1.1 This classification provides methods of calculating single-number acoustical ratings for laboratory and field measurements of sound transmission obtained in one-third octave bands. The method may be applied to laboratory or field measurements of the sound transmission loss of a partition in which case the single-number ratings are called sound transmission class (STC) or field sound transmission class (FSTC), respectively. The method may also be applied to laboratory and field measurements of the sound isolation between two spaces, in which case the single-number ratings are called the noise isolation class (NIC) or normalized noise isolation class (NNIC).