Abstract:
This invention is directed a sound system that groups a midrange horn with a HF horn to increase the sound pressure levels while minimizing interference problems. The HF horn may be coupled to at least two HF drivers where they sum or merge into a common throat or wave-guide. The midrange horn may be coaxially mounted with the higher frequency horn. The midrange horn may be coupled to at least two midrange drivers. And the midrange drivers may be mounted substantially perpendicular to the HF drivers. This configuration provides for smaller system sizes, than conventional mounting of the HF horn adjacent to the mid frequency horn. By coaxially mounting the midrange and HF horns, the off-axis interference (lobing) through the crossover region both in the horizontal and vertical planes may be minimized. This configuration produces increased sound pressure levels while minimizing acoustic crossover interference problems.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from a provisional application having Application Serial No. 60/273,844 that was filed on Mar. 7, 2001, and is incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention provides a sound system capable of grouping midrange and high frequency drivers together in an enclosure to increase the sound pressure level while minimizing interference problems.  
           [0004]    2. Related Art  
           [0005]    A sound system in a large spacious area such as an arena, outdoor, or stadium setting requires very high sound pressure levels (SPL) for adequate reproduction because of the long distances sound waves must travel in order to reach the listener. With the long distance, however, attenuation may develop in the sound waves. This may cause a drop of about 6 dB level of sound amplitude as sound waves travel twice the distances. Attenuation problems in the sound waves may be overcome by producing higher sound pressure levels at the origination of the sound. One way to do this is through grouping a number of loudspeakers together to increase the SPL.  
           [0006]    When a group of loudspeakers generate sound there may be an overlapping in the coverage area. Overlapping sound waves, however, interferer with other sound waves. This can cause the overall SPL produced from the group of loudspeakers to be less than the SPL produced from the individual loudspeakers. For example, two sources or drivers generating overlapping patterns may increase the average SPL to about 3 dB over one of the two sound sources. By comparison, a coherent summation, where there is little or no interference, between two sound sources, would increase the average SPL by about 6 dB over one of the two sound sources. Interference may also reduce the intelligibility and coherency of the sound because the sound waves may be arriving at the listener&#39;s ears at different times from different sound sources. Another problem may be reverberation within the auditorium due to sound waves bouncing off the walls, affecting the quality of the sound.  
           [0007]    In an attempt to minimize the problems of grouping loudspeakers some have tried to incorporate two or three midrange drivers and two or three high frequency drivers into one enclosure. Such an arrangement helps to raise the SPL but there may still be a problem with interference. Meaning, the drivers do not add up to produce the optimal SPL. Therefore, there still is a need for a sound system that may group midrange and high frequency (HF) drivers to increase the SPL while minimizing interference.  
         SUMMARY  
         [0008]    This invention provides a sound system that groups a midrange horn with a high frequency (“HF”) horn to increase the sound pressure level (“SPL”) while minimizing interference problems. The sound system may include the following features: (1) a HF horn having at least two HF drivers where they sum or merge into a common throat or wave guide; (2) the HF horn may be coaxially mounted within the mouth of a midrange horn, where the midrange horn has at least two midrange drivers; and/or (3) the midrange drivers may be generally perpendicular to the HF drivers.  
           [0009]    The HF horn may be coaxially aligned within the mouth of a midrange horn. For example, the HF horn may include at least two HF drivers or transducers within the mouth of the midrange horn. Each of the two HF drivers may have a vertical diffraction slot opening providing an exit for the sound waves. The two slots from each of the HF drivers may be merged to form a common exit. The shape of the common exit may be rectangular. The two slots may be adjacent to each other and together forming a throat. The two slots may be sized in terms of their height and width, with the vertical centerline for each of the two slots spaced apart from each other, so that the acoustic output of the two slots may be fully coherent. In this configuration, the wave fronts from the two slots may be in phase so that summation of the acoustic wave fronts occurs at frequencies between 500 Hz and 20 kHz and at angles within the nominal horizontal and vertical coverage of the sound system.  
