Abstract:
A high frequency waveguide and methods relating to the design and use of the waveguide are described. The waveguide can include an acoustic input to receive an audio input signal from a high frequency driver, an acoustic output to broadcast sound, and a plurality of acoustic paths extending from the input to the output. A first path of acoustic paths is divided into two paths when a width of the first path is greater than ½ wavelength of a highest frequency at the input. In an example, each of the plurality of acoustic paths carries across all frequencies from the high frequency driver. In an example, the paths each have a first port receiving audio and a second port outputting audio, and the paths enlarge from the first port to the second port.

Description:
TECHNICAL FIELD 
     Aspects as disclosed herein generally relate to acoustic waveguides, and more specifically to high frequency acoustic waveguides for loudspeakers. 
     BACKGROUND 
     In general multi-way loudspeaker systems are well known. Typical examples of multi-way loudspeaker systems include two-way loudspeakers and three-way loudspeakers. Generally, multi-way loudspeaker systems include multiple transducers (generally referred to as “loudspeakers,” “speakers,” “sound drivers,” or “drivers”) that operate at different frequency ranges. As an example, typical two-way loudspeakers include a low-frequency transducer and a high-frequency transducer, while typical three-way loudspeakers include a low-frequency transducer, a mid-frequency transducer (generally known as “midrange transducer” and “midrange driver”), and a high-frequency transducer. 
     Enclosures and horns, such as those used with loudspeakers, are designed to control the radiating direction of sound. Sound radiating from sources, in the absence of an enclosure, may spread in uncontrolled directions. 
     Although there may be a need to change the angle of coverage of sound radiated from the loudspeaker, the shape of a horn and the loudspeaker enclosure fixes the sound coverage angle of a loudspeaker system. A user of a loudspeaker system may want to direct sound at an angle to reach an audience. Moreover, the user may want to direct the sound away from walls or architectural boundaries that cause wall reflections. The shape and design of the horn affects the sound reproduction from the loudspeaker. The horn should be design to evenly distribute the sound on a listening plane or curve and to reduce excess sound at undesired locations. 
     SUMMARY 
     A high frequency waveguide and methods relating to the design and use of the waveguide are described. The waveguide can include an acoustic input to receive an audio input signal from a high frequency driver, an acoustic output to broadcast sound, and a plurality of acoustic paths extending from the input to the output. A first path of acoustic paths is divided into two paths when a width of the first path is greater than ½ wavelength of a highest frequency at the input. In an example, each of the plurality of acoustic paths carries across all frequencies from the high frequency driver. In an example, the paths each have a first port receiving audio and a second port outputting audio, and the paths enlarge from the first port to the second port. In an example, outer walls define cross sectional area of the waveguide and exponentially diverge from the acoustic input to the acoustic output. 
     In an example, the acoustic paths do not recombine until the acoustic output. 
     In an example, the acoustic paths have a same length from the acoustic input to the acoustic output. 
     In an example, the acoustic paths are defined by smooth walls. 
     In an example, the acoustics paths are mirrored about central plane symmetry. 
     In an example, the acoustic paths have outlets at the acoustic output oriented to achieve a desired wavefront curvature. 
     In an example, the acoustic paths have unequal lengths to compensate for a non-isophase input signal at the acoustic input. 
     In an example, the acoustic paths have unequal widths to compensate for a non-isobel input signal at the acoustic input. 
     In an example, the acoustic paths are curved and defined by smooth walls. 
     The present disclosure also describes a speaker line array element that can have an elongate, high frequency waveguide including: at least two high frequency drivers; at least two acoustic inputs to receive an audio input signal from the high frequency drivers; an acoustic output to broadcast sound; and at least two sets of a plurality of acoustic paths extending from the inputs to the output, wherein a first path of acoustic paths of each set is divided into two paths when a width of the first path is greater than ½ wavelength of a highest frequency at the throat. The array element can also have sound integrators. In an example, a first sound integrator extends outwardly from a first side of the acoustic output, the first sound integrator including a plurality of first slots. A first mid-range speaker can be positioned behind the first sound integrator to output a mid-range acoustic signal through the first slots. In an example, a second sound integrator extends outwardly from a second side of the acoustic output, the second sound integrator including a plurality of second slots. A second mid-range speaker can be positioned behind the second sound integrator to output a mid-range acoustic through the second slots. 
     In an example, each of the plurality of acoustic paths carries across all frequencies from the high frequency driver. 
