The transmission ratio, and thus the transmission loss in decibels, has been determined from a theoretical consideration of this problem, based on certain simplifying assumption such as zero stiffness compared with mass, an air layer between partitions small compared with the wavelength, etc. Three cases in particular are considered, the transmission loss being expressed as a function of wavelength of sound, weight per square foot of partitions, and distance between them: (1) Double partition wall; (2) Single wall (noting check with previous work); (3) Double partition and single partition loosely fixed to vibrating surface as a means of reducing sound radiation from that surface. Certain limitations of the theory are explained briefly.