Abstract:
A loudspeaker system for the reproduction of acoustic waves of music, sound and speech in a substantially circular horizontal plane. The loudspeaker system includes multiple spherical enclosures, each enclosure housing a pair of transducers, each pair of transducers producing acoustic waves of a predetermined frequency range.

Description:
[0001]    This application is a continuation of, and claims benefit of and priority to, U.S. patent application Ser. No. 11/324,649, filed Jan. 3, 2006, by J. Craig Oxford, et al., and is entitled to that filing date for priority. The specification, figures and complete disclosure of U.S. application Ser. No. 11/324,649 are incorporated herein by specific reference for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention involves a loudspeaker system for the reproduction of acoustic waves in music, sound and speech. Unlike traditional loudspeaker systems, the present invention houses various transducers in spherical enclosures to produce acoustic waves in substantially circular horizontal planes, each spherical enclosure houses a pair of transducers to produce acoustic waves in a predetermined frequency range. 
       BACKGROUND OF THE INVENTION 
       [0003]    Traditional loudspeakers, particularly those intended for employment in home two channel audio or multi-channel theater systems employ rectangular enclosures and transducers which direct acoustic energy towards an intended listening position. There are, however, a number of loudspeaker designers that have suggested the generation of non-directional radiation from a loudspeaker. The reason for this is the recognized advantages which are known to be achievable as a result of an improved relationship between room acoustics and the loudspeaker itself. Specifically, when acoustically reflective surfaces in a room such as its walls and ceiling are excited with the same sound that reaches a listener directly, the reverberant or reflected sound does not interfere with the perceptual functioning of the listener. A loudspeaker which would feature various kinds of box enclosures cannot accomplish this because of diffractions which appear about the speaker enclosures. These diffractions modify the off-access sounds which are the ones that excite room reverberations. As such, a listener is provided with a more satisfying audio experience when a loudspeaker is employed which radiates isotropically, or in all directions. Nevertheless, there are practical advantages in producing a loudspeaker which is slightly anisotropic by restricting radiation to a mainly circular pattern in a horizontal plane and being slightly attenuated above and below that plane. 
         [0004]    Loudspeaker systems such as those described herein achieve desired mild anisotropy and offer further advantages as well. The use of spherical enclosures minimize diffractions around those structures while providing a novel appearance. The use of driver elements in opposed pairs as suggested herein cause reactive forces to be completely contained and thus prevent undesirable transmission of those acoustic waves or forces to surrounding structures, particularly the floor upon which a loudspeaker is placed. 
         [0005]    It is thus an object of the present invention to provide a speaker system in a form of spherical enclosures each housing tiers of audio transducers of specific frequency ranges thus eliminating those various types of box enclosures of the prior art. 
         [0006]    It is yet a further object of the present invention to provide an improved loudspeaker system that fundamentally radiates acoustic energy isotropically with mild anisotropy, restricting radiation in a mainly circular horizontal plane and slightly attenuated above and below that plane. 
         [0007]    These and further objects will be more readily appreciated when considering the following disclosure and appended drawings. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention involves a loudspeaker system for reproduction of acoustic waves for music, sound and speech in a substantially circular horizontal plane, said loudspeaker system comprising multiple spherical enclosures, each enclosure housing a pair of transducers, each pair of transducers reproducing acoustic waves of a predetermined frequency range. Ideally, three such spherical enclosures are employed in producing a full range loudspeaker system. These enclosures would include a relatively large sphere enclosing a pair of low-frequency transducers upon which is positioned a smaller sphere housing opposed pairs of mid-range frequency transducers and located thereupon, a smaller spherical enclosure housing an opposed pair of high-frequency transducers 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0009]      FIG. 1  is a side perspective view of the enclosures of a typical loudspeaker system of the present invention. 
           [0010]      FIG. 2  and  FIG. 3  are schematic illustrations of the low-frequency or woofer enclosure housing low-frequency transducers as contemplated for use in the present invention. 
           [0011]      FIG. 4  is a schematic illustration of an enclosure and contained mid-range frequency transducers and supporting structure for use in the present invention. 
           [0012]      FIGS. 5 and 6  are schematic illustrations of a spherical enclosure, contained high-frequency transducers and supporting structure all for use in the present invention. 
           [0013]      FIGS. 7A and 7B  are front plan views of the external housing of the present loudspeaker system showing alternative ways in which the sub-enclosures interface with one another. 
