Patent Publication Number: US-6668969-B2

Title: Manifold for a horn loudspeaker and method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Applicants claim the benefit of provisional application No. 261,113, filed Jan. 11, 2001 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to horn loudspeaker systems and more particularly to manifolds for coupling one or more acoustic drivers to a loudspeaker horn. The invention still further relates to improvements in the horn and horn manifold of a horn loudspeaker system which improve the directional characteristics of the loudspeaker without introducing significant distortion. The invention is particularly useful in arraying horn loudspeaker systems to achieve desired coverage while avoiding undesirable interactions between the horns. 
     To optimize a horn speaker system array, it is often desirable to control the dispersion characteristics of the horn such that the dispersion is narrow in the direction of the array and wide in the direction perpendicular to the array. Thus, in the case of a vertical stack of horn loudspeakers, destructive interaction between the acoustic output from the individual horns is minimized by controlling vertical dispersion. At the same time broad horizontal coverage is maintained for achieving desired audience coverage. 
     The existing approaches to horn loudspeaker design involve coupling the output of an acoustic driver to the throat end of a horn wherein the dispersion characteristics of the horn are governed by the horn design itself. Improved horn designs have been devised to achieve improved control over the directivity of a horn over a broad range of frequencies. Such a loudspeaker horn is disclosed in U.S. Pat. No. 5,925,856 issued to John D. Meyer et al., wherein a loudspeaker horn is provided with a special rectangular throat geometry and pre-load chamber for achieving uniform frequency response and coverage characteristics with low distortion. Such designs, however, are limited in their ability to achieve a suitably narrow dispersion that would permit an optimal array of the horns. 
     Another prior art approach to coupling drivers to a loudspeaker horn is disclosed in U.S. Pat. No. 4,629,029 issued to David W. Gunness. This patent discloses a manifold for connecting multiple drivers to the throat end of a horn so as to increase the acoustic power delivered by the horn. Again, such arrangements are limited by the horn&#39;s directional control properties. Generally, highly directional horns can be achieved with long, slow, expanding horns, but even here the dispersion of the horn has a practical upper limit of about 20 degrees. Such long horn lengths are undesirable since distortion produced by the horn increases by the number of wavelengths over which the sound pressure waves are confined in the horn. 
     The present invention overcomes the inherent limitations of existing loudspeaker horn designs by providing a loudspeaker system and a manifold for a loudspeaker system which greatly improves the designer&#39;s ability to control the dispersion characteristics of the horn. More specifically, the present invention provides a horn loudspeaker system and horn manifold which permits a horn to be driven by one or more acoustic drivers in a manner which achieves a narrow dispersion characteristic in one direction and a wide dispersion characteristic in the other to permit the loudspeakers to be arrayed easily without destructive interaction between their acoustic outputs. 
     SUMMARY OF THE INVENTION 
     The invention involves a horn loudspeaker system wherein one or more acoustic drivers are coupled to the throat end of a horn having an elongated throat opening. At least one acoustic driver of a loudspeaker system is coupled to the horn&#39;s elongated throat opening by means of a manifold having an input end with at least one input port and an output end with at least two and suitably multiple aligned output ports. The aligned output ports of the manifold are connected to the input port by separate acoustic power waveguides. The acoustic power introduced to the input port of the manifold is divided between and passes through these waveguides so as to emerge from the manifold output ports as a virtual line array of acoustic power sources which are presented to the elongated throat opening of the horn. The manifold waveguides preferably have approximately equal acoustic path lengths such that the acoustical waves of the acoustic power divided between the waveguides arrives approximately in phase at the aligned output ports of the manifold. 
     For a horn whose elongated throat opening is oriented vertically, the manifold provides a vertical line array of output ports to simulate a vertical column of individual acoustic power sources in the throat of the horn. These individual acoustic power sources interact in accordance with well-known line array theory to control vertical dispersion from the line array. Thus, the vertical dispersion characteristics of the horn connected to the manifold are mainly governed by the line array characteristics of the horn&#39;s elongated throat opening instead of by the design characteristics of the horn itself. The horn provides an additional element of directional control, and acts to block any side lobes that may be generated at the horn&#39;s throat end by physical separation of the output ports of the driver manifolds. 
