Sound Transmission through Sandwich Panels Free

An expression for the transmission coefficient of an infinite, symmetric sandwich panel is obtained by modification of Feshbach's expression [L. L. Beranek, Noise Reduction (McGraw‐Hill Book Co., New York, 1960), p. 298, Eq. 13.28] for infinite homogeneous panels. Kerwin's theory of bending stiffness of a three‐ply sandwich is used to obtain a ldquo;critical frequency.” The effect of finite shear stiffness in the sandwich core is to introduce a frequency dependence in the bending stiffness, which in turn implies a critical frequency, which is a function of driving trace wavelength. The expression derived may be numerically integrated to determine transmission loss in a diffuse sound field. Sample computations are compared with experimental results from several different panels. The predicted results compare very favorably with TL tests on panels with nearly free‐free edges.