Abstract:
By providing a spherically shaped loudspeaker and/or closure containing one or more drivers or speaker motors, mounted in cooperative association with a uniquely constructed reflector, a loudspeaker system is achieved which controls and shapes the ultimate acoustical waveform produced thereby. The system of present invention controls and distributes the acoustical energy of the driver, while shaping the acoustical energy field in a true hemispherical pattern, within the system&#39;s power bandwidth. By employing the present invention, the point of summation of the hemispherical pattern is approximately eight times the diameter of the reflector, thereby achieving the desired hemispherical polar coverage patterns.

Description:
RELATED APPLICATIONS 
     This application is related to U.S. Provisional Patent Application, Ser. No. 60/140,568, filed Jun. 23, 1999 for a Spherical Loudspeaker System with Enhanced Performance. 
    
    
     TECHNICAL FIELD 
     This invention relates to loudspeaker systems and, more particularly, to loudspeaker systems constructed for controllably shaping the acoustical energy field into a true hemispherical pattern. 
     BACKGROUND ART 
     Loudspeakers are widely used for providing projection of voice and music in a variety of areas and for numerous purposes. One area in which loudspeakers are particularly important and have had substantial difficulty in providing good results is in large public areas. In such locations, the use of conventional loudspeakers is common, but there are difficulties because of the directional nature of the speakers&#39; sound projection. As a result, in order to assure maximum coverage, numerous or multiple speakers are employed with overlapping coverage areas which requires proper engineering and often considerable expense to attain the desired results. 
     In an attempt to reduce the necessity of having numerous loudspeaker components installed to provide the desired coverage, loudspeakers having a hemispherical coverage pattern have been developed. Although many of these prior art loudspeakers had been able to provide a projection of voice and music over a wider listening area, numerous problems have continued to exist in producing products which achieve a true full frequency hemispherical sound projection pattern from a single overhead sound source. 
     One of the principal problems which has plagued prior art spherical loudspeakers as well as conventional loudspeakers centers on the physical characteristics of acoustic wave patterns. In this regard, audio frequencies essentially occupy 11 octaves of the electromagnetic spectrum, with acoustical wave lengths varying across a ratio of more than 2000 to 1 (about 113 feet to about ½ in.). In most applications, a more reasonable and workable ratio is 1000 to 1 (about 56 feet to 0.68 inches). Regardless of which ratio is employed, it is apparent, due to their very nature, that these extremes of wavelength energy require the application and use of completely different areas and aspects of the laws of physics. 
     Another problem inherent in providing optimum projection of voice and music is the fact that lower frequencies of the audio spectrum produce spherical waves which tend to be fluid in nature and difficult to control in terms of shaping and directing. Furthermore, higher frequencies develop planar waves which exhibit directional characteristics and are, by their very nature, not easily dispersed or diffused into broad coverage patterns. Finally, midrange frequencies produce various combinations of these two extremes. 
     In attempting to overcome these prior art problems, while also providing maximum area coverage, spherical loudspeaker systems with shaped dishes or “reflectors” suffer from one or more shortcomings. One such common problem is a severe decrease of high frequency energy distribution at the wider points of coverage, typically beginning at about 45 degrees from the central axis. Another common problem is a significant increase in phase distortion from unwanted multiple reflections occurring between the sound source and the reflector, as well as a significant increase in intermodulation distortion due to the remodulation of one-wave by another of a different frequency. Finally, high intensity lobes of acoustic energy are often produced directly on axis with the reflector, expanding as wide as 20 to 30 degrees from the central axis. 
     SUMMARY OF THE INVENTION 
     By employing the present invention, all of the difficulties and drawbacks of prior art loudspeaker constructions are eliminated and a true hemispherical sound pattern producing loudspeaker system is achieved which controls and shapes the ultimate acoustical waveform produced thereby. In the present invention, a loudspeaker system is provided which incorporates a spherically shaped loudspeaker and/or closure containing one or more drivers or speaker motors. In addition, a uniquely constructed reflector is employed which is mounted in cooperative association with the spherical enclosure. In this way, the system of the present invention controls and distributes the acoustical energy of the driver, while shaping the acoustical energy field in a true hemispherical pattern, within the systems power bandwidth. By employing the present invention, the point of summation of the hemispherical pattern is approximately eight times the diameter of the reflector, thereby achieving the desired hemispherical polar coverage patterns. 
     In the preferred construction, the reflector of the present invention is designed to be rigidly and mechanically attached to the spherical cabinet forming the loudspeaker or, alternatively, built into the construction of the sphere during the fabrication or molding process as a homogeneous or integral component thereof. The center or apex of the reflector is intended to be physically close to and acoustically intimately coupled with the geometric center of the driver&#39;s diaphragm. 
     In addition, the reflector also incorporates uniquely designed and shaped vanes formed on the surface thereof which enhance the output from the reflector by distributing the high frequency energy out to the broader angles of the coverage pattern. In the preferred embodiment, the vanes are constructed as secondary reflector vanes and comprise an exponential cross-section that is continuously variable over their entire length. In the preferred construction, the axial profile of the vanes is also exponential. 
     By employing the present invention, a loudspeaker system is achieved which controls and defines the wave shape and coverage patterns of the various frequency bandwidths, utilizing the natural characteristics of the wave itself, with no forced or artificial control. Using the three basic elements of a loudspeaker system—(1) the driver, (2) the spherical enclosure, and (3) the reflector—in a unique integral design, a synergistic interaction of these components is achieved which produces true hemispherical coverage patterns across the entire rated power bandwidth of the loudspeaker. Furthermore, the incorporation of these secondary reflector vanes substantially enhances performance with wide angle dispersion of the high frequency band being realized. 
     The invention accordingly comprises an article of manufacture possessing the features, properties, and relation of elements which will be exemplified in the article hereinafter described, and the scope of the invention will be indicated in the claims. 
    
