Non-acoustical and acoustical properties of reticulated and partially reticulated polyurethane foams

A series of measurements on four polyurethane foam samples with pore membranes and a polyurethane foam sample without pore membranes have been made. Tortuosity has been deduced using the ultrasonic slope method. It has been found that the deduced value of tortuosity depends on the measurement temperature and for two of the polyurethane foam samples with many pore membranes physically meaningful values of tortuosity cannot be obtained at a temperature of around 25 °C. However more realistic values of tortuosity have been obtained by from measurements at or around the glass transition temperature of polyurethane foam (i.e. at −20 °C) when using the ultrasonic slope method. Flow resistivity, Young’s moduli and loss factors have been measured also. Vibration of the pore membranes has been observed to influence the effective density and characteristic impedance derived from the surface impedance measured in an impedance tube. This paper discusses relationships between membrane vibration and the slow and fast compressional waves. The relative merits of predictions based on rigid-porous models and the Biot–Johnson–Champoux–Allard model are discussed also.