Abstract: A device for simulating sound produced by certain equipment, for example a rotor-stator arrangement of a turbomachine, or for generation of opposing sound fields for active sound control, including active sound reduction and active sound amplification, comprises flow obstacles (2) provided in a flow duct (1) flown by a fluid at which vortices (5, 6) are shed at a certain frequency depending on the shape and size of the flow obstacles and the velocity of flow. The quantity and spatial arrangement of the flow obstacles is selected such that a periodically spatially and temporally changing pressure field for the excitation of a sound field (8) of a certain modal content is produced by the entirety of the vortices shed. This sound field reacts synchronizingly on the vortex shedding. The resonant circuit so formed, whose vortex shedding frequency is in the range of the resonant frequency of the sound field to be excited, is the sound source.

Abstract: An aircraft comprising an aeroengine and a noise reflective surface, the aeroengine capable of generating a hot exhaust jet and noise characterised in that the reflective surface is profiled to reflect noise from the aeroengine into the hot exhaust jet thereby attenuating reflected noise.