    
     THE DRAWINGS 
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying the drawings, in which: 
     FIG. 1 is a side elevation view, partially in cross-section, depicting the spherical loudspeaker system and reflector enhancement of the present invention; 
     FIG. 2 is a bottom plan view of the reflector of the present invention incorporating the secondary reflector vanes; 
     FIG. 3 is a side elevational view of the reflector of FIG. 2; 
     FIG. 4 comprises FIGS. 4A through 4D with each view being a cross-sectional side elevation view of the reflector and vanes of the present invention taken along different angles of the reflector; 
     FIG. 4A is a cross-sectional side elevation view taken along line A—A of FIG. 2, showing the cross-section between the vanes at the lowest angle; 
     FIG. 4B is a cross-sectional side elevation view taken along line B—B of FIG. 2, showing the cross-section along the sides of the vanes, with an increased angle; 
     FIG. 4C is a cross-sectional side elevation view taken along line C—C of FIG. 2, showing a cross-section halfway up the vanes at an angle approaching 90°; 
     FIG. 4D is a cross-sectional side elevation view taken along line D—D of FIG. 2, showing the cross-sectional at the top of the vanes depicting a full 90° angle; and 
     FIG. 5 is a bottom plan view of the reflector and vane construction of this invention, depicting the ray pattern reflection achieved by the present invention. 
    
