Measurement traceability of sound scattering coefficient of diffusive surfaces used in room acoustics and virtual acoustical environments

The best concert halls take benefit not only from the basic room shape but also from the corrugations of the walls. These diffusive surfaces are responsible for energy mixing, energy extraction from geometrical paths, for filling gaps and increasing reflections density in the impulse response. Hence, performance spaces are characterized by a complex sound field, due to the presence of absorptive and diffusive surfaces. The acoustic properties of these surfaces are characterized based on laboratory standardized measurements. Despite this, no sufficiently satisfactory databases exist. Thus, acousticians and practitioners alike rely on guidelines and experience to make their design choices. Based on this state of the art of diffusive surface design, the present work aims at giving more insight on their deployment by looking at the argument from a multidimensional point of view. First, it considers the estimation of the accuracy of the physical phenomenon measurements (only the random-incidence scattering coefficient has been considered), and further studies the effects of this accuracy on the objective room acoustic parameters, on the accuracy of simulation results and on perception. Knowing this interactions would give a measure of how much effort should be put into the acoustic characterization of diffusive surfaces and more freedom/ restrictions regarding the design of such surfaces could be determined. In Chapter 2, the experimental results aimed at providing a useful insight into the accuracy of the measurement procedure prescribed in the ISO 17497-1:2004 standard. The unsolved aspects of the measurements set-up have been systematically investigated and their contribution to the random-incidence scattering coefficient values has been estimated. It was found that some of these aspects contribute significantly to the measurement accuracy. In Chapter 3, in-situ evaluations of the acoustic effects that diffusive surfaces have on the objective room acoustic parameters have been investigated. To deepen such knowledge, acoustic measurements have been carried out in a variable-acoustic concert hall, the Espace de Projection, at the Institut de Recherche et Coordination Acoustique/Musique in Paris. The sensitivity of the sound field has been objectively investigated by observing the variation of the objective acoustic parameters, that is EDT, T30, C80, D50 and IACC, in either reflective and diffusive condition. It was found that some parameters are more affected by the degree of surface diffusivity, thus, its accuracy. In Chapter 4 has been investigated objectively the sensitivity of a virtual room sound field to the scattering coefficients accuracy. Two different prediction models have been used to simulate the sound field within a fan-shaped hall. It was found that some simulated parameters are affected by the random-incidence scattering coefficient accuracy, i.e. uncertainties of input data, which are higher than a limit value, lead to less reliable simulation results. In Chapter 5, an auditory experiment has been conducted to highlight some perceptual aspects regarding the use of diffusive surfaces in concert halls. These results provide more insight and help to understand whether listeners perceive the presence of diffusive surfaces, and how this perception is scattered throughout the audience area. Furthermore, the study is aimed at determining the objective measurements of a sound field which best correlate to the subject’s perception. This would give the measure of how much effort should be put into the determination of the diffusive properties of surfaces, and which could be the variables to relate in an analytic equation, which could readily express the effects of diffusion in room acoustic