Recent research demonstrates the 8-dB rule inherent in the Sound Transmission Class (STC) metric does not correlate with Zwicker loudness nor with human subjective response to sound transmission in buildings, contrary to statements within the current ASTM E413 standard. These studies have typically relied on a small number of assemblies with limited variation in assembly construction and dynamic range. This study provides a much larger volume sample with a far more diverse range of assemblies. This includes well over 2000 vertical (wall) and horizontal (floor–ceiling) assemblies, with STC ratings from 29 to 86. The data are used to calculate the STC ratings with and without the 8-dB rule, which are then compared to the Speech Privacy Class (SPC) and Zwicker loudness.
Shafer et al. (Wed,) studied this question.