The most common descriptor of airborne noise insulation in North America is sound transmission class (STC) defined in ASTM E90 and E413. In most of the rest of the world, the common index is weighted sound reduction index (Rw) defined in ISO 717-1. ISO 717-1 defines two spectrum adaptation terms which are intended to better account for different source spectra, for example, traffic noise with elevated levels at low-frequencies. These various ratings and methods are compared with a large set of sound isolation test data. Given these modified ratings systems, there appears to be a need to be more specific regarding airborne noise isolation, especially at low frequencies. This paper will determine if modifications to the STC rating may improve the information being provided to engineers to evaluate acoustical performance.
