Patent GB-448864-A (GB)
Title: Improvements in or relating to apparatus for the production, reception, conduction, transmission, reproduction, and/or location of sound
IPC: H04R1/32
Filed: 1934-12-10
Abstract: 448,864. Acoustic horns; mouthpieces; microphones. STEUART, D. S. S., St. Mark's House, St. Mark's Square, and HAMILTON & BRANDON, N. B. M. DOUGLAS-HAMILTON, DUCHESS OF, 25, St. Edmund's Terrace, both in Regent's Park, London. Dec. 10, 1934, No. 35418. [Class 13] [See also Group XXXIX] A sound conduit, such as a horn, speaking tube, or mouthpiece, adapted to vary the intensity of sound passing therethrough. has a passage having three or more distinct portions which are constructed and arranged in such a way that substantially all lines which are normal to a suitably bounded plane or line generated surface which determines the width of the passage at its widest part or parts fall into two groups, the lines of one group, which may include lines continued by reflection from one or more of the surfaces of the passage, passing right through the passage and the lines of the other group, which are continued as reflecting lines to cross the first group of lines at right angles, having their further continuation through the passage prevented. In one embodiment of the invention, Fig. 2d (Comp.), the passage is constituted by cylindrical portions C1, C2 and a frusto-conical surface FC inclined at 45‹ to the axis of the passage. In addition, a double conical surface X is included in the wider part of the passage. The group of lines OA reflected at the surface FC and at the lower surface of the double conical member X pass through the smaller end of the passage, whilst the groups of lines MA, IA reflected at the surface FC and at the upper surface of the double conical member X cross at right angles the lines which pass through the passage. The wider end of the passage may be divided into a number of separate openings formed by partition members concentric with or parallel to, two or more portions of the outer boundary wall of the passage, and in such constructions one or more double conical members may be interposed on the central axis of the passage. Some of the arrangements are constructed to produce a multi-directional effect, and in such a passage formed by rotation of the section shown in Fig. 4a (Comp.) about lines a b or c d, lines o diagrammatically representing incident sound waves, entering at the smaller end are reflected by surfaces S1, S2 through portions W1, W1 of uniform width to outwardly inclined portions W2, W2 in which waves are stated to pass transversely of the waves issuing at the outlet. Modifications of Fig. 4a (Comp.) are described in which the sound waves are produced by two diaphragms of a moving-coil loud-speaker. In further multi-directional arrangements, the passage is constituted by two portions partially nested within each other, Figs. 4b, 8 (Comp.), (not shown). In a further arrangement, Fig. 6 (Comp.) (not shown) and Fig. 2 (Prov.), a mouthpiece for a carbon granule microphone is formed with concentric partitions 2, 3, 4, 5, 6 and 9, 10, 11 defining two passages 1, 8 which are associated with cylindrical sound receiving surfaces 20, 21, the electrodes of the microphone being constituted by cylindrical carbon members 17, 18 of which the latter is provided with a conical deflector 16.