Sound Transmission through Multiple Structures Containing Flexible Blankets

A general theory of sound transmission for normal wave incidence is developed for a structure containing two impervious layers, an air space, and two acoustical blankets. Equations for more simple structures are derived from the general case by setting some of the parameters equal to zero. A number of design charts are presented giving attenuation in decibels vs. frequency for different structures with specific acoustic resistivity of the blanket material as a parameter. Experimental results are found to be in good agreement with the theoretical predictions. It is found that panels deviate from mass law behavior as their thickness is increased. Mass law behavior is obtained for panels of any thickness when a laminated construction is used to damp out flexural waves.