Acoustic properties of double-leaf membranes with a permeable leaf on sound incidence side

Double-leaf membranes with a permeable leaf on the sound incidence side are usually used as roofs in actual membrane-structure buildings. They are modelled as of infinite extent, and their acoustic properties are theoretically analysed. The theory is experimentally validated. The permeability can significantly improve the sound absorption performance at high frequencies, and makes the characteristics similar to those of cavity-backed porous absorbents. At low frequencies the permeability also affects the sound absorption and insulation performance. At middle frequencies, the characteristics changed according to the permeability: a mass-spring peak appears if it is very high, and vanishes if lower. These effects are strongly dependent upon the mass of leaves, flow resistivity, cavity depth, etc. A detailed discussion is also given to shed some light on the mechanism of these effects.