Abstract:
The sound generating and transmitting apparatus is based on a radiator including at least a first, and possibly two or more, shaped reflecting surface(s) having a forward radiant axis. Each of the shaped reflecting surfaces defines sets of equivalent acoustic input locations, with each set being a ring of non-zero circumference centered on the forward radiant axis. The sound source is a distributed, functionally continuous sound source adapted to exploit this feature. In its preferred form the sound source is a sort of closed line array of loudspeakers providing a torodial shaped acoustic source to direct at the hyperbolic cone, the transducers being disposed in a circle with all of the loudspeakers oriented inwardly toward or outwardly from the forward radiant axis.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The invention relates to a directional sound system and more particularly to an acoustic source and sound reinforcement system for delivering particularly intense sound energy to a remote location or for providing a particularly rich, but highly localized, surround-sound sound field. 
         [0003]    2. Description of the Problem 
         [0004]    At issue is the construction of a sound reinforcement system which can accept inputs from a large plurality of transducers and non-destructively sum the inputs to produce a sound beam which can be directed to a particular location. Of particular interest is producing a device capable of producing a beam with high acoustic energy intensities. Also of interest is providing a system which produces a highly localized sound field and one in which an listener can enjoy a highly realistic auditory environment, including providing auditory cues corresponding to the listener&#39;s locational perspective as presented by a video system. 
         [0005]    The parabolic dish is of natural interest at any time focusing and intensification of a propagated field is desired. Meyer et al., in U.S. Pat. No. 5,821,470 described a Broadband Acoustical Transmitting System based on a parabolic reflector incorporating two loudspeaker transducers. One transducer was spaced from the dish, forward along the intended axis of propagation of sound at the focal point of the dish, a conventional arrangement. This transducer was horn loaded and oriented to propagate sound backward along the radiant axis and into the dish for reflection in a collimated beam. The horn loaded transducer was intended to handle the higher frequency components of the overall field. A second transducer for low frequency components was located opposed to the horn loaded transducer on the radiant axis, preferably flush mounted in the dish and oriented for forward propagation of sound. At this location the low frequency transducer would derive relatively little benefit from the dish as such, though the dish would serve as a baffle. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides a sound generating and projection apparatus. The apparatus is based on a radiator including at least a first, and possibly additional, shaped reflecting surface(s) having a forward radiant axis. Where more than one reflecting surface is used the radiant axes of the surfaces are coincident. Each shaped reflecting surface defines its own sets of equivalent acoustic input locations, with each set being a ring of non-zero circumference centered on the forward radiant axis. The sound sources used on the focal rings are distributed but functionally continuous sources. In its preferred form, a sound source is, in effect, a line array of loudspeakers disposed in a closed loop. The transducers are disposed in a circle with all of the loudspeakers oriented inwardly toward or outwardly from the forward radiant axis, depending upon which shaped reflecting surface is used. 
         [0007]    In its preferred embodiments the radiator includes an inner reflecting surface or both inner and outer reflecting surfaces. The inner reflecting surface is formed from a cone reflector having its axis aligned on an intended radiant axis. The outer reflecting surface, if present, is a forward concave annular ring disposed around the cone reflector. Preferably the shapes of the reflecting surfaces are parabolic relative to the forward radiant axis and define an inner surface focal ring and an outer surface focal ring. A plurality of transducers is placed along each focal ring with the individual transducers turned into the reflecting surfaces. The transducers are arrayed with spacing between the transducers chosen by reference to the highest intended operating frequency of the device. 
         [0008]    Additional effects, features and advantages will be apparent in the written description that follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
           [0010]      FIG. 1  is a perspective view of a sound projector based on an interior cone reflector. 
           [0011]      FIG. 2  is a perspective view of a second embodiment sound projector having inner and outer reflecting surfaces with coincident forward radiant axes. 
           [0012]      FIG. 3  is a cross sectional diagram depicting operation of an inner reflecting surface for a sound radiator in accordance with the invention. 
           [0013]      FIG. 4  is a cross sectional view of the sound generating and transmitting apparatus of a first embodiment of the invention. 
           [0014]      FIG. 5  is a plan view illustrating operational divisions of the loudspeaker array for the first embodiment of the invention. 
           [0015]      FIG. 6  is a high level schematic of circuitry for the sound projector of  FIG. 5 . 
           [0016]      FIG. 7  illustrates an application for the embodiment of the invention illustrated in  FIGS. 5 and 6 . 
           [0017]      FIG. 8  is a cross sectional illustration of a embodiment of the invention having first and second reflecting surfaces. 
           [0018]      FIG. 9  illustrates an arrangement of high frequency transducer elements for the projector of  FIG. 8 . 
           [0019]      FIG. 10  is a cross sectional view of a variation of the projector of  FIG. 8 . 
           [0020]      FIGS. 11A-D  are, respectively, a top plan, a side elevation, a front elevation and a perspective view of a portable sound projector incorporating the radiator and toroidal radial array of the invention. 
           [0021]      FIGS. 12A-C  are side elevations illustrating characteristic dispersion for sound fields produced by the projector of  FIGS. 11A-D . 
