Abstract:
This invention provides a radiation boundary integrator (“RBI”) for integrating sound radiation from mid-range and high-frequency sources in multi-way loudspeakers. The RBI is a substantially solid boundary that is placed over the mid-range speakers to provide smooth, wave-guiding side walls to control the angular radiation of the high-frequency sound waves emanating from the high-frequency sound sources. To allow the mid-range frequency sound waves generated from mid-range sound sources to pass through the RBI, the RBI is designed with openings. To further prevent the possibility of having high-frequency sound radiate through the openings in the RBI, the RBI may be designed with porous material in the openings of the RBI. The porous material would be transparent to the mid-range sound radiation, but would prevent the high-frequency sound radiation from being disturbed by the openings in the RBI. As such, the RBI provides an outer or front surface area that forms an acoustical barrier to high frequencies radiating across the front surface, yet is acoustically transparent to mid-range frequencies radiating through openings in the RBI. The RBI may also serve as a volume displacement device to compression-load the mid-range sound sources by contouring the back side of the RBI to the shape of the mid-range sound sources thus reducing the space between the RBI and the mid-range sound sources and loading the mid-range sound sources to generate greater mid-range sound energy.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. patent application Ser. No. 09/921,175, filed Jul. 31, 2001, which claims priority to U.S. Provisional Patent Application Serial No. 60/222,026, filed Jul. 31, 2000. Both U.S. patent application Ser. No. 09/921,175 and No. 60/222,026 are incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to a system for integrating the sound radiating from multi-way loudspeakers. In particular, the invention relates to a radiation boundary integrator positioned over a mid-range sound source to prevent angular radiation from high frequencies from conforming to the contours of the cones or diaphragms of the mid-range frequency sound source.  
           [0004]    2. Related Art  
           [0005]    Loudspeakers and sound systems are designed to control the direction of the sound radiating from their sound sources. Sound radiating from a high-frequency sound source, with the absence of sidewalls or boundaries, will generally radiate in all directions and possibly wrap around the sound source. This severely limits the predictability and control of the direction of the sound radiation. If, however, boundaries or sidewalls are placed adjacent to the sound source, the sound radiation will generally conform to the angle between the boundary surfaces. Thus, one of the advantages with using boundaries is the ability to control the direction that sound radiates from the sound source.  
           [0006]    Another design objective of loudspeakers and sound systems is the ability to integrate a number of mid-range sound sources adjacent to a number of high-frequency sound sources into one housing. One common arrangement involves the positioning of several vertically stacked high-frequency sound sources having two adjacent side walls extending outward from the high-frequency sound sources, such that the high-frequency sound sources are at the vertex of the two adjacent side walls. The two adjacent sidewalls are positioned at an angle relative to one another and have mid-range sound sources positioned flush in the sidewalls. As such, the cones of the mid-range sound sources form part of the sidewalls extending outward from the high-frequency sound sources.  
           [0007]    One of the problems with the design of certain loudspeaker systems is that the cones of the midrange sound sources form a recess or depression in the adjacent sidewalls. Because the adjacent sidewalls serve as high-frequency wave-guides, the recesses or depressions in the sidewalls prevent uniform angular radiation of the high-frequency sound waves that pass over these depressions. The angular radiation of high frequencies conforms to the contours of the cones or diaphragms of the mid-range frequency sound sources, compromising both the frequency-directivity and the quality of the high-frequency sound energy.  
           [0008]    Another problem with the above design is the limitation on the size of multiple midrange sound sources that may be mounted into the two adjacent sidewalls. Larger diameter sound sources are usually desirable over smaller diameter sound sources because they can generate greater acoustic power. However, the upper frequencies generated by the larger midrange sources can ‘lobe’ or narrow in radiation angle if sources are large compared to the wavelength. This narrowing in radiation angle is due to the finite propagation velocity of sound. To avoid upper mid-frequency narrowing, a limit is placed on the size of the mid-range sound sources that can limit the acoustic output power of the mid-frequency range sound sources.  
           [0009]    Therefore, a need exists to integrate radiation from the mid-frequency and high-frequency sound sources to better control the angular radiation of high-frequency sound waves. Furthermore, a need exists to improve the acoustic power or energy that may be produced by the mid-range sound sources.  