     In a further aspect of the invention, the length of each waveguide of the driver manifolds is relatively short in length in relation to the wavelength of the acoustical waves passing through the manifold at the highest frequency at which the horn loudspeaker system is intended to operate. Preferably, the manifold waveguides have acoustic path lengths no longer than approximately three wavelengths at the highest operating frequency. Suitably, for a horn loudspeaker system having upper frequency range of 15,000 Hz, the length of the manifold would be in the range of 3 inches. Manifolds substantially exceeding 3 inches in length would produce relatively long acoustical path lengths between the input port and aligned output ports of the manifold at high frequencies, resulting in increased distortion in the sound pressure wave as it passes through the waveguides. On the other hand, in manifolds substantially shorter than 3 inches in length, the bends in the waveguides used to equalize acoustical path lengths would increase to the point where the bends would produce excessive reflections within the manifold. 
     In still a further aspect of the invention, each of the manifold waveguides increases in cross-sectional area from the input port of the manifold to the output port of each waveguide. Such expansion acts to further reduce the distortion effects the waveguide has on the acoustic sound waves as they pass through the manifold. 
     The invention also involves a method for providing control over the dispersion characteristics of a horn loudspeaker which includes providing both a source of acoustic power and a loudspeaker horn with an elongated throat opening, dividing the acoustic power produced by the acoustic power source between at least two acoustical paths, and propagating the divided acoustic power along the at least two acoustical paths to two separate aligned outputs at the elongated throat opening of the horn so as to simulate a line array of acoustic power sources at the elongated throat opening. 
     Therefore, it is a primary object of the invention to provide a manifold for a loudspeaker horn and a method of driving a loudspeaker horn which permits tighter control over the dispersion characteristics of a horn loudspeaker system. It is another object of the invention to provide a horn loudspeaker system which can be readily arrayed without destructive interaction between the acoustic outputs of the loudspeakers. It is a further object of the invention to provide a horn loudspeaker system and method with the foregoing advantages which can minimize distortion. Yet Other objects of the invention will be apparent from the following description and claims. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a horn loudspeaker system in accordance with the invention using two closely spaced compression drivers. 
     FIG. 2 is a cross-sectional view thereof taken along lines  2 — 2  in FIG.  1 . 
     FIG. 3 is a cross-sectional view thereof taken along lines  3 — 3  in FIG.  2 . 
     FIG. 4 is a front elevational view of the horn of the horn loudspeaker system shown in FIGS. 1-3. 
     FIG. 5 is a rear elevational view thereof. 
     FIG. 6 is a top perspective pictorial representation of a manifold in accordance with the invention for use with one acoustic driver. 
     FIG. 7 is another top perspective view thereof. 
     FIG. 8 is a top plan view thereof. 
     FIG. 9 is an end perspective view thereof. 
     FIG. 10 is a front elevational pictorial view of a manifold in accordance with the invention for two side-by-side acoustic drivers as shown in FIG.  1 . 
     FIG. 11 is a rear elevational view thereof showing eight aligned output ports of the manifold. 
     FIG. 12 is a end elevational view of a manifold block having two input ports and eight output ports as in the manifold pictorially illustrated in FIGS. 10-11, and showing how the block is sectioned in FIGS. 12B-12F to reveal the relative shapes and positions of the manifold waveguides as the manifold waveguides progress from the two input ports to the eight output ports of the manifold. 
     FIG. 12A is a front elevational view thereof as seen from lines  12 A— 12 A of FIG.  12 . 
     FIG. 12B is a cross-sectional view thereof taken along lines  12 B— 12 B of FIG.  12 . 
     FIG. 12C is a cross-sectional view thereof taken along lines  12 C— 12 C of FIG.  12 . 
     FIG. 12D is a cross-sectional view thereof taken along lines  12 D— 12 D of FIG.  12 . 
     FIG. 12E is a cross-sectional view thereof taken along lines  12 E— 12 E of FIG.  12 . 
