  Acoustic systems that are without limitations imposed by the Fermi level have
been demonstrated as significant platform for the exploration of fruitful
topological phases. By surrounding the nontrivial domain with trivial
"environment", the domain-wall topological states have been theoretically and
experimentally demonstrated. In this work, based on the topological crystalline
insulator with a kagome lattice, we rigorously derive the corresponding
Hamiltonian from the traditional acoustics perspective, and exactly reveal the
correspondences of the hopping and onsite terms within acoustic systems.
Crucially, these results directly indicate that instead of applying the trivial
domain, the soft boundary condition precisely corresponds to the theoretical
models which always require generalized chiral symmetry. These results provide
a general platform to construct desired acoustic topological devices hosting
desired topological phenomena for versatile applications.
