Sound insulation ratings—the STC revisited

About twenty years ago, building authorities and their acoustical experts were faced with a confusing variety of schemes for rating the sound insulation of walls and floors. There was need for a definitive rating system that would digest the 16 transmission loss values that characterize a partition and produce a single number that would describe its sound insulation performance, especially in respect to multi‐family dwellings. Two standards committees, ISO/TC 43 and ASTM E6 (now E33), began more or less together to develop a new improved rating system to fill this need. The product of these labors was what is known in North America as the ASTM sound transmission class (STC). This rating system was so successful that it was almost universally adopted—even in applications for which it was not intended. Despite the apparent success there is now increasing awareness of imperfections in the system. These are examined, in light of accumulated data and experience, to see whether the system could or should be imp...