A practical impedance tube method to estimate the normal incidence sound transmission loss of double wall structure.

摘要

The objective of this paper is to propose a practical impedance tube method to optimize thernsound transmission loss of double wall structure by concentrating on the sound packagernplaced inside the structure. In a previous work, the authors derived an expression thatrnbreaks down the transmission loss of a double wall structure containing a sound absorbingrnblanket separated from the panels by air layers in terms of three main contributions; (i)rnsound transmission loss of the panels, (ii) sound transmission loss of the blanket and (iii)rnsound absorption due to multiple reflections inside the cavity. The sound transmission lossrncontributions of the blanket can thus be estimated from three acoustic measurements usingrnimpedance tube techniques: two reflection coefficients at the front face and the rear face ofrnthe blanket placed in specific positions characteristic of its position inside the double wallrnstructure and its sound transmission coefficient. The method is first validated in the case ofrnan aeronautic-type double wall structure filled with a 3.5 inch fiberglass. Next, it is appliedrnto a multilayer sound package with a particular focus on the interlayer-interface conditions.