Abstract: The propagation of sound in flow channels is attenuated by a sound attenuating box comprised of cell-like chambers each with a bottom, an outer plate and a partition with an opening spaced from the outer plate such that the Helmholtz resonator established by the sub-chamber between the bottom and the partiton as well as by the opening is positively coupled to the outer plate as far as vibrations in the audible range are concerned through air flow through the openings and in the subchamber between partition and outer plate. The chambers share appropriately side walls, bottoms, partitions as well as aperture plates, and outer plates.