Abstract: An electropneumatic acoustic horn is disclosed, comprising an electric compressor unit for generating compressed air and a sound wave generator comprising at least an acoustic chamber associated to at least a volute wound acoustic duct adapted to propagate the produced sound to the outside. Air channelling means put the compressor unit in communication with each acoustic chamber. The compressor unit and the sound wave generator are mechanically connected in a removable way by fitting slidingly a collar.

Abstract: A signal-horn has an electromagnetically actuated oscillating membrane coupled to an acoustic amplifier having a volute wound duct formed of a first length with generally constant section having an inlet for the sound signal and a second length with variable section in the form of a conical exponential having an outlet for the sound signal. The ratio of the figure representing the volume defined by the oscillating membrane between two points of maximum elongation and the figure representing the area of the cross section of the first length is between 16 and 20.