Towards acoustic diffusers in realistic applications: free-field versus rigid baffle performance

Acoustic diffusers are commonly characterized under free-field conditions with ISO 17497-2. However, when applied as acoustic treatment in rooms, they are often placed over rigid surfaces, such as walls, which will likely alter the scattered sound field. This study investigates the impact of a rigid baffle on diffuser performance by comparing two diffusers under both free-field conditions and over a rigid baffle using the Boundary Element Method (BEM). A far-field point source is positioned at a distance of 100 m, while a hemispherical array of receivers at 50 m captures the scattered sound field. The analysis considers multiple angles of incidence and evaluates the 3D directivity and the resulting diffusion coefficient as metrics for performance assessment. The results provide insights into the influence of boundary conditions on diffuser effectiveness.