     FIG. 12F is a cross-sectional view thereof taken along lines  12 F— 12 F of FIG.  12 . 
     FIG. 12G is a rear elevational view thereof as seen from lines  12 G— 12 G of FIG.  12 . 
     FIG. 13 is a top perspective view of a manifold in accordance with the invention comprised of assembled molded manifold blocks, and illustrates a technique for fabricating a manifold with manifold waveguides or the sort pictorially illustrated in FIGS. 6-11. 
     FIG. 14 is a front elevational view thereof. 
     FIG. 15 is a rear elevational view thereof. 
     FIG. 16 is an exploded view of the manifold block assembly shown in FIG.  13 . 
     FIG. 17 is a top perspective view of one of the center blocks of the manifold block assembly shown in FIGS. 13-16. 
     FIG. 18 is a top perspective view of one of the end blocks of the manifold block assembly shown in FIGS. 13-16. 
     FIG. 19 is a top perspective view of another one of the end blocks of the manifold block assembly shown in FIGS. 13-16. 
     FIG. 20 illustrates a modified version of the loudspeaker horn shown in FIGS. 1-5, used to gain greater control over the dispersion characteristics of a horn loudspeaker using a manifold in accordance with the invention. 
     FIG. 21 is a front elevational view thereof. 
     FIG. 22 is a rear elevational view thereof. 
     FIG. 23 is a cross-sectional view thereof taken along lines  23 — 23  of FIG.  22 . 
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     Referring to FIGS. 1-3 of the drawings, a horn loudspeaker system  11  includes a horn  13  having mouth end  15  and two closely spaced compression drivers  17  mounted to the horn&#39;s back end  19 . The back end of the horn has an enlarged manifold mounting chamber  21  for holding the driver manifold hereinafter described. The placement of the driver manifold in mounting cavity  21  is illustrated in FIGS. 2 and 3, where a manifold is indicated by a phantom line representation of the acoustic power waveguides of a two driver manifold as hereinafter described. 
     The design of the horn of the horn loudspeaker system shown in FIGS. 1-3 is further illustrated in FIGS. 4-5. Referring to these figures, it can be seen that the horn&#39;s substantially square mouth  15  has a perimeter mounting flange  16  for mounting the horn to a speaker cabinet. As best shown in FIG. 5, flared vertical sidewalls  25  extend inwardly to form an elongated throat opening  27  which extends between slightly flared top and bottom sidewalls  29 . As hereinafter described, this elongated opening allows a virtual line array of acoustic sources to be created at the throat of the horn from the two compression drivers  17  which are mounted to a mounting flange  31  at the back end of the horn. 
     A simple single driver manifold in accordance with the invention is pictorially illustrated FIGS. 6-9. Referring to these figures, manifold  33  is shown as having an input port  35  and four aligned output ports  37 ,  39 ,  41 ,  43  connected to the single input port by four acoustic power waveguides  45 ,  47 ,  49 ,  51 . The waveguides are arranged in the manifold such that their acoustical path lengths between input port  35  and output ports  37 ,  39 ,  41 ,  43  are approximately equal. To provide for approximately equal acoustical path lengths between the input port and the four aligned output ports, the two outer waveguides  45 ,  51  are straight and angled while the two inner waveguides  47 ,  49  are curved. The curved inner waveguides  47 ,  49  are seen to terminate at the two inner output ports  39 ,  41  so as to place these output ports in alignment with the outer ports  37 ,  43  associated with the two straight outer waveguides. 
     Referring to FIG. 7, it can be seen that the input port  35  is partitioned into four quarter circles  35   a ,  35   b ,  35   c ,  35   d  which form the start or first ends of the four manifold waveguides  45 ,  47 ,  49 ,  51 . It is also seen that the four waveguides of the manifold transition from these quarter circular shapes to a rectangular shape at the second terminal end of the waveguides, that is, the ends that form the aligned output ports. As also shown and as further described below, the cross-sectional area of each waveguide expands from a relatively small cross-sectional area at the input port  35  to a larger cross-section at the output port as acoustic waves progress through the waveguide. It has been found that such cross-sectional area expansion will act to reduce distortion as the sound pressure waves pass through the manifold. A manifold might, for example, be provided with a circular input port measuring 1½ inches in diameter to couple to a compression driver having a four inch inverted dome. The circular input port bifurcates into clusters of four initially quarter-circle waveguide ends having a cross-sectional area of about 0.44 square inches. Each of the waveguides can suitably be allowed to expand to form a rectangular output port about ¾ inch wide and 1¼ inches long having a cross-sectional area of about 0.93 square inches. With such a transition and expansion, the cross-sectional area of each of the waveguides roughly doubles between the input or output ends of the manifold. 
