Abstract:
A mass notification system (MNS) loudspeaker having very high intelligibility. The MNS loudspeaker includes a plurality of transducers arranged in a symmetric pattern around an axis, so as to produce a substantially cylindrical wave front of sound pressure. The loudspeakers are coupled to a cap, and form a cylinder whose inner diameter is large enough to slip over a pole to which the loudspeakers are to be mounted. The under side of the cap may rest atop the pole. An inner cylinder encloses an air volume behind the transducers for acoustic loading and environmental protection of the transducers. An optional telescoping stand retracts into the inner cylinder.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field of the Invention 
         [0002]    This invention relates generally to acoustic loudspeaker systems, and more specifically to mass notification systems such as are used in broadcasting spoken public address announcements in very large venues. 
         [0003]    2. Background Art 
         [0004]    Mass notification systems (MNSs) are used in a variety of outdoor and indoor venues, for providing audio signaling simultaneously to a large number of listeners. MNSs are used on outdoor venues such as stadiums, fairgrounds, parking lots, theme parks, amusement parks, military bases, school campuses, and the exterior areas of cruise ships, aircraft carriers, and the like. MNSs are also used in indoor venues such as concert halls, sports arenas, exhibition halls, airports, aircraft hangers, warehouses, stores, shopping malls, and the interior areas of cruise ships, military ships, and the like. MNSs are typically used to broadcast spoken messages, rather than e.g. music. This reduces the need for them to reproduce full frequency signals across the entire spectrum of human hearing, and enables them to use loudspeaker technologies which may not be suitable for full frequency systems. But MNSs have design challenges of their own. 
         [0005]    The primary design criterion is often “intelligibility” and is measured using the Common Intelligibility Scale (CIS) defined by the International Electrotechnical Commission Standard 60849, or using the Speech Intelligibility Index (STI) defined by the American National Standards Institute Standard S3.5, or, less commonly, using the Articulation Index, the Articulation Loss of Consonants system, the Phonetically Balanced Word Scores system, the Modified Rhyme Test, or the Speech Transmission Index. 
         [0006]    One major factor contributing to reduced intelligibility is out-of-phase arrival at the listener&#39;s ear of signals emanating from multiple sources. One cause of this multi-path problem is simply reverberation and echoes; some sound travels directly from the loudspeaker to the listener over a path of length X, while sound from that same loudspeaker may also travel over a bouncing path of different length Y, thus arriving at the listener&#39;s position a fraction of a second later due to the longer path. Another significant cause of the multi-path problem is that MNSs almost of necessity use a multitude of loudspeakers distributed throughout the venue. Each loudspeaker is likely to be a unique distance from any particular listener, so even the direct paths will cause different arrival times, and the problem is further compounded by each loudspeaker having its own, unique echo pathways to each listening position. 
         [0007]    It is almost unavoidable that there be more than one loudspeaker in a large venue. Otherwise, in order to make the sound pressure level (SPL) sufficient at the remotest regions of the venue to provide a sufficiently high signal-to-ambient-noise ratio for the audio signal to be heard, the SPL in the immediate vicinity of a single loudspeaker would necessarily be uncomfortably, or even dangerously, high. The only viable solution is to have a large number of quieter loudspeakers scattered throughout the venue. 
         [0008]    Other factors contributing to reduced intelligibility are the comb filtering, lobing, and other interference issues that arise when two or more loudspeakers are near each other and have overlapping sound dispersion patterns. Practical design limitations prevent loudspeakers from being designed so as to have super-precisely-defined dispersion patterns. Therefore, in order to prevent “dead spots”, it is necessary to overlap the dispersion patterns of adjacent loudspeakers. This causes interference issues which can be detrimental to intelligibility. 
         [0009]    Another significant design consideration for MNSs, especially those which are intended for outdoor or marine installations, is weatherproofing to protect against moisture, ultraviolet light, and so forth. 
