  If a full band gap closes and then reopens when we continuously deform a
periodic system while keeping its symmetry, a topological phase transition
usually occurs. A common model demonstrating such a topological phase
transition in condensed matter physics is the Su-Schrieffer-Heeger (SSH) model.
As well known, two distinct topological phases emerge when the intracell
hopping is tuned from smaller to larger with respect to the intercell hopping
in the model. The former case is topologically trivial, while the latter case
is topologically non-trivial. Here, we design a 1D periodic acoustic system in
exact analogy to the SSH model. The unit cell of the acoustic system is
composed of two resonators and two junction tubes connecting them. We show that
the topological phase transition happens in our acoustic analog when we tune
the radii of the junction tubes which control the intercell and intracell
hoppings. The topological phase transition is characterized by the abrupt
change of the geometric Zak phase. The topological interface states between
non-trivial and trivial phases of our acoustic analog are experimentally
measured, and the results agree very well with the numerical values. Further,
we show that topologically non-trivial phases of our acoustic analog of the SSH
model can support edge states, on which the discussion is absent in previous
works about topological acoustics. The edge states are robust against localized
defects and perturbations.
