Sound transmission through foam‐lined double panel constructions

Abstract

This paper describes the sound transmission performance of foam‐lined double panel constructions, in particular, the acoustical effect of two foam mounting arrangements. The foam considered is relatively stiff and partially reticulated, the type most often used in noise control. A recent theory is used to model the foam [J.S. Bolton and E. Gold, J. Acoust. Soc. Am. Suppl. 1 77, S59 (1985)]; the theory allows for both a frame wave and an airborne wave. The applicability of the theory is demonstrated by comparing theoretical and measured transmission coefficients and impulse responses for freely suspended foam layers. The extension of the theory to allow for bonded or unbonded facing panels is then described. It is shown that when the foam lining is bonded directly to the facing panels sound transmission through the foam occurs largely via the high impedance frame wave. As a consequence, the transmission loss of foam‐lined double panels is improved, particularly at low frequencies, when the lining and panels are separated by a small air gap; in this case a larger fraction of the energy is carried by the more heavily damped airborne wave.