           [0010]    The midrange horn throat may be driven by at least two midrange drivers that are arranged so that they are substantially perpendicular to the HF drivers. The midrange drivers may be sized and spaced apart from each other so that the acoustic response combines fully coherent. In this configuration, a more ideal phase summation of the acoustic wave fronts may occur at frequencies between 100 Hz and 2 kHz and at angles within the nominal horizontal and vertical coverage of the sound system.  
           [0011]    With the HF horn coaxially positioned within the mouth of the mid-frequency horn, the size of the sound system may be reduced. The coaxial mounting may allow the off-axis interference (lobing) through the crossover region to be optimized equally in both the horizontal and vertical planes. The use of two midrange and two HF drivers may be arranged to sum coherently within the system&#39;s coverage angles. This may provide a 6 dB increase in the SPL as compared to a single driver. Therefore, increased SPL may be achieved while minimizing acoustic crossover interference problems.  
           [0012]    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 FIGURES  
       [0013]    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. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.  
         [0014]    [0014]FIG. 1 is a front view of the sound system with a high frequency horn within a midrange horn.  
         [0015]    [0015]FIG. 2 is a cross-sectional view of the sound system along a line A-A of FIG. 1 showing a plurality of high frequency drivers.  
         [0016]    [0016]FIG. 3 is a cross-sectional view of the sound system along a line B-B of FIG. 1 showing a plurality of midrange drivers.  
         [0017]    [0017]FIG. 4 is a graph of midrange impulse response with and without a damper covering the high frequency drivers of FIG. 2.  
         [0018]    [0018]FIG. 5 is a front view of the sound system illustrating a radiating area that may be divided into three areas.  
         [0019]    [0019]FIG. 6 is a front view of the sound system illustrating that as listening location is moved to the left, the vectors that sound travels through moves to the left.  
         [0020]    [0020]FIG. 7 is a top view of the sound system illustrating the vector moving to the left as shown in FIG. 6.  
         [0021]    [0021]FIG. 8 is a top cross-sectional view of two high frequency drivers coupled to two slots margining into a common exit.  
         [0022]    [0022]FIG. 9 is a top cross-sectional view of traditional drivers coupled to two slots.  
         [0023]    [0023]FIG. 10 is a perspective view of a common exit of two slots.  
         [0024]    [0024]FIG. 11 is a graph of unprocessed frequency response and impedance curve of a high frequency horn.  
         [0025]    [0025]FIG. 12 is a graph of horizontal off axis response of a high frequency horn.  
         [0026]    [0026]FIG. 13 is a graph of high-resolution frequency response of the processed midrange, high frequency, and the net system response.  
         [0027]    [0027]FIG. 14 is a graph of three horizontal beamwidth curves for unprocessed midrange and high frequency beamwidths, and a processed overall horizontal beamwidth of the system.  
         [0028]    [0028]FIG. 15 is top view of two slots that are curved.  
         [0029]    [0029]FIG. 16 is a flow chart of a method for grouping midrange and high frequency drivers together in an enclosure to increase sound pressure level while minimizing interference problems. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    [0030]FIGS. 1 through 3 illustrate a sound system  100  incorporating a midrange horn  102  with a high frequency (HF) horn  104  to increase the SPL while minimizing interference problems. The sound system  100  may include the following features: (1) a HF horn  104  coupled to a plurality of high frequency drivers  106  and  108  where they sum or merge into a common throat  110  or wave guide; (2) coaxially mounting the midrange horn  102  with the HF horn  104 , where the midrange horn  102  is coupled to a plurality of midrange drivers  112  and  114 ; and (3) mounting the plurality of midrange drivers  112  and  114  generally perpendicular to the plurality of HF drivers  106  and  108 .  
         [0031]    The HF horn  104  may be coaxially positioned within the mouth of the midrange horn  102 . A number of channels  156  may be used to coaxially couple the HF horn  104  to the midrange horn  102 . A plurality of diffraction slots  116  and  118  may be between the plurality of HF drivers and the HF horn. The plurality of diffraction slots  116  and  118  may couple the HF drivers  106  and  108  to the HF horn  104 . The plurality of slots  116  and  118  may merge to form a common exit  140  that is adapted to mate with the throat  110  of the HF horn  104 .  
