New measurement technique for 3D sound characterisation in theatres (plenary lecture)

The definition and measurement of 3D properties of the sound field has been strongly improved in last years, as nowadays spatial properties of sound propagation are considered quite important during design of theatres and auditorium. Besides, a proper assessment of the degree of spatial accuracy is requested during sound reproduction inside 3D listening rooms, initially designed for acoustical virtual reality, but nowadays being employed also in the entertainment/cinema industry (Immsound, Auro-3D, NHK 22.2). Normally, only monoaural or binaural measurements are performed, by means of omni-directional microphones and dummy heads, even though international standards like ISO 3382/1:2009 require measuring some spatial parameters (i.e. IACC, LE, LF): the last two parameters require to be measured with a pressure velocity (p/v) microphone, but still it is a 2-channels measurement only. 3D impulse responses are rarely measured and employed for sound reproduction. In this paper, an innovative procedure for measuring and analyzing the complete spatial sound information is presented. The description of this new technique is emphasized. Furthermore, the results of a wide campaign of measurements of spatial parameters among different rooms, including some ancient theatres, conducted with the novel methodology, are compared with the results of standard binaural and p/v measurements. The possibility to capture the complete spatial information in real spaces and the significance of 3D spatial parameters is then considered and presented in different cases.