           [0022]      FIG. 13  is a cross sectional view of the radiator and loudspeaker array of the projector of  FIGS. 11A-D . 
           [0023]      FIG. 14  is a graph of frequency response over distance for a representative system incorporating the invention. 
           [0024]      FIG. 15  is a polar graph of the conical output. 
           [0025]      FIG. 16  is a impulse response graph. 
           [0026]      FIG. 17  is a time over energy graph. 
           [0027]      FIG. 18  illustrates phase and energy over frequency. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Referring to the Figures and in particular to  FIG. 1  a first embodiment of the invention is illustrated. A sound projector  10  projects a sound field forward on the radiant axis RA of the device. Sound projector  10  incorporates a first reflecting surface formed by a cone reflector  14  mounted inside a cylindrical shell  12  to produce a highly collimated sound field. The central axis of cone reflector  14  lies on the radiant axis RA. 
         [0029]    In an alternative embodiment of the invention illustrated in  FIG. 2 , a sound projector  11  provides two primary acoustically reflective surfaces, the first corresponding to the outer surface of cone reflector  14  and a second surface formed by a forward concave annular ring  16  which is disposed outwardly from and surrounding the cone reflector  14 . Both surfaces are housed within a shell  20 . Also located within shell  20  circumferentially surrounding and just outside the base of cone reflector  14  is an annular transducer array section  18  from which sound is directed both inwardly on and outwardly from the radiant axis RA against the reflecting surfaces. 
         [0030]    An advantageous location of the annular transducer array section  18  is illustrated by reference to  FIG. 3 , which shows a cone reflector  14  which is shaped so that sections of the cone reflector, taken in planes including the radiant axis RA, are parabolic providing a global hyperbolic reflective surface  22  with a focal ring FR. The focal ring FR has a non-zero circumference and surrounds the cone reflector  14  and is centered on the radiant axis RA. Transducers are located on the focal ring of the cone reflector  14  and oriented to direct sound energy against the cone reflector. Such placement of the transducers results in a highly collimated forward sound field exhibiting little dispersion. It might be observed that if the transducers are moved forward and backward parallel to the radiant axis RA (as indicated by double headed arrow A), the field can be made more dispersive, or given a far field convergence point forward from cone reflector  14 . 
         [0031]      FIG. 4  illustrates placement of a plurality of loudspeaker transducers  26  at discrete, evenly spaced locations along a focal ring surrounding cone reflector  14 . In the illustrated embodiment the loudspeakers  26  are directed inwardly on the radiant axis RA with generated sound being reflected forward along the radiant axis in a low dispersion collimated beam. Some leakage occurs toward the tip of the cone reflector  14  due to lack of reflective surface area. In some embodiments a substantial portion of the tip of cone reflector  14  may be dispensed with. Loudspeakers  26  are arranged in what is in effect an annular, closed loop line array  24 , with the loudspeakers  26  installed in a sealed enclosure  30  and emitting sound through an annular baffle  28 . Loudspeakers  26  are located discretely spaced from one another by no more than one quarter of a wavelength of the highest intended operating frequency of the device. 
         [0032]    It is not necessary that every loudspeaker  26  be part of the same channel. An extraordinarily rich surround sound system can be provided a listener located directly forward of the unit by dividing the array into zones.  FIG. 5  illustrates division of the transducers  26  of an array into eight zones. The zones are categorized by a visual context to provided the listener by an associated video system (See  FIG. 7 ). The direction “forward” from the observer, that is the expected focus of interest in a field of view, may be correlated with center zone  32  (zone  2 ). Moving clockwise around the array are provided successively: a right front zone  33  (zone  3 ); a right side zone  34  (zone  4 ); a right rear zone  35  (zone  5 ); a stub rear zone  36  (zone  5 / 6 ) to which may be applied a mix of the signals from the fifth and sixth channels; a left rear zone  37  (zone  6 ); a left side zone  38  (zone  7 ); and a left front zone  31  (zone  1 ). Each zone receives its own input channel as illustrated in  FIG. 6 . In  FIG. 6 , for purposes of the exemplary block diagram circuit  40 , it is assumed that an audio signal is provided from a DVD player  42  or comparable source. The audio signal is applied to a receiver  44  for recovery and division into the basic set of channels. Each channel is applied to a digital signal processor  46  and from there the preamplifier  48 ,  52 ,  54 ,  56 ,  58 ,  60 ,  62 ,  64  for each channel plus the subwoofer  50  channel. 
         [0033]      FIG. 7  illustrates how a listener o may be positioned relative to a sound projector  70  incorporating a cone reflector  14  and zonal division of its transducer array. A sound field SF is produced which provides a surround sound experience oriented based on the visual context provided by video devices  66 . 
