Patent Publication Number: US-10334355-B2

Title: Multi-driver acoustic horn for horizontal beam control

Description:
This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/US2015/053024, filed Sep. 29, 2015, which claims the benefit of U.S. Provisional Patent Application No. 62/057,982, filed Sep. 30, 2014, and this application hereby incorporates herein by reference that provisional patent application. 
    
    
     FIELD 
     A loudspeaker array is disclosed with a continuously open circumferential horn that provides improved gain, directional sound control, and reduced spurious beams or side-lobes (that are typically generated above an aliasing frequency such that the generated beam is no longer well controlled.) Other embodiments are also described. 
     BACKGROUND 
     Loudspeaker arrays are often used by computers and home electronics for outputting sound into a listening area. Each loudspeaker array may be composed of multiple transducers that are arranged on a single plane or surface of an associated cabinet or casing. Acoustic horns may be used along with transducers to increase the efficiency by which these transducers output sound. In particular, horns may provide (1) extra acoustic gain in one or more frequency bands and (2) directivity control. 
     Although horns may provide some efficiency improvements, horns may also lead to aliasing issues between transducers. In particular, horns may increase the distance between the points where sound from adjacent transducers in a loudspeaker array is mixed. This distance defines the aliasing frequency above which sound may become distorted based on sound mixing between proximate transducers. 
     Further, traditional horn designs suffer from sharp cutoff frequencies caused by the shape and dimensions of the horn. Accordingly, sound produced by a transducer below this frequency is cut off or inconsistently modified in comparison to higher frequency content. 
     The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. 
     SUMMARY 
     An audio system operating within a listening area is described herein. The audio system may include an audio receiver and a loudspeaker array. The audio receiver may be coupled to the loudspeaker array to drive individual transducers in the loudspeaker array to emit various sound beam or radiation patterns into the listening area for a listener. In one embodiment, the loudspeaker array may include a continuously open circumferential horn for controlling sound produced by the transducers. In this embodiment, one or more transducers may be coupled proximate to a throat of the horn. The continuously open circumferential horn may 1) improve the power efficiency of the transducers without unwanted aliasing effects in audible frequency ranges and/or 2) provide vertical control for sound emitted by the transducers. 
     In particular, by providing an unobstructed and open cavity for sound emitted by the transducers to mix, the continuously open circumferential horn may decrease a mixing distance between adjacent transducers (e.g., transducers that are directly adjacent in the ring of transducers) such that a corresponding aliasing frequency is increased. This aliasing frequency describes the highest frequency that may be emitted by the transducers without generation or production of aliasing effects caused by mixing of sound between transducers. Accordingly, by decreasing the mixing distance, the continuously open circumferential horn increases the maximum frequency that may be produced by the transducers without unwanted effects. 
     Further, the continuously open circumferential horn may provide improved directional control for sound produced by the transducers, including both horizontal and vertical control. For example, the outer corners of the continuously open circumferential horn may be curved. These curved corners more uniformly improve gain across frequency ranges in comparison to horns that are abruptly cutoff at the mouth of the horn. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one. Also, in the interest of conciseness and reducing the total number of figures, a given figure may be used to illustrate the features of more than one embodiment of the invention, and not all elements in the figure may be required for a given embodiment. 
         FIG. 1  shows a view of a listening area with an audio receiver, a loudspeaker array, and a listener according to one embodiment. 
         FIG. 2  shows a component diagram of the audio receiver according to one embodiment. 
         FIG. 3A  shows a component diagram of the loudspeaker array according to one embodiment. 
         FIG. 3B  shows a view of a loudspeaker array with a continuously open circumferential horn according to one embodiment. 
         FIG. 4A  shows a set of example directivity/radiation patterns that may be produced by the loudspeaker array according to one embodiment. 
         FIG. 4B  shows a top view of a loudspeaker array emitting a forward facing cardioid radiation pattern in a horizontal plane using a set of transducers according to one embodiment. 
         FIG. 5A  shows a horn coupled to a transducer according to one embodiment. 
         FIG. 5B  shows a set of horns coupled to a set of transducers according to one embodiment. 
         FIG. 6  shows the mixing distance for a set of transducers when using the continuously open circumferential horn according to one embodiment. 
         FIG. 7  shows a set of transducers stored within an upper section of the loudspeaker array and directing sound through the continuously open circumferential horn according to one embodiment. 
         FIG. 8  shows a set of transducers stored within an upper section and a lower section of the loudspeaker array and directing sound through the continuously open circumferential horn according to one embodiment. 
         FIG. 9  shows a view of a loudspeaker array with a continuously open circumferential horn according to one embodiment. 
         FIG. 10  shows a view of a loudspeaker array with differently angled inner walls for a continuously open circumferential horn according to one embodiment. 
         FIG. 11  shows a loudspeaker array with different types of transducers according to one embodiment. 
         FIG. 12  shows an overhead view of a loudspeaker array with a set of dividers according to one embodiment. 
