Patent Publication Number: US-7590257-B1

Title: Axially propagating horn array for a loudspeaker

Description:
TECHNICAL FIELD OF THE INVENTION 
     The invention relates generally to the field of waveguides, and, more particularly, to a diffuse multiple-horn loudspeaker system 
     BACKGROUND OF THE INVENTION 
     With the advent of multi-channel audio technology for movie soundtracks encoded in formats such as DTS, DOLBY DIGITAL®, DVD Audio, DVD-A, Super Audio Compact Disc, SACD, or the like, surround-sound speakers capable of producing wide dispersion output have been in increasingly high demand for both auditorium and home theatre applications. Surround speaker requirements include diffuse dispersion in the horizontal axis to blur the time arrivals to the listener&#39;s ear. This concept is referred to as “reverb.” The audio source may be music, a sound effect, or the like. Multiple speakers can be grouped together to provide a wide dispersion of sound, but there is a nontrivial likelihood that the interaction between such acoustic sources will be acoustically destructive, degrading the sound quality heard by a listener. 
     Ideally, a point source solution is the answer to this difficulty, but due to size limitations (i.e., most compression drivers are roughly cylindrical with diameters between about 5 and 8 inches, making close placement difficult) and limitations of power output capabilities, such a design is impractical and unfeasible in most working applications. Accuracy and intelligibility of acoustic signal is a result of the way the loudspeaker reconstructs the temporal and spectral response of the reproduced wave front. Phase coherence of the signal or wave front is a result of the temporal response when reconstructed. A number of difficulties arise when attempting to sum acoustic wavefronts from multiple drivers including standing waves interference and phase cancellation between mutually acoustic sources. 
     In practice, the surround-sound speaker design has generally been approached by providing a bi- or tri-polar speaker with 180 degrees dispersion in the horizontal axis. The difficulty with this design is that most transducers tend to narrow the dispersion angle as the wavelength of the output increases to beyond the area of the transducer mouth. This effect is referred to as “beaming”. The waveguide geometry and/or the throat dimension of the compression driver and/or the diaphragm area of a dome tweeter are the primary contributors to beaming. To avoid beaming, multiple transducers can be used in an arc or array to maximize the dispersion angle in the horizontal axis. Unfortunately, the complication in this approach is that the polar patterns of dispersion tend to overlap or mesh, and thus do not sum acoustically in the axis wherein the transducers are placed due to phase differences. The phase differences give rise to destructive interference, which is interpreted by the listener as a reduction in fidelity and sound quality. Therefore, beaming is reduced at the expense of sound quality from incoherent phase contributions. 
     Thus, there remains a need for a surround-sound speaker design that can provide surround-sound without both beaming and destructive interference from the horns. The present invention addresses this need. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a surround-sound speaker system, including a plurality of waveguides or horns having noncodirectional acoustic emissions. Each speaker system includes an acoustic driver, a mouth, and a throat operationally connected between the acoustic driver and the mouth. The speaker system is characterized by an acoustic dispersion angle of at least about thirty degrees the vertical dispersion plane and at least about sixty degrees, and more typically between about ninety and about one-hundred and eighty degrees in the horizontal dispersion plane. 
     One object of the present invention is to provide an improved loudspeaker design. Related objects and advantages of the present invention will be apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a front plan view of a first embodiment speaker system of the present invention. 
         FIG. 1B  is a side plan view of the embodiment of  FIG. 1A . 
         FIG. 1C  is a top plan view of  FIG. 1A . 
         FIG. 2A  is a front plan view of a second embodiment horn assembly of the present invention. 
         FIG. 2B  is a rear plan view of the horn assembly of  FIG. 2A . 
         FIG. 2C  is a perspective elevation view of  FIG. 2A . 
         FIG. 2D  is a top plan view of  FIG. 2A . 
         FIG. 3A  is a front schematic view of a first embodiment speaker system having a first configuration. 
         FIG. 3B  is a front schematic view of a first embodiment speaker system having a second configuration. 
         FIG. 3C  is a front schematic view of a first embodiment speaker system having a third configuration. 
         FIG. 3D  is a front schematic view of a first embodiment speaker system having a fourth configuration. 
         FIG. 4A  is a front schematic view of a second embodiment speaker system having a first configuration. 
