The objective of this paper is to propose a simple tool to estimate theabsorption vs. transmission loss contributions of a multilayered blanketunbounded in a double panel structure and thus guide its optimization. Thenormal incidence airborne sound transmission loss of the double panelstructure, without structure-borne connections, is written in terms of threemain contributions; (i) sound transmission loss of the panels, (ii) soundtransmission loss of the blanket and (iii) sound absorption due to multiplereflections inside the cavity. The method is applied to four different blanketsfrequently used in automotive and aeronautic applications: a non-symmetricmultilayer made of a screen in sandwich between two porous layers and threesymmetric porous layers having different pore geometries. It is shown that theabsorption behavior of the blanket controls the acoustic behavior of thetreatment at low and medium frequencies and its transmission loss at highfrequencies. Acoustic treatment having poor sound absorption behavior canaffect the performance of the double panel structure.
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