Study of the sound transmission class system for rating building partitions: Another view

Abstract

In an earlier paper titled “Subjective Study of the Sound Transmission Class System for Rating Building Partitions,” D. M. Clark concluded that his results showed that the ASTM E413 method for determining a rating from measured transmission-loss data yields conservative values even when there are large dips in the TL characteristic. Clark's experimental procedure had the subjects match the annoyance produced by a degraded STC shaped sound channel by increasing the level transmitted by a pure STC contour shaped channel. By this method, instead of having a fixed reference annoyance, the reference first established in the pure STC channel is increased in proportion to frequency, bandwidth, and depth of the degradation introduced into the so-called TL channel. If instead the reference annoyance had been kept fixed and the degraded TL channel had been readjusted to match the chosen criterion value of annoyance, quite different results would have been obtained. By using speech articulation index computations, it is shown that instead of being conservative, the rating procedure can overrate TL characteristics with high-frequency octave band dips as much as five points. Instead of abandoning the 8-dB limitation completely, it is proposed that a limitation of 16 dB for the sum of any three adjacent bands be substituted.