An acoustic liner is provided. The acoustic liner includes a face sheet, a back sheet spaced from the face sheet, and a core layer defining a cellular structure disposed between the face sheet and the back sheet. The core layer includes a plurality of first resonant cells coupled to the back sheet. Each of the first resonant cells includes a first cell wall coupled to the back sheet along a first cell wall base edge, the first cell wall extending from the back sheet toward the face sheet, the first cell wall further coupled to the face sheet along a first cell wall top edge, wherein the first cell wall of each of the first resonant cells comprises a surface extension that extends from a surface of the first cell wall.