         FIG. 4B  is a front schematic view of a second embodiment speaker system having a second configuration. 
         FIG. 4C  is a front schematic view of a second embodiment speaker system having a third configuration. 
         FIG. 5A  is a perspective schematic view of a wall having a cavity for receiving a speaker system according to an embodiment of the present invention. 
         FIG. 5B  is a perspective view of  FIG. 5A  including a speaker system received in the cavity. 
         FIG. 5C  is an enlarged view of  FIG. 5C  showing the speaker system in more detail. 
         FIG. 6A  is a graphic representation of experimentally measured horizontal polar response curves at a frequency of 5 kiloHertz for a first embodiment speaker system of the present invention. 
         FIG. 6B  is a graphic representation of experimentally measured horizontal polar response curves at a frequency of around 10 kiloHertz for a first embodiment speaker system of the present invention. 
         FIG. 6C  is a graphic representation of experimentally measured horizontal polar response curves at a frequency of around 18 kiloHertz for a first embodiment speaker system of the present invention. 
         FIG. 6D  is a graphic representation of experimentally measured vertical polar response curves at a frequency of around 5 kiloHertz for a first embodiment speaker system of the present invention. 
         FIG. 6E  is a graphic representation of experimentally measured vertical polar response curves at a frequency of 10 kiloHertz for a first embodiment speaker system of the present invention. 
         FIG. 6F  is a graphic representation of experimentally measured vertical polar response curves at a frequency of 18 kiloHertz for a first embodiment speaker system of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Overview 
     A waveguide or horn loudspeaker may be thought of as an electro-acoustic transducer that translates an electrical signal into a directed acoustic signal. As used herein, “waveguide” means a conical or expanding duct or channel designed to confine and direct the propagation of modulated air pressure (i.e., acoustic waves) in a longitudinal direction. A waveguide typically consists of a coupling flange at its acoustical entrance for connecting a compression driver transducer thereto. The waveguide also typically includes a mouth defining an expanding waveguide or duct that exits to the ambient air and a mounting flange to affix the waveguide to a baffle board or other such enclosure, which may be an elaborate framework device or nothing more than a recess or cavity formed in a wall. A throat, such as the narrowmost area of a mouth cone or mouth duct with expanding walls or surfaces, extends between the mouth and the acoustical entrance. 
     Generally, a compression driver is operationally connected via a throat to the mouth of the horn to achieve proper acoustic impedance, high efficiency, low distortion and controlled dispersion. Horn speakers sound very dynamic and reproduce fast transients in the music due to their relatively low moving mass. For applications with dispersion of 100 degrees or less, a single horn using a single driver is usually adequate. For applications requiring wider dispersion angles at higher frequencies, additional horns and drivers are required. 
     The present invention relates to high frequency acoustic sources arranged in an array. The array or horn assembly can be defined by a plurality of horns, each characterized by at least about 30 degrees and more typically 60 degrees or more of dispersion. The coupling flange of each horn allows for mounting thereonto of a transducer with a “bolt on”, “screw on” or like mounting configuration. Multiple transducers are attached to the horn assembly and signal is applied in parallel to each transducer. The application of signal to the transducer results in the transduction of (typically electrical) signal energy into modulated air pressure or sound waves. In the case of compression drivers, this occurs through oscillation of the voice coil in a magnetic gap. Once produced, the longitudinal sound waves travel down the throat of the horn, following the area of expansion. This process happens simultaneously down the plurality of throats in the horn assembly. The path lengths down each throat are typically substantially identical so as to maintain phase angle between sound sources (i.e., transducers). The mouths or exit areas of each horn throat are positioned substantially adjacent to one another, so as to minimize the distance between mouth edges. This configuration gives rise to the maximization of the summation of acoustic output. 
     Constructive propagation may occur when two or more sound sources of the same frequency propagate in the same space. When the wavelength propagation is generally in phase and the same size as, or larger than, the spacing between the sound sources, the sources tend to reinforce one another. This phenomenon is known as mutual coupling. Mutual coupling has similar acoustic characteristics in a given bandwidth of frequency as a point source (i.e., sound emanating from one location) and is desirable. 
