A panel for attenuating noise is disclosed comprising a face skin having a first inner surface, a base skin having a second inner surface, a cellular core connected to and forming a plurality of cells between the face skin and the base skin, wherein the cellular core is defined by a cell structure having a plurality of cell walls extending between the face skin and the base skin defining each of the plurality of cells and a septum disposed within each of the plurality of cells, the septum defining an upper chamber proximate the face skin and a lower chamber proximate the base skin, wherein the face skin comprises a plurality of perforations fully through the face skin and in fluid communication with the upper chamber.