Here, we propose an isospectral reduction (IR) approach for the mapping of a trimer Su-Schrieffer-Heeger (SSH3) lattice into a simplified two-site model, whose coupling dynamics ingeniously results in a precise bulk-edge correspondence of the original lattice. The isospectrally reduced model has intercell couplings with dynamic response to the eigenstate energy, allowing for the control of topological phase transition by energy. We relate the bulk property of the reduced model to the band topology of the SSH3 lattice, allowing for three distinct topological phases with a different number of topological edge-state pair. An acoustic SSH3 chain is fabricated for experimental demonstration. The said topological edge-state pairs are measured. Our study takes a pivotal step toward the exploration of topology in multiple wave systems, opening up possibilities for advanced control of topological waves.

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• Acoustic metamaterials
• Edge localized mode
• Geometric & topological phases
• Topological effects in acoustic systems
• Su-Schrieffer-Heeger model
• Tight-binding model
• Topological tools