         [0010]      FIG. 1  illustrates an MNS loudspeaker system  10  such as may be used in a mass notification system, according to the prior art such as that available from American Technology Corporation of San Diego, Calif. An MNS would typically have a multitude of such systems scattered throughout the venue, but, for convenience, only a single system is shown. The loudspeaker system is typically mounted at or above the ear level of standing persons, and is commonly mounted on a pole  12  as shown. Pole mounted arrays are often located 25-40 feet above the ground. It is desirable to mount the loudspeakers in a high location, to prevent persons from standing too close to the transducers themselves, where the sound pressure level may be unacceptably high. 
         [0011]    The system includes a plurality of—typically four—loudspeakers  14  arranged around the pole on equal 90° spacing. Each loudspeaker is fastened to the pole by an upper bracket  16  and a lower bracket  18 , which are bolted or screwed to the pole. 
         [0012]    In order to improve the loudspeaker&#39;s life in an outdoor environment, each loudspeaker is equipped with a rain bill  20 . 
         [0013]    Other details, such as the electrical connections, are not significant in the context of this invention, and have been omitted in the interest of clarity and simplicity. Those of ordinary skill in the art are well able to select from any variety of suitable, existing technologies to handle such matters, within the purview of this invention. 
         [0014]      FIG. 2  is a top view of the MNS loudspeaker system  10  of  FIG. 1 , illustrating the pole  12 , loudspeakers  14 , top mounting brackets  16 , and rain bills  20 . 
         [0015]      FIG. 25  is a polar response graph resulting from a computer simulation of a 4-transducer MNS system such as that of  FIG. 1 . The graph shows response at 1 kHz, 2 kHz, 3 kHz, 4 kHz, and 5 kHz around the MNS system. It is plotted with a reference position arbitrarily assigned at the position marked 0°, and the transducers modeled as being at the 0°, 90°R, 90°L, and 180° positions. The outermost dashed circle represents a 0 dB reference level, and the successive inner dashed circles represent 5 dB, 10 dB, 15 dB, 20 dB, 25 dB, and 30 dB down levels, respectively. The closer to center a signal is at any particular angle, the quieter that signal will be when the listener is located at a listening position radially outward at that angle. 
         [0016]    For a 1 kHz signal, the prior art 4-transducer system has acceptably good performance at all listening angles. At the 45° and 135° positions, which are half-way between adjacent transducers, the 1 kHz signal is only down about 1 dB versus the on-axis (0°) reference level. At 2 kHz, the prior art 4-transducer system has already begun to demonstrate an unacceptable drop of 5 dB in the 45° and 135° positions. At 3 kHz the signal is down a whopping 18 dB at the 45° and 135° angles; in other words, it is only 1/64 th  as loud there as it is at 0°, 90°, or 180° directly in front of a transducer. The 4 kHz and 5 kHz signals suffer such severe lobing as to be essentially absent at any position not directly in front of a transducer. The prior art systems are very inadequate, if human speech intelligibility is important. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a pole-mounted MNS loudspeaker system according to the prior art. 
           [0018]      FIG. 2  shows the MNS loudspeaker system of  FIG. 1  in top view. 
           [0019]      FIG. 3  shows a pole-mounted MNS loudspeaker system according to one embodiment of this invention. 
           [0020]      FIG. 4  is a top view of the MNS loudspeaker system of  FIG. 3  with the raincap component removed for visibility. 
           [0021]      FIG. 5  is an exploded view of the MNS loudspeaker system of  FIG. 3 . 
           [0022]      FIGS. 6 and 7  are top and bottom perspective cross-sectioned views, respectively, of the raincap mounting mechanism of  FIG. 3 . 
           [0023]      FIGS. 8 and 9  are top and bottom perspective cross-sectioned views, respectively, of the lower mounting mechanism of  FIG. 4 . 
           [0024]      FIG. 10  shows a 270° embodiment of the MNS loudspeaker system of  FIG. 3 , as mounted to an outside corner. 
           [0025]      FIG. 11  shows a 90° embodiment of the MNS loudspeaker system of  FIG. 3 , as mounted to an inside corner. 
