sound transmission class

10.48  sound transmission class. Single-number rating of airborne sound insulation of a building partition, derived by fitting a reference rating curve to the sound transmission loss values measured in accordance with ASTM E90 for the 16 contiguous one-third octave frequency bands with nominal midband frequencies of 125 Hz to 4000 Hz, inclusive, by a standard method given in ASTM E413. Abbreviation, STC.

Annotation              A similar field measurement in existing buildings, often subject to flanking transmission, is made with sound transmission loss values obtained via ASTM E336, rated according to ASTM E413 and named the “apparent sound transmission class,” abbreviation ASTC.