We present a simple experiment that allows advanced undergraduates to learn the basics of the
acoustic properties of materials. The impedance tube-standing wave method is applied to study the
normal absorption coefficient of acoustics insulators. The setup includes a tube, a speaker, a
microphone, a digital function generator and an oscilloscope, material available in an undergraduate
laboratory. Results of the change of the absorption coefficient with the frequency, the sample
thickness and the sample density are analysed and compared with those obtained with a commercial
system.