GB1403354A - Loudspeaker cabinets - Google Patents

Abstract

1403354 Loud-speakers S Z M GABR 15 Aug 1972 [25 May 1971] 16964/71 Headings H4J and H4X A loud-speaker cabinet 12 (Fig. 1) has two or more acoustically distinct compartments 14, 16, 18, 20 each mounting one or more loud-speakers. At least one of the compartments is in acoustic relationship with a cavity the resonant frequency of which can be selectively adjusted. Each compartment provides loading for one or more loud-speakers 22, 26, 28, 30 mounted thereby over a respective part of the frequency range. The lowest compartment 20 receives a loud-speaker 22 for operation in the range 20 to 200 Hz compartment 18 and loud-speaker 26 are for operation in the range 200 to 3000 Hz while compartments 16 and 14 receive loud-speakers 28 and 30 suited to frequency ranges 3000 to 7000 Hz and 7000 to 20,000 Hz respectively. A tuning device 32, 34, 36, 24 may be provided in each compartment to ensure maximum efficiency. Device 24 (Fig. 2) is a block of moulded or extruded plastics material, or chipboard, having parallel bores 40 extending from one end to the other. Bores 40 can be connected together by U-shaped plastics tubes 42, and in addition the effective lengths of other bores can be controlled by plugs or plungers 44. The adjustment may be made by the listener or each compartment may be tuned during manufacture and then secured in place. The adjustment means may be accessible externally of the cabinet. Preferably the cabinet is tuned with the characteristics of other equipment (tuner, tape recorder, record player, preamplifier, main amplifier) in mind. The loudspeaker apparatus can be tuned to suit the characteristics of a particular room and the adjustment means then locked. Two or more tuning devices, tuned to different frequencies, can be associated with each compartment. A block or panel tuning device 46 (Fig. 1) may form part of the cabinet. One or more panels of the cabinet may have battens received in slots (Fig. 3, not shown) parallel to one another or arranged in a grid pattern, the assembly being held together and at least superficially impregnated with plastics material, e.g. acrylic resin or polymethyl methacrylate sprayed in a liquid state. Recesses formed between battens are filled with sound absorbent material. The panels may be of chip-board. Preferably no electrical cross-over network is provided, the compartments acting as crossover means. The loud-speakers may be connected in series or parallel and their impedances can be chosen or adjusted by additional circuit elements to obtain a desired power distribution over the audio-frequency range. Alternatively the loud-speaker or loud-speakers of each compartment can be connected to a separate amplifier arranged to amplify only the frequency range concerned.