       FIGS. 1A-1C  illustrate a first embodiment of the present invention, a speaker system  10  including a substantially flat frame or baffle board portion  12  having a horn assembly aperture  14  for supporting a horn assembly  16 . The horn assembly  16  typically includes a pair of waveguides or horns  18 . Each horn  18  further includes a mouth  20 , a throat  22  and a driver or transducer  24 . The throat  22  is essentially a hollow tube positioned between and acoustically connecting the mouth  20  and the driver  24  via the coupling flange  23 . Typically the driver  24  may be thought of as defining a substantially flat output plane  25  oriented parallel with the plane defined by the contact surface of the coupling flange  23 . The throat  22  is further characterized by a central axis  26  extending therethrough, which is also typically normal to the output plane  25 . It is convenient to note that the central axis  26  also defines the primary direction of acoustic output of the horn  18 , and that the central axes  26  of the horns  18  are typically not oriented in parallel with each other. In other words, the horn array  16  includes at least two horns  18  having throats  22  defining nonparallel axes  26 . Typically, the array  16  includes two horns  18  defining two nonparallel axes  26 ; more typically, the axes  26  are oriented at an angle of at least about 60 degrees relative each other; still more typically, the axes  26  are oriented at an angle of about 90 degrees relative to each other. When three horns  18  are arrayed, the outer horns  18  are typically oriented symmetrically about the middle horn, and more typically, each outer horn  18  is oriented at an angle of about 45 degrees with the middle horn  18 . 
     Typically, the frame  12  will include one or more additional apertures  28  for supporting additional speaker units, such as one or more woofers, midrange transducers, or the like. Various frame  12  configurations are illustrated in  FIGS. 3A-4C , and are discussed in greater detail below. 
       FIGS. 2A-2D  illustrate a second embodiment horn array  16 ′ operative in the speaker system  10  described above. The horn array  16 ′ is similar in most respects to the horn array  16  of  FIGS. 1A-1C  above, with the primary difference being that the horn array  16 ′ is effectively a single horn  18 ′ including a plurality of throats  22 ′, each respective throat  22 ′ acoustically connected between a respective individual driver  24  and the mouth  20 ′. The throats  22 ′ are each characterized by a respective central axis  26 ′, and the central axes  26 ′ of the throats  22 ′ are typically nonparallel with each other. As above, each driver  24  typically includes a substantially flat output plane  25  that is also typically normal to the axis  26 ′ associated with the respective acoustically connected throat  22 ′. Each horn array  16 ′ thus effectively produces acoustic output defining at least two distinct directions that effectively combine to generate a diffuse, wide-angle acoustic output. Typically, each throat  22 ′ defines two axes  26 ′; more typically, the axes  26 ′ are oriented at an angle of at least about 60 degrees relative to each other; still more typically, the axes  26 ′ are oriented at an angle of about 90 degrees relative to each other. 
       FIGS. 3A-3D  illustrate four different configurations of the system  10  described above in  FIGS. 1A-1C . The configurations are intended to be illustrative of some of the different possible configurations of the speaker system  10 , and accordingly are not intended to illustrate all possible configurations.  FIG. 3A  illustrates a speaker system  10  including a generally rectangular frame  12  including one or more horn assembly aperture(s)  14  and a (typically generally circular) speaker aperture  28 . The horn array  16  is typically oriented such that a first horn  18  is positioned between a second horn  18  and the speaker aperture  28  (which is configured to receive a woofer, a low frequency transducer, midrange transducer, or the like). The frame  12  is configured to be mounted or positioned such that the longer dimension is oriented substantially vertically, such that the first horn  18  is positioned atop the second horn  18 , and the axes  26  intersect in a nonzero angle when projected into a substantially horizontal plane. In other words, when the frame  12  is oriented as specified above, the horn assembly  16  produces diffuse, wide-angle output in a substantially horizontal plane. 
     The speaker system illustrated in  FIG. 3B  includes a generally rectangular frame  12  including one or more horn assembly aperture(s)  14  and a (typically generally circular) speaker aperture  28 . The horn array  16  is typically oriented such that a first horn  18  is positioned between a second horn  18  and the speaker aperture  28  (which is configured to receive a woofer, a low frequency driver, a midrange transducer, or the like). The frame  12  is configured to be mounted or positioned such that the longer dimension is oriented substantially horizontally, such that the first horn  18  is positioned beside the second horn  18 , and the axes  26  intersect in a nonzero angle when projected into a substantially horizontal plane. In other words, when the frame  12  is oriented as specified above, the horn assembly  16  produces diffuse, wide-angle output in a substantially horizontal plane. 
