GB473806A - Improvements in sirens - Google Patents

Abstract

473,806. Foghorns. EKMAN, O. I. H. Oct. 29, 1936, No. 29427. Convention date, Oct. 29, 1935. [Class 13] [Also in Group XXXIX] In a foghorn operated by compressed fluid, a plurality of diaphragms, vibrated either in groups or simultaneously, form parts of the wall of a receptacle for the fluid and are alternately subjected to the pressure prevailing in the receptacle and relieved from the pressure by a rotatable slide valve located adjacent the wall. As shown, the valve comprises a central portion 4 mounted on a rotatable shaft 5 and an annular portion formed with apertures 6 alternating with radial grooves 7 which co-operate with radial passages 8 in the wall of the receptacle 1 to relieve the pressure to which the diaphragms 9 have been subjected. The diaphragms 9 which are supported on projections 18, 19 carried by a fixed central portion 10 and a flanged portion 12 of the casing 2, are formed with bent-up outer ends clamped between members 13, 14, Fig. 6, which are adjustably secured to the flange 12 by bolts 16. The central portion 10 is connected to the portion 12 by wedge-shaped beams 20 which are located between successive diaphragms 9 and form sound-projection channels communicating with the space between walls 21, 22 terminating in a horn which is preferably rotatable. In one modification, Figs. 7, 8 (not shown), the width of the apertures 6 and grooves 7 is substantially less than that of the diaphragms 9 with the object of providing an arrangement to produce a sound of increased frequency, and in a further modification, Figs. 10, 11 (not shown), the slide valve has four equally spaced apertures 6 which co-operate with twenty diaphragms 9, the pressure on any diaphragm between its successive actuations being relieved by the provision of a small hole under the edge of the diaphragm. In a further modification, Fig. 9 (not shown), in which the widths of the diaphragms 9 and apertures 6 are approximately equal, the supporting members 20 are provided with projections which limit the application of the pressure to the central portion of each diaphragm.