Objective and perceptual evaluation of distance-dependent scattered sound effects in a small variable-acoustics hall

Performance spaces are characterized by a complex sound field, due to the presence of absorptive and diffusive surfaces. In situ evaluations of the acoustic effects that these surfaces have on the objective acoustic parameters and on sound perception have not yet been fully understood. To this aim, acoustic measurements have been performed in a variable-acoustic concert hall, the Espace de Projection, at the Institut de Recherche et Coordination Acoustique/Musique. These measurements have allowed the effects of one single wall to be determined. A diffusive and a reflective condition of one of the long lateral walls of the shoebox-like hall have been considered, while the other surfaces have been fixed in absorptive mode. 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 early decay time, reverberation time (T₃₀), clarity (C₈₀), definition (D₅₀), and interaural cross correlation, have been compared between both conditions. In addition to the objective indexes, a perceptual evaluation has been performed using listening tests that had the purpose of determining the maximum distance from a diffusive surface at which acoustic scattering effects are still audible.