New methods of evaluating the performance of acoustic materials especially at high sound levels are important if progress is to be made in such fields as aircraft noise source reduction. This project develops analytical models and new experimental procedures for determining surface sound absorption and internal sound propagation in a variety of common porous media at high sound pressure levels. The project contains both a theoretical and an experimental phase. In the experimental phase, an attempt is made herein to develop a simple nonlinear theory which predicts sound propagation in air saturated perfectly rigid media at high intensity. This theoretical development is based on work initially done by Forchheimer and normally used to describe steady flows at high particle velocity through porous media. The theory is experimentally tested on a variety of porous materials including cellular, layered fine fiber, and nonconsolidated granular materials all of varying porosity and structural frame stiffness. The results should be of great value to engineers and scientists who deal with sound propagation and absorptions at high intensity levels in both commercial and military applications.
