A correction method for the two-microphone transfer function technique in the free field using numerical modeling

Abstract

The two-microphone transfer function technique of measuring absorption coefficient in a free field has remained unchanged since its development in the 1980s. The free field technique has remained scarcely used due to usage restrictions caused by sound field contributions from diffraction of the test sample edge. Currently, the technique is only valid for instances where field contributions from edge diffraction is sufficiently minimized. This research uses acoustic numerical modeling to study the effects of error sources on the technique. Numerical models have been developed and used to quantify the effects of “image source deviation” and edge diffraction on the implementation of the free field technique. Each error source is quantified independently. Updated guidance on the usage restrictions of the free field technique is provided. Additionally, an improvement to the free field technique using a correction method is proposed. An experimental validation of the correction method was performed. The correct...