     The speaker system  10  shown in  FIG. 3C  includes a generally rectangular or square frame  12  including one or more horn assembly aperture(s)  14  and a (typically generally circular) speaker aperture  28 . The horn array  16  is typically oriented such that a first horn  18  is positioned beside or horizontally adjacent a second horn  18  and the speaker aperture  28  (which is configured to receive a woofer, a low frequency driver, a midrange transducer, or the like) is centered below the horn assembly  16  (i.e., below the first and second horns  18 ). The frame  12  is configured to be mounted or positioned such that the first horn  18  is positioned beside the second horn  18  and over the speaker aperture  28 , and the axes  26  intersect in a nonzero angle when projected into a substantially horizontal plane. In other words, when the frame  12  is oriented as specified above, the horn assembly  16  produces diffuse, wide-angle output in a substantially horizontal plane. 
       FIG. 3D  relates to a speaker system  10  that includes a generally rectangular frame  12  including one or more horn assembly aperture(s)  14  and a plurality of (typically generally circular) speaker apertures  28 . The horn array  16  is typically oriented such that a first horn  18  is positioned horizontally adjacent and between a second horn  18  and a third horn  18 . A row of speaker apertures  28  (which is configured to receive a woofer, a low frequency driver, a midrange transducer, or the like) positioned below the horn assembly  16  and is typically centered relative the horn assembly  16 . The frame  12  is configured to be mounted or positioned such that the horn assembly extends in a horizontally oriented row with any two axes  26  intersecting in a nonzero angle when projected into a substantially horizontal plane. In other words, when the frame  12  is oriented as specified above, the horn assembly  16  produces diffuse, wide-angle output in a substantially horizontal plane. 
       FIGS. 4A-4C  illustrate three typical configurations of the system  10 ′ described above and includes using the horn array  16 ′ of  FIGS. 2A-2D . Again, the configurations are intended to be illustrative of different possible configurations of the speaker system  10 ′, and are not intended to illustrate all possible configurations or numbers of waveguides  18 ′ and/or transducers  24 ′.  FIG. 4A  shows a system  10 ′ with a generally rectangular frame  12 ′ and including a horn assembly  16 ′ and a (typically generally circular) speaker aperture  28 . The horn assembly  16 ′ includes a horn  18 ′ positioned above the speaker aperture  28  (which is configured to receive a woofer, a subwoofer, or the like). The horn assembly  16 ′ includes at least two throats  22 ′ and drivers  24 ′. The frame  12 ′ is configured to be mounted or positioned such that the longer dimension is oriented substantially vertically, such that the horn  18 ′ is positioned atop the aperture  28  and the axes  26  intersect in a nonzero angle when projected into a substantially horizontal plane. In other words, when the frame  12 ′ is oriented as specified above, the horn assembly  16 ′ produces diffuse, wide-angle output in a substantially horizontal plane. 
     The speaker system  10 ′ configuration shown in  FIG. 4B  is similar to that shown in  FIG. 4A , but with the addition of an additional speaker aperture  28  in the rectangular frame  12 . The horn assembly  16 ′ is positioned between the two apertures  28  such that when the frame  12 ′ is positioned such that the longer frame dimension is oriented substantially vertically, the horn  18 ′ is positioned atop the aperture  28  and the axes  26  intersect in a nonzero angle when projected into a substantially horizontal plane. In other words, when the frame  12  is oriented as specified above, the horn assembly  16 ′ produces diffuse, wide-angle output in a substantially horizontal plane. 
     In  FIG. 4C , the frame  12 ′ includes horn assembly  16 ′ positioned beside a pair of vertically positioned speaker apertures  28 . When oriented as shown, the horn  18 ′ produces diffuse, wide-angle output in a substantially horizontal plane. 