         FIG. 13  shows a set of example sound velocity profiles for a set of loudspeaker arrays according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Several embodiments are described with reference to the appended drawings are now explained. While numerous details are set forth, it is understood that some embodiments of the invention may be practiced without these details. In other instances, well-known circuits, structures, and techniques have not been shown in detail so as not to obscure the understanding of this description. 
       FIG. 1  shows a view of an audio system  100  operating within a listening area  101  according to one embodiment. The audio system  100  may include an audio receiver  103  and a loudspeaker array  105 . The audio receiver  103  may be coupled to the loudspeaker array  105  to drive individual transducers  109  in the loudspeaker array  105  to emit various sound beam/radiation patterns into the listening area  101  for a listener  107 . In one embodiment, the loudspeaker array  105  may include a continuously open circumferential horn  113  for controlling sound produced by the transducers  109 . In this embodiment, one or more transducers  109  may be coupled proximate to a throat  115  of the horn  113 . As will be described in greater detail below, the continuously open circumferential horn  113  may 1) improve the power efficiency of the transducers  109  without unwanted aliasing effects in audible frequency ranges and/or 2) provide vertical control for sound emitted by the transducers  109 . 
     In some embodiments, the transducers  109  of the array  105  may be configured to generate beam patterns. The beam patterns may represent individual channels of a piece of sound program content. For example, the loudspeaker array  105  may generate beam patterns that represent front left, front right, and front center channels for a piece of sound program content (e.g., a musical composition or an audio track for a movie). 
     Each element of the audio system  100  shown in  FIG. 1  will be described below by way of example. In other embodiments, the audio system  100  may include additional components than those described below and shown in  FIG. 1 . 
       FIG. 2  shows a component diagram of the audio receiver  103  according to one embodiment. The audio receiver  103  may be any electronic device that is capable of driving one or more transducers  109  in the loudspeaker array  105 . For example, the audio receiver  103  may be a desktop computer, a laptop computer, a tablet computer, a home theater receiver, a set-top box, and/or a mobile device (e.g., a smartphone). The audio receiver  103  may include a hardware processor  201  and a memory unit  203 . 
     The processor  201  and the memory unit  203  are used here to refer to any suitable combination of programmable data processing components and data storage that conduct the operations needed to implement the various functions and operations of the audio receiver  103 . The processor  201  may be an applications processor typically found in a smart phone, while the memory unit  203  may refer to microelectronic, non-volatile random access memory. An operating system may be stored in the memory unit  203  along with application programs specific to the various functions of the audio receiver  103 , which are to be run or executed by the processor  201  to perform the various functions of the audio receiver  103 . 
     The audio receiver  103  may include one or more audio inputs  205  for receiving audio signals from an external device, e.g., a remote device. For example, the audio receiver  103  may receive audio signals from a remote server of a streaming media service. The audio signals may represent one or more channels of a piece of sound program content (e.g., a musical composition or an audio track for a movie). For example, a single signal corresponding to a single channel of a piece of multichannel sound program content may be received by an input  205  of the audio receiver  103 . In another example, a single signal may correspond to multiple channels of a piece of sound program content, which are multiplexed onto the single signal. The processor  201  of the audio receiver  103  may receive as inputs multiple audio channel signals simultaneously, and processes these to produce multiple acoustic transducer drive signals (to render the audio content in the input signals as sound), e.g., as a beamforming process to control relative phases and gains for each of the signals used to drive the transducers such that the transducers generate an acoustic beam pattern along the horizontal plane. 
     In one embodiment, the audio receiver  103  may include a digital audio input  205 A that receives digital audio signals from an external device and/or a remote device. For example, the audio input  205 A may be a TOSLINK connector or a digital wireless interface (e.g., a wireless local area network (WLAN) adapter or a Bluetooth adapter). In one embodiment, the audio receiver  103  may include an analog audio input  205 B that receives analog audio signals from an external device. For example, the audio input  205 B may be a binding post, a Fahnestock clip, or a phono plug that is designed to receive a wire or conduit and a corresponding analog signal. In another embodiment, the processor  201  may obtain its input audio channel signals by decoding an encoded audio file, e.g., an MPEG file. 
     In one embodiment, the audio receiver  103  may include an interface  207  for communicating with the loudspeaker array  105 . The interface  207  may utilize wired mediums (e.g., conduit or wire) to communicate with the loudspeaker array  105 , as shown in  FIG. 1 . In another embodiment, the interface  207  may communicate with the loudspeaker array  105  through a wireless connection. For example, the network interface  207  may utilize one or more wireless protocols and standards for communicating with the loudspeaker array  105 , including the IEEE 802.11 suite of standards, IEEE 802.3, cellular Global System for Mobile Communications (GSM) standards, cellular Code Division Multiple Access (CDMA) standards, Long Term Evolution (LTE) standards, and/or Bluetooth standards. 
