Abstract: A noise attenuating device for reducing the noise generated by a gas flow passing through an open butterfly valve having a disc pivotally mounted in a valve housing for rotation about a transversal axis between an open and a closed position thereof. The noise attenuating device comprises a first series of elongated members extending from the upstream side of the disc above the transversal axis and a second series of generally diametrically opposed elongated members extending from the downstream side of the disc below the horizontal axis. Typically, the elongated members extend at 45 degree from the disc of the butterfly valve.

Abstract: A sound suppressor liner for aircraft exhaust passages is described which is based on the Helmholtz resonator principle including an inlet passage leading into a closed cavity wherein the inlet passages defined by a pair of curved walls with one wall being concave and the other wall being convex and the space between the walls gradually diminishing from the inlet of the inlet passage to the outlet within the cavity in a sense simulating an acoustic horn in reverse.