US2722990A

US2722990A - Loudspeaker assemblies

Info

Publication number: US2722990A
Application number: US194473A
Authority: US
Inventors: West Ralph Leighton
Original assignee: Decca Record Co Ltd
Current assignee: Decca Record Co Ltd
Priority date: 1949-11-08
Filing date: 1950-11-07
Publication date: 1955-11-08
Anticipated expiration: 1972-11-08

Description

LOUDSPEAKER ASSEMBLIES Ralph Leighton West, London, England, assignor to The Decca Record Company Limited, London, England, a British company Application November 7, 1950, Serial No. 194,473

Claims priority, application Great Britain November 8, 1949 3 Claims. (Cl. 181-31) This invention relates to loudspeaker assemblies and has for its principal object to provide a construction in which the quality of the sound distributed is uniform throughout a room.

VThe normal type of loudspeaker cone tends to beam the higher frequency sounds. The higher the frequency, the narrower is the effective beam. Thus the distribution of the sound from such a loudspeaker lvaries with the frequency, so causing the quality to depend on the position of the listener with respect to the loudspeaker. In particular, the concentration of the higher frequencies in a narrow beam accentuates needle scratch, amplifier hiss and such like high frequency noises for a listener near the axis of the beam.

It is thus more particularly an object of the invention to ensure that the higher frequencies sounds are not concentrated into a narrow beam but are spread evenly.

According to this invention, a loudspeaker assembly comprises a cabinet adapted to fit in a corner of a room and a loudspeaker mounted in the cabinet, which loudspeaker is arranged, when the cabinet is located in the corner of the room, to direct the sound towards the room walls forming the corner at an upward angle such that the sound is refiected from the walls forming the corner back into the room over the top of the cabinet. By placing this assembly in the corner of a room, the high frequency sound beam from the loudspeaker is spread into the room evenly in all |directions from the corner. Furthermore, the overall effect is as though the sound emanated from an appreciable area of wall in the corner of the room and thus gives a fair compromise between the sharply defined source of sound required for a solo voice, a solo Violin and such like sounds which the listener expects to come from a source of small area and the extended source of sound required for a full orchestra the sound of which the listener would expect to come from a source of large area. The room walls must, of course, be rigid and the surface reasonably hard and smooth. It is found that surfaces ranging from wallpaper on plaster to bare brick are quite suitable.

The angle of upward tilt of the beam must be such that the sound is reflected back from the walls of the room over the top of the loudspeaker assembly. A large angle of tilt is generally undesirable since it may direct the reflected sound over the heads of the listeners and it has been found that with the loudspeaker mounted near the top of the cabinet and some 9-18 inches away from the corner satisfactory results are obtained when the up- Ward tilt is such that the geometric axis of the reflection just clears the top of the assembly.

According to another aspect, the invention also includes, in a room having a pair of walls forming a corner, a loudspeaker assembly comprising a cabinet disposed in said corner and a loudspeaker mounted in the cabinet, which loudspeaker is arranged to direct the sound towards the room walls forming the corner at an upward angle such that the sound is refiected from the United States Patent O 2,722,990 Patented Nov. 8, 195

ICC

walls forming the corner back into the room over the top of the cabinet.

Conveniently the cabinet may have parallel front an rear walls and have two upright side walls with at least their rearward portions lying in planes converging rearwardly at an angle of substantially ninety degrees to one another to fit the room walls at the corner. It will be appreciated, however, that many other shapes of cabinet can be used.

It is desirable that the side walls of the cabinet should not lie fiush against the room walls, in order to avoid the formation of a resonant cavity behind the cabinet. Usually this will be prevented by the skirting boards or the like on the room walls. A spacing of, for example, 3-6 inches is usually found desirable and, to ensure that the cabinet is suitably spaced from the room walls, spacing blocks may be provided on the cabinet.

Conveniently the loudspeaker assembly is provided with a bass Chamber, or other device, to increase output at the lower audio frequencies by providing better loading of the cone, and the loudspeaker is arranged so that one side of the diaphragm radiates into the corner of the room and the other side of the diaphragm drives the bass Chamber.

Instead of using the corner of a room, an auxiliary beam spreading refiector may be provided and thus according to a further aspect of the invention, a loudspeaker assembly may comprise a cabinet, a loudspeaker mounted in the cabinet and arranged to direct the sound at an upward angle and a beam spreading refiector mounted on the cabinet and having two Vertical walls set at an angle for example, ninety degrees) to form a corner, the loudspeaker and reflector being so arranged that the axis of the sound beam is directed into the corner of the refiector and is reflected back over the top of the cabinet. This assembly could therefore be disposed against a fiat wall, the reflector refiecting and spreading the sound into the room.

Further features of the invention will be apparent from the following description of one embodiment thereof, reference being made to the accompanying drawings in which:

Figure 1 is a perspective view of the rear of a loudspeaker assembly;

Figure 2 is a plan view showing how the assembly is located with respect to the room walls, and

Figure 3 is a diagrammatic sectional view along the line 3-3 of Figure 2.

The cabinet 10 has a front wall 11 in a Vertical plane and a rear wall 12 the lower part of which is parallel to the front wall. The upper part 13 of the rear wall slopes downwards from front to rear at an angle to the Vertical which in the embodiment illustrated is about 20. The side walls 14 of the cabinet are Vertical and have their rearward portions 15 lying in planes converging rearwardly at an angle of substantially ninety degrees to one another so that the cabinet may be Conveniently located in a corner of a room as is shown in Figure 2 where the cabinet 10 is disposed in a corner formed by the room walls 16.