           [0026]      FIG. 12  shows a 180° embodiment of the MNS loudspeaker system of  FIG. 3 , as mounted to a wall. 
           [0027]      FIGS. 13 and 14  show an MNS loudspeaker according to another embodiment of this invention, in upper and lower perspective cross-sectioned views, respectively. 
           [0028]      FIG. 15  shows an outer cylinder mounting frame to which the individual transducers of  FIG. 13  are mounted. 
           [0029]      FIG. 16  shows a trapezoidal implementation of a planar magnetic transducer. 
           [0030]      FIG. 17  shows a conical MNS loudspeaker according to another embodiment of this invention, utilizing the trapezoidal transducers of  FIG. 16 . 
           [0031]      FIG. 18  shows an outer conical mounting frame such as may be used in  FIG. 17 . 
           [0032]      FIG. 19  shows another embodiment of a MNS loudspeaker in which the array is enlarged such that the transducers do not touch edge-to-edge. 
           [0033]      FIG. 20  shows the MNS loudspeaker of  FIG. 19  in a slightly canted top view, with the raincap removed for visibility of the other parts. 
           [0034]      FIG. 21  shows an outer frame such as may be used in the MNS loudspeaker of  FIG. 19 . 
           [0035]      FIG. 22  shows a portable MNS system according to another embodiment of this invention. 
           [0036]      FIGS. 23 and 24  show one embodiment of a portable MNS system, with a retractable stand in a furled configuration and an unfurled configuration, respectively. 
           [0037]      FIG. 25  shows the polar response of the 4-transducer MNS system of  FIG. 1 . 
           [0038]      FIG. 26  shows the vastly better polar response of an 8-transducer MNS system according to this invention. 
           [0039]      FIG. 27  shows the still better polar response of a 16-transducer MNS system according to this invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0040]    The invention will be understood more fully from the detailed description given below and from the accompanying drawings of embodiments of the invention which, however, should not be taken to limit the invention to the specific embodiments described, but are for explanation and understanding only. 
         [0041]      FIG. 3  illustrates an MNS loudspeaker system  30  according to one embodiment of this invention, such as may be used in a mass notification system. For clarity of illustration, only a single such loudspeaker system is shown, although typically an MNS will have a large number of them scattered throughout the venue. The loudspeaker system is shown as mounted on a pole  32 , but it could also be e.g. hung from a ceiling or mounted to a wall. 
         [0042]    The loudspeaker system includes at least eight transducers  34  (and eighteen are shown) arranged in a substantially symmetric pattern around an axis of the loudspeaker system. The number of transducers should be determined, in some measure, according to the horizontal dispersion pattern of the particular transducers employed. It is desirable to use a sufficiently large number of transducers that the array presents a cylindrical wave front and behaves approximately like a pulsating cylinder in the target frequency range. It is desirable to reduce or eliminate comb filtering, lobing, and other interference artifacts which can arise if an insufficient number of transducers is used. 
         [0043]    Each transducer may, in some embodiments, be an elongated planar magnetic transducer. In one such embodiment, each transducer is approximately 25 inches tall. 
         [0044]    Rather than each transducer being individually mounted directly to the pole, as was done in the prior art, in the present invention each transducer is instead mounted directly to a rain cap  36  and, optionally, to a base  38 . Alternatively, the transducers may be coupled directly to each other, or to a common frame (not shown). 
         [0045]    In one embodiment, the rain cap serves triple duty; it not only fastens the transducers together, it also provides protection from rain etc., and serves to mount the transducers to the pole. Installation of this loudspeaker system is greatly simplified, as compared to the transducer-by-transducer installation process of the prior art. The manufacturer can ship a fully assembled loudspeaker system, which the installer can simply slip over the top of the pole. 
         [0046]      FIG. 4  is a top view of the loudspeaker system of  FIG. 3 , with the rain cap removed to provide visibility of the transducers  34  and the optional base  38  which fits around the pole  32 . 