    
     DETAILED DESCRIPTION 
     By referring to FIGS. 1-5, along with the following detailed discussion, the overall construction and operation of the present invention can best be understood. As will become evident to one of ordinary skill in the art, FIGS. 1-5 depict the preferred embodiment of the present invention. However, alternate constructions and variations of this invention can be made without departing from the scope of this invention. Consequently, it is to be understood that the construction shown in FIGS. 1-5 is provided for exemplary purposes only and is not intended to limit the present invention thereto. 
     As is well-known in the industry, every speaker system&#39;s performance is affected by seven basic acoustical modes of operation. These seven modes are reflections, diffraction, refraction, diffusion, coupling, loading, and summation. In order to produce a true hemispherical wavefront from a single loudspeaker enclosure, each of these modes must be carefully balanced and applied to the designs. Since many of these modes are competing, each must be controlled and defined in their own unique characteristic way, as they apply to the wavelength of the frequency being transmitted. By integrating these acoustical modes as well as the inherent natural wavefront shape of various frequencies, the desired operation and preferred wavefront pattern can be created. 
     As shown in FIG. 1, loudspeaker system  20  of the present invention comprises at least one driver  21 , spherical enclosure  22  and cooperatively associated reflector  23 . In the present invention, driver  21  is designed for optimum sensitivity or efficiency, bandwidth or frequency response, linearity or flatness of response, transient response, lack of distortion or coloration, power handling and maximum sound pressure level capability. In order to function in the intended manner, all of these qualities must be present in speaker or driver  21 , since spherical enclosure  22  and cooperating reflector  23  function as passive wave shaping and controlling devices, and cannot add to the purity, quality or fidelity of the acoustical signal generated by driver  21 . 
     Spherical enclosure  22  and reflector  23  are constructed using generally well known forming technology in order to achieve the desired shape and the desired diameter. Typically, spherical enclosure  22  and/or reflector  23  may be formed from a wide variety of fabrication materials. Although any desired material may be employed, the preferred materials for fabricating spherical enclosure  22 , and reflector  23  comprises one selected from the group consisting of fiberglass, plastics, structural foams, aluminum bonded to sound dampening materials, and steel bonded to sound dampening materials. In addition, although a wide variety of plastics made be effectively employed, the preferred plastics for forming these components are selected from the group consisting of acrylics, styrenes, polyvinyl chlorides and polycarbonates. 
     Reflector  23  is a principal component of the present invention in providing the desired hemispherical wavefront. As shown in FIGS. 1-5, reflector  23  comprises a radial concave shaped surface  26  extending from apex  24  at the center thereof and terminating at outer peripheral rim  25 . In addition, in this embodiment of the present invention, concave shaped surface  26  incorporates a plurality of reflector vanes  30  formed on surface  26  and radially extending from apex  24 . As detailed herein, vanes  30  provide a substantial enhancement to the dispersion of high frequency waves. 
     As depicted in FIGS. 1-5, the cross-sectional profile forming radically extending concave shaped surface  26  is not linear, but comprises a geometric form which defines an exponentially progressive curve. The form of the curve begins at the center or apex  24  of reflector  23  and proceeds in a radial fashion outwardly to rim  25 . The curve is symmetrical both radially and annularly about the entire circumference of reflector  23 . In addition, each reflector vane  30  is constructed with an exponential cross-section that is continuously variable over its entire length and with an axial profile that is also exponential. The feature of each vane being continuously variable over its profile is a function of, and an adjunct to, the ray analysis and wavelength propagation of the reflector surface profile. In analysis, the individual vane profiles emulate a specific section of the (host) reflector with the exception that they are physically positioned to cause acoustical reflections or secondary ray patterns at higher angles of incidence thereby supplementing the acoustical reflection properties of the reflector. The practical design of the vanes is in accordance with simple ray analysis based on the incidental and coincidental reflection properties of every wavelength of concern. The reflector is somewhat limited in its mathematically theoretical configuration to effectively allow both ideal lower frequency wave shaping and. at the same time, provide the ideal high frequency dispersion. Therefore, in order to avoid a significant compromise in reflector design, the reflector is primarily designed to control the reflections of the lower frequencies. Then, the vanes, as supplemental reflectors, can be designed to control the higher frequencies. When appropriate profile curves are designed for the reflector and the vanes, a synergistic harmony of full hemispherical reflections results. 
     In accordance with the present invention, the progression of radially extending concave shaped surface  26  of reflector  23  comprises a form/factor that is complementary to spherical enclosure  22 . Since the diameter of the spherical enclosure  22  is fixed, the diameter thereof becomes the reference baseline for calculating the profile shape of surface  26  of reflector  23 . Since the shape of surface  26  comprises a continuous exponentially progressive curve, the exponential form must become a variable in its progression in order to affect the desired result. This continuous exponential curve is best defined by the following formula: 
     
       
         De=(P 1 I) k , (P 2 I) k  . . . (P n I) k   
       
     
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 where: 
                 De = Linear axial distance between reflector and sphere at any 
               
               
                   
                 incremental position along the acoustical path. 
               
               
                 and: 
                 P 1 , P 2  . . . P n  = Linear axial distance of any 
               
               
                   
                 previous (numbered) De 
               
               
                 and: 
                   k  = wavelength coefficient factor (in exponential form). 
               