       FIG. 3A  shows a component diagram for the loudspeaker array  105  according to one embodiment. As shown in  FIG. 3A , the loudspeaker array  105  may include an interface  301  for receiving drive signals from the audio receiver  103 . The drive signals may be used for driving each of the transducers  109  in the loudspeaker array  105 . As with the interface  207 , the interface  301  may utilize wired protocols and standards and/or one or more wireless protocols and standards, including the IEEE 802.11 suite of standards, IEEE 802.3, cellular Global System for Mobile Communications (GSM) standards, cellular Code Division Multiple Access (CDMA) standards, Long Term Evolution (LTE) standards, and/or Bluetooth standards. In some embodiment, the loudspeaker array  105  may include power amplifiers  307  for amplifying the drive signals sent to each of the transducers  109  in the loudspeaker array  105 , as well as digital to analog converters (DACs)  303  for converting the drive signals from digital domain into analog domain, both of which may be integrated into the speaker cabinet  111 . Although described and shown as being separate from the audio receiver  103 , in some embodiments, one or more components of the audio receiver  103  may be integrated within a housing of the loudspeaker array  105 . For example, the loudspeaker array  105  may include the hardware processor  201 , the memory unit  203 , and the one or more audio inputs  205 . 
       FIG. 3B  shows a side view of a loudspeaker array  105  according to one embodiment. As shown in  FIG. 3B , the loudspeaker array  105  houses multiple transducers  109  in a cabinet  111 . The cabinet  111  may be a loudspeaker cabinet or loudspeaker enclosure composed of two frusto conical sections  117 A and  117 B rotated in relation to each other by 180°, and joined to each other at their respective smaller base regions, to form a waist region in which the transducers  109  are positioned. An interior volume of the cabinet  111  may be used to house associated electronic hardware such as amplifiers and crossover circuits that are mounted inside the cabinet  111 , but its primary role may be to prevent sound waves generated by rearward facing surfaces of diaphragms of the transducers  109  (not visible in  FIG. 3B ), interacting with sound waves generated off the front facing surfaces of the diaphragms of the transducers  109  (which are visible as illustrated in  FIG. 3B ) and emanating sideways and outward from the frusto conical sections  117 A,  117 B. As will be described in greater detail below, these frusto conical sections  117 A and  117 B (as joined) form a continuously open circumferential horn  113  at the waist region, which may be used for improving performance of integrated transducers  109  or for providing vertical sound control for the loudspeaker array  105 . One or both of the larger base regions of the frusto conical sections  117 A,  117 B may be joined to a respective outer wall, depicted as outer walls  127 A,  127 B in  FIG. 9  below. 
     Although described in relation to frusto conical sections  117 A and  117 B, in other embodiments, the cabinet  111  may be composed of any shapes or sections that provide a narrow inner circumference (or waist), to define a throat  115  of the continuously open circumferential horn  113 , and a flared or wider outer section that defines a mouth  119  of the horn  113 . For example, in other embodiments the cabinet  111  may be composed of one or more frustums, cones, pyramids, triangular prisms, spheres, or any other similar shape. 
     In some embodiments, the cabinet  111  may be defined by a hyperboloid shape that is similar to the cabinet  111  formed by the frusto conical sections  117 A and  117 B described above. In this embodiment, the cabinet  111  may include upper and lower sections that are wider than a middle or waist section. The upper and lower sections may taper inwards to meet the narrower middle section to form the throat  115  of the continuously open circumferential horn  113 . In each of these embodiments, a horizontal cross-section of the cabinet  111 , which lies in a horizontal plane that is perpendicular to the page showing  FIG. 3B  and that is positioned to cut through the middle section, may be circular such that the continuously open circumferential horn  113  uniformly extends around the entire perimeter of the cabinet  111 . 
     In some embodiments, the cabinet  111  may be at least partially hollow and may allow for the mounting of transducers  109  on an inside surface of the cabinet  111  with sound output holes formed in a cylindrical wall of the waist section, each of the output holes being aligned with the diaphragm of a respective one of the transducers, or on an outside surface of the cabinet  111  (e.g., where each transducer is mounted such that its diaphragm is positioned outside or spaced outward of the cylindrical surface of the waist section). The cabinet  111  may be made of any material, including metals, metal alloys, plastic polymers, or some combination thereof. 
     As shown in  FIG. 3A  and  FIG. 3B  and described above, the loudspeaker array  105  may include a set of transducers  109 . The transducers  109  may be any combination of full-range drivers, mid-range drivers, subwoofers, woofers, and tweeters, although in one embodiment they may all be replicates of each other. Each of the transducers  109  may use a lightweight diaphragm, or cone, connected to a rigid basket, or frame, via a flexible suspension that constrains a coil of wire (e.g., a voice coil) to move axially through a cylindrical magnetic gap. When an electrical audio signal is applied to the voice coil, a magnetic field is created by the electric current in the voice coil, making it a variable electromagnet. The coil and the transducers&#39;  109  magnetic system interact, generating a mechanical force that causes the coil (and thus, the attached cone) to move back and forth, thereby reproducing sound under the control of the applied electrical audio signal coming from an audio source, such as the audio receiver  103 . Although electromagnetic dynamic loudspeaker drivers are described for use as the transducers  109 , those skilled in the art will recognize that other types of loudspeaker drivers, such as piezoelectric, planar electromagnetic and electrostatic drivers are possible. As shown in  FIG. 3B  and  FIG. 4B , in one embodiment, the rear face of the diaphragm of each transducer  109  faces inward (into the ring formed by the entire group of transducers  9 ) while the front face is facing outward. 
