The test method used to determine critical radiant flux is ASTM E-970. Higher numbers indicate better sound insulation performance. STC tests are conducted in accordance with ASTM E90. A single number rating that indicates the sound absorbing characteristic of a material. The NRC rating is determined in accordance with ASTM C423.
Greatest usage is with acoustical material such as acoustical ceiling tile.
As with STC ratings, a higher number indicates better performance. IIC tests are conducted in accordance with ASTM E492. The greatest improvement in IIC rating results simply from the addition of a carpet and pad. A National Evaluation Report eliminates the need to obtain a separate report from each of the 3 model code groups when acceptance of a material or method of construction is wanted nationwide. ASTM C553 - Test method for moisture absorption.