         [0032]    The cross-section of the plurality of slots  116  and  118  may have a variety of shapes such as rectangular, square, triangular, oval, and circular. As the plurality of slots  116  and  118  merge, the common exit may have a variety of cross-sectional shapes as well such as rectangular, square, triangular, oval, and circular. The plurality of slots  116  and  118  may be sized so that the acoustical output of the plurality of slots may be fully coherent. In this configuration, the wave fronts from the plurality of slots may be in phase so that the summation of the acoustic wave fronts occurs at frequencies between about 500 Hz and about 20 kHz. The summation may also occur at angles within the nominal horizontal and vertical coverage range of the horns.  
         [0033]    The plurality of slots  116  and  118  may expand in area gradually from the HF driver&#39;s side to the throat  110  of the HF horn  104 . The cross-sectional area may increase smoothly without discontinuities in the growth rate. The cross-sectional area may grow approximately in an exponential or other desirable manner. The HF horn  104  and the midrange horn  102  may expand gradually as well until they both form a HF lip  150  and a midrange lip  152 , respectively. This allows the wave fronts from the HF drivers and midrange drivers to propagate in a smooth manner.  
         [0034]    As illustrated in FIG. 2, the HF horn  104  may be configured so that it does not interfere with the expansion of the midrange horn  102  for proper acoustic loading. The HF horn  104  may be designed with both an interior surface  132  and a molded outer surface  134 . The outside surface  134  may expand to maintain the area growth of the midrange horn  102  in an exponential manner. The space between the inside and outside surfaces  132  and  134  may be filled with urethane foam that provides structural rigidity and acoustic damping.  
         [0035]    [0035]FIGS. 2 and 3 illustrate the midrange horn  102  may be coupled to two midrange drivers  112  and  114 , where the two midrange drivers  112  and  114  are aligned so that they are substantially perpendicular to the two HF drivers  106  and  108  that are aligned. The midrange drivers may be sized and spaced apart from each other so that the acoustic summed response may be fully coherent as well. For example, the centerline to centerline distance between the midrange drivers may be about 6.5 inches (165 mm) and about 12 inches (305 mm); and in certain applications the center of the two midrange drivers may be spaced about 8.5 inches (216 mm) apart. This allows the summation of the acoustic wave fronts to occur at frequencies between about 20 Hz and about 20 kHz. The summation of the wave fronts may also occur at angles within the nominal horizontal and vertical coverage range of the horn. The midrange driver may generate wave fronts with frequencies between about 20 Hz and about 3 kHz. The diameter of the midrange drivers may be about 8 inches (203 mm) as described in U.S. Pat. No. 5,748,760, and is incorporated by reference.  
         [0036]    The HF drivers  106  and  108  may be placed close to the midrange drivers so the reflection of the wave fronts from the midrange drivers  112  and  114  off the backside of the HF drivers  106  and  108  is minimized. At higher frequency levels, wave fronts between about 500 Hz and 2.0 kHz from the midrange drivers  112  and  114  may reflect off the back of the HF drivers  106  and  108 . This may cause the sound waves to reflect back to the throat of the midrange horn  102 , causing aberration in the frequency and polar response. To minimize or eliminate such reflections, an acoustic throat damper  130  may be used to wrap around the HF drivers  106  and  108 . The damper  130  may be specified to be moderately acoustically absorptive above 700 Hz, but not to be absorptive below 700 Hz. Hence, the portion of the wave fronts between 500 Hz and 2.0 kHz that would be reflected from the rear of HF drivers  106  and  108  are absorbed by the damper  130  rather than reflecting back into the midrange horn  102 . The damper  130  may be constructed with an inside and outside shell of flame-retardant-treated and acoustically transparent woven fabric. The damper  130  may be made of fiberglass wool, grill cloth, Dacron, or any other material known to one skilled in the art.  
