Birdseye view of flat plate (solid black bar), with sound source S (blue cross), image source S’ (faint blue cross) and two receiver positions R1 and R2 (red circles). Paths between (image) source and receivers are shown via the geometrical reflection points P1 and P2 (virtual, outside the physical plate), and the reflection point P2* constrained to the plate. The angle γ between the reflection paths and the plate normal are shown for P1 and P2*.