               
                   
                 Expressed as the expansion factor of the prime parameter A C /P L   
               
               
                 where: 
                 A C  = coupling; area of cross section 
               
               
                 and: 
                 P L  = loading; pressure units per area unit 
               
               
                 when: 
                 I = a fixed linear increment. 
               
               
                   
               
             
          
         
       
     
     In addition, any linear distance between reflector  23  and spherical enclosure  22 , at any mutual point along the radial dimension, is a numerical factor in the exponential progression. Accordingly, the specific exponential shape of surface  26  of reflector  23 , along with reflecting ray patterns between the diaphragm of driver  21  and reflector  23 , combine together to define the performance qualities of the ultimate objective, namely the acoustical spatial wave shaping which, in turn, describes a hemispherical polar coverage pattern within the system&#39;s power bandwidth at a point of summation of approximately eight times the reflector&#39;s diameter. 
     Furthermore, in this embodiment, vanes  30  are strategically placed about apex  24  of reflector  23  with the position and size of vanes  30  being determined by calculations based upon the wavelengths or frequencies of particular concern. The top or point end of each vane  30  is designed to represent the highest practical frequency of the system&#39;s power bandwidth, while the radiused or wide end of the vane is designed for the lowest or the cutoff frequency. 
     In accordance with the present invention, the cooperation of driver  21 , spherical enclosure  22 , and reflector  23  with vanes  30  on surface  26  establishes the final shape and coverage patterns of all of the frequencies produced by driver  21 . By constructing surface  26  of reflector  23  and secondary reflector vanes  30  in the manner detailed above, an optimum, highly desirable, hemispherical sound wave pattern is achieved. 
     As discussed above, by forming the plurality of secondary reflector vanes  30  on surface  26  of reflector  23 , high frequency dispersion is substantially enhanced and greater polar coverage linearity is achieved. As detailed above, the particular size, shape, number, and position of reflector vanes  30  are determined by the construction of surface  26  of reflector  23  and the polar coverage characteristics which result in conjunction with the acoustical energy source, namely driver  21 . 
     In practice, secondary reflector vanes  30  function in exactly the same way as surface  26  of reflector  23 . However, reflector vanes  30  are variable in profile at different angular positions. As a result, as is clearly depicted in FIGS.  4 ( a )- 4 ( d ), the performance achieved by reflector  23  incorporating vanes  30  is substantially enhanced. 
     By referring to FIG.  4 ( a ), the acoustical ray pattern produced by surface  26  of reflector  23  is depicted. As shown therein, as the acoustic wave front impinges upon surface  26  of reflector  23 , the waves or rays reflect off of surface  26  at different angles, with the reflected rays converging at a point away from reflector  23 . 
     In order to eliminate or reduce the convergence of the reflected rays, it has been found that the incorporation of secondary reflector vanes  30  produce the desired enhanced result. In FIGS.  4 ( b )- 4 ( d ), the reflected ray pattern at different cross-sectional positions along vanes  30  are clearly shown. As is evident from a review of these Figures, vanes  30  produce a substantial enhancement to surface  26  of reflector  23 . In this regard, the acoustical rays are reflected from vanes  30  on surface  26  of reflector  23  in an ever increasing parallel configuration, depending upon the radial position along the vanes  30  being considered. As a result, the convergence of the rays is substantially reduced or effectively eliminated. 
     In effect, vanes  30  represent segmented sections of surface  26  of reflector  23 , with the acoustical near field being substantially unchanged. However, in the acoustical far field, passed the point of summation, the effect of incorporating vanes  30  on surface  26  is substantial. In this regard, the lobes produced by the incorporation of vanes  30  are summed and averaged, providing a smoothing condition due to the convex shape along the entire length of each vane  30 . 
     As shown in FIG. 5, by incorporating vanes  30  on surface  26  of reflector  23 , with vanes  30  being properly designed, correctly oriented, a substantially improved total or overall effect is achieved. In this regard, the high frequency band acoustical energy output is increased at the more obtuse or off-axis coverage angles of the hemispherical polar coverage pattern. 
     It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above article without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.