  Inspired by the discovery of quantum hall effect and topological insulator,
topological properties of classical waves start to draw worldwide attention.
Topological non-trivial bands characterized by non-zero Chern numbers are
realized with external magnetic field induced time reversal symmetry breaking
or dynamic modulation. Due to the absence of Faraday-like effect, the breaking
of time reversal symmetry in an acoustic system is commonly realized with
moving background fluids, and hence drastically increases the engineering
complexity. Here we show that we can realize effective inversion symmetry
breaking and effective gauge field in a reduced two-dimensional system by
structurally engineering interlayer couplings, achieving an acoustic analog of
the topological Haldane model. We then find and demonstrate unidirectional
backscattering immune edge states. We show that the synthetic gauge field is
closely related to the Weyl points in the three-dimensional band structure.
