Effects of flanking and test environment on lab–field correlations of airborne sound insulation

Abstract

Previous attempts to correlate lab and field sound-insulation performance have been based on a comparison of the lab sound-transmission class (STC) and the field sound-transmission class (FSTC). In this study comparisons of the 1/3-octave-bandwidth transmission loss (TL) values are made taking into account partition transmission, flanking transmission, and test-environment factors. An experimentally determined flanking TL is obtained through a quantitative relationship between the partition, flanking, and field TL. This determination allows separation of test environment factors related to diffuseness and modal distribution from flanking transmission. Also noted under field conditions are interactions between the coincidence phenomena and the sound field under absorptive room conditions (reverberation time = 0.5 sec), demonstrating that the properties of a partition depend in part on the dwelling-unit furnishings. Because all the test-environment effects observed resulted in TL values higher than those of a properly adjusted classical lab, the conclusion is drawn that for replicate partitions field TL data may under certain conditions exceed lab TL data by as much as 5 dB when no flanking exists. Specific field TL values are likely to be lower than lab TL values owing to the accumulated effects of flanking, leaks, and assembly differences. Subject Classification: 55.75.