1.1 ,The purpose of this classification is to provide a method to calculate single-number ratings that can be used for assesing the isolation for the outdoor sound provided by a building or comparing building facade specimens including walls, doors, windows, and combinations thereof, including complete structures. These ratings are designed to correlate with subjective impressions of the ability of building elements to reduce the penetration of outdoor ground and air transportation noise that contains strong low-frequency sound.2 These ratings provide an evaluation and rank ordering of the performance of test specimens based on their effectiveness at controlling the sound of a specific outdoor sound spectrum called the reference source spectrum.