Abstract: The invention relates to a Helmholtz resonator (6) for damping airborne sound in a space, particularly in a conduit (4, 5) transporting airborne sound, comprising a housing (8) surrounding a resonance volume (9), comprising at least one neck (10) for connecting the resonance volume (9) to the space or to the conduit (4, 5) transporting the airborne sound. The Helmholtz resonator (6) obtains at least two resonance frequencies if the housing (8) has at least one wall section delimiting the resonance volume (9), said wall section being formed by a vibratory membrane (11), and if the membrane (11) is tuned such that the resonance frequency thereof corresponds to the first order of the resonance frequency of an identically constructed Helmholtz resonator that does not have such a membrane (11).

Abstract: Plastic parts are formed to have a relatively high wall stiffness by utilizing a pair of spaced plastic plates. One of the plates may be a simple plate. The other plate has a plurality of ribs extending from a base. The ribs are welded to the other plate. Use of the ribs provides a relatively high degree of stiffness to the final molded plastic part, for a relatively lightweight part.

Abstract: Plastic parts are formed to have a relatively high wall stiffness by utilizing a pair of spaced plastic plates. One of the plates may be a simple plate. The other plate has a plurality of ribs extending from a base. The ribs are welded to the other plate. Use of the ribs provides a relatively high degree of stiffness to the final molded plastic part, for a relatively lightweight part.