  We introduce the acoustic equivalent of 'supercoupling' by studying the
anomalous sound transmission and uniform energy squeezing through ultranarrow
acoustic channels filled with zero-density metamaterials. We propose their
realization by inserting transverse membranes with a subwavelength period along
the channel, and we prove a novel form of acoustic tunneling based on impedance
matching and infinite phase velocity at the zero-density operation. We envision
applications in sensing, noise control, cloaking and energy harvesting.
