Abstract: A sound-suppressing panel for use on the surface of a structure adjacent which a fluid is to flow. The panel includes a top sheet (which may be conveniently referred to as a cover) and a bottom sheet, and plurality of walls which are generally perpendicular to the two boundary sheets; the walls have various orientations and intersect one another at various locations so as to form cells which are similar to well-known "honeycomb" cells. Unlike true honeycomb formed by bees, the cells of an optimum construction according to this invention are not uniform. Ideally, there are at least three different cell sizes, and the cells are intermixed (side by side) so that the fluid passing adjacent the cover will sequentially encounter cells of differing sizes. Throughout the cover are provided a plurality of linear passages which permit the fluid which is flowing above the cover to communicate with the plurality of cells below the cover.