     Referring back to  FIG. 3A , each transducer  109  may be individually and separately driven using the power amplifiers  307  to produce sound in response to separate and discrete audio drive signals received from an audio source (e.g., the audio receiver  103 —see  FIG. 1 ). By allowing the transducers  109  in the loudspeaker array  105  to be individually and separately driven according to different parameters and settings (including delays and voltage levels), the loudspeaker array  105  may produce numerous directivity or beam radiation patterns that accurately represent each channel of a piece of sound program content received from the audio receiver  103 . In some embodiments, digital filtering techniques may be used that impart variable gains and phases (relative to each other) upon the individual drive signals for the transducers  109 , in the digital domain, e.g., by the processor  201  which may be part of the audio receiver  103  (see  FIG. 2 ). A beamforming process may be performed upon a give set of two or more input audio channels, e.g., by the processor  201 , to produce a number of desired acoustic output patterns, which are rendered by transferring the individual transducer drive signals (in digital form) to the DACs  303  via the interface  301 . 
     For example, in one embodiment, the loudspeaker array  105  may produce one or more of the directivity or radiation patterns shown in  FIG. 4A  along a horizontal plane that is perpendicular to the upright stance of the cabinet  111  as seen in the earlier figures (or that is perpendicular to the central upright axis  102 ). In  FIG. 4A , an omnidirectional pattern is shown on the right (having a low directivity index, DI), a hypercardiod pattern is shown on the right (having a high DI), while a cardiod pattern is shown in the middle.  FIG. 4B  shows a top view of a loudspeaker array  105  emitting a forward (or right) facing cardioid radiation pattern in a horizontal plane using a set of transducers  109  according to one embodiment. Simultaneous directivity patterns produced by the loudspeaker array  105  may not only differ in shape, but may also differ in the direction of their respective reference axes. For instance, different directivity patterns may be “pointed” in different directions in the listening area  101  to represent separate channels or separate pieces of sound program content for separate zones or separate listeners  107 . 
     Power or gain performance from the transducers  109  may be lacking, if the transducers  109  have to be made smaller in order to fit into a smaller cabinet  111 . To improve the performance of the transducers  109 , a horn may be used at the primary sound output opening of each transducer  109  (or selected ones of the transducers  109 ). In particular, an acoustic horn may be used to 1) increase the efficiency of a transducer  109  (e.g., add acoustic gain for sound output by a transducer  109 ) and/or 2) to control the direction in which the sound is radiated into the listening area  101 . 
     For example, as shown in  FIG. 5A , a single transducer  109  is connected to the throat  403  of a horn  401 , and the cross sectional area of the horn  401  increases with distance from the throat  403  to the mouth  405  of the horn  401 . The change in cross section with distance and the detailed shape of the horn  401  may be chosen to add a specified level of gain to sound emitted by the transducer  109  for a specified frequency range of operation. In this sense, the horn  401  may be considered an acoustic transformer that provides impedance matching between the diaphragm material of the transducer  109  and the less-dense air surrounding the loudspeaker array  105 . The result is greater acoustic output power from transducer  109 . The shape of the horn  401  may also be designed to give different passive directivity properties. 
     Historically, horns were very useful in increasing acoustic gain when amplifiers were not yet available. Although amplifiers are now readily available, horns may continue to be useful as they still improve the gain performance of transducers  109  in particular frequency ranges and may provide passive directional control. Accordingly, horns may allow the use of smaller transducers  109  in mobile or other compact devices where amplifiers may not be suitable options (e.g., size or thermal considerations). 
     In some embodiments, the horn  401  shown in  FIG. 5A  may be used with multiple transducers  109  arranged alongside each other. For example, as shown in  FIG. 5B , multiple horns  401  may be used with multiple transducers  109 , respectively, that are positioned side by side in a ring or circular formation. In this embodiment, sound from each transducer  109  travels through a corresponding throat  403  of its horn  401 , and mixes with sound from adjacent transducers  109  upon exiting at the mouth  405  of its horn  401 . Accordingly, the horn  401  in this arrangement provides a sound barrier between adjacent transducers  109 , where this barrier extends from the throat  403 , which is proximate and coupled to the transducer  109 , to the mouth  405  such that sound from adjacent transducers  109  is not permitted to mix until after escaping the horn  401 . 
     The distance D shown in  FIG. 5B  represents the separation between points where sounds from adjacent transducers  109  are allowed to mix together (i.e., the point in this case where sounds leave respective horns  401 ). The horns  401  shown in  FIG. 5B  draw sound outward and away from the transducers  109  (using a set of barriers or walls that define the shape of the horns  401 ) before a sound can be mixed with sound from other transducers  109 , and this may dictate the distance D. In particular, since the horn  401  flares outward, as the design of the horn  401  increases in length (e.g., calculated from the throat  403  to the mouth  405 ), the horns  401  and their corresponding transducers  109  may need to be more greatly separated from each other. This increased distance or spacing between the transducers  109  results in a similar increase to the mixing distance D between adjacent horns  401 . For simplicity and consistency, this distance D may be measured (for each adjacent pair of horns  401 ) along any suitable, mathematically defined curve that connects the centers of the mouths  405  of adjacent horns  401 . Similarly, for the embodiment of  FIG. 6 , the mixing distance D may be measured along a suitable, mathematically defined curve (in front of the transducers  109 ) that connects the centers of the diaphragms of adjacent transducers  109 . 
