Interlaboratory Comparison and Analysis of Bidirectional Scattering Coefficients for Various Surfaces

Accurate modeling of acoustic scattering is essential for realistic sound-propagation simulations in architectural environments. Traditional random-incidence models fail to represent directional scattering from structured surfaces, motivating the need for detailed bidirectional datasets. A reproducibility analysis of random-incidence and bidirectional scattering coefficient (BSC) measurements was conducted across two laboratories (RWTH Aachen University and The University of Sydney) using different free-field setups and two control surfaces—a 1D-sinusoidal and a 2D-rectangular profile. Measurements were compared with diffuse-field measurements (ISO 17497-1) and numerical simulations replicating the physical setups. Both laboratories produced consistent random-incidence scattering coefficients and BSCs for the 1D-sinusoidal surface. The 2D-rectangular surface showed larger deviations, attributed to edge effects and setup differences. Additional surfaces—including singular objects, random and modular geometries, and small-scale building façade elements—were measured or simulated. The method reliably captures directional scattering across various surface types. Setup geometry, edge effects, and signal-to-noise ratio were identified as key accuracy factors. The resulting coefficients together with its surface and setup descriptions provide a standardized foundation for future acoustic simulations and architectural applications.