Experimental study on the widening of the sound isolation characteristics of light weight sound isolation structure using inflated membrane with air

Light sound insulation structure by using membrane and air pressure (hereinafter refer to as MSI), which consists of meshes and pressurized membranes, exhibits varying sound insulation characteristics and can be effective for the isolation of low-frequency sound even at a lightweight. However, MSI is ineffective for broadband noise owing to the limited valid frequency range of its sound insulation characteristics. Additionally, the stiffness of the frame of MSI, which constrains the meshes and membrane, must be enhanced as the sound insulation performance in the stiffness-law region depends on the stiffness. To resolve these issues, we focused on the specification of the meshes and the constraint condition of MSI. In this study, first, we evaluated the sound reduction index of a MSI combined with meshes of different specification on the surface and rear of the pressurized membrane. The results revealed that the MSI exhibited sound insulation characteristics with less reduction in sound insulation performance compared to the MSI consisting of mesh with the same specification. Second, we evaluated the sound reduction index of MSI divided by glazing bars within the frame that reinforce the stiffness of MSI. The results revealed that the sound insulation performance in the stiffness-law region can be improved by narrowing the space between bars.