     In an example, the paths each have a first port receiving audio and a second port outputting audio, and the paths enlarge from the first port to the second port. 
     In an example, the outer walls define cross sectional area of the waveguide and exponentially diverge from the acoustic input to the acoustic output. 
     In an example, the acoustic paths do not recombine until the acoustic output. 
     In an example, the acoustic paths have a same length from the acoustic input to the acoustic output. 
     In an example, one of a set of acoustic paths is receives an acoustic signal from one of the drivers and the one set of the acoustics paths is mirrored about a central plane symmetry. 
     Methods are described of designing and fabricating the above structures. A method for a high frequency waveguide can include determining a rate of expansion for a high frequency waveguide, determining a number of acoustical paths for the waveguide with a dimension of the acoustical paths to be no greater than ½ wavelength of a highest frequency at an input, laying the acoustical paths in the waveguide; and when any acoustical path has a dimension greater than ½ wavelength of a highest frequency, inserting a dividing structure to divide the acoustic paths to maintain the limit on the dimension. 
     In an example, each of the steps is performed for a half of the waveguide and then a minor image of the half of the waveguide is constructed about a line of symmetry. 
     In an example, the rate of expansion is exponential. 
     In an example, the acoustic paths have outlets at the acoustic output oriented to achieve a desired wavefront curvature. 
     In an example, laying the acoustical paths includes compensating for a non-isophase input signal at the acoustic input by adjusting the acoustic paths to have unequal lengths; and 
     In an example, laying the acoustical paths includes compensating for a non-isobel input signal at the acoustic input by adjusting the acoustic paths to have unequal widths. 
     In some examples, at least one acoustic path is asymmetric with respect to other acoustic paths about the center plane or other plane of symmetry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view of a speaker assembly according to an embodiment. 
         FIG. 2  is a view of half of the  FIG. 1  speaker assembly according to an embodiment. 
         FIG. 3  is an enlarged view of part of the  FIG. 2  speaker assembly according to an embodiment. 
         FIG. 4  is a schematic view of a design stage for an acoustic waveguide according to an embodiment. 
         FIG. 5  is a schematic view of a design stage for an acoustic waveguide according to an embodiment. 
         FIG. 6  is a schematic view of a design stage for an acoustic waveguide according to an embodiment. 
         FIG. 7  is a schematic view of a design stage of an acoustic waveguide according to an embodiment. 
         FIG. 8  is a schematic view of a design stage of an acoustic waveguide according to an embodiment. 
         FIG. 9  is a view of a speaker assembly according to an embodiment. 
         FIG. 10  is a view of a line array element according to an embodiment. 
         FIG. 11  is a view of a line array of speakers according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present disclosure. 
     The present inventors have recognized some difficulties of combining multiple sound sources and having the sound sources emit the same acoustical content. When combining multiple sound sources the designer must attempt to evenly distribute sound on a listening plane and reduce excess sound emitted outside the listening plane, i.e. side lobes. There are several criteria, so-called Wavefront Sculpture Technology Criteria, used to describe conditions necessary to combine multiple sound sources in a variable-angle vertical array of loudspeakers. See e.g., “Wavefront Sculpture Technology”, Urban, Heil and Bauman, Acoustic Engineering Society, Reprint #5488, 2001, which is hereby incorporated by reference. For high-frequency devices that are vertically spaced greater than a half a wavelength of the maximum operating frequency, the criteria states the wavefront emitted by the device should have a curvature less than one quarter the wavelength of the maximum operating frequency. Devices that do not satisfy the criteria result in unevenly distributed sound to the listening plane and excess sound emitted outside the listening plane. 
     In addition, the device used to create the wavefront must have a desired area expansion of the wavefront from the input to the output. The desired area expansion is related to the function:
 
 S ( x )= S   t   *e   (mx)  
 
     This expansion maximizes the acoustic load to the source while minimizing the propagation distortion output of the source. See e.g., Acoustics, Leo L. Beranek, ISBN 0-88318-494-X, pp. 268 to 276, which is hereby incorporated by reference. A constant area is highly undesirable; although it presents a constant acoustic load to the source, it creates a high amount of propagation distortion. A constant expansion of area is also undesirable as it has reduced propagation distortion at the expense of poor acoustic loading of the sound source. A series of stepped, constant expansion areas can be used to approximate the desired area expansion function. However, true stepped expansion areas are undesirable as steps can create reflections, delays and interference in the acoustic path. 
