An acoustic liner may include an acoustic core having an array of resonant cells, and an acoustic screen disposed across the array of resonant cells. The resonant cells include a plurality of cell walls and a resonant space defined by the plurality of cell walls. The acoustic core may include a folded acoustic core. Additionally, or in the alternative, at least some of the resonant cells may include an oblique polyhedral cellular structure and/or a multitude of sound-attenuating protuberances. The acoustic screen may include a reticulate membrane and a support lattice.