  Recently, the higher-order topological phases from the chiral AIII symmetry
classes are characterized by a Z topological invariant known as the multipole
chiral numbers, which indicate the number of degenerate zero-energy corner
states at each corner. Here, we report the first experimental realization of
higher-order topological insulators protected by multipole chiral numbers with
using acoustic crystals. Our acoustic measurements demonstrate unambiguously
the emergence of multiple corner states in the middle of the gap, as predicted
by the quantized multipole chiral numbers. Our study may provoke new
possibilities for controlling sound, such as acoustic sensing and energy
trapping.