     The present disclosure describes a method to design a structure that will allow the loudspeaker device to maintain a wavefront curvature of less than one quarter the wavelength of the maximum operating frequency. This will improve the ability of the loudspeaker to emit sound to the listening plane and reject noise going outside the listening plane. In addition, it allows the designer to specify the area expansion rate from the input of the structure to the exit of the structure. Thus the designer can specify the desired exponential rate of area expansion. The present disclosure also gives the designer a method for designing a device which emits a chosen non-isophase, non-isobel acoustic wavefront. 
       FIG. 1  shows a speaker assembly  100  with a vertically elongated waveguide  101  that operates to emit acoustical content that is received from an acoustic source. The waveguide  101  processes the acoustic signal and waves to induce curvature/time delay as the acoustic signal travels from the input side to the output side of the waveguide, right to left in  FIG. 1 . Acoustic sources can include high frequency drivers that convert an electrical signal to an acoustic wave signal. In the  FIG. 1  embodiment, there are a plurality of acoustic inputs  102 A,  102 B and  102 C that receive the acoustic signal from drivers (not shown in  FIG. 1 ), respectively. A plurality of acoustic outputs  103  are on the output side of the waveguide  101 . The acoustic outputs  103  are greater in number than the inputs  102 . This requires that the acoustics paths in the waveguide  101  be divided as the waveguide progresses from the input side to the output side. The number of outputs  103  may be 2 N  greater than the number of inputs  102 , where N is greater than one. In an example, N is at least three such that each input  102  results in eight outputs  103 . 
     The speaker assembly  100  includes flared structures  110  that can direct the acoustic output from the waveguide. The flared structures can operate as a bell to guide the sound from the waveguide output. The flared structures  110  can be removably positioned at the output side of the waveguide  101 . In the illustrated embodiment of  FIG. 1 , the flared structures  110  can operate as sound integrators. The sound integrator structures  110  may be used to direct both mid-frequency and high frequency sound to predetermined areas, such as directly toward listeners or locations within a venue or an auditorium. The sound integrators  110  may send substantially the same quality sound to listeners located in different parts of a venue. The sound integrators  110  flare outwardly from the waveguide  101  and may be removably connected at the inner edge to a side of the waveguide  101 . The waveguide  101  and sound integrators  110  may be fixed within a housing of the loudspeaker  100 , but may also be removably connected to the housing. The sound integrators  110  include a leading section  112  forms a smooth transition to the outer surface  114  of the sound integrator  110 . The sound integrators  110  are positioned adjacent to each other forming an angle relative to each other to function as a smooth wave-guide for the high frequency sound waves output from the waveguide outputs  103 . The sound integrators  110  may by positioned at a predetermined angle to control a direction of the high frequency sound waves generated from a high frequency sound source(s), which can include the driver, associated electronics and waveguide  101 . 
     The outer surface  114  of the sound integrators  110  may be shaped to project sound from a sound source at predetermined angles depending on the shape of the outer surface  114 . The angular direction of the projected sound waves may be varied with the sound integrators  110  even though the shape of a loudspeaker enclosure remains fixed. In an example, sound is radiated from the loudspeaker  100  at an angle of about ninety degrees from the loudspeaker  100 . In another example, sound integrators  110  may be used to control the projection of sound at an angle of about 120 degrees or 160 degrees. 
       FIG. 2  shows the left half of the  FIG. 1  speaker assembly  100  to illustrate the interior of the waveguide  101  and the plurality of acoustic paths from the inputs  102 A- 102 C to the outputs  103 . The other half of the speaker assembly  100  is a mirror image of  FIG. 2  and can be fixed to the left half to form the complete, designed waveguide  101 . The waveguide  101  is divided into sub-waveguides  201 - 203  that are each dedicated to a single one of the inputs  102 A,  102 B and  102 C and, hence, to a single driver that outputs acoustic signals into the inputs  102 A,  102 B and  102 C. Each of the sub-waveguides  201 - 203  is identical. Accordingly, the description will focus on the sub-waveguide  201  with the understanding that the other sub-waveguides  202  and  203  are identical to the sub-waveguide  201 . However, the present disclosure is not so limited. In some embodiments, the sub-waveguides  201 - 203  may have different acoustic paths from other sub-waveguides. The input  102 A is divided into four acoustic transmission paths  211 - 214 , with paths  211  and  214  being on the outside and paths  212  and  213  being on the interior. Acoustic paths pairs  211 ,  214  and  212 ,  213  are minor images of each other along a center plane  215  of the sub-waveguide  201 . That is, the acoustic paths  211  and  214  are the same but inverted relative to one another. The acoustic paths  212  and  213  are the same but inverted relative to one another. The acoustic paths  211 - 215  are defined by walls  221 - 226  in the body of the waveguide  101 . All of the walls of the waveguide that define acoustic paths are smooth and continuous. The walls can be fabricated to have the shapes as described herein from polymers, metals, fibers, resins and the like. 