         [0047]      FIG. 5  is an exploded view of the loudspeaker system  30  of  FIG. 3 . A variety of techniques can be used to fasten each transducer  34  to the rain cap  36  and to the base  38 . In this embodiment, each transducer comprises a self-enclosed loudspeaker assembly, either having a cabinet or a self-enclosed motor structure. 
         [0048]      FIG. 6  illustrates one embodiment of a rain cap  36 , in cross-sectioned view from a top perspective. The rain cap includes a central body  40  which is sufficiently strong to support the loudspeakers (not shown). The rain cap optionally but advantageously includes a brim  42  which extends beyond the transducers to provide protection from rain, sun, and so forth. The brim may be integrally formed with the body, or it may be attached to the body. 
         [0049]      FIG. 7  illustrates the rain cap  36  in cross-sectioned view from a bottom perspective. The body  40  may include a shaped channel  44  for holding the transducers in a tightly controlled orientation and positioning. The body may be provided with e.g. mounting posts  44  for indexing and retaining the individual transducers. The posts may be integrally formed with, or attached to, the body. Alternatively, the transducers may be fastened to the rain cap by bolts extending downward through the rain cap, but it is desirable to provide gaskets or other means of preventing moisture intrusion through the holes. 
         [0050]      FIG. 8  illustrates one embodiment of a base  38 , in cross-sectioned view in a top perspective. The base may include a shaped channel  50  for holding the transducers in a tightly controlled orientation and positioning. The base includes a central hole  52  enabling it to pass over the pole (not shown). The body may include a brim  54  which extends beyond the transducers. The body may be provided with e.g. mounting posts  56  for indexing and retaining the individual transducers. The posts may be integrally formed with, or attached to, the body or, alternatively the transducers may be coupled to the base with bolts extending upwardly through holes in the base. The channel may be provided with one or more weep holes  58  to prevent rain water and other moisture from collecting in the channel and soaking the bottoms of the transducers. 
         [0051]    In some embodiments, in which it is desirable that the transducers be mounted lower than the top of the pole (not shown), the rain cap may be provided with a central hole like that of the base, enabling the rain cap to slip lower than the top of the pole. In such embodiments, bolts or other suitable means can be used to affix the rain cap to the pole at the desired location. 
         [0052]      FIG. 9  illustrates the base  38  in a cross-sectioned view from a bottom perspective. 
         [0053]      FIG. 10  illustrates a 270° implementation of an MNS loudspeaker  62  mounted to an outside corner where two walls  64 ,  66  meet. In this embodiment, the loudspeaker would include only ¾ the number of transducers as would a similar 360° loudspeaker. 
         [0054]    The transducers are coupled together into a single, contiguous group which covers 270° of the 360° cylinder. 
         [0055]      FIG. 11  illustrates a 90° implementation of an MNS loudspeaker  70  mounted to an inside corner where two walls  64 ,  66  meet. In this embodiment, the loudspeaker would include only ¼ the number of transducers as would a similar 360° loudspeaker 
         [0056]    The transducers are coupled together into a single, contiguous group which covers 90° of the 360° cylinder. 
         [0057]      FIG. 12  illustrates a 180° implementation of an MNS loudspeaker  74  mounted to a wall  72 . In this embodiment, the loudspeaker would include only ½ the number of transducers as would a similar 360° loudspeaker 
         [0058]    The transducers are coupled together into a single, contiguous group which covers 180° of the 360° cylinder. 
         [0059]      FIG. 13  illustrates an MNS loudspeaker  80  according to another embodiment of this invention. The MNS loudspeaker includes a plurality of planar magnetic transducers  82  coupled to a frame  90 . A rain cap  84  and an optional lower ring  86  are also coupled to the frame. An inner cylinder  88  is coupled to the raincap and to the lower ring. A sealed air volume  94  is enclosed in the space between the frame (and back sides of the transducers), the inner cylinder, the raincap, and the lower ring. This enclosed air volume serves as the cabinet air load for the transducers. It also seals and protects the back sides of the transducers from the outside environment, which may be contaminated with moisture, particulates, and so forth. 
