Intercomparisons of laboratory determinations of airborne sound transmission loss

An analysis of transmission loss (TL) data from seven north american laboratories was organized by ASTM Subcommittee E33.05 to study ASTM E 90 accuracy performance for single- and double-panel partitions. Several mass law expressions are reviewed and compared with TL data from seven laboratories for four different limp-mass panel materials. It is noted that the laboratory TL data are not as linear with frequency as generally assumed, and examples are found where TL variation from mass law exceeds that suggested by E 90 precision requirements. In addition, an interlaboratory difference of 2 dB was found for some laboratories. For double-panel walls, TL data from two laboratories for similar constructions (STC ≳50) showed unexpectedly large variation in TL (up to eight points) and in STC (six points). Using double-panel theory, these TL differences are explained on the basis of interlaboratory differences in mass law and flanking (perhaps due to the test frame liners). A TL performance test series is illustrated with recent data from two laboratories and suggested as a basis for improving laboratory TL accuracy.