     In some cases, mixing of sounds produced by transducers  109  may cause aliasing issues. Aliasing may be restricted to particular frequency bands based on the distance D. For example, aliasing may occur when a wavelength of sound produce by the transducers  109  is smaller than the mixing distance D. In other words, the sound produced by adjacent transducers  109  (and as heard by the listener  107 ) may exhibit aliasing at wavelengths that are smaller than a threshold wavelength (or equivalently at frequencies that are higher than a threshold frequency.) Since higher frequency sounds have shorter wavelengths in comparison to lower frequency sounds, as the distance D increases the frequencies of sound that may be produced by the transducers  109  without aliasing effects decreases (e.g., an inverse relationship between the mixing distance D and the aliasing frequency). In other words, the “aliasing frequency” (the frequency above which there is substantial aliasing in the sound that may be heard at a position of the listener  107 ) drops, as the mixing distance D increases. Accordingly, to ensure that sounds may be produced at higher frequencies by the loudspeaker array  105  without the occurrence of aliasing effects, the mixing distance D should be decreased. 
     In one embodiment, the loudspeaker array  105  described herein reduces the distance D by providing a continuously open circumferential horn  113 . As described above and shown in  FIG. 3B , the continuously open circumferential horn  113  may include a throat  115 , a mouth  119 , and a set of inner walls  123   a ,  123   b . The throat  115  is defined by the narrowest end of the horn  113  and is proximate or coupled to the ring of transducers  109 . In contrast, the mouth  119  is formed at the opposite end of the horn  113  and is defined by the widest end of the horn  113 . The inner walls  123   a ,  123   b  mark the upper and lower halves, or upper and lower bounds, respectively, of the horn  113  and may provide a tapered or angled connection between the throat  115  and the mouth  119  such that the horn  113  flares outwards (i.e., increases in diameter moving from the throat  115  to the mouth  119 ). 
     The combined throat  115 , mouth  119 , and inner walls  123  may extend the entire circumference or perimeter of the cabinet  111  (e.g., 360° around a center upright axis  102  of the cabinet  111 ) such that the horn  113  is circumferentially open and no barriers are present between transducers  109 . In comparison to the arrangement in  FIG. 5B  in which each individual horn  401  creates a sound barrier for each corresponding transducer  109 , the continuously open circumferential horn  113  depicted in  FIG. 3B  may allow the placement of multiple transducers  109  side by side at the throat  115 , without barriers between each transducer  109 . Although the inner walls  123  form upper and lower barriers for sound produced by the transducers  109 , these inner walls  123  do not restrict mixing of sound between transducers  109 . For example,  FIG. 6  shows a top view of an arrangement of as in  FIG. 3B , in which the transducers  109  are side by side around the throat  115  of the continuously open circumferential horn  113 . Since in this embodiment no barriers are present between each adjacent pair of the transducers  109 , sound from each of the transducers  109  may be mixed together soon after being produced or emitted by the transducers  109  (e.g., they are mixed in the throat  115  of the horn  113 ). In particular, the mixing distance D at which sound from adjacent transducers  109  is mixed may be reduced in comparison to the distance D shown in  FIG. 5B . 
     Based on this reduced mixing distance D between sounds from adjacent transducers  109  entering into the same environment (e.g., see  FIG. 1 , the throat  115  of the horn  113 ) and being allowed to mix together, the aliasing frequency may be increased when using the continuously open circumferential horn  113 . As noted above, the aliasing frequency is the frequency at which higher frequency sounds may cause undesirable aliasing effects, based on the mixing distance D. Accordingly, since the continuously open circumferential horn  113  provides a higher aliasing frequency based on the reduced mixing distance D in comparison to the closed or segmented horns  401  shown in  FIG. 5B , the transducers  109  in  FIG. 3B  and  FIG. 6  may be driven with higher frequency sounds without the presence of aliasing effects. Further, the continuously open circumferential horn  113  may still provide efficiency improvements (i.e., improved gain performance) and vertical sound control similar to traditional horn designs. 
     In one embodiment, the continuously open circumferential horn  113  may be formed using components of the cabinet  111 . For example, as described above, the cabinet  111  may be formed of the two frusto conical sections  117 A and  117 B, which are joined together as shown in  FIG. 3B . In particular, one of the two frusto conical sections  117 A and  117 B may be rotated 180° in relation to the other and then joined to form a generally hourglass or hyperboloid shape for the cabinet  111 . The bottom of the lower section  117 B may be flat so as to enable the cabinet  111  to stably rest on a flat surface such as a tabletop as shown in the example of  FIG. 1 , or on a floor. This generally hourglass or hyperboloid shape has a narrow or tapered section that defines the throat  115  of the horn  113  and a wide or flared section that defines the mouth  119  of the horn  113 . Although described as being formed of separate sections  117 A and  117 B that are joined or otherwise coupled together, the cabinet  111  may be made in different ways such as two or more vertically or horizontally continuous pieces that are joined together. The continuously open circumferential horn  113  may have a curved surface at the corners  125 A,  125 B of its mouth  119  so that the cabinet  111  has a true hyperboloid shape, as depicted in  FIG. 9 , for example. 
