GB981729A - Loudspeaker system - Google Patents

Abstract

981,729. Stereophonic systems; loud-speakers; acoustic reflectors. D. K. GREENFIELD. May 7, 1962, No. 17506/62. Headings H4J, H4R and H4X. A stereophonic loud - speaker sys - tem comprises a central loudspeaker unit located between a pair of flanking loud-speaker units, the units all being arranged to direct sound away from a listening area towards a plane reflecting surface and each unit being sufficiently close to its adjacent reflecting surface for the sound waves from the unit to diffuse across the whole reflecting surface and to merge with the sound waves from the other units. A reflected wavefront is obtained such that the aural impression and perspective are substantially constant throughout the listening area. A stereophonic system comprises a central enclosure 20 (Figs. 1, 3) housing two loudspeakers 27 and two flanking enclosures 21, each housing a loud-speaker 26. The enclosures 20, 21 are close to a vertical wall 22. Audio-frequency signals from a source 36 are applied by cables 37, 38 to amplifiers 39, 40 and the entire frequency spectrum outputs of amplifiers 39, 40 are fed to loud-speakers 27. A capacitor (Fig. 4, not shown) restricts the signals applied to loud-speakers 26 to frequencies above about 200 to 250 cycles/second. The central enclosure 20 (Figs. 6, 7) comprises two symmetrical chambers separated by a partition 58 and a barrier 61 of resin impregnated glass wool which absorbs high and mid-range frequencies. In the bass frequency range the energy absortion decreases with decreasing frequency so that the back wave radiation from each loud-speaker increasingly loads the other. Reflexing ports 57 are provided. Barriers 60 of resin impregnated glass wool smooth the response below 40 cycles/second and absorb high and mid-range frequencies. One side panel 53 is shorter than the other side panels 50, 51 so that when the enclosure 20 is placed on the floor a third chamber is formed, together with a slot out of which the sound issues. Alternatively a bottom panel may be provided, the third chamber being formed between panel 54 and the bottom panel. The output of enclosure 20 is restricted to bass and mid-frequencies by the restricted volume of the third chamber, by the rear slot, by the restricted volume between panel 53 and wall 22 and by carpeting. The flanking enclosures 21 (Fig. 10) are identical. They are completely lined with absorbent material. At the front a plate glass baffle 25 is secured at the top by a nylon strap 69 and a metallic clip 70, and at the bottom by two metal clips 72 and nylon straps (not shown). The central enclosure 20 may be located on the floor 33 (Fig. 3) concealed from view beneath and behind a cabinet 34 which houses the flanking enclosures 21. A plurality of loudspeakers may be located in each symmetrical compartment of enclosure 20. The enclosures may be concealed above ceiling level. Other concealed arrangements are described.