         SUMMARY  
         [0010]    This invention provides a system for integrating sound radiation from mid-range and high-frequency sources in multi-way loudspeakers. This sound integration system provides improved control of the angular sound radiation of mid-range and high-frequency sound energy. The sound radiation system of this invention is formed of a substantially solid boundary that is placed over mid-range sound source speakers to provide a smooth, wave-guiding sidewall to control the angular radiation of the high-frequency sound waves emanating from the high-frequency sound sources. For purposes of illustration, this substantially solid boundary or sound integrator shall be referred to as a radiation boundary integrator (“RBI”).  
           [0011]    At least a portion of the RBI is substantially transparent to sound waves from the mid-range sound source. This may be accomplished by providing an opening in the RBI. Thus, the RBI is acoustically solid to high frequencies radiating across the outer surface, yet acoustically transparent to mid-range frequencies radiating through the openings in the surface.  
           [0012]    Besides integrating the mid-range and high-frequency sound waves, the RBI may be used to compression load the mid-range frequency sound waves to improve the acoustic power output of the mid-range sound sources. Compression loading is accomplished by contouring the surface of the RBI that faces the mid-range sound sources, i.e., the back surface of the RBI, to the shape of the mid-range sound sources or speakers. Contouring the back surface reduces the space between the back surface of the RBI and the sound sources. The reduced space compression loads the mid-range frequency sound sources, enabling greater mid-range frequency sound output.  
           [0013]    The RBI may be designed with porous material in the openings of the RBI. The porous material is designed with certain porosity to substantially minimize the possibility of having high-frequency sound radiate through the opening in the RBI, yet transparent to the midrange sound waves. With the porous material within the opening of the RBI, the high-frequency sound waves are substantially undisturbed by the openings in the RBI, and allow the mid-range sound waves to substantially pass through the opening.  
           [0014]    Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The invention can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.  
         [0016]    [0016]FIG. 1 is a perspective view of a multi-way loudspeaker having three vertically stacked high-frequency sound sources positioned at the vertex of two radiation boundary integrators.  
         [0017]    [0017]FIG. 2 is a front view of the two radiation boundary integrators of FIG. 1 as they may appear relative to various sound sources absent the housing.  
         [0018]    [0018]FIG. 3 is a cross-sectional top view of the two radiation boundary integrators taken along line a-a of FIG. 2.  
         [0019]    [0019]FIG. 4 is a front view of a radiation boundary integrator having foam in the openings of the radiation boundary integrator.  
         [0020]    [0020]FIG. 5 is a side view of the radiation boundary integrator illustrated in FIG. 4.  
         [0021]    [0021]FIG. 6 is a bottom view of the radiation boundary integrator illustrated in FIG. 4.  
         [0022]    [0022]FIG. 7 is a rear view of the radiation boundary illustrated in FIG. 4.  
         [0023]    [0023]FIG. 8 is a cross-sectional view of the radiation boundary taken along line b-b of FIG. 7.  
         [0024]    [0024]FIG. 9 is a cross-sectional view of the radiation boundary taken along line c-c of FIG. 7.  
         [0025]    [0025]FIG. 10 is a front view of an alternative embodiment of a radiation boundary integrator.  
         [0026]    [0026]FIG. 11 is a front view of an alternative embodiment of a radiation boundary integrator.  
         [0027]    [0027]FIG. 12 is a perspective view of a series of the speakers illustrated in FIG. 1 stacked together to form a line array. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    [0028]FIG. 1 is a perspective view of a multi-way loudspeaker  110  use two sound integrators or radiation boundary integrators (“RBIs”)  100 . FIG. 1 illustrates the two RBIs  100  as they would appear positioned within a multi-way loudspeaker housing  102  (“housing”). In the exemplary line array speaker  110 , a plurality of high-frequency sound sources  104  are stacked vertically in the mid-section of the housing  102 . Two adjacent side walls (not shown) extend outwardly from the high-frequency sound sources  104  forming an angle relative to each other such that the high-frequency sound sources  104  are at the vertex of the two adjacent side walls. Flush within each of the side wall is at least one mid-range sound source (see FIG. 3). Each side wall is covered with the RBI  100  so that the high-frequency sound sources  104  are at the vertex of the two RBIs  100 . Besides the high frequency  104  and mid-range frequency sound sources, the housing  102  may also incorporate low-frequency sound sources  106  and  108 . The size and number of sound sources that are incorporated into a housing  102  may vary. In this example, the housing  102  may incorporate three (3) high-frequency sound sources  104 , four (4) mid range sound sources (see FIG. 3) (two (2) mid-range sound sources positioned on each side wall), and two (2) low-frequency sound sources  106  and  108 , totaling eleven ( 11 ) sound sources into line array speaker  110 .  