           [0014]      FIG. 8  is a side plan view of a typical computer monitor on a desk employing the present invention as the audio system connected thereto. 
           [0015]      FIG. 9  is a plan view of a further iteration of the present invention employing it as a satellite-sub system commonly employed in residential installations. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Turning first to  FIGS. 2 and 3 , relatively large spherical enclosure composed of lower hemisphere  2 F and upper hemisphere  2 E is shown to enclose low-frequency driver units  2 A and  2 B. Opposed driver units  2 A and  2 B ideally operate in phase with each other causing a pressure wave to emanate from the “equator” of the sphere. The upper and lower hemispheres  2 A and  2 F, composed of, for example, fiberglass, carbon fiber, spun metal or molded polymers further can include an acoustically transparent grill  2 C, common to traditional loudspeaker designs traditionally referred to as a “grill cloth.” As noted, low-frequency loudspeaker transducers,  2 A and  2 B are mounted in the structural hemispheres which, themselves, are spaced apart by spacers  2 D preferably located in three positions, 120° apart from one another in polar view. Typically, this enclosure would have a diameter of, for example, 20 or so inches. 
         [0017]      FIG. 3  has been included in the present description in order to further illustrate low-frequency transducers  3 A and  3 B in order to show the diaphragms of each transducer. As a design requirement, it is noted that the active area of a low-frequency transducer diaphragm is approximately bounded by the mid point of the outer suspension or surround noted by radius  3 C. The area of the cylinder whose radius is  3 C and whose height is  3 D must be equal or greater than the sum of the areas of the two diaphragms, specifically, 
         [0000]      (3 C× 2π×3 D )≧(3 C× 3 C× 2π)
 
         [0000]    wherein: 
         [0018]      3 C=The radial distance between the geometric center of each speaker and the circumference of each speaker diaphragm as it is connected to each structural surround; 
         [0019]      3 D=The distance between opposing diaphragms measured at their circumference. 
         [0020]    As is further quite apparent by viewing  FIGS. 2 and 3 , hemispheres  2 E and  2 F present completely closed surfaces behind each of the opposed low-frequency transducers. Those skilled in the loudspeaker art certainly appreciate the requirements of low-frequency transducers&#39; small-signal parameters and/or the application of external equalization. The mutual coupling of the low-frequency transducers will result in measured parameters somewhat different from calculated values. Typically, the system resident frequency F tc  and total Q, Q tc  will both be lower than expected. Further, the opposed mounting of low-frequency transducers  2 A and  2 B with their in-phase operation causes the entire reaction force to be coupled through spacers  2 D. Thus, there is no need to absorb reaction forces external to the low-frequency transducer system. 
         [0021]    Wires connecting an external source with low-frequency transducers  2 A and  2 B can be introduced to low-frequency enclosure  100  ( FIG. 1 ) through base  400  at its “south pole” and through its “north pole” to the “south pole” of mid-range frequency transducer enclosure  200  and on to high frequency transducer enclosure  300 . 
         [0022]    Being a multi-transducer system and one intended to embrace the entire audio spectrum, the present system is also intended to include mid-range sphere  200  ( FIG. 1 ) shown in detail in  FIG. 4  as upper hemisphere  4 E, lower hemisphere  4 F and acoustically transparent grill cloth or covering  4 C. As to scale, if low frequency or woofer sphere  100  was 20 to 21 inches in diameter, mid-range sphere  200  would be approximately 8 to 9 inches in diameter. 
         [0023]    As background, it is generally understood that providing suitable mid-range frequency transducers for use herein is a more complicated matter than is the case in designing the appropriate low-frequency portion of the present system. In that wave lengths are much shorter, mid-range frequency transducers cannot be viewed as simple sources of acoustic waves. In acoustics, a simple source is one where ka is less than 1 noting that ka is the wave number times the diaphragm radius. The wave number is 2π F/C where F is frequency in Hz and C is the speed of sound and air, 345.45 m/s at sea level at 25° Celsius. If the diaphragm radius is 2 inches (0.051 m), ka equals 1 at 1082 Hz. Thus, the radiation from the driver ceases to be nondirectional beyond about 1 kHz. 
