  In this paper, we report on the design, fabrication, and experimental
characterization of a 3D single-port labyrinthine acoustic metamaterial. By
using curled perforations with one end closed and with appropriate loss inside,
the proposed metamaterial can perfectly absorb airborne sounds in a low
frequency band. Both the position and width of the band can be tuned flexibly.
A tradeoff is uncovered between the relative absorption bandwidth and thickness
of the metamaterial. When the relative absorption bandwidth is as high as 51%,
the requirement of deep subwavelength thickness (0.07{\lambda}) can still be
satisfied.
