Objective and perceptual evaluation of acoustic scattering from a variable-acoustic wall in a small hall

The presence of interior surfaces with different sound absorbing and sound diffusing properties contribute to the generation of a complex sound-field inside the performance spaces. In-situ evaluations of the acoustic effects that these surfaces have on the objective acoustic parameters and on the sound perception have not yet been fully understood, and further research on this matter is necessary. To this aim, acoustic measurements have been made in a variable-acoustic concert hall, the Espace de Projection, a small performance space at the Institut de Recherche et Coordination Acoustique/Musique in Paris. The diffusive and a reflective condition of one of the long lateral walls of the shoebox-like hall has been considered in this experiment, while the other surfaces have been fixed in an absorptive condition. Measurements have been carried out at different distances from the test wall, using an artificial head and an array of omnidirectional microphones. Objective acoustic parameters, such as EDT, T30, C80, D50 and IACC, have been compared for both conditions. In addition to the objective indexes, a perceptual evaluation has been performed through listening tests using the 3AFC method. The purpose was determining the maximum distance from the lateral wall at which acoustic scattering effects are still audible.