A passive acoustic liner system (50) for attenuating a sound field comprising, in acoustic series, a mode-scattering segment (48) and a sound-absorbing segment (40), wherein the mode scattering segment (48) provides a reactance between -12 and -2 .rho.c and the sound absorbing segment (40) provides a reactance between -1 and 0 .rho.c thereby providing a reactance discontinuity such that mode-scattering of the sound field enables the sound-absorbing segment (48) to further absorb the scattered sound.