Theoretical and experimental analysis of the diffuseness in room sound fields

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Room impulse responses have an extremely complicated fine structure as concerns temporal and spatial features. In applied acoustics, therefore, often the idea of a diffuse field is used. The theoretical concept of the diffuse field plays a very important role in room acoustics and in acoustic measurements in reverberation chambers. The objective in this project is the definition and experimental validation of a metric for characterization of the diffuseness at receiver positions in a room sound field in the sense of isotropy of incoherent sound waves and of decay curves. Parts of this project are arranged in collaboration with three partners (Rostock University, IRCAM Paris, and DTU Copenhagen). This proposal leads to the extension of knowledge by evaluating the Plane Wave Distributions in room sound fields depending on temporal and spectral filter approaches, by comparing efficient array signal processing methods, by exploration of the potential of the known spatial signal processing methods and extension towards spatial decomposition of Schroeder decay curves. Finally, the diffuseness metric for reverberation room qualification and calibration will be tested with statistical models in slightly varied source and microphone positioning (error sensitivity analysis) with the focus on measurement of absorption coefficients. In order to identify practical aspects such as the influence of the required spatial resolution and the (dodecahedron) loudspeaker directivity in such measurements, a high-order experimental system for MIMO (array-to-array) room impulse response measurement will be used. The results are relevant for array signal processing as well as for room acoustics in general, and for standard absorption measurements in particular.