       FIG. 3  shows a simplified waveguide  301  to better illustrate the acoustic paths defined by the waveguide according to various embodiments. Waveguide  301  is simplified relative to the waveguide  101  in that waveguide  301  has fewer acoustic paths than waveguide  101 . The acoustic input  102 A receives high frequency acoustic signal from a high frequency (“HF”) acoustic source. The input  102 A has two acoustic paths  311  and  312  at the input  102 A. The paths  311  and  312  are minor images of each other about a central plane  315  of the sub-waveguide being described. The paths  311  and  312  are divided at the input by a center vane  317  that includes smooth, continuous and curved walls. The acoustic path  311  is divided into acoustic paths  311 A and  311 B by a further vane  318 , which also has smooth, continuous and curved walls. The acoustic path  312  is divided into acoustic paths  312 A and  312 B by a further vane  319 , which also has smooth, continuous and curved walls. The acoustic paths  311 ,  312 ,  311 A,  311 B,  312 A and  312 B are have a same length such that the sound wave that enters the input  102 A and travels through the acoustic paths  311 ,  312 ,  311 A,  311 B,  312 A and  312 B emits at the output  103  with the designed properties. In an example, the acoustic paths within a sub-waveguide have the same length that can be different the acoustic paths in other sub-waveguide(s). It will be understood that a modifications to at least one of the acoustic paths such that the sub-waveguide is not symmetrical with respect to its acoustic paths or with respect to other sub-waveguides in the construction shown in  FIG. 3 . 
       FIG. 4  shows a design stage of the waveguide  101  that includes an input  102 A and an output  103 . Only the top half of the waveguide  101  is illustrated for clarity of illustration. The bottom half of the waveguide  101  is a mirror image of the illustrated top half about the center plane  215 . The method of designing the waveguide  101  first establishes the input dimension, e.g., the height of the input  102 A, and output dimension, e.g., the height of the output  103 . The expansion between the input and the output is defined. The dimensions are then reduced in half, which results in a waveguide  101  with a plane of symmetry  215  with a normal contained in a design plane, which is perpendicular to the desired propagation direction, e.g., right to left in  FIG. 4 . Circles are now defined based on the chosen area expansion and a number of paths to be created, defining the interior height of the sound paths. In an embodiment described herein the waveguide contains eight total sound paths (see  FIGS. 2 and 8-9 ). These circles are defined to have a diameter one-eighth of the area expansion. It will be recognized that any number of paths can be chosen (1, 2, 3, etc. or 2 N , where N is an integer) to use the present method to design a desired waveguide. In an example, each of the paths created in the waveguide  101  must have a maximum dimension of one half the wavelength (λ/2) at the highest frequency being propagated through the waveguide  101 . However, it is undesirable to have a constant dimension (or cross section) acoustic path as such a path would have poor acoustic loading of the sound source. 
     The specific embodiment shown in  FIG. 4  has a design criterion of eight acoustic paths, with four on one side of the symmetry plane  215  and four on the other side of the symmetry plane  215 . A specific example with units will be used to describe the present methodology to design and construct the acoustic paths in the waveguide. It will be recognized that other values can be used to create acoustic paths with different rates of expansion and different sizes throughout the acoustic paths. The outer wall  401  of the waveguide is defined to have the exponential rate of expansion relative to the center plane half of the height of the input  102 A is set to be 19.18 mm. The dimension of the waveguide is given at successive locations as the identified by the variable θ. With the variable θ defined and illustrated, e.g., on a computing system, the dimension of the acoustic paths can be determined. As the  FIG. 4  embodiment shows half of the waveguide  101  and there are to be eight total acoustic paths, there are four acoustic paths that must fit into this half of the waveguide  101 . The variable θ is then divided by four to arrive at the value Σ, which represents the width of an acoustic path at that point in the waveguide. This calculation can be performed by a computing device and displayed for inspection by a designer. For example, at a first position shown in  FIG. 4 , at a location greater than 80 mm, from the input  102 A, the waveguide has a half height of 19.62 mm (θ), which results in an acoustic path with a height of 4.91 mm (Σ). At the last calculation, the waveguide has a half height of 51.08 mm, which results in an acoustic path height of 12.77 mm (Σ). As a design rule, the acoustic paths increase in dimension (waveguide dimension)/N, wherein N is the number of acoustic paths. 