     Preferably, the length of the manifold from its input port  35  to its aligned output ports  37 ,  39 ,  41 ,  43  is kept as short as possible such that sound waves are retained in the manifold for as short a period of time as possible. Physically, it is desirable to keep the length of the manifold no longer than approximately three wavelengths at the highest operating range of the horn loudspeaker system. For a horn loudspeaker having a high end operating range of 15,000 cycles, a manifold length of approximately 3 inches would be suitable. 
     FIGS. 10-11 pictorially illustrate a manifold for use with two side-by-side drivers as shown in FIGS. 1-3. It is understood that this manifold could be fabricated as a single manifold or as two separate side-by-side manifold sections. 
     Specifically, manifold  53  has two side-by-side input ports  57 ,  59  for receiving acoustic power from two compression drivers, and four aligned output ports  61 ,  63 ,  65 ,  67  and  69 ,  71 ,  73 ,  75  associated with each input port for a total of eight aligned output ports. The aligned array of output ports are positioned in front of the elongated throat opening  27  of the loudspeaker system&#39;s horn  13  to produce a line array of eight virtual acoustic power sources along the throat opening. Each output port has an associated straight or curved acoustic power waveguide connecting the output port with its associated input port. Thus, output ports  61 ,  63 ,  65 ,  67  are seen to be connected to input port  57  by straight outer waveguides  62 ,  68  and curved inner waveguides  64 ,  66 , while output ports  69 ,  71 ,  73 ,  75  are connected to input port  59  by straight outer waveguides  70 ,  76  and curved inner waveguides  72 ,  74 . As with the single driver embodiment of FIGS. 6-9, the acoustical path lengths of all eight waveguides of the two driver embodiment are preferably approximately equal, such that the power delivered by the two compression drivers  17  arrive at the eight aligned output ports approximately in phase. 
     FIGS.  12  and  12 A- 12 G show a two driver, eight output port manifold as depicted in FIGS. 10 and 11 fabricated as a manifold block  80  having an input end  82  and output end  84 . These figures also show how the two sets of waveguides of the manifold transition from clustered quarter circles at the two manifold input ports to a line array of eight rectangular output ports. FIG. 12A shows the quarter partitioned input ports  57 ,  59  at the input end of the manifold block. Proceeding from the input end  82  toward the output end  84  of the manifold block as shown in FIGS. 12B-12F, the waveguides  62 ,  64 ,  66 ,  68 , and  70 ,  72 ,  74 ,  76  formed in the block diverge from a cluster of guides into an aligned orientation; they also expand from a quarter round shape to an almost rectangular shape of a larger cross-sectional area. At the block&#39;s output end  84  the waveguides emerge as eight fully aligned and fully rectangular output ports  61 ,  63 ,  65 ,  67 ,  69 ,  71 ,  73 , and  75  as shown in FIG.  12 G. This block is inserted into the manifold mounting chamber  21  at the back end of the horn  13  shown in FIGS. 1-5, with the output end  84  and its eight aligned output ports facing the elongated throating opening of the horn. 
     With line array of eight rectangular output ports shown in FIGS. 10-12, and with rectangular openings having a 1¼ inch long dimension aligned in the direction of the elongated throat opening, a suitable separation for the output ports is approximately 1¾ inches center-to-center. With such a separation, dispersion in the direction of the elongated throat opening of the horn can be tightly controlled at most frequencies within the operating frequency range of the horn, with a dispersion of 10 degrees or better being achievable at high frequencies. Such tightly controlled dispersion characteristics can be extended into lower frequency ranges by increasing the length of the line array at the throat end of the horn, however, physical limitations will dictate trade-offs in these regions. 