         [0060]    Optionally, various ones of the frame, the inner cylinder, the raincap, and the lower ring may be formed as integral, monolithic components rather than as separate components. 
         [0061]    In one embodiment, the MNS loudspeaker mounts to a pole (not shown) by slipping over the top of the pole. In such an embodiment, the lower ring is equipped with a hole  92  sized to fit over the pole. 
         [0062]      FIG. 14  illustrates the MNS loudspeaker  80  from a lower perspective view, and further illustrates one embodiment of a mounting system which may be used to affix the loudspeaker to the pole (not shown). The lower ring is equipped with one or more, and preferably three or more, adjustable mounting brackets. In one embodiment, each bracket includes a length of channeled steel beam  91  such as that available from Unistrut Corporation. An angled bracket  93  is coupled to the beam by a bolt  95  which engages a nut (not visible) riding inside the channel of the beam. The angled bracket is coupled to the pole by a lag bolt  97 . Once the lag bolts are snugged into position, the bolts  95  are tightened, locking the nut into position in the beam. 
         [0063]      FIG. 15  illustrates a frame  90  such as may be used in the MNS loudspeaker of  FIG. 13 . The frame includes a lower portion  92  adapted to engage with or be coupled to the lower ring (not shown), and an upper portion  94  adapted to engage with or be coupled to the raincap (not shown). Viewed in gross, the frame has a generally cylindrical shape. This generally cylindrical shape includes a plurality of facets or faces  96  each contoured to engage the back surface of a respective one of the transducers (not shown). Optionally, each facet includes a hole  98  ventilating the rear surface of the transducer&#39;s diaphragm into the enclosed air volume between the frame and the inner cylinder (not shown) of the loudspeaker. A variety of sealing mechanisms, such as gaskets or o-rings, may be used to seal the mating surfaces of the frame and the transducer; these are well within the ordinary skill of loudspeaker manufacturers, and are omitted from the drawings here in the interest of clarity. 
         [0064]      FIG. 16  illustrates a trapezoidally shaped transducer  100  which may be employed in an MNS loudspeaker according to another embodiment of this invention. The transducer includes a wide end  102  and a narrow end  104 . In embodiments in which the front surface of the transducer includes ventilation holes or slots, the number and/or size of these may be varied from the wide end to the narrow end of the transducer. In the example shown, the wide end includes one or more rows  106  having a large number of slots, the narrow end includes one or more rows  108  having a small number of slots, and the middle includes one or more rows  110  having an intermediate number of slots. 
         [0065]    In implementations in which the trapezoidal transducer is constructed as a planar magnetic transducer, the wide end may include a greater number of columns of magnets than the lower end. 
         [0066]    In other embodiments, the transducer need not be strictly trapezoidal in shape, but may take on other shapes having a wide end and a narrow end. 
         [0067]      FIG. 17  illustrates an MNS loudspeaker  120  which utilizes the trapezoidal transducer of  FIG. 16 . The loudspeaker has, in gross, a shape which is a cone section. The loudspeaker includes a raincap  122  which optionally is larger than the lower ring  124 . The transducers  100  are coupled to a generally conical frame  126 . The inner cylinder  128  may be cylindrical (as shown, although an optical illusion may present some readers with an impression that it is slightly conical with a larger bottom end), or it may be conical, as desired, and encloses an air volume  130 . The ring includes an opening  132  sized to fit over the pole (not shown). 
         [0068]      FIG. 18  illustrates the generally conical frame  126  of  FIG. 17 . The frame includes a lower portion  134  which engages the lower ring, an upper portion  136  which engages the raincap, facets  138  for coupling to the transducers, and optional holes  139  for ventilating the rear surfaces of the transducers&#39; diaphragms. 