     The present disclosure modifies the acoustic paths in height as modifying in height is best for using the waveguide in a vertical mounting in a speaker, e.g., speaker  100  ( FIG. 1 ), speaker  1000  ( FIG. 10 ) and vertical speaker array  1100  ( FIG. 11 ). However, it is within the scope of the present disclosure to also modify the acoustic paths in a width as opposed to height. 
     The present disclosure further shows the acoustic paths to have a polygon cross section, more specifically a rectangular cross section. This cross section increase in size exponentially from the input to the output in at least one dimension. In various embodiments, the acoustic paths only increase exponentially in one dimension, e.g., either height or width. While the present example shows a single dimension for each acoustic path, it will be within the scope of the present disclosure to have at least one acoustic path as having a different dimension that the other acoustic paths. However, such a path may also increase in size from the input to the output. 
       FIG. 5  shows a further design stage for the waveguide  101  in which spline curves are laid out to show the center of the acoustic paths that will form the waveguide  101 . The spline curves determine the length of the acoustic paths. Each path is designed to carry all frequencies that are input into the acoustic path. The dashed circles  501  show a representation of a dimension of an acoustic path. The dashed circles are a design tool to position the acoustic path and create the spline lengths of the acoustic paths to be equal. In an example, state the spline lengths are substantially equal in arc length. The solid circles  503  represent the height of an individual acoustic path, which must increase in height from the input  102 A to the output  103 . Note that this design stage is limited by the size of the input and output from  FIG. 4 . That is, the input  102 A has the same height in both  FIGS. 4 and 5 . The output  103  has the same height in both  FIGS. 4 and 5 . When the solid circles  503  no longer touch or overlap, then the acoustic path must be separated from another path. As shown in the top two acoustic paths,  505 ,  507 , this occurs at about point  509 . Here, the two acoustic paths  505 ,  507  must be mechanically separated by a wall, e.g., a vane as described herein. The acoustic paths  511 ,  513  must be separated at about point  515 . These points are readily visualized by the separation of the solid circles  503 , representing the heights of the acoustic paths  505  and  507  or  511  and  513 . It is further recognized that the top pair of acoustic paths  505 ,  507  must be mechanically separated from the bottom pair of acoustic paths  511 ,  513  essentially immediately at the input  102 A, for example at point  520 . It will be recognized that the splines that define the acoustic paths  505 ,  507 ,  511 ,  513  are smooth curves without discrete discontinuities or corners. Moreover, the bends in the splines and lack of discrete discontinuities or corners operates to reduce and essentially eliminate reflections of the acoustic signal in the acoustic paths. 
     At this design stage the acoustic paths  505 ,  507 ,  511  and  513  may be modified to achieve desired acoustic effects on the signals to be propagated through the paths. Multiple paths are created in the design plane shown in  FIG. 5  to link the input and output of the device with equal length paths. For example, the path  511  in the nearest the center plane must curve more than the other paths  505 ,  507  and  513  to ensure the equal lengths for the paths. In an embodiment, the separate sound paths can have unequal length to allow a sound path to be longer or shorter than other sound paths within the waveguide. This can compensate for sound sources with non-isophase wave fronts (unequal time/phase). Additionally, sound paths of varying widths can be imagined to compensate for sound sources with non-isobel wave fronts (unequal amplitude). 
