Acoustic contributions of a sound absorbing blanket placed in a double panel structure: Absorption versus transmission

Abstract

The objective of this paper is to propose a simple tool to estimate the absorption vs. transmission loss contributions of a multilayered blanket unbounded in a double panel structure and thus guide its optimization. The normal incidence airborne sound transmission loss of the double panel structure, without structure-borne connections, is written in terms of three main contributions; ͑i͒ sound transmission loss of the panels, ͑ii͒ sound transmission loss of the blanket and ͑iii͒ sound absorption due to multiple reflections inside the cavity. The method is applied to four different blankets frequently used in automotive and aeronautic applications: a non-symmetric multilayer made of a screen in sandwich between two porous layers and three symmetric porous layers having different pore geometries. It is shown that the absorption behavior of the blanket controls the acoustic behavior of the treatment at low and medium frequencies and its transmission loss at high frequencies. Acoustic treatment having poor sound absorption behavior can affect the performance of the double panel structure.

Transfer matrix modeling and experimental validation of cellular porous material with resonant inclusions

“…The good transmission loss performance at the HR resonance frequency of the composite panel coupled to sound package HR2 can be attributed to the combination of two positive contributions of the sound package: (1) the sound transmission loss peak and (2) the sound absorption peak; the latter dampens the multiple acoustic wave reflections in the inner air layer between the panel and the material, as commented in Ref. 32. Above f 0 , the performance of the resonant sound package depends on the configuration.…”

“…These two phenomena have to be related to the combination of the sound package transmission loss and sound absorption in the air cavity as described in Ref. 32. Indeed, both positions give identical transmission loss for all frequencies as shown in Fig.…”

Numerical and experimental investigations on the acoustic performances of membraned Helmholtz resonators embedded in a porous matrix

“…The framework proposed in this paper is particularly appropriate for investigating the acoustic potential of the developed devices. This analysis is performed in term of transmission loss (typically in accordance with aeronautical application), however, understanding the absorption behavior remains essential since practical applications involve double-wall configuration [32]. A discussion using the classical admittance sum method (ASM) [33] is also conducted to better understand the contribution of each element (porous layer and resonator) on the behavior of the composite material.…”

Experimental estimation of the transmission loss contributions of a sound package placed in a double wall structure

“…The objective of this paper is to propose a simple experimental method to estimate the influence of the sound package when placed in a double wall structure. According to the authors' previous work [7], the normal incidence airborne sound transmission loss of a double wall structure, without mechanical links, is written in terms of three main contributions; (i) sound transmission loss of the panels, (ii) sound transmission loss of the blanket and (iii) sound absorption due to multiple reflections inside the cavity. The transmission loss contributions of the blanket can thus be estimated from three impedance tube measurements: two reflection coefficients of the blanket placed in specific configurations related to its position inside the double wall structure and its sound transmission loss.…”