Recently, the non-Hermitian skin effect (NHSE) has attracted significant interest in condensed-matter physics due to its distinctive phenomenon of the bulk states’ localization at boundaries. With the establishment of non-Bloch framework, the NHSE can be characterized accurately using the generalized Brillouin zone in one-dimensional systems, and classified into $\mathbb{Z}$ and ${\mathbb{Z}}_2$ skin effects based on their current functional. Here, we experimentally demonstrate a 1D ${\mathbb{Z}}_2$ NHSE in a passive acoustic system using a bilayer sonic crystal with tailored lossy couplings. By introducing an artificial gauge field via staggered interlayer couplings, we establish spinful anomalous time-reversal symmetry, while tunable dissipation, implemented by sound-absorbing sponges in intracell coupling tubes, enables the ${\mathbb{Z}}_2$ NHSE. We observe spin-polarized skin localization, where spin-up and spin-down states accumulate sound at opposite ends of the structure. This effect is confirmed through band dispersion, spatial field mapping, and transmission spectroscopy. Our Letter presents the first purely passive platform for the ${\mathbb{Z}}_2$ NHSE in acoustics, opening avenues for spin-momentum locked wave control in non-Hermitian topological metamaterials.

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• Acoustic metamaterials
• Acoustics
• Non-Hermitian systems
• Topological materials