Abstract: A porous acoustic element is disclosed having a configuration comprised of individual cross-wound porous layers of widely varying porosity, with transition plenum layers interposed therebetween having a configuration so as to prevent formation of blockages and small area openings which would be created by a direct overlay winding of differing pitch. The porosity of each wound layer increases in successive layers to compensate for expansion of the gas as it flows through the element. The resulting porous element allows gaseous flow therethrough, with maximum pressure energy dissipation and controlled velocity to minimize aerodynamic noise created by flow through valves and other flow restrictions. A specific embodiment is disclosed in which the porous layers are created by variable pitch wire ribbon cross windings and the transition layers are provided by wire mesh having relatively large openings.

Abstract: A porous laminate is disclosed consisting of a plurality of lamina each having a parallel slot series formed therein, stacked with the respective adjacent slot series overlapping and extending transversely to each other and bonded to each other to form the porous laminate. Variations disclosed include tapering the slots in one or more of the lamina to create a variable porosity and the inclusion of tying sections at intermediate points along the slots for reinforcement purposes.The disclosed process includes the steps of photoetching metal sheets to create the slot pattern, stacking a plurality of the sheets together with the slots in adjacent sheets extending transversely to each other, diffusion bonding the stacked sheets to form a porous laminate, and calendering the finished sheet to modify or adjust permeability.