RESEARCH AND TECHNICAL NOTES ACOUSTIC PROPERTIES OF RIGID CLOSED-CELL PLASTIC FOAMS

Acoustic properties of typical rigid c1osed-cll plastic foams have been studied experimentallyas functions of skeleton materials and cells.Longitudinal sound speed perpendicular to the rise direc-tion for PAPI polyurethane foam can be related to foam density by an equation C=aρ~b.Polyurethanefoams present acoustic orthotropy as a result of elongated cells in rise direction.For an air-backedfoam layer in a water-filled pulse tube,phase angles of complex reflection coefficients are always near180°when cell sizes are about 0.5mm.Frequency and temperature dependences of sound speed,as wellas attenuation at audiofrequencies in foams,are governed primarily by properties of skeleton materials.