Measurement of the directional properties of non-diffuse sound fields in ordinary rooms

Abstract

Reverberation time measurements are often inadequate in predicting the acoustical behavior of small ordinary rooms, particularly in spaces with non-uniform placement of absorptive materials (such as classrooms, offices, and clinical rooms). On the other hand, numerical predictions depend strongly on the quality of input data (i.e., absorption and scattering coefficients), which are generally inaccurate due to the lack of reliable experimental methods to measure them. This work investigates how spatially distributed measurements can be used to characterize the spatio-temporal properties of the sound field in non-Sabine spaces, and how this information can supplement traditional methods in tasks related to room acoustical design. In this study, measurements are conducted in a classroom with absorbing ceiling using a programmable robotic arm. It is shown that by expanding the measured sound field into an elementary wave basis, it is possible to reconstruct and extract the spatial distribution of sound pressure and energy flows in the room. Additionally, spatio-temporal post-processing enables to characterize the decay process and to assess the dominant directions of sound propagation, leading to a time-dependent analysis of the properties of the sound field.