         [0024]    In continuing with the appropriate placement of mid-range frequency transducers as an opposed pair shown in  FIG. 4 , acoustic wave emission must be substantially uniform on the radius, not axis of the mid-range frequency transducers. Below ka=1, this occurs naturally. Above ka=1, guidance can be taken from the expression for radiation from a piston in a plane which is a good approximation given the mid-range frequency transducer mounting as shown in  FIG. 4  as follows: 
         [0000]        R∝=[ 2 J   1 ( ka )sin ∝]/ ka  sin ∝
 
         [0000]    wherein: 
         [0025]    R∝=The linear scale response function at an angle or away from the axis of the piston (or diaphragm) 
         [0026]    k=The wave number=2π/λ 
         [0027]    λ=wavelength=c/f 
         [0028]    f=frequency (Hz) 
         [0029]    c=speed of sound in air=345.45 m/s 
         [0030]    a=radius of the piston or diaphragm (m) 
         [0031]    J 1 =first order Bessel function of the first kind 
         [0032]    If R∝ (on axis so ∝=0 degrees)=1, the relative response in dB is given by 20 log R∝. 
         [0033]    On the radius, the expression simplifies to R∝=[2J 1 (ka)]/ka because sin 90°=1. 
         [0034]    At ka=3.8, R∝=0, f=4096 Hz 
         [0035]    To illustrate this matter further, it is contemplated that sphere  200  emanates mid-range frequency output from about 100 Hz to about 4 kHz. The existence of a null response at 4 kHz deforms the frequency response down to about 2 kHz because the response is falling down the asymptote into the null. In order to confine the null to a usefully higher frequency, it would be necessary to reduce the diaphragm radius to 1 inch (0.025 m). Such a small transducer cannot be used to the desired lower limit of 100 Hz because it cannot radiate sufficient acoustic power at that frequency. In order to overcome this issue to ameliorate the null while retaining the radiating area of a usefully large diaphragm, it is first necessary to intuitively understand why the null occurs. 
         [0036]    A visual way of looking at why a null occurs is that from any radial point of observation, sounds originating from the near part of the diaphragm and those originating from the far part will destructively interfere with each other at certain wave lengths. It follows that if the “view” of the far side of the diaphragm can be obstructed, then the interference would be reduced or eliminated. Actual measurements show that this is the case. 
         [0037]    Turning back to  FIG. 4 , the use of an obstacle positioned between the opposed pair of mid-range frequency transducers works well to minimize or eliminate the null. In this illustration, two obstacles are shown, namely, obstacles  4 H and  4 L. They can be conveniently supported by mounting them directly to the center poles  4 G and  4 K of the transducers. The optimum diameter of the obstacles is not arbitrarily selected. If the obstacles are small compared to the wave length of acoustic energy being emitted from the mid-range frequency transducers, its effect is negligible. Even so, it causes the diaphragms  4 A and  4 B to resemble ring sources. The expression for ring source&#39;s response function is 
         [0000]        R∝=Jo ( ka )sin ∝
 
         [0000]    wherein: 
         [0038]    Jo=the zero Bessel function of the first kind 
         [0000]    As previously noted, on the radius, sin 90°=1. R∝=0 at ka=2.4 (however, the value of “a” must be determined). Assuming an outer diameter of the diaphragm d 1 , and an obstacle diameter d 2 , the diameter of the apparent ring source, d 3 =(d 1 +d 2 )/2. The obstacle will become significantly large as this diameter exceeds λ/4. If λ coincides with the null frequency in the response function, the obstacle will ameliorate the null. There thus exists an optimum relationship between the diameter of the obstacle, d 2 , and the diameter of a diaphragm, d 1 . Further, an iterative calculation will show that for the obstacle diameter to be safely equal to λ/2 at the null frequency, d 2 =0.0486×d 1 . To continue with this example, if d 1 =0.102 m and d 2  equals 0.0496 m then the apparent ring source diameter, d 3 , would=0.0758 m. Thus, a=0.0379 m, the radius of the equivalent ring source. At ka=2.4, λ=0.0992 m, and d 2 =λ/2. In fact, measurements have shown that the null is eliminated and that the final response is within a conveniently equalizable range. This enables a geometry to exist per the illustration shown in  FIG. 4  while achieving highly desirable mid-range frequencies emanating from the air created by spacers  4 D which are positioned, ideally, 120° from each other employing 3 about the entire circumference of sphere  200  behind grill cloth  4 C. 