     In one embodiment, the ring of transducers  109  may be located around the throat  115  of the continuously open circumferential horn  113 . As shown in  FIG. 3B  and  FIG. 6 , the transducers  109  may be aligned in a horizontal plane, around the throat  115 , such that each of the transducers  109  is vertically equidistant from the larger base of the upper section  117 A and is vertically equidistant from the larger base of the lower section  117 B of the cabinet  111 . 
     Although as shown in  FIG. 3B  and  FIG. 6  and described above the transducers  109  are arranged uniformly at the throat  115  of the horn  113  with their diaphragms oriented substantially vertically, in other embodiments the transducers  109  may be differently arranged around or about the throat  115  of the horn  113 . For example, since the throat  115  of the continuously open circumferential horn  113  is formed at a narrowest or waist section of the cabinet  111 , arranging all of the transducers  109  along this section, with their diaphragms in a vertical orientation, may be difficult. Namely, the constricted space provided by the throat  115  may not allow the use of large, more powerful transducers  109  (unless the diameter of the throat is made larger, and the top and bottom sections  117   a ,  117   b  of the cabinet are also made larger.) The limited space may also result in heat issues caused by poor thermal dissipation in a confined area with a high density of transducers  109 . To alleviate these space constraints, some or all of the transducers  109  (that together may form a ring) may instead be located within a hollow portion of the upper section  117 A, which is above the throat  115  (and below a top of the upper section  117   a ) as shown in  FIG. 7 . Since the horn  113  tapers such that the throat  115  is the narrowest element of the cabinet  111  (from a side view, as in  FIG. 7 ), any portion of the progressive widening upper section  117 A above the throat  115  may afford more space for the placement or mounting of the transducers  109 , and in particular their motors which are directly behind, and attached to drive, their respective diaphragms, in comparison to mounting of the transducers  109  at the throat  115 , e.g., all oriented vertically as shown in  FIG. 3 b    and  FIG. 4 b   . In the embodiment of  FIG. 7 , sound produced by the transducers  109  may be directed to flow into the continuously open circumferential horn  113  through the slots  701 . The slot  701  may be a passageway that extends into the cabinet  111 , from the outer surface of a side wall of the upper section  117 A, and that acoustically joins the front surface of the diaphragm of each respective transducer  109  to the throat  115  (of the continuously open circumferential horn  113 .) In some embodiments, one or more of the slots  701  may include one or more bends or curves. The bends or curves allow the transducers  109  to be placed or mounted in different positions and orientations within the cabinet  111  while still allowing for sound produced by each transducer  109  to reach the throat  115  of the continuously open circumferential horn  113 . In the version shown in  FIG. 7 , the slots  701  are such that they enable their respective transducers  109  to be oriented so that their diaphragms are substantially horizontal (instead of vertical as in  FIGS. 3 b , 4 b   ), thereby allowing more space for their respective motors within the upper section  117   a . Since the slots  701  deliver sound produced by corresponding transducers  109  at the same point around the throat  115  as when the transducers  109  are mounted at the throat  115  as shown in  FIG. 3B , the mixing distance D between adjacent transducers  109  may remain the same or nearly identical. Given that the mixing distance D remains small (in comparison to the horns  401  shown in  FIG. 5A  and  FIG. 5B ), the aliasing frequency for the loudspeaker array  105  shown in  FIG. 7  may remain high as described above, such that high frequency sounds may be emitted by the transducers  109  without the presence or occurrence of aliasing effects. 
     Although as described above and shown in  FIG. 7  all of the transducers  109  are housed entirely within the upper section  117 A, in another embodiment all of the transducers  109  (together still forming a ring) may be similarly placed or mounted entirely within the lower section  117 B. In some other embodiments, the transducers  109  may be alternately placed within (alternating between) the top and lower sections  117 A and  117 B as shown in  FIG. 8 . In this embodiment, within each top or bottom section  117   a ,  117   b , there is even more space between adjacent ones of the transducers  109  that are within the same section  117   a ,  117   b  of the cabinet  111  for mounting, since the transducers  109  are alternately placed above and below the throat  115 . Similar to the loudspeaker array  105  shown in  FIG. 7 , the loudspeaker array  105  shown in  FIG. 8  may utilize slots  701  to direct sound from the transducers  109  to the throat  115  of the continuously open circumferential horn  113 . 
     As described above, the continuously open circumferential horn  113  reduces aliasing effects between adjacent transducers  109  in the loudspeaker array  105 . In particular, the mixing distance D between adjacent transducers  109  (e.g., transducers  109  that are directly adjacent in the ring of transducers  109 ) may be decreased such that a corresponding aliasing frequency is increased. This aliasing frequency describes the highest frequency that may be emitted by the transducers  109  without generation or production of aliasing effects caused by mixing of sound between transducers  109 . Accordingly, by decreasing the mixing distance D, the continuously open circumferential horn  113  increases the range of frequencies that may be produced by the transducers  109  without unwanted effects. 