         [0034]    Referring to  FIGS. 8-10  an alternative embodiment of the invention is illustrated incorporating a reflector with inner and outer reflecting surfaces. The inner reflecting surface  82  is provided by the cone reflector  14 , which is preserved from the first embodiment of the invention. A second, outer reflecting surface  84  is provided by a forward concave annular ring  16 . Outer reflecting surface  84  is preferably parabolic in its sections, but differs from a conventional parabolic dish in that the bases of the parabolic sections to not meet at a single point in the base of the dish, but instead surround an annular gap in which cone reflector  14  may be placed. The term “parabolic” is intended to include functionally equivalent surfaces constructed from flat segments which average to a parabola. The term parabola is applied to curves of the reflecting surfaces in planes. The overall reflective surfaces are considered hyperbolic because they do not have focal points but rather “focal rings”. In addition, outer reflecting surface  84  would function without inner reflecting surface  82 , though such an arrangement would have a larger than necessary footprint. 
         [0035]    In  FIGS. 11A-D  an application of sound projector  110  mounted on a tripod  112  is illustrated from various perspectives and contrasted in size with an operator T, who may be taken as standing about 6 feet in height. The aperture A of projector  110  is about 30 inches and exposes a radial torodial array  114  disposed around the base of cone reflector  116 . Sound projector  110  is installed on an altazimuth mount  118  which allows rotation on the tripod  112  base to control azimuth and pivoting on a fork  120  to control altitude. A gun sight type element  117 , potentially including a camera for remote control, may be provided to aim sound projection  110 . 
         [0036]    In  FIGS. 12A-C  the characteristic sound field dispersions illustrating a polar sound field SF 1 , a focused sound field SF 2  with a far field convergence CP and a sound field SF 3  with 30 degrees of dispersion. Far field convergence CP and the angle of dispersion are selectable using the mechanism of  FIG. 13 . For a hyperbolic cone reflector  116  which, by virtue of its parabolic sectional shape has a focal ring, the dispersion characteristics of a forward projected sound field are controllable by relative movement of the toroidial radial array  114  parallel to the radiant axis of the reflector. This of course can be achieved by movement of either the array  114  or the reflector  116 . As illustrated the reflector has been equipped with a worm drive  124  driven by a simple servo actuator motor  126  for displacing the cone reflector  116  relative to the ring array  114 . The worm drive  124  could also drive a pointer to a graph indicating neutral, dispersion angle and meters to the convergence point. Naturally the system could be equipped with sophisticated range finding allowing automation of focus selection once a target had been selected by an operator. 
         [0037]    The parabolic section for a hyperbolic cone reflector follows the equation: 
         [0000]        Y=X   2 /4 F    
         [0038]    where F is the focus, X is width and Y is height. Non-parabolic section curves are conceivable, as is a cone reflector with flat faces. Most such faces would not provide focusing as do the preferred hyperboloids. 
         [0039]      FIG. 14  illustrates frequency response over distance for a representative system incorporating the invention by a series of response curves, each representing a doubling of distance over the next higher curve along the center radiant axis of the projector. The projector response follows a near inverse square (−6 db per doubling of distance) in the lower frequencies but a substantially smaller drop at higher frequencies. In the highest frequency bands the output of the projector can be focused to a beam waist in a manner analogous to light allowing higher outputs at distance than close to the device. The lowest frequency knee point of the coherent focus phenomena is a function of the hyperboloid shape and the diameter (which effects the available surface area) of the cone reflector used. The larger diameter used the lower the frequency obtainable for coherent focus. The kneepoint wavelength seems to be about 4× the diameter of the cone reflector. The reflector works at lower frequencies, but outputs follow the inverse square law. 
         [0040]      FIG. 15  is a polar graph for a radiator having a hyperbolic reflector and an 18 inch diameter and shows a 2 to 3 degree dispersion centered on the radiant axis of the device (0 degrees). The strongest line is just counterclockwise from 0 degrees (at 2 degrees) at the 97.5 db output level. The other eight lines are substantially less at the 90 to 91 db range and vary to both sides of the 0 degree line. The larger the diameter of the hyperboloid reflector the greater the degree of coherent focus obtainable. A 12 inch diameter device obtains 6 to 7 degrees of dispersion while a 48 inch device has less than 1 degree of dispersion in its usable bandwidth. 
         [0041]      FIG. 16  is an impulse response graph showing that a sound beam produced by the device has almost no resonance relegated energy. 
         [0042]      FIG. 17  is a graph of time versus energy. Showing an extremely sharp peak in the pulse defining the precise time alignment of a system incorporating  30  loudspeakers in a toroidal radial array. Again a high degree of coherence of the summation of multiple sources into a single beam with high efficiency. 
         [0043]      FIG. 18  illustrates phase (bottom curve) and energy (top curve) over usable frequency (12 Khz to 23 Khz) for a system using 30 input sources. Typically high efficiency horn loaded loudspeakers exhibit several hundred degrees of phase shift over their operating range, however here the total phase shift over used bandwidth is less than 150 degrees. This result is highly consistent with very precise and linear high amplitude output. 
         [0044]    The present invention provides a sound system which allows inputs from a potentially large plurality of sources located at acoustically equivalent locations with non-destructive summing of the sources to produce a collimated sound field. In some embodiments different zones within the sound field can be used to produce a rich surround sound environment keyed to visual ques provided over visual display devices. 
         [0045]    While the invention is shown in only a few of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.