         [0069]      FIG. 19  illustrates an MNS loudspeaker  140  according to another embodiment of this invention. The MNS loudspeaker includes as few as eight transducers  82 . Each transducer is sufficiently narrow (left to right in the drawing) that if eight transducers were packed edge to edge, the inner diameter of the octagonal “cylinder” they form would have a diameter too small to fit around some common poles. Therefore, in the MNS loudspeaker  140 , the transducers are spaced apart, rather than being packed edge to edge. This is not especially detrimental, given that MNSs operate in the “far field”. 
         [0070]    The transducers are coupled to first segments  144  of the frame which are shaped to mate with them and provide a good air seal. Between the first segments, the frame includes second segments  146  to which there are not transducers coupled; the second segments provide the spacing between adjacent transducers. Optionally but advantageously, the second segments may be substantially aligned with the front faces of the transducers, to provide a smooth front baffle and reduce edge diffractions. 
         [0071]      FIG. 20  illustrates the MNS loudspeaker  140  in a slightly canted top view, with the raincap removed, providing a better view of the first segments  144  to which the transducers  82  are mounted and the second segments  146  between the transducers. In some embodiments, the fronts of the second segments have a linear cross-section, but in others, such as that shown, they are arc segments. The arc segments may either be simple segments of a circle, or they may be slightly more complex curves so as to be tangent to the front faces of the transducers. 
         [0072]      FIG. 21  illustrates the frame  142  in perspective view, providing a clearer view of the various segments. 
         [0073]      FIG. 22  illustrates one embodiment of a portable MNS system. The system includes a portable MNS loudspeaker including at least eight transducers. In one embodiment, there are 4*N transducers coupled into four sets of N transducers each, and N is a positive integer greater than 1. 
         [0074]    Each set of transducers can be independently driven. In the example shown, N=2; the first set includes transducers T 1 A and T 1 B coupled to be driven by Amplifier  1 , the second set includes transducers T 2 A and T 2 B coupled to be driven by Amplifier  2 , the third set includes transducers T 3 A and T 3 B coupled to be driven by Amplifier  3 , and the fourth set includes transducers T 4 A and T 4 B coupled to be driven by Amplifier  4 . In another embodiment, there may be just a single amplifier (as all the transducers are being driven with the same signal) with a downstream switch mechanism (not shown) for selecting which sets of transducers are driven. 
         [0075]    The system further includes a Portable MNS Director unit which receives source signals from one or more internal and/or external audio signal sources. By way of example only, the system is illustrated as having: an MP3 player; a public radio receiver for receiving FM radio, AM radio, satellite radio, and/or television audio signals; a private radio receiver for receiving secure or private audio signals from e.g. a command post; and a microphone input for receiving audio signals from a locally connected microphone. Electrical power connections are well-known, and are omitted for simplicity of illustration. 
         [0076]    The Portable MNS Director includes a switch matrix which determines the transducer set(s) which receive the audio signal. In the embodiment shown, the switch matrix is “upstream” from the amplifiers; in another embodiment, the switch matrix could be “downstream” between the amplifiers and the transducers. 
         [0077]    In one embodiment, the switch matrix is operated by a user-controlled set of switches. For example, there may be switches for setting the portable MNS loudspeaker to generate sound  11  in a 90° pattern (one out of four transducer sets is driven), a 180° pattern (two adjacent transducer sets are driven), a 270° pattern (three transducer sets are driven), or a 360° pattern (all transducer sets are driven). The particular sets thus selected may be predetermined or, in other words, hard wired. For example, transducers T 1 A and T 1 B may always be driven, and transducers T 2 A and T 2 B may be driven if any selector other than the 90° selector is activated, transducers T 3 A and T 3 B may be driven if either the 270° or 360° selector is activated, and transducers T 4 A and T 4 B may be driven only if the 360° selector is activated. 