     FIGS. 13-19 illustrate a means for constructing a driver manifold of the invention from molded parts, suitably using an ABS plastic material. FIGS. 13-16 show a manifold block assembly  81  comprised of two identical center blocks  83  and two pairs of end blocks  87 ,  89 . As hereinafter described, these blocks, when assembled, form the waveguides of the two driver manifold  53  illustrated in FIGS. 10 and 11. When assembled, eight aligned rectangular output ports  61 ,  63 ,  65 ,  67 ,  69 ,  71 ,  73 ,  75 , appear along assembled block&#39;s rear face  91 . This forms the output end of the manifold. When assembled, the block assembly further creates two input ports  57 ,  59  on its front face  93  which constitutes the manifold&#39;s input end (see FIG.  15 ). 
     FIGS. 17-19 illustrate the individual blocks of the manifold block assembly  81 . In describing these blocks, and their assembly, it again noted that the output ports and waveguides of the manifold can be divided into two sets of output ports and waveguides corresponding to the manifold&#39;s two input ports. More specifically, the manifold block assembly has a first set of output ports  61 ,  63 ,  65 ,  67 , which include outer ports  61 ,  67  and inner ports  63 ,  65 . A corresponding first set of acoustic power waveguides  62 ,  64 ,  66 ,  68  include substantially straight outer waveguides  62 ,  68  and curved inner waveguides  64 ,  66 . Similarly, a second set of output ports  69 ,  71 ,  73 ,  75  include outer output ports  69 ,  75  and inner output ports  71 ,  73 . A second set of corresponding acoustic power waveguides  70 ,  72 ,  74 ,  76  include outer substantially straight waveguides  70 ,  76  and two curved inner waveguides  72 ,  74 . 
     Referring to FIG. 17, each of the two center blocks  83  are seen to include an interior face  95 , back wall  97  (corresponding to the output end of the manifold), a front wall  99  (corresponding to the input end of the manifold), and slightly angled end walls  101 ,  103 . Straight channels  105 ,  107 , which are formed in the interior face  95  of the block, angle inwardly from the block&#39;s front wall  99  at corners  109 ,  111  to the block&#39;s back wall  97 . The channels terminate near the center of the back wall to provide half rectangular openings  113 ,  117  which form one-half of two of the outer output ports of the manifold. Specifically, the half opening  113  of channel  105  forms one-half of the outer output port  67 , whereas the half opening  115  of channel  107  forms one-half of the outer output port  69 . 
     It is seen that each of the channels  105 ,  107  have different transitional shapes. Channel  105  transitions from the half rectangular opening  113  down to a quarter circle opening  117  at the far corner  109  of front wall  99 . Conversely, channel  107  transitions from a half rectangular opening  115  down to a straight edge  119  at the near corner  111  of the front wall. When the interior faces  95  of the two center blocks  83  are placed together as shown in the exploded view of FIG. 16, channel  105  of one center block will oppose channel  107  of the other center block to form two of the straight waveguides of the manifold. 
     It is further seen that the near end wall  103  of each of the center blocks  83  includes a curved channel  121  for providing one of the curved waveguides of the manifold. Curved channel  121  terminates at the block&#39;s back wall  97  in a partial rectangular opening  123 ; at the other end it terminates at the block&#39;s front wall  99  to produce opening  125 . The partial opening  123  forms a portion of one of the inner output ports of one of the two sets of output ports, whereas opening  125  is a quarter circle which forms one quadrant of one of the manifold&#39;s circular input ports. 
     The back wall of each center block additionally includes an angled notch  127  along the block&#39;s interior edge  129  at the end of the block opposite curved channel  121 . When the two center blocks are assembled face-to-face, this notch will provide a completion of the rectangular opening  123  to form one of the inner rectangular output ports of the block assembly. When assembled, the two center blocks of the manifold block assembly will thus provide one outer and one inner output port for each set of output ports of the manifold (a total of four output ports), as well as their corresponding straight and curved waveguides. As best shown in FIG. 15, the two center blocks, when assembled, also provide one-half of each of the input ports of the manifold. 