The loudspeaker 17 is mounted in the cabinet near the top of the sloping portion 13 of the rear wall so that the centre of the sound beam is directed at an upward angle into the corner formed by the junction of the room walls 16. This angle is chosen so that Ithe centre of the reflected beam just clears the top edge of the cabinet when the latter is disposed as shown in Figure 2, that is to say, with the side walls of the cabinet spaced a short distance away from the room walls. A distance of 3 to 6 inches between the cabinet and the room walls has been found suitable in the case of a cabinet about 31/2 feet tall.

The loudspeaker is loaded in the known manner by 3 means of bass chamber 18 which forms a folded, near resonant tapered air column as described in British Patent No. 447,749 (filed October 17, 1934), the loudspeaker being arranged so that one side of the diaphragm radiates into the corner of the room and the other side of the diaphragm drives the bass chamber.

By using the loudspeaker in the corner of a room, as described, the loudspeaker works into one eighth of a Sphere; this increases the loading still further, raises the electro-acoustic efficiency and contributes materially to the damping. Most of the high frequency energy spreads into the room after refiection from the room walls thus providing an effectively larger source area than if the loudspeaker were arranged to direct the sound straight into the room. As previously explained this larger source area provides a reasonable compromise between the requirements for the small source area needed for a solo voice or certain solo instruments and the large source area required for an Orchestra. It is found that a solo voice appears to emanate from somewhere behind the top of the cabinet. Due to the reflection, the apparent source of sound is partialiy beyond the room walls, so effectively increasing the distance between the source and the listener, which is particularly desirable in small and medium-sized rooms and is not undesirable in larger rooms.

From a loud speaker the high frequency sounds are most strongly concentrated towards the centre of the beam. With the arrangement described, the sound in the centre of the beam is widely scattered due to the very small radius of curvature of the reflecting surface at the junction of the room walls and thus a very even distribution of the high notes is obtained.

instead of using the corner of a room, the cabinet might be placed against a flat wall and an auxiliary beam Spreading reflector provided. Such a reflector might comprise 'A two rigid Vertical plates set at an angle of ninety degrees. The loudspeaker would be arranged to direct the sound into the corner between the two plates which are disposed so as to rellect the sound into the room. Such an arrangement will operate in exactly the same manner as that previously described with reference to Figures 1 to 3. It will be appreciated, however, that the angular spreading of the beam required to distribute the sound evenly throughout the room will be minimized by locating the loudspeaker assembly in a suitable corner of the room.

Pursuant to section ll9, title 35, United States Code, claim is hereby made to the priority benefits of the filing date of my earliest foreign application on this invention; to wit: British application No. 28,638/49; filed by me on November 8, 1949; and entitled Improvement in or Relating to Loud Speaker Assemblies.

While I have illustrated and described the preferred embodiment of my invention, the same is not to be limited to the details shown and described, except as defined in the appended claims.

I claim:

l. In combination with a room having a pair of intersecting Vertical. walls forming a corner, a loudspeaker assembly comprising a cabinet disposed in said corner, said cabinet having parallel Vertical front and rear Walls joined by two vertical side Walls, said side walls of said cabinet having at least their rearward portions lying in planes converging rearwardly at an angle of substantially ninety degrees to one another to extend in spaced parallel relation to said room walls, and a loudspeaker mounted in Said cabinet, said loudspealter being arranged to direct the sound emanating therefrom towards said room walls and into said corner at an upward angle such that the sound is refiected from said room walls back into the room over the top of said cabinet.

2. The combination of claim l wherein said rear wall comprises a Vertical lower part and an inclined upper part which slopes downwardly from front to rear at an angle to the Vertical, and wherein said loudspeaker is mounted in said cabinet near the top of said sloping portion with the aXis of said loud speaker directed outwardly and perpendicularly to the plane of said sloping portion, the angle of slope of said sloping portion being such that the axis of the sound beam refiected from said room walls just clears the top of said cabinet.

3. The combination of claim 1 wherein there is provided a horizontal bottom Wall joining said front and side walls and having an opening therethrough, and wherein there is provided within said cabinet partition means coacting with the walls of said cabinet to define an elongated bass cbamber having one end communicating with the exterior of said cabinet, through said opening, said loudspeaker being arranged so that one side of the diaphragm thereof radiates into the corner' of said room, and the other side of said diaphragm drives the other end of said base Chamber.

References Cited in the file of this patent UNITED STATES PATENTS l,645,23l Dietrich et al Oct. ll, 1927 1,770,771 Garrett July 15, 1930 1,984,550 Sandeman Dec. 18, 1934 l,9'85,88l Buckley lan. 1, 1935 2,50,575 Krause Aug. ll, 1936 2.109,431 McDonald Feb. 22, 1933 2.124,575 Karnes July 26, 1938 2,160,283 Roberts May 30, 1939 2,3l0,243 Klipsch Feb. 9, 1943 2.337,213 Topping Dec. 21, 1943 2.539,327 Reid et al. Jan. 23, 1951 OTHER REF ERENCES Radio Exhibition Review, Article in Wireless World, October 1956, pages 346-347.