The effect of variation in acoustic environment on nonlinear acoustic properties of perforates

In a previous paper the effect of changing the downstream termination conditions on the nonlinear acoustic properties of a perforate mounted in a plane wave two-port test rig was studied. It is often assumed that the nonlinear acoustic properties of perforates, which are found for high level acoustic excitation, are local and can be determined separately for the perforate. A model for a backing cavity can be added to give the complete acoustic properties in terms of an impedance for a liner configuration. It was found that there were indications showing that the nonlinear acoustic properties in terms of a transfer impedance were changed depending on the acoustic properties of the downstream passive termination. The results were, however, not completely conclusive. The aim of the present study is therefore to extend the previous study to a wider frequency range and to higher acoustic excitation levels. A related question is if a transfer impedance is sufficient to describe the acoustic reflection and transmission properties of perforates under high level nonlinear excitation conditions.