     The center blocks are seen to additionally include dowel pins  131  and dowel holes  133  on the end walls of the blocks to permit the attachment of end blocks  87 ,  89  to the center blocks in a proper alignment. Key slots  135 ,  137  are additionally provided at the ends of the center blocks to allow the center blocks and end blocks to be locked together with a locking key member (not shown). 
     Referring to FIG. 18, the two end blocks  87  of the manifold block assembly include interior face  139 , back wall  141 , front wall  143 , and an end wall  145  which is slightly inclined to match the angle of end walls of the center blocks. As with the center blocks, the back wall of these end blocks correspond to the output end of the manifold whereas the front wall  143  corresponds with the input end. Dowel pins  147  are provided in the end wall  145  which insert into the dowel holes of the center blocks. 
     The end blocks  87  are seen to include a single substantially straight channel  149  formed in the blocks interior face  139 . This channel extends at an angle through the block from the block&#39;s front wall  143  at upper corner  151  to the block&#39;s back wall  141 . This straight channel also transitions from a corner circle opening  153  at the block&#39;s front wall, to a one-half rectangular opening  155  at the block&#39;s back wall. Opening  155  provides one-half of one of the outer rectangular output ports of the manifold, while opening  153  provides one-quarter of one of the manifold&#39;s input ports. The back wall  141  of each end block  87  still further includes an angled notch  157  for providing a portion of one of the inner output ports when the center block is matched with one of the end blocks  89  described below. Key slot  159  in the end block provides a link to key slot  137  in the center block for locking the blocks together with a key lock member. 
     FIG. 19 shows one of the end blocks  89  which, in the assembled manifold block, faces one of the end blocks  87 . End block  89  includes interior face  161 , back wall  163 , front wall  165 , and an inclined end wall  167  with dowel holes  169 . It also includes a key slot  170  for key locking these end blocks to the center blocks. An angled straight channel  171  formed in the interior face  161  of the block terminates at the back wall  163  in a one-half rectangular opening  173  and at the front wall  165  at an edge  175 . When an end block  87  is placed together with one of the end blocks  89 , the straight channels  149 ,  171  in the two end blocks will form one of the straight outer waveguides of the manifold assembly in a manner similar to the above-described way the two straight waveguides are formed by the two center blocks. When the end blocks are placed together, the one-half rectangular openings  155 ,  173  formed by these channels similarly form one of the outer output ports of the manifold (either output port  61  or output port  75 ). 
     The end block  89  shown in FIG. 19 also includes a curved channel  176  which terminates at the back wall  163  in a partial rectangular opening  177  and at the front wall  165  in a quarter-circle opening  179 . Similar to the curved channel  121  of center blocks  83 , the curved channel  176  in end block  89  provides one of the curved inner waveguides of the manifold. Also, when blocks  87  and  89  are assembled, the partial rectangular opening  177  in block  89  and the notch  157  of block  87  will meet to form one of the inner output ports of the manifold&#39;s aligned array of output ports (either output port  63  or output port  73 ). Similarly, the curved opening  179  will form one-quarter of one of the input ports of the manifold. 
     Thus, it can be seen that the assembly of the center blocks  83  with the end blocks  87 ,  89  of the manifold as illustrated in FIG. 16 will provide a manifold block assembly having two input ports and two sets of four output ports connected to the input ports by straight and curved waveguides. By providing curved waveguide paths, the acoustical path length of inner waveguides of the two sets of waveguides can be made approximately equal to the acoustical path length of the outer straight waveguides. Also, the waveguides can be constructed such that the first end of the waveguide, that is, the end at one of the input ports of the manifold, has the shape of a quarter-circle, and such that the first ends of the four waveguides associated with the input port meet in a cluster to form a completely circular input port. The waveguides can also be made to transition from quarter-circles at the input port to rectangular shapes at the manifold&#39;s output ports. This transition occurs while the cross-sectional area of the waveguide progressively increases through the manifold. 
