Three-dimensional directivity measurement of acoustic diffusers using regularized holography and sound field separation

Characterizing acoustic diffusers poses significant challenges due to the complex space-time dependence of the scattered sound fields they generate. This study proposes using regularized plane wave expansion to measure real-sized rigid diffusers in free-field. The formulated inverse problem enables the separation of incident and scattered sound fields in the wave-number domain. Furthermore, a tailored wave-number grid facilitates the computation of three-dimensional directivities directly identified in the wave-number spectrum. The proposed technique is validated through measurements conducted in the near field of three diffusers with distinct geometries. The results obtained from regularized plane wave expansion were compared against reference simulations using the Boundary Element Method. The unique directivity characteristics of different diffusers are accurately characterized, and good agreement is found with the reference simulations. The use of finer spatial resolution and 1/3-octave band averaging further improves the reliability of directivity and diffusion coefficient estimates. Thus, the method provides an alternative path for a robust and more practical characterization of acoustic diffusers.