Higher-order topological insulators have expanded the conventional bulk-boundary correspondence by hosting lower-dimensional boundary states, in which Benalcazar-Bernevig-Hughes model is pivotal in unraveling quadrupole topological phases in two-dimensional systems. Recent theoretical study has revealed that multilayer systems with engineered interlayer couplings can host a richer variety of topological phases compared to their monolayer counterparts. However, such multilayer Benalcazar-Bernevig-Hughes system with heterogeneous topological layers remains underexplored in experiments. Here, we experimentally realize a trilayer Benalcazar-Bernevig-Hughes sonic crystal comprising two topological nontrivial outer layers and a trivial middle layer. By modulating the interlayer coupling strength, we induce a topological phase transition characterized by the multipole chiral number and obtain hybrid topological corner states with different pressure field patterns. Leveraging 3D-printed cavity-tube structures, we experimentally observe these distinct acoustic corner states and distinguish them via the symmetric rules of the acoustic phase distributions. Our work not only establishes a framework for realizing multilayer topological systems, but also demonstrates the potential for designing topological acoustic devices.

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• Acoustic metamaterials
• Topological effects in acoustic systems
• Topological phase transition
• Tight-binding model