On the measurement of wave propagation in systems by means of spherical microphone array: a case study

The measurements of wave propagation in linear and non-systems represent an important research topic. The study of wave propagation becomes very important especially when related with sound propagation in enclosures, as pipes, theatres, and other electro-acoustic systems, that are normally considered non linear. In this article, a new method for recording the spatial properties of the wave propagation is described. The spatial distribution of air-pressure waves passing at a point in space is sampled by means of a number of virtual directive microphones, covering the surface of a sphere. This represents a discretization of the spatial information, which corresponds to the spatial equivalent of the PCM sampling of a waveform. In this article the measurements of air-pressure wave propagation in enclosures is analysed starting from a traditional b-format microphone , and compared with a 32-channels probe. The method is applied to a historical Italian theatre, located in Bologna, i.e. the 1763 theatre in Villa Mazzacorati. In order to properly evaluate the early components of the multichannel Impulse Response, a panoramic picture of the theatre was considered. On this picture, the early reflections were plotted into different circles on the figure, where the dimension and the intensity are related with the characteristics of the early components. Furthermore, also the influence of the height of the microphone in the calculation of the physical parameters was analysed. The measurements were repeated at different height and different position on a transversal line in the theatre, and statistically analysed. Key-Words: Wave propagation in systems; Spherical array probe; 3D Impulse Responses; Uncertainty; linear and non linear systems