       FIGS. 5A-5C  relate to the typical wall mounted configuration of the speaker system  10 .  FIG. 5A  illustrates a typical speaker enclosure or cavity  30  formed in a wall  32 , and  FIG. 5B  shows the enclosure  30  as occupied by a speaker system  10 . As shown in more detail in  FIG. 5C , the frame  12  is typically mounted either flush with the wall  32  or such that it protrudes only a slight distance from the wall  32 . The horn assembly  16  and any woofer or the like supported by the aperture  28  are received in the cavity  30 . The wall  32  defines a wall plane  40 , and the mouth(s)  20  of the horn assembly  16  substantially define a mouth plane  42 . (While in some embodiments the horn mouth(s)  20  may be imparted a slight convex curve for aesthetic reasons, the mouth(s)  20  are still considered to be substantially planar for practical acoustic purposes.) The wall and mouth planes  40 ,  42  are typically either coplanar or substantially parallel and spaced a relatively small distance apart. 
     In operation, the drivers  24  are connected to a signal source, such as an audio amplifier, a tuner, an A/V receiver, or the like, and are energized by a signal from the same. Each driver  24  transduces the signal into an acoustic signal (i.e., modulated pressure waves) that propagates along the connected throat  22  and exits the mouth  20  of the respective horn  18 . (In the case of the embodiments of  FIGS. 2A-2D , the respective throats  22 ′ are connected to a common mouth  20 ′). The mouths  20  are positioned sufficiently close to one another such that the separation distance of the mouths  20  is less than or equal to the wavelengths of the sounds produced by the horns  18 , such that the horns  18  are mutually coupled when in operation regarding the desired bandwidth of the application. For applications having desired outputs in the 5-10 kHz range, the mouth-to-mouth separation distance is typically less than about 2 inches, more typically less than about 1 inch, still more typically less than about ½ inch, and yet more typically less than about ¼ inch. It is understood that the speaker system  10 ′ embodiment shown in  FIGS. 2A-2D  may be readily substituted for the speaker system  10  as shown in  FIGS. 3A-3D  and  4 A- 4 C. 
     As shown in  FIGS. 6A-6F , the polar directivity of the acoustic output of the speaker system  10  is substantially smooth and generally constant over a wide dispersion angle over a broad range of frequencies in a first (horizontal) plane; the polar directivity in a second plane normal to the first plane (vertical) is typically substantially narrower over the same range of frequencies. The data comprising  FIGS. 6A-6F  was generated experimentally on a vertical speaker stack (such as illustrated in  FIG. 3A ) via well-known acoustic techniques of rotating the speaker system  10  on a standard baffle in a spherical pattern every 5 degrees to closely approximate an in-wall speaker system. 
     As can be seen, at a frequency of 5000 Hz, the acoustic dispersion of the speaker system  10  is substantially constant over a 150-degree angle, with the −6 dB down points occurring at about +/−55 degrees from center in the horizontal plane. (See  FIG. 6A ). At 10,000 Hz in the horizontal plane, the speaker system  10  exhibits a substantially constant acoustic dispersion over about 115 degrees, with −6 dB down points at about +/−50 degrees from center; at 10,000 Hz, the acoustic output does exhibit some lobing formation due to the interference effects of phase summation. (See  FIG. 6B ). At 18,000 Hz in the horizontal plane, the speaker system  10  exhibits a substantially constant acoustic dispersion over about 130 degrees, with −6 dB down points at about +/−60 degrees from center; at 18,000 Hz, the acoustic output exhibits multiple lobing formation due to the interference effects of the phase summation. (See  FIG. 6C ). 
     Likewise, in the vertical plane at a frequency of 5000 Hz, the acoustic dispersion of the speaker system  10  is already tri-lobed (i.e., the dispersion pattern exhibits three distinct major lobes), with the −6 dB down points occurring at about +/−20 degrees from center in the horizontal plane. (See  FIG. 6D ). At 10,000 Hz in the vertical plane, the speaker system  10  exhibits five lobes and has −6 dB down points in the center lobe at about +/−15 degrees from center. (See  FIG. 6E ). At 18,000 Hz in the vertical plane, the speaker system  10  exhibits multi-lobed acoustic dispersion that approximates a smooth output over about 120 degrees, with −6 dB down points at about +/−35 degrees from center. (See  FIG. 6F ). 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the invention are desired to be protected.