Measurement system and method to investigate the directional characteristics of sound fields in enclosures

Measurements in existing halls show that the sound field is not diffuse. Specular and diffuse surface reflections not only vary from one room to another but also from seat to seat in the same room and, therefore, must influence the subjective impression of acoustic quality. To quantify this phenomena, both spatial and temporal diffuseness needs to be investigated. This work describes a personal-computer-based system developed to measure the spatial information of sound fields in large rooms. The system utilizes sound intensity measurements from three microphone pairs arranged in Cartesian coordinates or one pair in three successive orientations to establish three-dimensional intensity vectors. The sound field can then be visualized on an energy directional basis versus arrival time and, hence, analyzed in greater detail than hitherto possible. In addition, measuring the directional characteristics of sound in existing halls provides the prospect of quantifying such distribution while investigating their relation to existing room-acoustic indicators. The potential for quantifying directional information and/or sound field diffusion is discussed and example results presented. Such results may lead to new acoustical indices with respect to direction-dictated quality and also to new means of identifying specific causes of acoustical problems in a space.