3D Sound characterisation in theatres employing microphone arrays

The analysis of the sound field’s 3D properties has been strongly improved in recent years, after spatial properties of sound propagation have been acknowledged to be important during the design or correction of theatres and auditoriums. Besides, a proper assessment of spatial accuracy is requested for 3D sound reproduction systems, initially designed for acoustical virtual reality and now also employed in the entertainment/cinema industry (Immsound, Auro-3D, NHK 22.2). Often only monoaural or binaural measurements are performed by means of omni-directional microphones and dummy heads, although international standards like ISO 3382/1:2009 also define some “truly spatial” parameters such as JLF and JLFC. The two latter parameters are derived from measurements made with a pressure velocity (p/v) microphone, but this is still a 2-channel measurement. 3D Impulse Responses (4-channel B-format) have for many years been measured and employed for sound reproduction. Recently, higher-order 3D Impulse Responses have been measurable thanks to the availability of compact microphone arrays employing a much larger number of transducers. In this paper, two procedures for measuring and analysing the complete spatial sound information are presented, which are aimed to create easy-to-understand images and videos showing the direction-of-arrival of the room reflections. The description of these techniques is emphasised. Furthermore, results are illustrated of experiments conducted with the novel methodologies in different rooms, including some ancient theatres.