Estimation and minimization of errors caused by sample size effect in the measurement of the normal absorption coefficient of a locally reactive surface

In this paper the effects of the finite size of a sample on the measurement of the normal absorption coefficient are explored with the aid of a BEM model. Both the experimental method and BEM simulations assumed free-field conditions and are based on the measurement of pressure and particle velocity at the same point. They will be referred to herein as the PU method. Before exploring the BEM model, measurements were performed in a semi-anechoic room for experimental validation. A direct comparison of the BEM model and experimental data does not appear to have been presented elsewhere, at least under the conditions presented herein. This validation may help to improve confidence in the PU experimental technique and the use of the BEM as a tool to enhance the quality of experiments. After experimental validation the measurement parameters are varied in the BEM model in order to investigate their effect on the measurement and to find strategies to minimize the error induced by the sample size effect. The strategies found with use of BEM simulations were also tested experimentally in order to test its validity. Recommendations for improved precision in the measurement of finite samples are given at the end of this paper.