Abstract:
The present invention involves a speaker system for sound reproduction. A low frequency transducer is mounted in one end of the elongated speaker enclosure, and the other end of the enclosure is at least partially open. The speaker enclosure is completely open, i.e., without stuffing, and is dimensioned such that the length of the internal chamber is about one-eighth the length of the wavelength of the lowest frequency sounds to be produced by the transducer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to sound reproduction systems. More particularly, the field of the invention is speaker enclosures for such audio reproduction systems. 
     2. Description of the Related Art 
     Sound reproduction systems are well known, and typically include a generation circuit (e.g., a radio receiver or a compact disc player), an amplification circuit (for amplifying the signal from, e.g., the radio or disc player), and a speaker consisting of one, two, or three, etc., transducers; a typical three-way speaker system consisting of high frequency transducers (tweeter, HF), a mid-range transducer (middle range frequencies, MF), and a low frequency transducer (woofer, LF). Various arrangements are known for speaker designs for each of these types of transducers, and the speaker design may be specially constructed to benefit the audio band which the transducer produces. In particular, low range transducers (woofers) are well known to include a cone diaphragm (typically 4″ to 30″) which vibrates according to the signal received by the transducer. The diaphragm may be conically shaped, and while air on one side of the diaphragm is compressed, air on the opposite side of the diaphragm is rarified. This results in the sound resonating from one side of the transducer being 180° out of phase with sound resonating from the other side of the transducer. In order to separate the compressed air from the rarefied air, a low frequency transducer must be placed in an enclosure designed to isolate its front radiations from rear radiations. There are many such configurations. 
     One of the simplest is a circular baffle with the transducer mounted in the center. This configuration requires a baffle approximately 40 feet in diameter to produce bottom A on a piano or 27.5 Hz. 
     A large sealed enclosure with the transducer mounted in such a manner as to isolate the transducer front radiation from its rear radiation is known as an infinite baffle. Large infinite baffles produce good low range sound but are relatively large and only utilized one side of the mounted low frequency transducer. 
     An infinite baffle cabinet can be reduced in size by adding a vent or port. This configuration is known as a reflex cabinet or vented box and produces low frequency more efficiently and with better impedance match to an amplifier than the infinite baffle but does not produce low frequency sound as “open” as the above baffle. 
     To achieve a more open sound and a good impedance match to an amplifier, a cabinet configuration referred to as an acoustic labyrinth can be employed. 
     An acoustic labyrinth is a pipe or duct, folded to conserve space, and connected to the rear of the transducer cone. The far end of the duct is left open and in the same plane as the transducer. The pipe is arranged to be a quarter wavelength at some low frequency near to the resonant frequency of the loudspeaker when loaded by the labyrinth. Around this frequency, the transmission delay along the pipe brings the energy radiated from the open end approximately in phase with the front radiation on the unit. The low frequency range of the system is therefore reinforced, and since the transducer is looking into a high impedance when the pipe is a quarter wavelength, cone excursions are much reduced, resulting in less non-linear distortion. A loudspeaker with a loaded resonance at 40 Hz would require a duct 7′ long. At frequencies below the quarter wavelength mode, the port and diaphragm radiation are out of phase and the response falls off steeply. At higher frequencies, the port radiation would be in and out of phase according to wavelength, and would tend to produce irregular response characteristics in the middle registers; sound absorption is therefore necessary. 
     The labyrinth actually lowers the frequency of cone resonance owing to the mass of air in the duct which operates directly on the cone surface. As enclosures go, it produces very good bass. G. A. Briggs,  Loudspeakers , Wharfedale Wireless Works Limited, 1948, Chap. 18, “Cabinets”, p. 191. 
     The transmission line (TL) has its design roots in the Stromberg-Carlson acoustic labyrinth (circa 1930). It first consisted of a long pipe (open at one end and the driver mounted at the other), with a cross-sectional area about the same as that of the driver. The line length was made about 25% of the driver resonance&#39;s wavelength and then folded to make it into a practical shape. Without any stuffing or damping material in the line, the enclosure dampened output at resonance, and reinforced the frequencies about one octave above resonance. 