         [0078]    Or, alternatively, the Portable MNS Director may include a user-controlled set of switches for dynamically determining the orientation of the portable MNS loudspeaker. For convenience, these may be referred to as North, East, South, and West orientations, selected by an N selector switch, an E selector switch, a S selector switch, and a W selector switch, respectively (or a single dial switch which selects the position). If the portable MNS loudspeaker is physically placed in the correct orientation, these NESW selector switches will, in fact, produce the indicated directivity. Alternatively, the NESW switches may simply switch predetermined ones of the transducer sets on and off, giving the user more direct control over the sound directivity. This enables the user to select a non-contiguous group of transducer sets, for example to send sound N and S but not E or W. 
         [0079]    The portable MNS system and Portable MNS Director are not limited to having exactly four selectable sets of transducers and four corresponding orientations; that is merely an example chosen to illustrate the principles of the invention. 
         [0080]    Optionally, the portable MNS system may also include an Intelligibility Controller for performing a variety of functions upon the signals to be sent to the transducers. For example, it may include a low pass filter (LPF) with a user-settable control mechanism such as a knob, and a high pass filter (HPF) with a user-settable control mechanism such as a knob. These and other such filtering and signal processing means will enable the MNS system to be fine-tuned for maximum performance at a particular venue. 
         [0081]      FIG. 23  illustrates another embodiment of a portable MNS system  150  having an MNS loudspeaker  152  equipped with a built-in base  156 . The base is shown in a furled configuration. The lower ring  154  of the MNS loudspeaker may be modified to work with the base. For example, the lower ring may include an integral inner cylinder providing both a mounting fixture for the base as well as a rear wall of the enclosed air chamber behind the transducers. In one embodiment, the base is a tripod, but in other embodiments it could have other configurations. 
         [0082]      FIG. 24  illustrates the portable MNS system  150  with the built-in base  156  in an unfurled configuration. The base includes a telescoping set of tubes  158 ,  160 ,  162  of any suitable number, length, and shape. The number and length may be selected to provide an optimal listening height for the MNS loudspeaker. In one embodiment, the lowermost telescoping tube is adapted with three or more deployable legs for stabilizing the MNS system, and may include a plurality of channels or recesses in which the legs are held when the base is furled. In another embodiment, the lowermost telescoping tube may be adapted for coupling with a permanent fixture (not shown) in the ground, stage, or other location at which the MNS may periodically be deployed. Such a fixture may be as simple as a vertical pipe stuck in the ground and cut off at ground level. 
         [0083]      FIG. 26  is a polar response graph resulting from a computer simulation of the performance of an 8-transducer MNS system according to one embodiment of the present invention. At all frequencies in the 1 kHz to 4 kHz range, there is essentially no drop-off at any listening position. And even at 5 kHz, which is at the very upper end of what is considered important for human speech intelligibility, the 22.5° etc. listening positions have a mere 1-1.5 dB drop off. This 8-transducer system represents a truly vast improvement over the 4-transducer system of the prior art. 
         [0084]      FIG. 27  is a polar response graph resulting from a computer simulation of the performance of a 16-transducer MNS system according to another embodiment of the present invention. At all frequencies in the 1 kHz to 5 kHz range, there is essentially no drop-off at any listening position. The 16-transducer system behaves almost exactly as a pulsating cylinder, in the frequency range of human speech intelligibility. 
         [0085]    By comparing  FIGS. 26 and 27  to  FIG. 25 , the significant improvement in speech intelligibility of this invention is readily observed. 
       CONCLUSION 
       [0086]    When one component is said to be “adjacent” another component, it should not be interpreted to mean that there is absolutely nothing between the two components, only that they are in the order indicated. 
         [0087]    In some embodiments, the various transducers may not be of identical construction, and may have different widths, and may be on non-identical spacings. 
         [0088]    The various features illustrated in the figures may be combined in many ways, and should not be interpreted as though limited to the specific embodiments in which they were explained and shown. 
         [0089]    Those skilled in the art, having the benefit of this disclosure, will appreciate that many other variations from the foregoing description and drawings may be made within the scope of the present invention. Indeed, the invention is not limited to the details described above. Rather, it is the following claims including any amendments thereto that define the scope of the invention.