         [0029]    [0029]FIG. 2 illustrates a front view of the two RBIs  100  of FIG. 1 as they would appear relative to various sound sources  104  absent the housing  102 . One RBI  100  is positioned on each side of the three vertically stacked high-frequency sound sources  104 , such that the three vertical high-frequency sound sources  104  are positioned at the vertex of the two RBIs  100 . The RBIs  100  are positioned on each side of the high-frequency sound sources  104  and act as boundaries to control the direction of the sound waves from the high-frequency sources  104 . The RBIs  100  have substantially flat and solid surfaces to control frequency-directivity and improve the quality of the high-frequency sound energy. Each RBI  100  is designed with at least one opening  200  to allow the mid-range frequency sound waves generated from mid-range sound sources (see FIG. 3) to pass through the RBIs  100 .  
         [0030]    [0030]FIG. 3 is a cross-sectional view of the two RBIs taken along line a-a of FIG. 2. FIG. 3 illustrates the positioning of the RBIs  100  relative to the high-frequency sound sources  104  and the mid-range sound sources  300 . One RBI  100  is positioned on each side of the high-frequency sound sources  104  such that the high-frequency energy or sound waves from the high-frequency sound sources  104  propagate across the front surface  304  of the RBIs  100 . The surfaces of the RBIs  100  are angled relative to one another, with the exception of a leading edge  302  that is angled inward, toward the high-frequency sound sources  104 . The leading edges  302  are shaped to form a smooth transition between the high-frequency sound sources  104  and the substantially flat and solid front surface  304  of the RBIs  100 . The two RBIs  100  are thus positioned adjacent to each other to function as a smooth wave-guide for the high-frequency sound waves generated by the high-frequency sound sources  104 . As seen in FIG. 3, the two RBIs  100  are at a predetermined angle θ to control and direct the high-frequency sound waves emanating from the high frequency sound sources  104 . The predetermined angle θ between the two RBIs  100  may vary from about 60° to about 100°, depending upon the application. In an auditorium setting, the predetermined angle is generally about 90°. Depending upon the application, the predetermined angle θ may be chosen by one of ordinarily skill in the art to optimize the performance of the speaker system.  
         [0031]    [0031]FIGS. 2 and 3 illustrate the openings  200  in the RBIs  100  as four slots  200 . Each slot  200  may be configured into an elongated rectangle and formed on each of the four quadrants of the RBI  100 : (1) the upper right, (2) the upper left, (3) the bottom right, and (4) the bottom left. The width (“W”) of each slot  200  may range from about ½ inch to about 1 inch. The distance (“D”) between the two slots  200  may range from two to four times the width W or, D=K×W (where K ranges from two to four). Thus, if W is 1 inch, then D may be between about 2 inches and about 4 inches. In the example embodiment, the width is about {fraction (13/16)} inch (≈2.0 cm) and the distance is about 2{fraction (9/16)} inches (≈6.5 cm). The height (“H”) of the slots  200  may be configured to be substantially equal to the diameter of the mid-range frequency sound source  300 . Although the above example illustrates how the openings  200  may appear with three high-frequency  104  and four mid-range frequency sound sources  300 , the size and shape of the openings  200  may be modified to accommodate any number of mid-range frequency or high-frequency sound sources  300  and  104 , respectively.  
         [0032]    [0032]FIG. 4 is a front view of the RBI  100  having a porous material  400  in each of the slots  200 . In certain applications, the slots  200  may act as a cavity that interferes with the high-frequency sound waves passing along the front surface  304  of the RBIs  100 . To minimize such an effect, the slots  200  in the RBIs  100  may be filled with the porous material  400 , such as foam. The foam pieces  400  may be shaped to fit the openings  200 , and may be inserted into the openings  200  to create a substantially solid acoustic surface  304  for the high-frequency energy generated by the high-frequency sound sources  104 . As such, the porous material  400  substantially blocks the high-frequency sound waves that pass across the front surface  304  of the RBI  100  from passing through the slots  200 . The porous material  400 , however, is substantially transparent to the mid-range frequency sound waves to allow sound waves from the mid-range sound sources  300  to pass through the slots  200 . Accordingly, the RBI  100  is substantially solid to high-frequency sound waves passing across the front surface  304  yet substantially transparent to mid-range sound waves passing through the slots  200 . An example porous material  400  is foam having a porosity between about 60 porosity per square inch (PPI) and about 100 PPI. A foam section, having a porosity of about 80 PPI, may be optimal for appearing transparent to mid-range frequency. In addition to foam, any material that is substantially transparent to midrange frequencies, yet substantially blocks high frequencies may be used.  
