Patent GB-402847-A (GB)
Title: Improvements in or connected with loud speakers
IPC: H04R7/00
Filed: 1932-06-14
Abstract: 402,847. Loud - speakers. ALLEN, G. T., Kingsmead Hotel, Eastern Esplanade, Broadstairs, Kent. June 14, 1932, No. 16806. [Class 40 (iv).] Relates to a hornless loud-speaker comprising a frame or frames carrying a diaphragm or diaphragms of a flexible or elastic material under tension and a separate support, secured to a fixed frame or cabinet, carrying the actuating unit, the armature of said unit being connected to the centre of the diaphragm or diaphragms. According to the invention, the frame or frames carrying the diaphragm or diaphragms is or are coupled to the fixed frame or cabinet through a resilient or flexible connection, whereby the frame or frames can have a limited amount of movement relative to the actuating unit. Figs. 1 and 3 show a construction employing three diaphragms 1, 3 and 5. The diaphragms 1 and 3, which are preferably made of linen, are mounted on square or oblong frames 2, 4 and are tensioned by adjusting side extensions 7 of the frame 4 on threaded rods 8 projecting from blocks 9 on the frame 2. The diaphragm 5, which is preferably of pig's bladder or other thin strong skin, is mounted on a smaller circular frame 6. The frames 2, 4 and 6 are provided with slotted plates 14, 13 and vertical bars 12 respectively which are mounted on threaded cross rods 11 as shown, the ends of the rods 11 being mounted in pieces of resilient material 21, such as spongy rubber, located in holes 16b in the side members 16 of a further frame which may either engage in a cabinet or be provided with a base 16a to form a stand. A cross bar 17 carrying the actuating unit 18 is mounted on threaded rods 19 projecting from the side members 16. Figs. 4 and 7 show a modified construction employing a single frame for the diaphragms consisting of two side members 22, 23, each constructed from end plates 24, 25 secured at a distance apart by two rails 26, 26a and 27, 27a. The side members 22, 23 are held at an adjustable distance apart by threaded cross rods 29. The diaphragms are formed from a single tapered sheet of linen, one end of which is secured to the rail 27 and, after passing around the rails 26, 27a as shown, the other end is secured to the rail 26a thereby forming three differently sized diaphragms 30, 31, 32 which can be tensioned by adjusting the side members 22, 23 on the rods 29. The faces of the rails are preferably formed with undulated surfaces 28 so as to give the diaphragms corrugated surfaces. Each of the rods 29 is encircled by spongy rubber rings 33 around which are clamped spring clips 34, the free ends 34a of which are secured to cross members 35 secured to the top and bottom of the cabinet 36. The cross bar 17 carrying the actuating unit 18 is mounted on threaded rods 19 projecting from blocks 37 secured to the sides of the cabinet 36. Fig. 8 show a modification of the construction shown in Figs. 4 and 7 in which, instead of mounting the rods 29 on resilient supports, the end plates 24, 25 are connected on each side to soundboxes 38, 38 and these boxes are resiliently mounted in the cabinet 36 by cords or wires 39 secured to the top and bottom of the cabinet and to screw eyes 39a in the centre of each box. The diaphragms may be corrugated as described in Specification 340,374.