         [0037]    [0037]FIG. 4 illustrates the midrange impulse response with and without the damper  130 . The solid curve  400  indicates the response with the damper  130 , and the dash curve  402  indicates the response without the damper  130 . The solid curve  400  shows a smoother polar response and cleaner impulse response than the dash curve  402 . FIG. 4 also indicates that since the damper  130  is absorptive above 700 Hz, there may be a net reduction in the SPL of about 1 dB between frequency range of about 1 kHz and 2 kHz. The damper  130  is optional depending on the application considering the trade off between the 1 dB reductions in the SPL versus smoother responses.  
         [0038]    Shadowing may occur if the HF horn  104  blocks too much area of the midrange horn  102 . This can cause the midrange horn  102  to behave as distinct “cells.” When this happens, the midrange off-axis response may have nulls within the nominal coverage angle due to destructive interference of the acoustic energy produced by the distinct cells. This effect may be minimized by reducing the size of the HF horn  104 . On the other hand, the size of the HF horn  104  needs to be large enough to maintain a pattern control at the crossover because the lower frequency limit of desirable pattern control may be limited by the mouth size of the HF horn.  
         [0039]    [0039]FIGS. 5 through 7 illustrate the effect of shadowing that causes the midrange horn to be divided into separate acoustical radiating areas. In this example there are three distinct areas defined by: two large areas labeled “A” formed above and below the HF horn; and two smaller areas “B” and “C” formed on both sides of the HF horn. FIGS. 6 and 7 illustrate that the listening or measurement location may be moved to the left, as indicated by the left arrows. In such instances, sound must travel through the vector (X) shifted to the sidewall of the horn. At this angle of observation, acoustic energy originating from areas “A” and “B” may be in the same vertical plane, but energy arriving from area “C” may be offset in time. If the “shadowed” area or area “C” is too large the difference in arrival time may cause narrowing of the beamwidth, and visible lobing in the polar response may occur. Similarly, the same effect may occur in the vertical plane.  
         [0040]    The effect of shadowing may be minimized if the height  158  and width  156  of the HF horn  104  is about 0.25 to about 0.4 ratio of the height  158  and width  160  of the midrange horn  102 , respectively. This means that the masked area “C” may be between about 13% and about 19% of the total radiating area of the midrange horn. For 13% masked area and 19% mask area, there may be about 2 dB and about 4 dB maximum variations in response, respectively, assuming the following: (1) the intensity of the sound field is uniform across the radiating area of the midrange horn; and (2) the energy radiating from the “shadowed” zone is shifted 180° out-of-phase compared to the primary arrival of energy at some frequencies. If the HF horn is not square, then the percentage of masking may be different. With reference to FIGS. 1 through 3, the ratio between the HF horn  104  versus the midrange horn  102  may be about 0.33 vertically, and about 0.28 horizontally.  
         [0041]    The output from the two midrange drivers  112  and  114  may be combine coherently so that the SPL may increase up to 6 dB in the coverage area. The midrange drivers may be JBL&#39;s 2250J Neodymium Differential Drives having a diameter of about 200 mm (8 in.) that provides about 350 watt power handling, per transducer. Other midrange drivers with different diameters may be used with this invention. Using two 200 mm (8 in.) diameter midrange drivers allows the bandwidth of the driver to extend to higher frequencies. The two smaller diameter drivers may also be placed edge-to-edge where the centerline to centerline distance is between about 7 inches (178 mm) and 8¼ inches (210 mm) apart. This minimizes the off-axis interference in the dual driver system.  
