Patent GB-1462919-A (GB)
Title: A loudspeaker cabinet
IPC: H04R1/30
Filed: 1974-07-24
Abstract: 1462919 Loudspeakers NECKERMANN VERSAND KGAA 24 July 1974 [27 July 1973] 32764/74 Headings H4J and H4X An exponential loudspeaker cabinet has a front wall 2 (Fig. 1), a back wall 3 and an intermediate wall 7. The front wall 2 defines a first sound exit hole 6 and at least one further sound exit hole 15, 16 (Fig. 2). Subsidiary walls 11, 20, &c. (Fig. 3) between the walls 2 and 7 provide a pressure chamber 27 and a spirally extending first portion of a substantially exponential horn. The first portion extends from the pressure chamber 27 via an aperture 17 in intermediate wall 7 to a sound passage 13, 13a (Fig. 4) defined between the intermediate wall 7 and the back wall 3. One of the subsidiary walls 8 is an inclined wall which assists in forming the end of the exponential horn. Two or more loudspeakers 18, 19 have diaphragms which radiate sound into the pressure chamber from one side of the diaphragm and through the at least one further sound exit hole 15, 16 from the other side of its diaphragm. A tweeter 12 is also provided. The loudspeakers 18, 19 and the tweeter 12 occupy a volume substantially outside the free space of the exponential horn. If desired a wedge member (29), Fig. 5 (not shown) may be provided between the loudspeaker baffles 22, 23 to minimize the air in the pressure chamber 27 and to direct the sound to the acoustic exit 28. Alternatively the air volume in the pressure chamber 27 may be minimized by arranging that the loudspeaker baffles 22, 23 are in contact at one end and are inclined to form a wedge shaped pressure chamber (27), (Fig. 6) not shown. A thin partition (30) divides the pressure chamber (27) into two parts. The tweeter 12 may be in the intermediate wall 7 and situated in a region slightly offset in relation to the acoustic exit 28 (Fig. 7, not shown), so that the tweeter 12 is directed on to the back wall 3. However the tweeter may be directed forwards in the same position or may be installed in the front wall 2 (Fig. 8, not shown). If desired the loudspeakers 18, 19 (Fig. 3) may be installed in reverse manner, so that the backs of the diaphragms radiate into the pressure chamber 27 and the fronts into the sound exit holes 15, 16. If desired, a triangular labyrinth (31), Fig. 9 (not shown) may be at the end of the first horn portion, just before the sound reaches aperture 17, and compensates undesired resonance effects. The tweeter 12 may then be installed within the cabinet on the back wall 3 facing the sound exit hole 6. An alternative cabinet (Fig. 15) has loudspeakers 18, 19 radiating through holes in the front wall 2. Their rear sides operate into a pressure chamber 27 having an aperture 33 in a back partition 35. Between the back partition 35 and the intermediate wall 7, partition walls (34), Fig. 14 (not shown) define a spirally extending first horn portion and this leads, via aperture 17, to the sound passage 13, 13a is in Fig. 4. As many loudspeakers as there are sound walls may operate into the pressure chamber 27. Another embodiment has four loudspeakers housed in the cabinet and located to radiate forwardly of the cabinet through an aperture in the front wall 2. The four loudspeakers have a common diaphragm 41 and are in a common support dish 36 which acts as a pressure chamber having a central acoustic exit 38. The diaphragm 41 is provided, between the loudspeaker cones, with creases or folds and with an on-edge cross 42 (see Fig. 17, not shown), the arms of which taper at their ends. The arms of the cross 42 are of foamed plastics.  Local circuit.-A panel L (Fig. 12) has sockets S and D and an earth terminal M. Matching resistors R 1 , R 2  are provided together with an input level control P 1  and a manual control P 2 . There is an"off"position for the tweeter Tw and also a volume control for it.