     Working with the same basic concept in the early 1960&#39;s, A. R. Bailey experimented with different damping materials and techniques in folded labyrinth lines. A. R. Bailey, “A Non-Resonant Loudspeaker Enclosure Design”, Wireless World , October 1965; T. Jastak, “A Transmission Line Speaker”,  Audio Amateur , January 1973;. A. R. Bailey, “The Transmission Line Loudspeaker Enclosure”,  Wireless World , May 1972. This work has since become the basic bible for most TL designs. Using Bailey&#39;s density criteria of 0.5 lb. cu. ft., A. J. Bradbury published his 1976 paper (A. J. Bradbury, “The Use of Fibrous Materials in Loudspeaker Enclosures”,  JAES , April 1976) which described changes in the speed of sound for different types of damping material (fiberglass and long fiber wool). Vance Dickason,  The Loud Speaker Design Cookbook , Audio Amateur Press, Peterborough, N.H., 1995, Chap. 4, “Transmission Line Low-Frequency Systems”, p. 73. 
     Transmission lines are enclosures filled with a sound absorbing material, such as long fiber Dacron wool, in order to delay the low frequency acoustic waves so that the transducer compression and rarefactions are in phase, i.e., that cancellation does not occur. Packing the enclosure with sound delaying and absorbing material (equal to 0.5 lb. cu. ft. of wool or more) produces an undesirable acoustic result by dramatically reducing the “openness” of the bass sound. 
     SUMMARY OF THE INVENTION 
     The present invention is a speaker system which has an enclosure about one-eighth of the length of the lowest frequency sound which one wants to produce using a transducer.        wavelength   =       speed                 of                 sound                 in                 air       desired                 frequency                   (     c   /   s     )                   cabinet                 length     =     wavelength   8                            
     The enclosure defines an interior space having two ends, one end mounting the speaker and the other end having an opening which allows the rearward directed sound waves to escape. The sound produced by the interior side of the speaker travels for one-eighth of a wavelength of the sound to be produced to the opening, and travels an additional one-eighth of a wavelength to the front side of the speaker so that the sound is in phase with the sound waves produced by the exterior face of the transducer. The interior channel of the enclosure of the present invention is open (i.e. not obstructed by excessive sound delaying stuffing) to provide a high quality, life-like “open” bass sound. Tweeters and mid-range speakers may also be accommodated within the speaker enclosure by including a layer of sound absorbing material on the interior wall or walls of the enclosure or utilizing fibrous material at such a density (less than 0.5 lb. per cu. ft.) that low frequencies (approximately 150 cps or less) are not absorbed or isolating them in separate small cabinets within the main enclosure. The enclosure may have a cross-sectional shape of circle, triangle, square, rectangle, trapezoid, pentagon, hexagon, heptagon, octagon, other polygons, etc., and may be disposed horizontally or vertically. A conically shaped baffle may be used to distribute the rearwardly transmitted sound out of the speaker enclosure, and is particularly useful with vertically disposed speaker enclosures. Further embodiments of the present invention include providing two or more transducers mounted in oppositely directed chambers. A transducer mounted at one end of an enclosure having internal baffles which create a serpentine path for sound, a transducer mounted in the center of an enclosure and other variations. The present invention provides a sound path from the transducer to the enclosure opening having a distance of approximately one-eighth of the wavelength of the low frequency sound to be produced. The sound escaping through the opening thus will be in phase when it reaches the front of the speaker, thereby utilizing 100% of both sides of the woofer and at the same time creating a full and open bass sound. By taking advantage of phase reinforcement, the efficiency of the speaker is increased because the sound energy from the interiorly facing side of the transducer diaphragm is effectively combined with the sound energy emanating from the exteriorly facing side of the speaker diaphragm. Also, this produces a flatter impedance curve which results in a better transducer match to the amplifier output. The present invention thus has a greater power handling capability because of its increased efficiency and matching with the amplifier output. 