         [0042]    [0042]FIG. 3 illustrates the midrange drivers aligned edge-to-edge vertically so that the HF drivers  106  and  108  may be located between the two-midrange drivers  112  and  114 . Arranging the high and midrange drivers in this configuration may reduce the masked area due to the HF drivers being in front of the midrange drivers. The two HF drivers may be JBL&#39;s compression drivers Model 2430 or 2435, both manufactured at 8500 Balboa Blvd. Northridge, Calif. 91329, U.S.A. In this regard, U.S. patent application Ser. No. 09/921,149 entitled Two-Stage Phasing Plug System in a Compression Driver, and filed on Jul. 31, 2001, is incorporated by reference. The driver Model No. 2430 may be used with a diaphragm made of aluminum, and the driver Model No. 2435 may be used with a diaphragm made of Beryllium. These HF drivers may be relatively small yet able to produce high acoustical output due to their efficiency, and they may generate wave fronts with a frequency range between about 500 Hz and about 20 kHz. Both the 2330 and 2435 may have a 4¼ inches (108 mm) diameter with a 3 inch (75 mm) diaphragm, and a height of about 2 {fraction (5/16)} inches (67 mm). In contrast, traditional large format high frequency compression drivers may have a diameter ranging from 6.5 inches (165 mm) to 10 inches (254 mm). This means that the rear side of the HF drivers  106  and  108  that face the midrange drivers, have relatively smaller surface areas so that they minimize wave fronts from the midrange drivers  112  and  114  from reflection off the HF drivers  106  and  108 . HF drivers having a diameter size of other than 5.5 inches (140 mm) may be used to minimize reflecting of the wave fronts from the midrange drivers.  
         [0043]    [0043]FIG. 8 illustrates two 4¼ inch diameter HF drivers  106  and  108  coupled to its respective slots  116  and  118 . FIG. 9 illustrate two traditional HF drivers  906  and  908  having a diameter between 6.5 inches (165 mm) and 10 inches (254 mm) coupled to its respective slots  916  and  918 . Because of the larger diameter of traditional drivers  906  and  908 , the half-included angle φ for slots  916  and  918  is greater than the half-included angle θ for the slots  116  and  118 . This means that the offset arrival of the wave front at the common exit  140  (D2 minus D1) for the slots  116  and  118  is less than at the common exit  902 . Accordingly, minimizing the included angle between the HF drivers also minimizes the path length difference (D2 minus D1) to the common exit. Using smaller HF drivers may reduce the half-included angle to minimize the path length difference.  
         [0044]    [0044]FIG. 10 illustrates the two slots  116  and  118  merging to form a common exit  140 . The total width “W” for the common exit  140  may between about 0.75 inches (19 mm) and about 3.00 inches (76 mm); and the total height “H” may be between about 0.5 and 30.0 inches (13 mm and 762 mm). The distance “C” between the two centerlines  1002  and  1004  through the respective slots  116  and  118  may be between about 0.5 inches (13 mm) and 3.0 inches (76 mm). The common exit  140  may be divided by a wall  1000  having a thickness “t” that is between about 0.06 inches (2 mm) and about 0.25 inches (6 mm). As further illustrated in FIG. 8, the length “L” for the two slots  116  and  118  may be between about 4.0 inches (102 mm) and about 30.0 inches (762 mm). In particular, the length “L” may be about 11.0 inches (279 mm).  
         [0045]    Using smaller diameter HF drivers  106  and  108  allows the two slots  116  and  118  to merge so that the distance “C” between the centerline to centerline at the common exit may be small. This allows the wave fronts from the two HF drivers  106  and  108  to sum coherently at the common exit. For example, for the two slots  116  and  118  having the following dimensions: L=11 inches (279 mm); W=2.12 inches (54 mm); C=1.0 inch (25 mm); and t=0.12 inches (3 mm), the included angle θ between the primary axis  800  and the slots may be about 8.5° . This may reduce the offset in arrival of the wave front (D2 minus D1) at the common exit  802  to about 3.5 mm (0.14 in.). This may translate into about 63 μsec offset in arrival.  