     As shown in  FIG. 3B  and  FIG. 4B  and described above, the loudspeaker array  105  may include a single ring of transducers  109  that are positioned side by side as shown. In one embodiment, each of the transducers  109  in the ring of transducers  109  may be of the same type or model, e.g., replicates. The ring of transducers  109  may be aligned along or in a horizontal plane such that each of the transducers  109  is vertically equidistant from a planar, larger base of the top frusto conical section  117 A and is vertically equidistant from a planar, larger base of the bottom frusto conical section  117 B of the cabinet  111 . Further, this horizontal plane may be perpendicular to the upright stance of the cabinet  111  (as it is shown in the figures). Although a single ring of transducers  109  aligned along a horizontal plane may provide dynamic horizontal beam control through adjustment of relative gains and phases of drive signals applied to each transducer  109 , vertical control of sound emitted by the loudspeaker array  105  may be limited. In particular, by lacking multiple stacked rings of transducers  109 , dynamic directional control of sound may be limited to this horizontal plane. 
     Since dynamic vertical control of sound produced by the single ring of transducers  109  may not be possible, more passive solutions may be used. For example, the continuously open circumferential horn  113  may be used to assist in controlling the vertical spread of sound from the ring of transducers  109  into the listening area  101 . As shown in  FIG. 9 , the continuously open circumferential horn  113  may be flared to control the direction of sound along a vertical axis. The horn  113  may be adjusted during manufacture to accommodate for different performance requirements of the loudspeaker array  105 . For example, the angle of the upper and lower inner walls  123   a ,  123   b  (relative to the horizontal plane) and the corresponding size of the mouth  119  may be adjusted to create a larger or smaller vertical spread of sound into the listening area  101  (see  FIG. 1 .) In other embodiments, the corners  125   a ,  125   b  that connect the inner walls  123   a ,  123   b  to the outer walls  127   a ,  127   b , respectively, and which define the entrance of the mouth  119 , may be curved or rounded as shown in  FIG. 9 . This curvature may provide a more consistent frequency response in comparison to a sharp or abrupt corner  125  such as depicted in  FIG. 3B . 
     Although the design of the horn  113  in  FIG. 3B  may reduce aliasing effects as described above, its sharp corners  125  may apply an inconsistent improvement or increase in gain across all frequencies. Instead, the sharp corners  125  may lead to peak improvements in gain across some frequencies while providing less or no increases in gain in other frequency ranges (e.g., particularly with low frequency content). This inconsistent response across frequencies may create undesirable changes to sound produced by the loudspeaker array  105 . In contrast, the curved corners  125  of the horn  113  shown in  FIG. 9  may provide a more desirable horn design that is less likely to have reduced gain at low frequencies. In particular, in the horn  113  of  FIG. 9  the sidewall  123   a  may gradually flare off at the corner  125   a  and join the vertically oriented outer wall  127 ; similarly, the sidewall  123   b  flares off at the corner  125   b  and joins the vertically oriented outer wall  127   b . A more consistent frequency response for sound produced by the transducers  109  using these curved corners  125  may be expected. 
     Although shown in  FIG. 9  as being identical, the angle and shape of the inner wall  123   a  (along or defined by the upper section  117 A) may, alternatively, be different in comparison to the angle and shape of the inner wall  123   b  (along or defined by the lower section  117 B.) For example, as shown in  FIG. 10 , the inner wall  123   b  along the lower section  117 B may be planar and perpendicular relative to the vertically oriented center upright axis  102 , e.g., entirely horizontal, while the inner wall  123   a  along the upper section  117 A remains similar as in the earlier embodiments, such as  FIG. 9 , that is not planar and sloped upward (in relation to the horizontal plane.) Further, the corner  125   b  of the lower section  117 B may be sharper in comparison to the corner  125   a  of the upper section  117 A, as shown. In this embodiment, the lack of slope to the inner wall  123   b  and the sharply angled corner  125   b  (of the lower section  117 B) may assist the horn  113  in directing sound away from a possibly reflective surface upon which the loudspeaker array  105  may be situated (e.g., a table or a floor). The upward slope of the inner wall  123   a  and curved corner  125   a  of the upper section  117 A may direct sound produced by the transducers  109  towards the listener  107 . In other embodiments, the upper and lower sections  117 A and  117 B of the horn  113  (cabinet  111 ) may be formed in different fashions to provide desired vertical control of sound output. 