     Conventional cross-over circuits are utilized to limit the frequency of the sound produced by the bass transducer to a low level, for example below 150 hertz or, preferably, below 75 hertz. If a mid-range transducer and/or tweeter are disposed within the enclosure so that higher frequency sounds are transmitted through the interior channel of the enclosure, means are provided for absorbing these higher frequency standing waves. One such technique is to line the interior wall or walls of the enclosure with sound absorbing material. However, it is critically important that the channel itself remain an open cross-section area and should not be less than approximately 25% of the woofer&#39;s effective cone radiating area so that the low frequency acoustic waves can travel rearwardly through the channel and out the opening without being damped or delayed. This combination of high frequency attenuation and completely unobstructed transmission of the low frequency acoustic waves produces the high quality open bass sound that is characteristic of the present invention. The present invention involves, in one form, a speaker system for the reproduction of low frequency sounds. The speaker system comprises a low frequency transducer for reproducing sounds in a low frequency band, a filter, and an elongated enclosure. The filter provides signals for reproducing sound which does not exceed 150 hertz in frequency, and is connected to the transducer and is adapted for connection to the audio system. The enclosure has an interior channel having two ends. The low frequency transducer is mounted at one end and has a front vibrating surface facing exteriorly and a rear vibrating surface facing interiorly. The other end has an opening adapted to allow sounds produced by the speaker to escape the interior space. The distance between the speaker and the opening is approximately one-eighth the length of the wavelength of the lowest frequency sound to be produced by the speaker. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic view of the present invention. 
     FIG. 2 is a side elevational view, in partial cutaway, of a first embodiment of the present invention. 
     FIG. 3 is a front view taken along view line 3—3 of FIG.  2 . 
     FIG. 4 is a side elevational view, in partial cutaway, of a second embodiment of the present invention. 
     FIG. 5 is a front view taken along view line 5—5 of FIG.  4 . 
     FIG. 6 is a side elevational view, in partial cutaway, of a third embodiment of the present invention. 
     FIG. 7 is a sectional view taken along view line 7—7 of FIG.  6 . 
     FIG. 8 is a sectional view of a fourth embodiment of the present invention. 
     FIG. 9 is a front view taken along view line 9—9 of FIG.  8 . 
     FIG. 10 is an elevational side view, in partial cut-away, of a fifth embodiment of the present invention. 
     FIG. 11 is a top view taken along view line 11—11 of FIG.  10 . 
     FIG. 12 is a sectional view of a sixth embodiment of the present invention. 
     FIG. 13 is a top view taken along view line 13—13 of FIG.  12 . 
     FIG. 14 is a sectional view of a seventh embodiment of the present invention. 
     FIG. 15 is a sectional view of an eighth embodiment of the present invention. 
     FIG. 16 is an enlarged fragmentary sectional view of FIG.  10 . 
     FIG. 17 is an enlarged fragmentary sectional view of FIG.  12 . 
     FIG. 18 is a front elevational view of a further embodiment. 
     FIG. 19 is a sectional view taken along line 19—19 of FIG.  18 . 
     FIG. 20 is a rear elevational view of the embodiment of FIG.  18 . 
     FIG. 21 is a longitudinal sectional view of another embodiment of the present invention. 
     FIG. 22 is a sectional view of another embodiment of the invention. 
     FIG. 23 is a sectional view of yet another embodiment of the invention. 
     FIG. 24 is a front elevational view of a still further embodiment of the present invention. 
     FIG. 25 is a sectional view taken along line 25—25 of FIG.  24 . 
     FIG. 26 is a sectional view of a further embodiment of the present invention. 
     FIG. 27 is a view taken along line 27—27 of FIG.  26 . 
     FIG. 28 is a front elevational view of the embodiment of FIG.  26 . 
     FIG. 29 is a sectional view of yet another embodiment of the invention. 
     FIG. 30 is a rear elevational view of the embodiment of FIG.  29 . 
     FIG. 31 is a view taken along line 31—31 of FIG.  29 . 
     FIG. 32 is a rear elevational view of a further embodiment of the invention. 
     FIG. 33 is a sectional view taken along line 33—33 of FIG.  32 . 
     FIG. 34 is a perspective view of the modification of the speaker shown in FIGS. 32 and 33. 
