A method for forming a fiber-reinforced thermoplastic acoustic panel may comprise: stacking plies of thermoplastic composite sheets to a first thickness to form a top sheet; stacking plies of thermoplastic composite sheets to a second thickness to form a backskin; staking plies of thermoplastic composite sheets to a third thickness to form a stiffening member; forming the top sheet in a first contour; forming the backskin in a second contour, the second contour being different from the first contour; forming the stiffening member comprising a shape having a plurality of peaks and troughs; bonding the stiffening member to the top sheet and the backskin; and perforating the top sheet.