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.

Abstract: The invention relates to a signal-horn (1) of electromagnetic type comprising a generator (2) of sound waves having an oscillating membrane (4) actuated by an electromechanical propulsor unit (5) coupled to an acoustic amplifier (3) consisting of a duct (6) wound as a volute in which there is a first length (7) with generally constant section (8) provided with an inlet (9) for the sound signal to be amplified and a second length (10) with variable section (11) according to a conical exponential rule ending with an outlet (12) for the amplified sound signal. The ratio of the figure representing the volume (13) defined by the oscillating membrane (4) between the two points of maximum elongation (14, 15) and the figure representing the area of a cross section (8) of the first length is a number comprised between 16 and 20.

Abstract: An improved acoustic unit base for electropneumatic horns, of the type comprising a main body peripherally seamed to an end piece with a diaphragm therebetween. Said main body is formed by connecting together a first and a second member of deep-drawn sheet metal, the first comprising a central hole and the second forming a cylindrical seat for receiving a bush with a lipped opening which rests on the diaphragm.