         [0039]    It is also proposed that separator  4 J be employed. This is preferably made of a semi-rigid material which is acoustically non-reflective, such as Poron® to prevent reflections between the diaphragms  4 A and  4 B of the mid-range frequency transducers. The diameter of the separator can be slightly less than the diameter of the mounting circle of the three spacers,  4 D. 
         [0040]    As with the low frequency transducer section housed within sphere  100 , individual hemispheres  4 E and  4 F enclose the back of each mid-range frequency transducer diaphragm  4 A and  4 B. Those skilled in the art of acoustic engineering will fully appreciate requirements of small-signal parameters to suit available closure volumes. 
         [0041]    To complete the full range system contemplated herein, reference is made to  FIGS. 5 and 6  showing the details of high frequency transducers to be included within sphere  300  ( FIG. 7 ). In this instance, lower hemisphere  5 A serves to support high frequency transducer pair  5 C and  5 D. Upper hemisphere  5 B is intended to be substantially acoustically transparent comprised of, for example, acoustically “transparent” grill cloth commonly used in loudspeaker fabrication. The use of these upper and lower hemispheres visually completes the audio loudspeaker system as shown in  FIG. 1 . 
         [0042]    Although there are a number of choices for the pair of opposing high-frequency transducers for use herein, one ideal choice would be the high frequency transducers disclosed in U.S. Pat. No. 6,061,461, the disclosure of which is incorporated by reference. Such high frequency transducers include a rigid frame and permanent ring magnet mounted to the frame. A small bobbin, preferably formed of aluminum foil, is sized and arranged to fit within the open end of the magnetic gap while permitting motion of the bobbin therein. A voice coil is wound on the bobbin and connectable to receive an audio signal, similar to a conventional voice coil driver system. A pair of flexible, curved diaphragms, shown in  FIG. 5  are disposed on a frame, generally free to move except for their distal ends which are fixed at the frame. The diaphragms can be generally cylindrical or partial-cylindrical. Again, such a configuration is shown in U.S. Pat. No. 6,061,461, although other more conventional tweeter pairs can be used herein. 
         [0043]    As with the mid-range frequency and low frequency transducer assemblies described above, the use of opposing pair of high frequency transducers again causes all of the reaction forces to be locally contained. 
         [0044]    For clarity,  FIG. 6  shows a suitable high frequency transducer sphere from a top view. In this instance,  6 A is the top of the lower hemisphere, that is, the surface upon which the high frequency transducers are mounted and the two high frequency transducers are depicted as  6 B and  6 C. 
         [0045]    Turning now to  FIG. 1 , there are a number of ways in which spheres  100 ,  200  and  300  can be mechanically and electrically joined in order to produce a functional loudspeaker system upon base  400 . As shown in  FIG. 1 , low frequency transducer sphere  100  can be flattened on its “south pole” end to reside upon base  400 . Suitable input connectors from a power amplifier and a cross over network to direct acoustic energy of specific frequencies to the low frequency, mid-range frequency and high frequency transducers can be also placed within base  400  or adjacent thereto. Alternatives to mounting or otherwise placing mid-range frequency transducer sphere  200  upon low frequency transducer hemisphere  100  at interface  500  as well as high frequency transducer sphere  300  upon mid-range frequency transducer sphere  200  at interface  600  will now be described. In this regard, reference is made to  FIGS. 7A and 7B . 
         [0046]    Turning first to  FIG. 7A , it is noted that low frequency transducer hemisphere  100  is employed as a support for mid-range frequency transducer hemisphere  200  which is in turn employed to support high frequency transducer hemisphere  300 . In order to stabilize this structure, low frequency transducer hemisphere  100  is somewhat flattened at its “north pole”  101  which mates with mid-range frequency transducer hemisphere  200  at its “south pole”  202  at interface  500 . Similarly, mid-range frequency transducer hemisphere  200  is flattened at its “north pole”  201  which mates with the “south pole”  302  of high frequency transducer hemisphere  300  at interface  600 . Appropriate cabling to provide electrical connections between the various transducers can enter and exit the various hemispheres in these flattened regions. The details of a suitable arrangement is shown in  FIG. 5  wherein a cable entry arrangement is shown at  5 E allowing entry of cables  5 H emanating from mid-range frequency transducer hemisphere  200  to high frequency transducer hemisphere  300 . 
