Behavioral criterion quantifying the edge-constrained effects on foams in the standing wave tube

The influence of mounting conditions on the measurement of the sound absorption coefficient is investigated. More specifically, the effects of a circumferential edge constraint applied on elastic foams in a standing wave tube are studied. The objective is to identify the foams for which it is possible to measure the theoretical absorption coefficient using the tube. This identification relies on the evaluation of a new parameter, the Frame Acoustical Excitability (FAE), based on the foams' physical properties. In order to quantify the difference between the measured and theoretical absorptions, a linear correlation coefficient is evaluated for a wide range of foams with various sample sizes. The calculated correlation coefficients are then sorted in terms of the FAE. It is shown that as the value of FAE increases, the difference between the measured and theoretical absorption coefficients becomes more significant. A critical value of FAE, below which the theoretical absorption can be efficiently measured using the tube, is established. Through the use of this elasto-acoustic criterion, an experimenter can make an educated guess as to which absorption is measured with the tube: the theoretical absorption or one that is affected by either the edge constraint or the sample's dimensions. (C) 2003 Acoustical Society of America.