Patent GB-1500711-A (GB)
Title: Loudspeaker systems
IPC: A47B81/06
Filed: 1974-01-26
Abstract: 1500711 Loud-speakers I S TIEFENBRUN 24 Jan 1975 [26 Jan 1974] 03726/74 Headings H4J and H4X A loud-speaker system comprises a casing housing two loud-speaker diaphragms, one behind the other, so as to define between them an air chamber, the diaphragms in use being operated such that the air pressure in the chamber remains substantially constant. A sound absorbing curtain is located in the air chamber between the diaphragms. Cabinet 10 (Fig. 1) has an internal partition 12 defining chambers 14a, 14b. Mounted in chamber 14a on a front wall 16 is a bass loud-speaker 18 and mounted in chamber 14b on partition 12 is a bass loud-speaker 20. Each loud-speaker 18, 20 includes a conical diaphragm 22 mounted by a resilient surround 24 on a chassis 28 secured to the wall 16 or partition 12. Coils 32 wound on formers 26 are mounted in the annular flux gap of a permanent magnet assembly 38 and are driven independently but in phase. The rear chamber 14b may be a sealed chamber, transmission line, labyrinth or reflex cabinet. The upper and lower limits of the response may be tailored by separating the diaphragms by a distance which by virtue of the phase cancellation effects induced, enable elimination or reduction of complexity of a cross-over network where separate mid range units and treble units, or a combined mid/treble range unit, are also used. The magnetic fields of the speakers must not interact unfavourably but preferably the diaphragms 18, 20 are separated by considerably less than <SP>#</SP>/ 2  of the highest wavelength to be produced. Each chamber 14a, 14b may require a vent to equalize pressure changes brought about by atmospheric or temperature changes. The loud-speakers may be mid range/bass units or full range units. Additional treble and mid range units or a combined unit pointing in another direction may be used to give a unidirectional characteristic. Distortion components are absorbed by a curtain 44 of absorbent material. In a modification (Fig. 2, not shown) the housing (48) has a front flange (50) for mounting in a cabinet. The front bass driver (52) has no chassis and is mounted by a resilient surround (50) directly on the front of the housing (48). The magnet assembly is mounted on an apertured partition (62). A resilient suspension for the former is mounted on the magnet assembly and the leads from the coil are connected to the terminals (57) provided externally on the housing (48). A rear bass driver (58) identical to driver (52) has its magnet assembly secured to the rear wall (60) of the housing (48). The diaphragms have a curtain (55) between them. This wall has openings (66). The rear bass driver 58 has no chassis and its resilient surround is mounted on the side of the housing. A resilient suspension for the former is mounted on the magnet assembly. A housing 68 (Fig. 3) with an annular mounting flange 70 has two cones 72, 74 driven independently. Cone 72 has former 76 and cone 74 has former 78. The formers 72, 74 are located around a common central cone 80 of a permanent magnet assembly 82. The cones 72, 74 are mounted on housing 68 by a resilient suspension 88 and the formers 76, 78 are mounted on magnet assembly by suspensions 92, 94. The magnet assembly 82 is supported on the rear wall 104 of the housing 68. Wall 104 has apertures 106. The chamber defined between the cones has an absorbent curtain 108. A seal 110 extends between the cones 72, 74. Diaphragms of shapes other than conical (e.g. flat) may be used.