This is a measurement system of the flow resistivity which is the most important parameter of Biot model that characterize acoustical properties of the poroelastic materials.
Propagating the air-borne sound in the porous materials (left) and
Ppropagating the structure-borne sound (vibration) (right).
Flow resistivity is one of the materials parameters for Biot model which represent flow rate of the porous materials. Sound is vibrations in the air, so it is easy to imagine that sound cannot easily propagate through materials which air can hardly pass through. In other word, flow resistivity can represent the difficulties of the propagation of sound (air-borne sound) in the gap in porous materials. A material such as iron and rubber etc. which air cannot pass through easily does not propagate the air-borne sound but propagate only the structure-borne sound (vibration).
To obtain the flow resistivity, you need to measure the air flow velocity and the differential pressure between the front and back (primary side and secondary side) of the material when passing the air through the material. The flow velocity when measuring is regularized to 0.5 mm/s in ISO 9053. This is the extremely low winds that is less than 1/1000 of the breeze. Therefore, differential pressure between the material is also extremely small and a highly accurate differential pressure sensor is needed. There are two kinds of measuring methods in ISO 9053, one is the direct current method (Direct method, DC method) and alternative current method (Alternative method, AC method).
| Method | Direct current method (ISO 9053) |
|---|---|
| Size of sample (diameter) | 40mm (can be used for our acoustic tube measurement) |
| Range of flow speed | 0.1 - 1.0 mm/s |
| Effective flow resistivity range | 2.6 x 102 - 2.6x107 N·s/m4 (10mm in thickness) (depending on the thickness) |
| PC | OS: Microsoft Windows 2000 / XP |