Numerical investigation of the niche effect in sound insulation measurement

摘要

The reverberation room method for measuring sound insulation performance of building elements, such as glass panes, window assemblies and so on, involves the "niche effect" as a bias error factor. It is known that the niche effect occurs when a specimen is mounted inside an aperture in the common wall between two rooms, and the dependence of the measured transmission loss on the specimen position in the aperture is not negligible. In this study, a vibro-acoustic coupling analysis is employed to investigate the niche effect, where one or two-sided niches are modeled as thin fences around the specimen. Numerical results demonstrate that sound reduction index decreases below the critical coincidence frequency due to niches, while it increases above the frequency. It is also confirmed that the effect of the two-sided niche with a centrally located specimen is largest at low frequencies. Additionally, the incidence angle dependence of the niche effect, the state of near sound fields and vibration field are observed in detail.