Modeling sound transmission through apertures with diffraction

Sound transmission through an aperture in a thin wall is a classical scattering problem with various applications in building and room acoustics. In particular, the use of active noise control for open windows can be viewed as an aperture scattering problem. Diffraction-based modeling of scattering is very efficient and accurate for convex scattering objects but has been shown to be less accurate for the transmission through circular apertures, at low frequencies. In this study we investigate the accuracy of edge-diffraction based modeling of sound transmission through rectangular apertures. Reference solutions are computed with a boundary element formulation for this case. Results confirm that the diffraction modeling gives accurate results for mid-to-high frequencies. For low frequencies and skewed transmission angles, the diffraction-based method gives larger errors. For aspect ratios between 1:1 and 10:1, the sound power transmission ratio predicted by the edge diffraction approach is maximally ±1.5 dB in error for very low frequencies.