Challenges testing high transmission-loss walls in a laboratory

High transmission-loss walls present challenges for laboratory testing. One challenge is the limitation of the test chambers, commonly referred to as the "flanking limit", where the sound that is transmitted through the test specimen begins to compete with interference from other sound transmission paths which flank around the test specimen. Another challenge is where there isn't enough noise in the source chamber for sufficient signal-to-noise in the receiving chamber. Both situations are "flagged" when reporting results according to ASTM E90, which merely means that the specimen offers greater isolation than the laboratory is capable of measuring. To further complicate matters, some wall assemblies seem to exhibit different "flanking limits" which are context-specific to a framing assembly, that is one wall will start to exhibit diminishing returns to transmission loss when adding mass, and another framing assembly will exhibit similar diminishing returns at a different level, as if it's reaching a different flanking limit. This paper explores some of these issues but does not offer specific solutions; these issues require further study.