         [0047]    As an alternative, reference is made to  FIG. 7B . In this instance, low frequency transducer hemisphere  100  can be fitted, at its “north pole” with a suitable magnet  801 . Opposing magnet  801  is magnet  802  located on the “south pole” of mid-range frequency transducer  200  at interface  500 . Similarly, a suitable magnet  803  can be situated at the “north pole” of mid-range frequency transducer hemisphere  200  opposing magnet  804  located on the “south pole” of high frequency transducer hemisphere  300  at interface  600 . A typical ring magnet employed for this purpose is shown as  5 F in  FIG. 5 . These magnets are intended to be magnetized longitudinally with the same pole of each magnet opposing its companion magnet. For example, magnet  801  would have its south pole facing upwards while magnetic  802  has its south pole facing downwards. This will cause the magnets to repel one another and result in mid-range frequency transducer hemisphere  200  to magnetically levitate above low frequency transducer hemisphere  100  and below high frequency transducer hemisphere  300 . Cabling  810  and  820  can be employed to “tether” the various hemispheres to one another. 
         [0048]    It should be apparent that a speaker system could be configured to combine the physical structures of  FIGS. 7A and 7B . For example, mid-range frequency transducer hemisphere could be flattened at its “south pole” to enable it to physically reside upon low frequency transducer hemisphere  100  while appropriate magnets are located at the “north pole” of mid-range frequency transducer hemisphere  200  and the “south pole” of high frequency transducer hemisphere  300  to enable the latter to seemingly levitate in space. 
         [0049]    Although the present invention, to this point, has suggested the use of three hemispheres housing low frequency, mid-range frequency and high frequency transducers, the present invention can also be employed in other ways while achieving its intended sonic benefits. In this regard, reference is made to  FIGS. 8 and 9 . 
         [0050]    Turning first to  FIG. 8 , computer monitor  850  is shown being supported on table  890  in a typical residential installation. Computers, being more commonly employed as sources of acoustic input to satellite speaker systems, can now be used with speakers  860  and  870  wired to a desk top or lap top computer. 
         [0051]    In that most computer installations, particularly those employed in residential environments, value compactness, very few audio systems appended to computers are full range systems. As such, speakers  860  and  870  are employed with mid-range frequency hemispheres  861  and  871  and appended high frequency transducer hemispheres  862  and  872 , respectively. In such an installation, it is generally not desirable to include low frequency transducers noting that, when properly configured, the mid-range frequency transducers housed in hemispheres  861  and  871  provide sufficient low frequency output to satisfy most computer users. Further, the acoustic benefits described above are readily achievable in the installation shown in  FIG. 8 . 
         [0052]    Even when it comes to two channel or multi-channel home theater installations intended for use by serious audiophiles, it is not always necessary that a three hemisphere system such as that depicted in  FIGS. 1 ,  7 A and  7 B be employed. For example, many audiophiles, either because of space considerations or for aesthetic reasons, install satellite-sub systems while achieving excellent music reproduction. In this regard, reference is made to  FIG. 9  showing stands  911  and  921  supporting satellite systems  910  and  920 . 
         [0053]    A “two channel” system is shown in  FIG. 9  whereby mid-range frequency transducer hemisphere  912  is provided in conjunction with high frequency transducer hemisphere  913  as the left channel and hemisphere  922  supporting high frequency transducer hemisphere  923  constitutes the right channel of this system. Because low frequencies loose their directionality, the low frequency acoustic energy produced in system  900  can be provided by centrally-located low frequency transducers within low frequency hemisphere  950 . Alternatively, a pair of low frequency transducers housed in suitable low frequency transducer hemispheres could be placed adjacent to stands  911  and  912  to create two channel low frequency output in conjunction with the mid-range frequency transducer hemispheres and high frequency transducer hemispheres shown in  FIG. 9 . Further, low frequency transducers could be self powered by including an amplifier within or adjacent to low frequency hemisphere  950 . 
         [0054]    Lastly, where low frequency transducer hemisphere  100  of  FIG. 1  was shown supported on a suitable base  400 , as an alternative, any of the hemispheres described herein can be supported by legs or spikes  960  such as those depicted in  FIG. 9 . Such spikes could also be used to support mid-range frequency transducers hemispheres  912  and  922  upon bases  911  and  920  or upon table  890  ( FIG. 8 ) while high frequency hemispheres  913  and  923  could either be caused to levitate above mid-range frequency transducer hemispheres  912  and  922 , respectively, as discussed above or their interface surfaces could be flattened, again, as previously discussed.