     FIG. 35 is a front elevational view of yet another embodiment of the invention. 
     FIG. 36 is a sectional view taken along line 36—36 of FIG.  35 . 
     FIG. 37 is a longitudinal sectional view of a further embodiment. 
     FIG. 38 is an end view of the speaker shown in FIG.  37 . 
     FIG. 39 is a longitudinal sectional view of yet a further embodiment of the invention. 
     FIG. 40 is an end view of the speaker shown in FIG.  39 . 
     FIG. 41 is a longitudinal sectional view of another embodiment of the invention. 
     FIG. 42 is an end view of the speaker shown in FIG.  41 . 
     FIG. 43 is a sectional view of yet another embodiment of the invention. 
     FIG. 44 is a sectional view taken along line 44—44 of FIG.  43  and viewed in the direction of the arrows. 
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate preferred embodiments of the invention, in several forms, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is illustrated in schematic form in FIG.  1 . Sound reproduction system  20  includes sound system  22 , amplifier  24 , cross-over or low pass filter  26 , and audio transducer  30  (e.g. a conventional speaker). Sound system  22  may be a radio receiver, a phonograph player, a tape player, a compact disc player, or other sound signal generating device. Amplifier  24  receives the sound signals generated by sound system  22  and amplifies them for reproduction by transducer  30 . Filter  26  connects amplifier  24  and transducer  30 , and prevents sound signals for frequencies greater than a predetermined amount from reaching transducer  30 . For example, low pass filter  26  may prevent signals representing sound of greater than 150 hertz from reaching transducer  30 . Low pass filter  26  may also have a cut-off value of 100, 75 or 50 hertz, etc. In accordance with the present invention, speaker unit  28  comprises transducer  30  and enclosure  32 . Transducer  30  is a conventional low frequency transducer having a diaphragm with an exteriorly facing surface  34  and an interiorly facing surface  36 . Transducer  30  is mounted at one end of enclosure  32 , which defines interior space or duct  38  within its walls, and includes opening  40  at the other end. Enclosure  32  is structured and arranged so that the distance from interiorly facing surface  36  to opening  40 , labeled as L 1  in FIG. 1, is about one-eighth the length of the wavelength of the lowest sound to be generated by transducer  30 , for example, 27.5 hertz, which is low A on a piano. Further, the distance from opening  40  to exteriorly facing surface  34 , labeled as L 2  in FIG. 1, is also about one-eighth the length of the wavelength of the sound being generated by transducer  30 . Therefore, sound emanating from interiorly facing surface  36  travels one-fourth of its wavelength (L 1 +L 2 ) to reinforce sound emanating from exteriorly facing surface  34 . FIGS. 2 and 3 show a cylindrical embodiment of the present invention. Speaker unit  42  includes low frequency transducer  44 , cylindrical enclosure  46 , mid-range transducer  48 , tweeter  50 , a layer of high frequency sound absorbing material  52 , and two supports  54 . Transducer  44  is mounted at one end of enclosure  46 , and opening  56 , which is preferably at least as large in cross-sectional area as speaker cone  45  (as indicated by arrows  51 ), is present at the other end of enclosure  46 . The cylindrical shape of enclosure  46  is advantageous in that the creation of standing waves off parallel surfaces is minimized. Mid-range transducer  50  and tweeter  48  are disposed within enclosure  46  along with sound absorbing material  52  which absorbs sound from mid-range transducer  50  and tweeter  48  which passes through the interior of enclosure  46 . 
     A layer of sound absorbing material  52 , such as Dacron wool or fiberglass, is disposed on the inner surface  47  of enclosure  46 . Supports  54  are in the form of blocks having a cylindrically shaped depression to receive the exterior surface of enclosure  46 . 
     FIGS. 4 and 5 show a rectangular embodiment of the present invention. Speaker unit  58  includes low frequency transducer  60 , rectangular enclosure  62 , and two supports  64 . Enclosure  62  acoustically mounts transducer  60  at one end and has opening  66  located at its other end which can vary in size to say ½ cone area of said transducer. Supports  64  have an upper member attached to enclosure  62  and a lower member adapted to be located on a flat surface. 
