GB375994A - Improvements in and relating to sound emitting devices - Google Patents

Abstract

375,994. Sound magnifying and directing appliances. PINTSCH AKT.-GES., J., 71, Andreasstrasse, Berlin. June 22, 1931, No. 18041. Convention date, June 24, 1930. [Classes 13 and 118 (ii).] A sound emitter for use in air, emitting sound uniformly in all directions in a plane, comprises two electrically or otherwise operated units A, B having their diaphragms 1 excited at their natural frequency and arranged parallel and opposite to one another, the air space a between the units being pretuned to the natural frequency of the diaphragm vibrations. The distance between the units is made small relatively to the length of the waves emitted, and the diameter of the diaphragms is preferably at least half this wavelength. The shape of the air space a may deviate from that of a cylinder. Thus, Fig. 2, the diaphragms may be shaped so as to approach one another at the centre, or, Fig. 3, a member 3 may be disposed in the air space. Again, the air space may contain open-ended cones 4, Fig. 5, with or without funnels 6, which may alternatively be arranged as shown in Fig. 6. Fig. 7 shows the funnels 6 fed from a common source of sound. In another modification, each sound unit A, B has a common funnel fed from two diaphragms. A linear group of sound sources may be arranged to give a directional effect by spacing them apart at distances equal to half the wave-length of the sound emitted. Specification 180,357, [Class 118 (ii), Signals], is referred to.