     Although described above in relation to a single ring of identical transducers  109 , the loudspeaker array  105  may include additional transducers arranged along and within the cabinet  111 . For example,  FIG. 11  shows a loudspeaker array  105  with a first set of transducers  109 A used for producing, or designed to be driven by, a first set of audio frequencies (where the first set of transducers  109 A may be a single ring of transducers such as the transducers  109  depicted in  FIG. 3B , a second set of transducers  109 B used for producing, or designed to be driven by a second set of frequencies, and a third set of transducers  109 C used for producing, or designed to be driven by a third set of frequencies. In this example, there is a group of transducers  109 B,  109 C that are housed within the section of the cabinet  111  that is below the horn  113  and defined by the outer wall  127 B, and another group of transducers  109 B,  109 C that are housed within the section of the cabinet  111  that is above the horn  113  and defined by the outer wall  127 A. For instance, the first set of transducers  109 A may be used or designed for high frequency content (e.g., 5 kHz-10 kHz), the second set of transducers  109 B may be used or designed for mid frequency content (e.g., 1 kHz-5 kHz), and the third set of transducers  109 C may be used or designed for low frequency content (e.g., 100 Hz-1 kHz). These frequency ranges for driving each of the transducers  109 A,  109 B, and  109 C may be enforced using a set of filters that may be integrated within the loudspeaker array  105  (not shown). Since the wavelengths for sound waves produced by the first transducers  109 A are smaller than wavelengths of sound waves produced by the transducers  109 B, the mixing distance D associated with these transducers  109 A (see  FIG. 6 ) should be designed to be smaller than the mixing distance D associated with the transducers  109 B. In particular, to prevent aliasing effects the mixing distance D for the transducers  109 A should be small enough such that the small wavelengths produced by high frequency content are not smaller than the distance D. However, since the transducers  109 B produce lower frequency content (i.e., mid frequency content) with larger wavelengths, the distance D for transducers  109 B may be made larger, e.g. the transducers  109 B do not need to be as tightly packed as the transducers  109 A. Similarly, the transducers  109 C may be arranged to have a larger mixing distance D than both the transducers  109 A and the transducers  109 B. Since the mixing distances D for the transducers  109 B and the transducers  109 C may be made larger without the occurrence of aliasing effects, a continuously open circumferential horn  113  that enables a reduction in the distance D may not be necessary for these transducers  109 B and  109 C. In these embodiments, a traditional horn  401 , such as those shown in  FIG. 5A  and  FIG. 5B , may be added to one or more of the transducers  109 B,  109 C, if gain efficiency improvements or directional control for these rings of transducers  109 B and  109 C are desired. 
     Although the open circumferential horn  113  is described above as a “completely open” circumferential horn  113 , in some embodiments a divider  129  may be added or placed between an adjacent pair of transducers  109  as shown in  FIG. 12 . A divider  129  may be a flat, rigid piece or segment that extends outward from the throat  115  between an adjacent pair of transducers  109 , generally transverse to or perpendicular to the inner walls  123   a ,  123   b , along a of the horn  113  (in the case where the horn  113  defines a circular mouth  119 .) Although not shown in the drawings, the divider  129  may be joined to both of the inner walls  123   a ,  123   b  and may widen in the vertical direction (as it extends outward and along the inner walls  123   a ,  123   b .) An adjacent pair of the dividers  129  may be viewed as partitioning=a portion of the mouth  119  of the horn  113  for each transducer  109 . The length dimension of the divider  129 , e.g., measured along the radius (r) taken from the center of a circular mouth  119  which may be concentric with a circular throat  115  as shown in  FIG. 12 , may be selected to trade off between the frequency where aliasing begins and the amount of directivity control that may be achieved at lower frequencies for a given amplifier power and transducer  109  excursion. For example, a set of the dividers  129  as shown in  FIG. 12 , for all of the transducers  109 , may each be between 25 millimeters and 60 millimeters long between its inner end point at the throat  115  and its outer end point. In contrast to the embodiment of  FIG. 12 , in other embodiments the dividers  129  extend the entire distance from the mouth  119  to the throat  115  (of the otherwise continuously open circumferential horn  113 .) The dividers  129  may be sized (as in  FIG. 12 ) to extend to only a fraction of the distance from the mouth  119  to the throat  115 . 
     Additionally, the dividers  129  may provide an effective “short horn” for the sound emerging from the transducers  109  prior to being mixed within the shared space of the circumferential horn  113  (that is within the boundary of mouth  119  depicted in  FIG. 12 ). Providing a short horn section before mixing can have the effect of smoothing out particle velocity across the exits of the short horns formed by the dividers  129  such that aliasing effects are reduced. For example, a set of small transducers  109 , wherein each adjacent pair is spaced a distance d apart from each other (e.g., a straight line that joint a center of the diaphragm of one to the center of the diaphragm of another, and noting that this may not be the mixing distance D referred to above), may have worse aliasing effects than a set of larger transducers  109  (wherein each adjacent pair is also spaced the same distance d apart), due to the additional empty spaces between the smaller transducers  109 .  FIG. 13  shows two example velocity profiles A and B that may be produced by rings of small and large transducers. In both situations, aliasing occurs at the same frequency, but profile A (of the ring of smaller transducers) has worse aliasing effects than profile B. The short horns created by the dividers  129  have the effect of making the velocity profile of a set of small transducers  109  as illustrated by profile A look more like profile B such that aliasing effects are reduced. 
     While certain embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that the invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those of ordinary skill in the art. The description is thus to be regarded as illustrative instead of limiting.