Patent GB-439561-A (GB)
Title: Improvements in or relating to acoustic reproducers
IPC: H04R9/04
Filed: 1934-03-19
Abstract: 439,561. Loud-speakers. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of Ringel, A. S.) March 19, 1934, No. 8631. Convention date, March 17, 1933. [Class 40 (iv)] The driving system of a moving coil sound-reproducer comprises at least two coil sections each mounted upon a section of a common coil former, the sections of the former being connected together by compliant coupling means so that one coil section is effective to drive the diaphragm system at lower audio frequencies only. Fig. 1 shows a construction of loudspeaker employing a diaphragm system consisting of a high frequency portion 19 directly connected to or formed integrally with the coil former and a low frequency portion 18 connected to the coil former through a compliant coupling 20. A small opening 21 in the apex of portion 19 provides access to the screw for securing the centring spider 15 to the central magnet pole 10. The coil former itself consists of two portions 34, 35 connected by a compliant coupling such as the corrugation 36 the part 34 carrying a high frequency winding 37 composed of a small number of turns of aluminium wire whilst the part 35 carries a low frequency winding 38 composed of a larger number of turns of preferably copper wire. The windings are connected in series or parallel and fed from a source AFS through high pass and low pass filters 39, 40 respectively. According to a modification, Fig. 2 (not shown), a small horn may be supported above the diaphragm portion 19 which, according to a further modification, Fig. 3 (not shown), is made somewhat larger than in the form shown in Fig. 1 and is connected to the coil former by a further frusto-conical portion. The driving system shown in Fig. 1 may also be used to drive an ordinary frustoconical diaphragm. Fig. 5 shows a further construction in which the diaphragm portion 18 is itself formed as an exponential horn, the corrugation 36 is arranged to extend inwardly and the magnet poles 10, 11 are cut away at 41, 42. According to a further modification, Fig. 7 (not shown), the diaphragm portion 18 is divided into two frusto-conical portions interconnected by compliant coupling means and the coil former is divided into three portions interconnected by compliant coupling means and carrying a high frequency winding. an intermediate frequency winding and a low frequency winding respectively. The Specification as open to inspection under Sect. 91 comprises also a construction, Fig. 11 (Cancelled), in which in order to prevent breakage of leads due to the relative movement between the respective windings, the coil former is made of conducting material and is divided by two longitudinal cuts or slots 134 into two semi-cylindrical sections 136, 138 having compliant coupling means 132 formed therein. The leads 144 form the source AFS are stapled at 146 to the diaphragm 112 and one of the leads is connected at 148 to one terminal of the high frequency winding 130 whilst the other is connected at 150 to coil former section 136. The other terminal of winding 130 is connected at 152 to coil former section 138 and the terminals of the low frequency winding 128 are connected to sections 136, 138 at 154 and 156 respectively. When it is desired to limit the frequency range at its upper end, the diaphragm system 205 may be connected to the driving system 206 as shown in Fig. 12 (Cancelled), by a flexible member 213 consisting of a cylindrical portion 214 secured to the coil former, an annular portion 215 and a conical portion 216 secured to the diaphragm. The member 213 instead of being formed as a separate member as shown may be formed as a continuation of the diaphragm, coil former or centring spider. Modifications of this arrangement are also described in which the portion 216 is increased in mass so as to load the cone and in which the compliant coupling consists of corrugations in the apex of the cone or of corrugations in both the apex of the cone and in the inner end portion of the coil former. The diaphragm systems of Fig. 1 and Figs. 2 to 4, (not shown), are also described with a single coil drive. This subject-matter does not appear in the Specification as accepted.