         [0046]    As illustrated in FIG. 2, the common exit  140  may be coupled to the throat  110  of the HF horn  104 . The curvature of the inner surface  132  may be smoothly curved in shape where the minimum horizontal width “M” may be about 45 mm ({fraction (1/4)} in.), that is about 0 to about 6 inches (152 mm) in front of the common exit  140 . The HF horn  104  integrates the two wave fronts from the two HF drivers  106  and  108  in a coherent fashion. FIG. 11 illustrates an unprocessed frequency response curve  1100  and an impedance curve  1102  of the high frequency section. Note the smooth frequency response throughout the entire usable piston band of the HF drivers. The response is substantially free of performance aberrations to frequencies above 11 kHz. FIG. 12 shows the horizontal off-axis response for the same horn. These curves further illustrate that the two HF drivers  106  and  108  and the HF horn  104  behave substantially as a single unified signal source beyond 16 kHz at 0°, 10°, 20°, 30° and 40° off axis.  
         [0047]    The sound system  100  may behave symmetrically through horizontal and vertical crossover regions. Such symmetry may provide a degree of freedom in the crossover design. In a non-coaxial system, where the HF horn is displaced to one side of the midrange horn, the two pass bands may need to be in phase and at a level of −6 dB at the crossover point. For a symmetrical loudspeaker, however, the crossover region may be manipulated to optimize the system response both on and off axis to achieve substantially consistent frequency response at angles along the on and off-axis, horizontally and vertically.  
         [0048]    Signal processing may improve the performance of the sound system  100 . The performance may be improved by tuning a number of variables in a digital loudspeaker processor such as: (1) Crossover frequency; (2) High pass filter slope; (3) High pass filter type; (4) low pass slope; (5) low pass filter type; (6) interchannel delay; (7) polarity; and (8) all-pass filtering. Each of these variables may be optimized to yield a desired result. Tuning may be available through such processors as: JBL DSC-260, BSS Soundweb, and dbx Driverack.  
         [0049]    The filter slopes and alignments may allow the interaction between the pass-bands to be controlled. By determining the correct amount of interaction to occur at each frequency, the beamwidth, and directivity interaction between the pass-bands may be adjusted to assume the characteristic of either pass-band at each frequency. FIG. 13 illustrates a high-resolution frequency response plot of the processed midrange frequency band  1300 , high frequency band  1302 , and the net system response  1304  for the sound system  100  using the signal processing. The net result is a clean system response  1304  based on the contribution from the midrange and high frequency bands  1300  and  1302 .  
         [0050]    [0050]FIG. 14 illustrates three horizontal beamwidth curves: unprocessed midrange section beamwidth  1400 ; unprocessed high frequency beamwidth  1402 ; and the overall horizontal beamwidth  1404  that has been processed to optimize the performance of the sound system  100 . With the signal processing there is a more uniform angular and frequency response coverage.  
         [0051]    Alternatively, as illustrated in FIG. 15, two slots  1500  and  1502  may be curved in certain applications to produce a flatter wave front as the common exit  1504 . With the curve slots, as the two curve slots merge they are more parallel with each other so that the wave fronts from the HF drivers may be flatter. This may be desirable depending on the required horizontal coverage angle. The radius of curvature of the two slots may be such that the two HF drivers are as close to each other as possible to minimize interfering with wave fronts from the midrange drivers. The length of the two slots may determine the vertical coverage angle.  
         [0052]    [0052]FIG. 16 illustrates a method  1600  for grouping a plurality of midrange drivers and a plurality of high frequency drivers in an enclosure to increase SPL while minimizing interference problems. In  1602 , the HF horn  104  may be coaxially coupled to the midrange horn. In  1604 , a plurality of midrange drivers  112  and  114  that are aligned may drive the midrange horn  102 . In  1606 , a plurality of HF drivers  106  and  108  may drive the HF horn within the midrange horn. In  1608 , the plurality of HF drivers may be aligned so that they are substantially perpendicular to the midrange drivers that are aligned. In  1610 , the wave fronts from the plurality of HF drivers may be coherently summed into the throat of the HF horn. In  1612 , if smoother response is preferred over 1 dB reduction in SPL, then in  1614 , a damper may be used to cover the HF drivers so that the wave fronts above about 700 Hz which may reflect off drivers are absorbed rather than reflecting back off the HF drivers. In  1614 , a digital loudspeaker may be tuned to improve the performance of the sound system.  
         [0053]    While various embodiments of the invention 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.