     FIGS. 6 and 7 show a horizontally oriented, upwardly facing embodiment of the present invention. Speaker unit  68  includes low frequency transducer  70 , enclosure  72 , and eight supports  74 . Horizontally disposed enclosure  72  acoustically mounts transducer  70  at its upper surface at one end with a curved reflecting surface  76  disposed under transducer  70  to reflect sound to the other end of enclosure  72  where opening  78  is located. Supports  74  are small blocks arranged in a rectangular pattern and which extend from the lower surface of enclosure  72 . The cross-sectional area of opening  78  represented by arrow  79  can be as large as the effective cross-sectional area of the cone of transducer  70 , which is represented by arrow  71 . 
     FIGS. 8 and 9 show a double speaker embodiment of the present invention. Speaker unit  80  includes low frequency transducers  82  and  84 , enclosure  86 , and divider wall  88 . Enclosure  86  has two interior chambers  90  and  92  defined by divider wall  88 . Chamber  90  has transducer  82  acoustically mounted at one end, and has opening  94  located at the other end. Speaker  84  is acoustically mounted in chamber  92  adjacent to opening  94  of chamber  90 , and chamber  92  also includes opening  96  opposite transducer  84  and adjacent to transducer  82 . By having the transducers mounted adjacent to the other chamber&#39;s opening as shown in FIG. 9, the transducer&#39;s resonances are lowered. The areas of openings  94  and  96  match the effective cross-sectional areas of the cones of transducers  84  and  82 , respectively. 
     FIGS. 10 and 11 show a vertically disposed embodiment of the present invention. Speaker unit  98  includes low frequency speaker  100 , cylindrical enclosure  102 , and support  104 . Enclosure  102  mounts transducer  100  at its top end and has one opening  106  located at its bottom end. Conical support  104  supports enclosure  102  by means of a plurality of brackets  105  while defining annular opening  106  between it and the cylindrical wall  107  of enclosure  102 . The cross-sectional area of annular opening  106  is preferably at least as large as the effective cross-sectional area of speaker cone  109 , as indicated by arrow  111  although it can be smaller or larger in some cases. 
     FIGS. 12 and 13 show a vertically disposed rectangular embodiment of the present invention. Speaker unit  108  includes low frequency bass transducer  110 , rectangular enclosure  112 , and pyramid support  114 . In this embodiment, transducer  110  also has an additional higher frequency speaker  116  coaxially disposed in the center of midrange/low frequency transducer  110 . Enclosure  112  acoustically mounts transducer  110  at its top end and has one annular opening  118  located at its bottom end. Pyramid shaped support  114  is connected to and supports enclosure  112  by means of brackets  115  in the form of rounded rods while defining opening  118  between it and the cylindrical wall of enclosure  112 . Support  114  comprises four triangularly shaped refracting surfaces  120  extending upwards into enclosure  112 . 
     Because of the presence of sound waves above approximately 150 cps from transducer  110 , the interior wall of enclosure  112  is provided with a layer of sound absorbing material  123  to reduce standing waves. Similarly to the other embodiments, the cross-sectional area of opening  118  should approximate the effective cross-sectional area of the cone of transducer  110 . 
     FIG. 14 is a sectional view of a baffled embodiment of the present invention, with its top view being similar to FIG. 13 but without higher frequency speaker  116 . Speaker unit  124  includes low frequency transducer  126 , enclosure  128 , and pyramid support  130 . Enclosure  128  has transducer  126  mounted at its top end, is supported by pyramid support  130  which with enclosure  128  defines one opening  132 , and has a plurality of baffles  134  disposed within enclosure  128 . Disposed between adjacent baffles  134  are reflectors  136  for channeling sound through a serpentine path within enclosure  128 . The serpentine path is labeled L 3  in FIG. 14, and extends from the inside of speaker  126 , around the plurality of baffles  134 , to opening  132 . Sound may then traverse exteriorly to enclosure  128  to the outside of speaker  126  along path L 4 . In accordance with the present invention, the resonating distance of L 3 +L 4  is equal to about one-fourth the wavelength of the desired sound to be produced by speaker  124 . 
