A simple method to optimize the sound package in a double wall structure.

Abstract

The acoustic contributions to the transmission loss of an unbounded sound package in a double panel structure are investigated. For this purpose, a simple analytic expression of the normal incidence sound transmission loss of the double panel structure is proposed in terms of three main contributions: sound transmission loss of the panels, sound transmission loss of the blanket, and sound absorption due to multiple reflections inside the structure. It is shown that (i) at high frequencies, the transmission loss contribution of the blanket is preponderant compared to the absorption contributions;(ii) at the cavity resonance frequencies, the absorption contribution allows to attenuate the dips of insulation; and (iii) at medium and low frequencies, when the absorption performance of the porous layer is poor, the absorption contributions in the air‐gaps can decrease the sound transmission loss performance of the double panel. The proposed methodology can also be used to estimate, from classical impedance tube measurements of the sound package only, the transmission loss of the whole double wall configuration. Testing the influence of various sound packages in a given double panel structure thus becomes quick and much less expensive compared to classical tests.