Abstract:
Stereo electroacoustical transducing apparatus for providing acoustical reproduction in a room at least partially bounded by a room bounding surface including a floor, sidewalls, and a ceiling, the apparatus including a nonlocalizable woofer module that is mounted outside of the room and communicates with an opening in the room bounding surface, upper frequency drivers located within the room, and electronics for providing audio electrical signals to the nonlocalizable woofer module and the upper frequency drivers.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates in general to electroacoustical transducing and more particularly concerns an improved system for providing acoustical reproduction in a room. 
     A prior art room speaker system, available from Bose Corporation under the AM-5 trade designation, is described in Hirsch, J., &#34;Bose AM-5 Speaker System,&#34; Stereo Review (April 1987) (&#34;Hirsch&#34;), which is hereby incorporated by reference. The AM-5 system includes a ported woofer module that is nonlocalizable; i.e., the location of the woofer module cannot be determined by listening. The woofer module enclosure is in the shape of a box with two openings and is usually located on the floor near a wall. The structure and operation of the nonlocalizable ported woofer used in the AM-5 speaker system is described in U.S. Pat. No. 4,549,631, which is hereby incorporated by reference. 
     SUMMARY OF THE INVENTION 
     In general, the invention features an improved system for providing acoustical reproduction in a room using a nonlocalizable woofer module that is mounted outside of the room and communicates with an opening in a surface bounding the room (i.e., a sidewall, a floor, or a ceiling) and upper frequency drivers that are located within the room. The relatively bulky woofer module thus need not take up space within the room, and the nonlocalizable nature of the woofer module provides good low-frequency sound throughout the room. 
     In a preferred embodiment, the woofer module has an enclosure with a baffle that carries a woofer driver and divides the interior into first and second subchambers; the subchambers are ported to an end chamber in the enclosure, and the end chamber communicates with the opening in the room bounding surface. In another embodiment, the nonlocalizable woofer module includes acoustic wave guides. 
     Other advantages and features of the invention will be apparent from the following description of a preferred embodiment thereof and from the claims. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment will now be described. 
     Drawings 
     FIG. 1 is a diagrammatic, perspective view of a room including a speaker system according to the invention. 
     FIG. 2 is a block diagram of the FIG. 1 room speaker system and associated electronics. 
     FIG. 3 is a perspective view of a woofer module used in the FIG. 1 speaker system. 
     FIG. 4 is a perspective view, partially broken away, showing mounting of the FIG. 3 woofer module under the floor of a room. 
     FIG. 5 is a perspective view, partially broken away and exploded, of the FIG. 4 woofer module. 
     FIG. 5A illustrates a modification of the embodiment of FIG. 5 using drone cones. 
     FIG. 6 is a plan view of an embodiment of the invention using an acoustic waveguide. 
    
    
     Structure 
     Referring to FIG. 1, sidewalls 10, ceiling 12 and floor 14 of a room are shown. Mounted underneath floor 14 is nonlocalizable woofer module 16. It is ported to opening 18 in floor 14 under grill 20. Mounted on tracks 22 on ceiling are left speaker cubes 24 and right speaker cubes 26. Speaker cubes 24, 26 are identical, each cube of a pair aiming in a different direction. Each speaker cube 24, 26 is approximately four inches along each side, has a 3-inch driver, and has a frequency response of 200 Hz to 18 kHz, ± 6 dB. Speaker cubes 24, 26 thus provide upper frequency drivers. Nonlocalizable woofer module 16 is about 23 inches by 12 inches by 7 inches, includes two 6-inch low-frequency drivers, and has a frequency response of 40 Hz to 180 Hz, ± 6 dB. Nonlocalizable woofer module 16 is described in detail in U.S. Pat. No. 4,549,631 (&#34;&#39;631 patent&#34;). Opening 18 in floor 14 is about 6 inches from the sidewall 10 behind it and on the same side of the room as speaker cubes 24, 26. Opening 18 is located at least eight feet from the main listening area in the room. Volume control switch 28 is mounted on a sidewall 10. 
     Referring to FIG. 2, nonlocalizable woofer module 16 and speaker cubes 24, 26 are provided with audio electrical signals by amplifier 30. Wall mounted volume control switch 28 is also connected to amplifier 30, which in turn receives audio electrical signals from music center 32, which includes, for example, a tuner and a cassette player. 
     Referring to FIGS. 3-5, nonlocalizable woofer module 16 has a slotted opening 34 at one end of its box-shaped enclosure 36. Enclosure 36 is mounted between adjacent joists 38 underneath floor 14 via brackets 40. Six-inch low frequency drivers 42 are mounted within enclosure 36 on inclined baffle 44, which divides a woofer region within enclosure 36 into two subchambers. Each subchamber is ported via a respective port tube 46, 48 through wall 50 to end chamber 52, communicating with slotted opening 34. By having end chamber 52 at the end of enclosure 36 and slotted opening 34 in one of the two sides of enclosure 36 that have the largest area, enclosure 36 can be mounted with its smallest dimension extending downward from floor 14, to facilitate mounting and avoid taking up space. 
     Nonlocalizable woofer module 16 could be mounted to be ported to openings in other room bounding surfaces, e.g., sidewalls 10 or ceiling 12. Opening 18 is preferably near a boundary of two such surfaces, for example, in ceiling 12 near a sidewall 10, or in a sidewall 10 near ceiling 12 or floor 14, but is preferably spaced from a corner of a room, to avoid undesirable bass boost with this embodiment. Opening 18 is preferably located at least eight feet from the main listening area for better balance of sound from cube speakers 24, 26 and woofer module 16. Generally, nonlocalizable woofer module 16 is preferably located at the same end of the room as cube speakers 24, 26; however, because the bass provided by nonlocalizable woofer module 16 is nonlocalizable, it may be located elsewhere. If nonlocalizable woofer module 16 is mounted at the opposite end of the room from cube speakers 24, 26, it is preferably placed further away from the listener than cube speakers 24, 26. Opening 18 is preferably located within six inches of one of the walls, for improved bass response. Opening 18 is preferably adjacent to or in a sidewall 10 that is an outside wall of the building to reduce the chance of bass sound being heard in the other rooms. 
     Operation 
     In operation, speaker cubes 24, 26 provide the mid and high frequencies, and nonlocalizable woofer module 16 provides the low frequencies. Nonlocalizable woofer module 16 operates as described in the &#39;631 patent and Hirsch article, except that end chamber 52 and associated slotted opening 34 divert sound energy from port tubes 46, 48 to opening 18. Port tubes 46, 48 comprise acoustic masses that resonate with the compliance of the air in the respective subchambers to establish a cutoff frequency sufficiently low so that the low frequencies provided by nonlocalizable woofer module 16 are nonlocalizable. Listeners thus cannot easily identify the location of the woofer module, and the relatively bulky woofer module enclosure need not be located within the room. 
     Other Embodiments 
     Other embodiments of the invention are within the scope of the following claims. E.g., nonlocalizable woofer module 16 could employ other passive radiators (e.g., drone cones 46&#39; and 48&#39; mounted on wall 50&#39; as shown in FIG. 5A) in place of port tubes 46, 48 and could be of a type that an acoustic wave guide, as described in U.S. Pat. No. 4,282,605, which is hereby incorporated by reference as shown in FIG. 6, which is a reproduction of FIG. 1 of the latter patent. Nonlocalizable woofer module 16 could also be design other technology that gives it acoustic low pass filtering such as to render it nonlocalizable. Nonlocalizable woofer module 16 could also be designed for optimum operation spaced from a sidewall or near a corner of a room.