       FIG. 6  shows a further design stage for the waveguide  101  in which the mechanical separation structures, i.e., vanes  601 ,  603 , are added to the waveguide to separate the acoustic paths at the designed locations, here, points  509 ,  515  and  520  as determined in the prior design stage ( FIG. 5 ). The first vane  601  begins at point  520  and separates the top acoustic path pair  505 ,  507  from the bottom acoustic path pair  511 ,  513  and ends at the output  103 . The vane  601  separates the top acoustic path pair  505 ,  507  from the bottom acoustic path pair  511 ,  513  throughout the length of the waveguide. Hence the acoustic signals in the top acoustic path pair  505 ,  507  from the bottom acoustic path pair  511 ,  513  are prevented from recombining until the outlet  103 . The leading part of the vane  601  at point  520  is smooth and rounded to prevent reflections of the acoustic wave input into the waveguide  101 . The vane  601  has smooth walls that define one wall of the acoustic path  507  and one wall of the acoustic path  513 . A vane  603  separates the top acoustic path pair  505 ,  507  at point  509 . Hence the acoustic signals in the top acoustic path pair  505 ,  507  are now separate and cannot recombine until the outlet  103 . The leading edge of the vane  603  at point  509  is smooth and rounded to prevent reflections of the acoustic wave at point  509 . The vane  603  has smooth walls that define one wall of the acoustic path  505  and one wall of the acoustic path  507 . A vane  605  separates the bottom acoustic path pair  511 ,  513  at point  515 . Hence the acoustic signals in the bottom acoustic path pair  511 ,  513  are now separate and cannot recombine until the outlet  103 . The leading edge of the vane  605  at point  515  is smooth and rounded to prevent reflections of the acoustic wave at point  515 . The vane  605  has smooth walls that define one wall of the acoustic path  511  and one wall of the acoustic path  513 . The vanes  601 ,  603  and  605  can have varying thickness to control the dimension of the adjacent acoustic paths. None of the acoustic paths exceed the maximum dimension as defined design stage shown in  FIG. 4 . In the specific example, none of the acoustic paths  505 ,  507 ,  511  or  513  exceed 12.77 (Σ). 
     The area expansion circles are spaced evenly upon the acoustic paths to define the interior width of the acoustic paths. These can be used to define any interior and exterior walls used to divide the acoustic paths. The walls are intended to maintain a sound path width less than one half the wavelength of the maximum operating frequency. In an example, the maximum frequency is about 16 kHz, so the maximum sound path width is about 10 mm. The sound paths are left combined from the input of the waveguide until the interior width of the acoustic path reaches the maximum acoustic path width. The acoustic paths are then split and continue to expand until the maximum acoustic path width is exceeded again, or until the output of the waveguide is reached. 
     It is also desirable to have the sound paths exit normal to the intended wavefront. The last section of the device then is constrained to force the paths to be substantially parallel with the intended direction of projection. 
       FIG. 7  shows the relationship of the design stages of  FIGS. 4-6  to the devices shown in  FIGS. 1-3 . The vanes  601 ,  603 ,  605  and  607  define various walls that in turn define the acoustic paths  211 ,  212  and  211 A,  211 B,  212 A,  212 B. In an example, the vanes  601 ,  603 ,  605  and  607  can have solid bodies and be formed from a polymer, a metal or other sufficiently rigid material that can mold the continuous, smooth walls required. The outer wall  701  defines the uppermost surface of an acoustic path  211  and  211 A. It will be recognized that acoustic path  211  includes both the acoustic paths  505  and  507 . However, as the acoustic paths  505 ,  507  are combined in path  211 , there is a single open path. The vane  601  has an upper surface  702  that with wall  701  defines the acoustic path  211 . The vane  603  has an upper surface  712  and a lower surface  713 . The upper surface  712  and wall  701  define the acoustic path  211 A. The lower surface  713  and upper surface  702  of vane  601  define the acoustic path  211 B. The vane  601  has a lower surface  703  that with the upper surface  704  of the bottom vane  607  defines the acoustic path  212 . The vane  605  has an upper surface  716  and a lower surface  717 . The upper surface  716  and bottom surface  703  of vane  601  define the acoustic path  212 A. The lower surface  717  and upper surface  704  of vane  607  define the acoustic path  212 B. All of the surfaces that define the acoustic paths are smooth and not discontinuous. In an example, at least one acoustic path is asymmetrical about a center plane or with respect to other acoustic paths. 
       FIG. 8  shows a complete sub-waveguide  800  that was designed using the methods of  FIGS. 4-6 . As can be seen in drawings,  FIG. 8  is the same as  FIG. 7  but includes the bottom half of the sub-waveguide. The bottom half of this sub-waveguide is a mirror image of  FIG. 7  about the plane of symmetry  215 . The acoustic paths of bottom half are number the same as in  FIG. 7  but with the numbers including a bar there over to indicate that it is the same but reflected into the bottom half. The output of each acoustic path is designated by  103 A- 103 H. As described in the design embodiment herein, there are eight acoustic paths that result in eight distinct outputs  103 A- 103 H. 