     FIGS. 20-23 illustrate an alternative embodiment of a loudspeaker horn which can be used to gain greater control over the dispersion characteristics of a horn loudspeaker using a manifold in accordance with the invention. In FIGS. 20-23, the horn  183  is similar to the horn illustrated in FIGS. 1-5, except that the horn includes the addition of a series of fins  185   a - 185   g  which extend between the horn&#39;s flared side walls  187 , and from the horn&#39;s elongated throat opening  189  toward its mouth opening  191 . The fins are distributed along the elongated throat opening such that they will be positioned between the output ports of a manifold placed in the manifold mounting chamber  193  at the back end of the horn. 
     Specifically, this horn design is shown as having seven fins which would correspond to a two driver manifold such as illustrated in FIGS. 10-11 having eight rectangular output ports arranged in two sets of four output ports corresponding to two input ports. Referring to FIGS. 10 and 11, the first set of output ports  61 ,  63 ,  65 ,  67  correspond to input port  57 , and the second set of output ports  69 ,  71 ,  73 ,  75  correspond with input port  59 . Of these two sets of output ports, the outer ports of each set, namely ports  61 ,  67  and  69 ,  75 , are associated with the straight waveguides of the manifold, namely, waveguides  62 ,  68  and  70 ,  76 , whereas the inner output ports of each set, namely ports  63 ,  65  and  71 ,  73 , are associated with the inner curved waveguides of the manifold, namely, waveguides  64 ,  66  and  72 ,  74 . Inset blocks  195   a - 195   d  are inserted between the fins governing the inner output ports  63 ,  65  and  71 ,  73  associated with the curved waveguide paths. Each of these inset blocks include a steeply angled wall  197  having a base end  199  which has the effect of decreasing the area of the horn&#39;s throat at inner rectangular output ports, as shown in FIG. 22 by the restricted openings  200  in elongated throat  189 . 
     The fins of this horn design provide two primary functions. The first is to vertically straighten the higher frequency sound delivered by the center-most output ports of the manifold&#39;s eight output ports, namely, output ports  67 ,  69 . The other is to provide isolation between the output ports of the manifold so that the effects of the curved acoustical paths on the sound passing through the manifold can be corrected for on an individual basis. The effects of the curved acoustical paths are corrected by the blocks placed between those fins which surround the output ports associated with the curved paths, namely, between fins  185   a  and  185   b ,  185   b  and  185   c ,  185   e  and  185   f , and  185   f  and  185   g.    
     More specifically, the inset blocks are used to counteract the tendency of curved acoustical paths to steer the higher frequencies. To keep the coverage of the horn loudspeaker relatively even and distributed properly at high frequencies, inset blocks  195   a - 195   d  cause the walls of the horn to effectively be brought into the horn&#39;s throat at a steeper angle adjacent those output ports of the manifold associated with curved waveguide paths. Also, by effectively restricting the horizontal width of these output ports, the ports receiving acoustic power through the curved waveguide paths will tend to disburse the high frequency sound emanating from the curved acoustic paths more evenly. 
     Also, it is noted that the angled wall  197  of the inset blocks projects up pass the block&#39;s cross wall support  201  to create a projecting tower structure  203 . It is found that such a tower structure creates more favorable boundary conditions at the top of the inset block for producing more even and properly distributed coverage of the sound. 
     The horn shown in FIGS. 20-23 is illustrative of horn modifications that can be made to achieve desired dispersion characteristics of a horn loudspeaker using the manifold of the invention over a desired frequency range. Specific designs to achieve specific dispersion characteristics are achieved through trial and error. It is understood that the variety of horn designs and modifications could be implemented with the manifold of the invention to achieve desired results. 
     Therefore, it can be seen that the present invention provides for a manifold for a horn loudspeaker that can be used in conjunction with a horn having an elongated throat opening and that can be used to simulate a line array of acoustic power sources at the throat end of the horn to permit greater control over the dispersion characteristics of the loudspeaker. While the invention has been described in considerable detail in the foregoing specification, it shall be understood that it is not intended that the invention be limited to such detail, except as necessitated by the following claims.