Abstract
Scottfelt, Grade 900, polyurethane foam is used by the Boeing Company as a relatively inexpensive test material for jet engine nacelle acoustic studies. The design and analysis of Scottfelt acoustic panels are facilitated by expressions relating panel material properties to acoustic impedance. Impedance math models originally developed for glass-fiber blankets and rigid frame materials were extended to Scottfelt, Grade 900, polyurethane foam and are compared to impedance tube measurements of many Scottfelt samples. The acoustic impedance of Scottfelt is controlled by firmness number and panel thickness. Panel impedance properties may also be controlled by stacking layers of foam with different firmnesses. Presented also is an application of a multidimensional impedance model for layered foam acoustic panels.
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