An acoustic liner (22; 22") comprising: a first panel (38"); a permeable panel (40") spaced from the first panel (38"); a first wall (46") located between the first and permeable panels (38", 40") and facing in a first direction away from the first panel (38"), wherein the first wall (46") is non-permeable; and a permeable wall (54") located between the first and permeable panels (38", 40") and facing in a second direction away from the first panel (38") and traversing the first direction; and a plurality of sidewalls spaced from one-another, extending between and engaged to the first panel (38") and the permeable panel (40"), and through the first and permeable walls (46", 54"); wherein each one of a plurality of cells (52a", 52b", 52c") are defined between the first and permeable panels (38", 40") and adjacent sidewalls of the plurality of sidewalls, and the first and permeable walls (46", 54") are each one of a plurality of first and permeable walls (46", 54") with each one of the plurality of first and permeable walls (46", 54") being generally in a respective one of the plurality of cells (52a", 52b", 52c"); wherein the plurality of permeable walls (54a") each have opposite first and second edges (56a"; 58a") with the first edge (56a") engaged to the first wall (46a") and the second edge (58a") engaged to the permeable panel (40"), and the plurality of first walls (46") each have opposite first and second edges (48, 50) with the first edge engaged to the first panel (38") and the second edge engaged to the permeable panel, characterised in that: at least one of the first edges (56a") of the plurality of permeable walls (54a") is engaged to a respective first wall (46a") at a position spaced from the first panel (38"). a first panel (38"); a permeable panel (40") spaced from the first panel (38"); a first wall (46") located between the first and permeable panels (38", 40") and facing in a first direction away from the first panel (38"), wherein the first wall (46") is non-permeable; and a permeable wall (54") located between the first and permeable panels (38", 40") and facing in a second direction away from the first panel (38") and traversing the first direction; and a plurality of sidewalls spaced from one-another, extending between and engaged to the first panel (38") and the permeable panel (40"), and through the first and permeable walls (46", 54"); wherein each one of a plurality of cells (52a", 52b", 52c") are defined between the first and permeable panels (38", 40") and adjacent sidewalls of the plurality of sidewalls, and the first and permeable walls (46", 54") are each one of a plurality of first and permeable walls (46", 54") with each one of the plurality of first and permeable walls (46", 54") being generally in a respective one of the plurality of cells (52a", 52b", 52c"); wherein the plurality of permeable walls (54a") each have opposite first and second edges (56a"; 58a") with the first edge (56a") engaged to the first wall (46a") and the second edge (58a") engaged to the permeable panel (40"), and the plurality of first walls (46") each have opposite first and second edges (48, 50) with the first edge engaged to the first panel (38") and the second edge engaged to the permeable panel, characterised in that: at least one of the first edges (56a") of the plurality of permeable walls (54a") is engaged to a respective first wall (46a") at a position spaced from the first panel (38").