         [0033]    In addition to substantially blocking the high-frequency sound waves from passing through the slots  200 , the foam  400  further serves as a low pass filter for the higher frequency sound waves generated by the mid-range sound sources  300 . Without having foam  400  in the slots  200 , the higher frequency sound waves from the mid-range sound sources  300  may pass through the slots and interfere with the high-frequency sound waves from the high-frequency sound sources  104 . Thus, the foam in the slots  200  substantially prevents distortion of the higher frequency sound waves generated by the mid-range frequency sound sources  300 .  
         [0034]    [0034]FIG. 4 illustrates an example configuration of a RBI having a right side  402 , a left side  404 , and a base  406  sized to substantially mask or cover the mid-range frequency sound sources  300 . In this example, the right side  402  may be greater in length than the left side  404  so that the space between the two RBIs  100  expands in the lateral direction and also in the vertical direction. In one example implementation, the right side  402  may range from about 16 inches to about 18 inches in length and the left side  404  may range from about 15 inches to about 16.5 inches in length. The base  406  may range from about 7 inches to about 9 inches in width.  
         [0035]    [0035]FIG. 5 illustrates a side view of the RBI of FIG. 4. FIG. 5 illustrates how the RBI may further operate as a volume displacement device, in addition to providing a smooth flat front surface  304  for the high-frequency sound waves generated from the high-frequency sound sources  104 . As shown in FIG. 5, the back side  500  of the RBI  100  may be formed to substantially contour the cone and/or the dome shape of the mid-frequency sound sources  300 . To minimize the interference at the upper range of the middle frequencies, the back side  500  may be configured to be as closely adjacent as possible to the mid-frequency sound sources  300  without allowing the cone of the mid-frequency sound sources  300  to touch the back side  500  of the RBI when the cone vibrates. For example, the back side  500  may be separated from the mid-frequency sound sources  300  by about 0.2 inches to about 0.4 inches. The distance between the back side  500  and the mid-range frequency sound sources  300  may be about 0.375 inches.  
         [0036]    By contouring the back side  500  of the RBI  100  to substantially match the cone and/or dome shape of the mid-frequency sound sources  300 , the RBI effectively attenuates the higher frequencies, while improving the efficiency at the lower mid-range frequencies. The space in front of the mid-range sound source  300  may be substantially closed except for the openings  200  in the RBI  100 . As such, the RBI  100  compression loads the mid-range frequency sound source  300  by making the cone surface of the mid-range sound sources  300  substantially oppose a solid surface leading to the slots  200  in the RBI, which allows for the transparency of the mid-range frequency sound waves. In other words, the acoustic load in front of the cones is greater with the RBI  100  masking the sound sources  300  than without the RBI  100 . The diaphragm or cone surfaces of the mid-range sound sources  300  are then effectively transformed to a larger equivalent air mass, thus increasing the efficiency of the acoustic system at the lower frequencies.  
         [0037]    In general, the mid-range frequency sound sources  300  are not designed to operate at frequencies where it may not be efficient. That is, as the effective size of the diaphragm becomes bigger, it is less efficient at higher frequencies than at lower frequencies because the total mass of the air load on the front of the diaphragm at higher frequencies is substantially greater. As such, the mid-range sound sources  300  using the RBI  100  may generate more midrange frequency to take advantage of the improved efficiency.  
         [0038]    [0038]FIG. 6 is a bottom view of the RBI  100  illustrated in FIG. 4. Like FIG. 5, FIG. 6 illustrates the contouring of the back side  500  of the RBI  100  to compression load the mid-range frequency sound sources  300 . Unlike FIG. 5, FIG. 6 illustrates the openings  200  in the RBI  100  extending through the contouring.  