     FIG. 15 shows a vertical rectangular embodiment of the present invention which includes a tweeter  148 , with its top view being similar to FIG. 13 but without higher frequency speaker  116 . Speaker unit  138  includes mid frequency/low frequency transducer  140 , rectangular enclosure  142 , and pyramidal support  144 . Enclosure  142  has transducer  140  mounted at its top end, is supported by support  144  which with enclosure  142  defines one opening  146 , and has enclosed tweeter  148  disposed within enclosure  142 . 
     FIGS. 18-20 illustrate a further embodiment of the present invention. Speaker unit  150  includes a low frequency transducer  152  mounted within a front opening  153  of enclosure  154 . A rear opening  156  is provided as shown in FIGS. 19 and 20. A plurality of internal baffles such as baffles  158 - 166  define an internal duct  168  leading from the rear surface of transducer  152  to rear opening  156 . The length of internal duct  168  plus the shortest distance from rear opening  156  around the cabinet to the plane defined by front opening  153  is equal to one-fourth of the wavelength of the lowest desired sound to be produced by speaker  150 . Transducer  152  is depicted as a coaxial speaker having a horn tweeter  170  mounted in the center of woofer  172 . In order to absorb high frequency sounds transmitted rearwardly by horn tweeter  170 , the interior duct  168  is lined with sound absorbing material  174 . 
     FIG. 21 illustrates yet another embodiment of the present invention wherein the enclosure  174 , which may be circular, rectangular or another cross-sectional shape, tapers inwardly in at least one plane from the median point  176  to the open ends  178  and  180 . Transducer  182  is mounted at the median point  176  within enclosure  174  and the distance from the front of transducer  182  to opening  178  is {fraction (1/16)} of the wavelength of the lowest frequency sound to be produced by transducer  182  and the distance from the rear surface of transducer  182  to opening  180  is similarly {fraction (1/16)} of the wavelength. Thus, adding together the delay from the front of transducer  182  to the midpoint  176  ({fraction (1/16)}+{fraction (1/16)}) and the delay from the rear of transducer  182  to the midpoint  176  ({fraction (1/16)}+{fraction (1/16)}) results in a total delay of one-fourth of the wavelength of the lowest sound to be produced. In this embodiment, enclosure  174  is one-eighth of the wavelength of the lowest sound to be produced. 
     FIG. 23 illustrates a further variation on the speaker  184  shown in FIG. 22 wherein enclosure  190  is constructed similarly to the enclosure of speaker  184  but two matched transducers  192  and  194  are mounted in facing arrangement on central baffle  196 . Transducers  192  and  194  are driven 180° out-of-phase. The distance from the rear surface (facing forwardly) of transducer  192  to the front opening of speaker  190  added to the distance from the rear surface (facing rearwardly) of transducer  194  around the enclosure  190  is equal to one-quarter wavelength of the lowest frequency to be produced by speaker  191 . 
     FIG. 23 illustrates a further variation on the speaker  184  shown in FIG. 22 wherein enclosure  190  is constructed similarly to the enclosure of speaker  184  but two matched transducers  192  and  194  are mounted in facing arrangement on central baffle  196 . Transducers  194  are driven 180° out-of-phase. The distance from the rear surface (facing forwardly) of transducer  192  to the front opening of speaker  190  added to the distance from the rear surface (facing rearwardly) of transducer  194  around the enclosure  190  is equal to one-quarter wavelength of the lowest frequency to be produced by speaker  191 . 
     The speaker  198  illustrated in FIGS. 24 and 25 is a further variation wherein transducers  200  and  202  are driven in phase and both face forwardly. Transducers  200  and  202  are mounted within enclosure  203  and the sum of the distance from the front of transducer  202  to the midpoint of enclosure  204  and the distance from the rear surface of transducer  200  to the midpoint of enclosure  204  is equal to one-quarter wavelength. 
