjective assessment. This paper, therefore, after reviewing the conventional model to calculate airborne sound insulation, introduces a calculation scheme based on loudness level linked with specific fluctuation strength, yielding a weighted normalised loudness level difference, Lnor,w. By analysing the difference between standard airborne sound insulation values and the introduced weighted normalised loudness level difference, it is revealed that the sound pressure level that is transmitted through a partition decreases with increasing frequency, and this is independent of the type of signal and of the airborne sound insulation values (Rw′-values), whereas if the transmitted signal is converted into a loudness level, it tends to rise with increasing frequency. Moreover, it is found that, whereas a simple level difference does not exhibit the effect of a given signal to the frequency-dependent airborne sound insulation curve, using Lnor,w, a significant change can be observed, in terms of both computed and measured results. Furthermore, the frequency-dependent results allow more details to be investigated for a certain sound insulation. A comparison between the measured and predicted airborne sound insulation with no obvious malfunction suggests that at some frequency ranges, a hypothetical subjective related failure might occur. Overall, the proposed Lnor,w could reveal detailed insights into the in situ measured airborne sound insulation compared with standard airborne sound insulation values. The frequency-dependent values discussed in this paper form a basis for developing a single-number index.