         [0039]    [0039]FIG. 7 is a rear view of the RBI illustrated in FIG. 4. FIG. 7 illustrates the positioning of the openings  200  in the RBI  100  when the openings  200  are designed as slots  200  extending through the rear contouring of the RBI  100 .  
         [0040]    [0040]FIG. 8 is a cross-sectional view of the RBI taken along line b-b of FIG. 7. In particular, FIG. 8 illustrates the vertical mid-section of the RBI  100 , having a substantially flat front surface  304  and contoured back side  500 . While the RBI  100  may be solid or hollow, to be acoustically inert for damping purposes, the RBI  100  may be designed with solid exteriors, such as a vacuum foamed plastic, or like material. The interior of the RBI  100  may be filled with foam  800  or made of another porous material to keep the RBI  100  from being resonant and/or hollow sounding. Another advantage of using foam  800  in the interior is that it reduces the weight of the RBI  100 . Although the exterior, or front surface and back sides  304  and  500  of the RBI  100  are described as being made of a vacuum foamed plastic, the exterior shell of the RBI  100  may be made of any variety of materials that provide an acoustical boundary to the high-frequency sound waves generated by the high-frequency sound sources  104 .  
         [0041]    [0041]FIG. 9 is a cross-sectional view of the RBI  100  taken along line c-c of FIG. 7, and illustrates how the width of the slots  200  may gradually expand from the back side  500  to the front surface  304  of the RBI  100 . For example, an acute angle φ may be formed between the two outer surfaces of two slots  200 , and the slot  200  may expand at an acute angle α. In this example, the acute angle φ may be between about 30° and about 50°, and in particular about 40°. The acute angle α may be about 15° to about 25°, and in particular about 20°. Alternatively, the slot  200  may expand in a curved line to provide a smooth transition or expansion from the back side  500  to the front surface  304 .  
         [0042]    [0042]FIGS. 10 and 11 illustrate alternative formations for the openings  200  that may be formed within the RBI  100 . For example, the number of openings and their configurations may vary in size and shape to achieve the desired result of having the front surface  304  of the RBI  100  be substantially acoustically solid to high-frequency sound waves. FIG. 10 shows a smaller circular opening  1000  filled with foam  400  within a larger circular opening  1002  also filled with foam  400 . FIG. 11 illustrates six slots  1100 ,  1102 ,  1104 ,  1106 ,  1108 , and  1110  within the RBI  100 , where each of the slots  1100 ,  1102 ,  1104 ,  1106 ,  1108 , and  1110  has a smaller width than the slots  200 , illustrated in FIG. 2. The RBI  100  may also be configured to have one continuous slot such as a slot forming an “O,” “S” or “Z” shape, among other shapes.  
         [0043]    In general, the size and configuration of the openings  200  may be modified to achieve the optimal sound. In certain applications, the foam inserts  400  may not be adequate to form a substantially solid acoustic surface for the high-frequency sound waves if the openings  200  are too large in size or number. Similarly, if the area of the openings  200  is too small, or if there are not enough openings  200 , then the mid-frequency sound may not adequately pass through the openings  200 .  
         [0044]    [0044]FIG. 12 is a perspective view of a series of multi-way loudspeakers  110  illustrated in FIG. 1 stacked together to form a line array  1200 . Use of the RBIs  100  in the speakers  100  of a line array  1200  is particularly advantageous in that they are able to better direct sound radiation to a predetermined area. Accordingly, listeners seated within a predetermined area would receive substantially the same quality of sound as other listeners at other locations within the same area. This feature is particularly advantageous when used in large area performance environments, such as auditoriums.  
         [0045]    Furthermore, line arrays typically are suspended from overhead, forming vertical lines of transducer arrays within their original bandwidths bass, mid-range, and treble. By forming those individual lines and curving these speaker arrays, improved dispersion uniformity and better control of the radiated sound may be realized. The sound radiating from the array of loudspeakers may be further improved by improved integration of the sound radiation from the mid-range and high-frequency elements by providing a RBI  100  for the high frequencies while allowing the mid-frequency sound to be emitted through the RBI  100  by way of openings  200  in the RBI  100  positioned in front of the mid-frequency speakers  300 . This arrangement may also act as a volume displacement device to improve loading and efficiency of the mid-range frequency elements.  
         [0046]    While various embodiments of the application have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of this invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.