Acoustic Orbital Angular Momentum Hall Effect at Metasurfaces

We report the first direct experimental observation of the acoustic orbital Hall effect at metasurfaces using airborne vortex beams generated by a four-speaker source. Unlike traditional geometric or topological descriptions, we directly measure Hall-induced extrinsic orbital angular momentum (OAM) as a signature of twist-dependent Imbert-Fedorov shifts of the refracted beam. Through field decomposition, we reveal the coexistence of transverse energy flow and reconstructed axial angular-momentum symmetry, providing insight into extrinsic and intrinsic OAM in realistic systems beyond shift-based or topological arguments. In addition, we observe a geometric Hall effect in the tilted refracted beam. This Letter establishes a framework for measuring and interpreting acoustic Hall phenomena and advances emerging OAM-metasurface applications.