       FIG. 9  shows a schematic view of a high frequency speaker assembly  900  with a waveguide  101  that receives acoustic signals from drivers  9001 - 903 . The drivers  901 - 903  receive electrical signals from a source  910 , for example, power amplifiers, sound boards, musical instruments, etc. The drivers  901 - 903  convert the electrical signals to acoustic signals that are input into the waveguide  101 . 
       FIG. 10  shows a line array element  1000  in which the high frequency waveguide  101  is positioned between the sound integrators  110 . The low frequency sound sources  1002  may be positioned to the sides of the sound integrators  110 . The sound integrators  110  may provide a substantially solid boundary for the high frequency sound waves produced by the high frequency waveguide  101  and may allow mid-range sound waves from the mid-range sound sources  1004  to pass through. The sound integrator  110  may include slots  115  or other openings that allow the mid-range sound from sources  1004  to pass through the sound integrators  110 . In another example, the sound integrators  110  may include no openings. The high frequency sound waves pass along a substantially smooth surface of the integrators  110  to integrate the sound waves radiating from both the high and mid-range frequency sound sources for better sound control and to minimize distortion of the high frequency sound wave front shapes. The sound integrator  110  may also act as a volume displacement device to improve loading and efficiency of the mid-range frequency elements. In an example, a line array element can include the sound integrators that have a curvature radius of ¼ the highest frequency of the sound signal traveling in the acoustic waveguide. 
     The high frequency sound sources, which can include the waveguide  101  and the drivers, generate high frequency energy or sound waves, which propagate across the sound integrators  110 . The surfaces of the sound integrators  110  are angled relative to each other with the exception of a leading section that is proximal to the waveguide outputs  103   
       FIG. 11  shows a speaker array  1100  of speakers  100 . The loudspeakers  100  may be arranged vertically on top of another or hung from an overhead support structure  1110  within a venue. The arrangement shown in  FIG. 11  is a speaker array with the high frequency waveguides  101  of the speakers being aligned with each other along a vertical or a vertical arc. The loudspeakers  100  can be suspended above an audience to form vertical lines of transducer arrays within the bass, mid-range and treble band (high frequency) passes. The speaker array may be curved to increase vertical angular coverage and to provide better control of the radiated sound. The sound radiating from the array may be further controlled by utilizing sound integrators  110  to control the direction angle θ, or angular coverage, of the sound radiated from one or more of the loudspeaker enclosures. The controlled direction may include the horizontal direction, and can also include any other direction such as the vertical direction or an oblique direction. The angular coverage may vary from loudspeaker  100  to loudspeaker  100  within the array  1100 . As such, the loudspeakers  100  arranged near a top of the array may provide one coverage angle and the loudspeakers  100  arranged near a bottom of the array may provide a different coverage angle. Additional disclosure with regard to speaker arrays can be found in U.S. Pat. Nos. 7,324,654 and 7,333,626, which are assigned to the current assignee and are incorporated herein by reference for any purpose. 
     It is believed that the present methods and structures described herein improve on existing technology in when combining multiple sound sources, emitting the same acoustical content, to 1) evenly distribute sound on a listening plane 2) reduce excess sound emitted outside the listening plane (i.e. sidelobes). Moreover, the present disclosure further describes a method to design a structure that will allow the loudspeaker device to maintain a wavefront curvature of less than one quarter the wavelength of the maximum operating frequency. This will improve the ability of the loudspeaker to emit sound to the listening plane and reject noise going outside the listening plane. In addition, the present methodology allows the designer to specify the area expansion rate from the input of the structure to the exit of the structure. Thus the designer can specify the desired exponential rate of area expansion. The present methodology and structures also gives the designer a method for designing a device which emits a chosen non-isophase, non-isobel wavefront. 
     The present disclosure refers to “high frequency” for use in acoustics and the design of a waveguide. As used herein high frequency may refer to high frequency sounds as heard by a human, e.g., in music or in other listening. High frequency can be greater than 1 kHz, 2 kHz, 3 kHz or 5 kHz. In the case of human hearing the top end of high frequency is about 20 kHz, based on the typically accepted human hearing range of between 20 Hz and 20 kHz. High frequency in some specialty cases can go up to 100 kHz. However, for purposes of loudspeakers for presenting acoustic content to people such a high frequency, 100 kHz, is not required. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.