  Topological boundary and interface modes are generated in an acoustic
waveguide by simple quasi-periodic patternings of the walls. The procedure
opens many topological gaps in the resonant spectrum and qualitative as well as
quantitative assessments of their topological character are supplied. In
particular, computations of the bulk invariant for the continuum wave equation
are performed. The experimental measurements reproduce the theoretical
predictions with high fidelity. In particular, acoustic modes with high
Q-factors localized in the middle of a breathable waveguide are engineered by a
simple patterning of the walls.
