Topological interface states exhibit exceptional potential for robust sound transmission, owing to their distinctive topological characteristics. However, current studies are primarily concentrated on the sound transmission along well-defined passages, disregarding the potential significance of multichannel energy transfer between coupled topological interface states. In this work, by introducing coupled interface states in $C_4$-rotationally symmetric composite sonic crystals, we experimentally observe the topological energy transfer between adjacent channels for both symmetric and antisymmetric interface states. Leveraging the varied coupling wavelengths of interface states, we implement a functional acoustic frequency splitter that spatially splits acoustic signals of different wavelengths into different waveguide channels. Interestingly, the mirrored topological channels support the propagating eigenmodes with recognizable symmetries, creating the opportunity for selective acoustic transmission and communication. Our work offers unique strategies to precisely control the topological interface state transport in sonic crystals, enabling advanced acoustic devices, such as directional couplers, wavelength demultiplexers, and acoustic signal processors.

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• Acoustic signal processing & noise
• Crystal symmetry
• Symmetry protected topological states
• Topological effects in acoustic systems
• Acoustic metamaterials
• Interfaces
• Phononic crystals
• Topological insulators