Experimental Modelling of High Transmission Loss Layered Materials via Transfer Matrix Method

Impedance tube systems struggle to accurately measure test articles with high transmission loss because of acoustic leakage at the sample perimeter and acoustic flanking paths through the tube walls. Many products used in high transmission loss applications are constructed in layers of materials such as foams, fibers, films, barriers, and air gaps. Instead of measuring all layers at once, each layer can be measured individually, under the appropriate boundary conditions, to obtain frequency-dependent transfer matrices describing the acoustic impedance at each layer interface. The individual matrices can then be combined via established methods to calculate the total transmission loss of the layered system. This paper demonstrates the transfer matrix method as it applies to high transmission loss layered materials and presents experimental results of several materials and layer configurations, including comparisons of results obtained via the transfer matrix method to results from bulk measurements.