Comparative analysis of acoustic testing methods of a multi-layered material: uncovering the membrane effect

This paper presents a comprehensive investigation into the differences observed when evaluating the acoustic properties of a multi-layered material using different standardized methods. The primary focus is on the membrane effect of the upper aluminum layer, which has been shown to contribute to the overall acoustic absorption. This phenomenon, crucial for applications requiring enhanced acoustic performance at lower frequencies, is observed in tests conducted with large sample sizes but remains undetected in impedance tube measurements. Through a series of experiments, including reverberant chamber, impedance tube, and in-situ absorption measurements, this study investigates the complexities of accurately estimating sound absorption characteristics in multi-layered materials. Additionally, 2D colormaps to visualize the spatial distribution of sound absorption across different samples are examined, offering deeper insights into the uneven absorption patterns that standard testing methods may overlook. The experimental findings highlight the importance of selecting an appropriate evaluation technique for multi-layered materials, particularly in applications where acoustic performance is critical at lower frequencies.