     FIGS. 26-28 illustrate an alternative enclosure arrangement wherein the enclosure  205  for speaker  206  includes front opening  208 , rear opening  210  and a pair of rectangular internal baffles  212  and  214  that form internal ducts  216  and  218 , respectively. Once again, the combined distance from the front of transducer  220  through opening  208  to the midpoint of enclosure  205  and from the rear of transducer  220  through opening  210  to the midpoint of enclosure  205  is equal to one-fourth of the wavelength of the lowest frequency sound to be produced by speaker  206 . 
     FIGS. 29-31 show a modification of the speaker  206  of FIGS. 26-28 wherein two transducers  222  and  224  are mounted on respective sides of enclosure  226  and face in opposite directions. Opening  230 A is the rear opening for transducer  224  and opening  230  is the front opening for transducer  224 . Opening  228  is the front opening for transducer  222  and opening  228 A is the rear opening therefor. 
     FIGS. 32 and 33 illustrate an embodiment of the invention incorporating an electrostatic&#39;speaker panel. Speaker  232  comprises an enclosure  234  having an opening  236  in which is mounted transducer  238  which could be, for example, a  12  inch woofer. Enclosure  234  defines an interior duct  240  that is tapered from the low end thereof at the position where transducer  238  is mounted to the upper opening  242 , and includes a reflector  244  made of styrofoam or other appropriate material to channel the soundwaves upwardly through duct  240 . By way of example, enclosure  234  could have a height of 72 inches and a depth of 18 inches, and the effective length of internal duct  240  is one-eighth wavelength so that this system therefore will produce bass sounds to 27 hertz. 
     A conventional electrostatic speaker panel  246  is mounted to the front surface of enclosure  234  by means of a plurality of standoffs and may be covered with a grill cloth  250 . Electrostatic speaker panels provide excellent high, midrange, and high bass reproduction in the range of approximately 100 hertz to inaudibility and the sub-woofer  238  would generate bass sound below 100 hertz, down to 27 hertz and below. A cross-over would be provided between sub-woofer  238  and electrostatic speaker  246 . 
     FIG. 34 illustrates a speaker  252  that is substantially identical to speaker  232  (FIG. 33) except that electrostatic panel  254  is curved. 
     FIGS. 35 and 36 show a multiple stacked transducer speaker  256  wherein transducers  258  are mounted in front openings of enclosure  260 . The axial dimensional characteristics are the same as discussed in connection with the speaker of FIGS. 1 and 2. 
     FIG. 37 illustrates a speaker  262  similar to speaker  20  shown in FIG. 1 but wherein transducer  264  is mounted at the midpoint of enclosure  266 . The dimensions of enclosure  266  are the same as those discussed in connection with the speaker of FIGS. 1 and 2. 
     FIG. 39 illustrates a modification to speaker  262  of FIG. 37 wherein the length of enclosure  268  is one-half the length of enclosure  266  and includes a plurality of internal baffles  270  that lengthens the acoustic length of speaker  272  internally within enclosure  268  to match the acoustic length of speaker  262 . The sound is emitted through openings  274 . 
     FIG. 41 is a modification of the speaker  272  of FIG. 39 wherein the length of enclosure  276  has been further shortened to be approximately 33% of the length of enclosure  268 , and which includes internal baffles  278  that provide an acoustic length that is identical to that of speakers  262  and  272  (FIGS.  37  and  39 ). Sound is emitted through openings  280 . 
     The speaker  282  shown in FIGS. 43 and 44 is similar to the speaker shown in FIG. 29 except that the mounting of transducer  284  and internal baffles  286  have been rotated 45°. The sound is emitted through openings  288 . Transducer  284  is mounted to center panel  290 . 
     The enclosures described above can be made of conventional materials, such as particle board, PVC or other plastics, metal, styrofoam, laminate, or other more or less nonresonating material, and the transducers are conventional in nature and can be purchased commercially from a variety of suppliers. The effective vibrating area of the transducer cone is a projection of the cone onto a plane that is perpendicular to the axis defined by the cone of the transducer. In other words, the effective vibrating area is essentially the area defined by the diameter of the face of the transducer cone. The transducer can take any suitable form including coaxial, triaxial, etc. 
     While this invention has been described as having a preferred design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.