Abstract: A sound absorbing structure for a flow duct composed of a bundle of parallel, terminated, acoustical waveguides. The bundle of waveguides is cut obliquely so that the individual waveguides vary substantially in length along the cut. The bundle is arranged within a structure which is revolvable about its longitudinal axis. The exterior surface of the structure is spaced from the interior wall of the duct. The longitudinal axis of each of the waveguides is located substantially perpendicular to the axis of revolution. The structure revolves during passage of gas through the duct.

Abstract: An exhaust device is provided comprising a first diverging portion extending into a cylindrical envelope into which is axially displaceably mounted a streamlined conically shaped member adapted to be moved in relationship to the engine rating.

Abstract: The invention comprehends a sound proofed valve for fluid under pressure, comprising a movable obturator for progressively uncovering a series of fluid expansion orifices positioned inside an expansion area, a sound proofing means also positioned inside said expansion area and located opposite fluid jets issuing, in operation of said valve, from said orifices, and a permeable splash guard obstacle placed between said orifices and said sound proofing means and spaced from said sound proofing means.