Patent Publication Number: US-9848259-B2

Title: Loudspeaker

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2015-0116105, filed on Aug. 18, 2015, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     The disclosure relates to loudspeakers for reproducing sound using an electrical signal. 
     2. Description of Related Art 
     The power of sound generated by a loudspeaker may be defined as the product between the square of the volume velocity of a medium (e.g., air) that moves due to vibration of a diaphragm and a radiation resistance caused by the shape of the diaphragm and the medium. 
     The volume velocity is proportional to the product of the area and dynamic range of the diaphragm. The volume velocity is determined by the dynamic range of the diaphragm when the fixed area of the diaphragm is considered. The radiation resistance corresponds to a real number of a radiation impedance of the diaphragm and is a physical quantity that directly contributes to acoustic power, which is effective power. The radiation resistance of a loudspeaker that includes a disc type driver installed on an infinite baffle decreases remarkably in a low-frequency band. 
     A woofer is designed to mainly reproduce sound in a low frequency band and is thus required to have a high volume velocity so as to reproduce sound at a desired level regardless of a low radiation resistance at a low frequency band. Thus, the woofer is required to have a much larger diaphragm area and dynamic range than a mid-range speaker or a tweeter. The volume of an enclosure should be increased to increase the area of the diaphragm of the woofer and maintain a low-frequency reproduction limit. Thus, it is difficult to manufacture the woofer of a slim type. 
     If increasing the volume of the enclosure is restricted, the dynamic range of the diaphragm may be increased to achieve a high volume velocity. When the dynamic range of the diaphragm is increased, a high volume velocity may be achieved, but the vibration energy increases and an electronic device in which the woofer is installed and peripheral structures may vibrate unnecessarily. 
     SUMMARY 
     A loudspeaker with increased degree of freedom of an acoustic emission direction is provided. 
     A loudspeaker with reduced decrease of an output sound level is provided. 
     A loudspeaker with reduced vibration is provided. 
     A loudspeaker with improved sound articulation is provided. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description. 
     According to an aspect of an example embodiment, a loudspeaker includes an enclosure including a resonance chamber and a main acoustic emission aperture for communication of the resonance chamber with an outside of the enclosure; and a plurality of speaker units, each speaker unit including a speaker, the plurality of speaker units including a first speaker unit arranged in a first direction and a second speaker unit arranged in a second direction, the plurality of speaker units being accommodated in the enclosure in a non-coaxial arrangement, wherein front slit spaces of the plurality of speaker units are in communication with the resonance chamber. 
     The plurality of speaker units may be arranged in a non-coaxial force-moment compensation arrangement. 
     The enclosure may include a first baffle in which the first speaker unit is arranged; and a second baffle in which the second speaker unit is arranged. The first baffle and the second baffle may form a step with respect to each other in a first direction. 
     The loudspeaker may further include a duct configured to connect the resonance chamber to the main acoustic emission aperture. 
     The loudspeaker may further include a passive radiator arranged in the main acoustic emission aperture. 
     The loudspeaker may further include an attenuator arranged in a plurality of communication apertures connecting the front slit spaces and the resonance chamber and configured to apply an acoustic resistance. 
     At least two back chambers from among back chambers of the plurality of speaker units may be arranged to communicate with each other. 
     Each of back chambers of the plurality of speaker units may have a sealed enclosure structure, a vented enclosure structure, or a passive radiator type enclosure structure. 
     The plurality of speaker units may be divided into a first speaker group arranged at one side of the resonance chamber and a second speaker group arranged at another side of the resonance chamber. Back chambers of the first speaker group may communicate with one another, and back chambers of the second speaker group may communicate with one another. 
     The loudspeaker may further include first and second acoustic emission apertures in communication with the main acoustic emission aperture. The resonance chamber may include first and second resonance chambers, and the plurality of speaker units may include a first speaker group including front slit spaces in communication with the first resonance chamber; and a second speaker group including front slit spaces in communication with the second resonance chamber. Back chambers of the first speaker group may communicate with one another, and back chambers of the second speaker group may communicate with one another. The enclosure may further include an additional chamber configured to communicate with back chambers of the first and second speaker groups. 
     According to an aspect of another example embodiment, a loudspeaker includes a plurality of speaker units arranged in a non-coaxial structure; and an enclosure configured to accommodate the plurality of speaker units. The enclosure includes an acoustic emission aperture; and a band-pass amplifier configured to communicate with front slit spaces of the plurality of speaker units, to band-pass amplify a sound emitted from the plurality of speaker units, and to emit the sound via the acoustic emission aperture. 
     The band-pass amplifier may include a resonance chamber configured to communicate with the front slit spaces; and a duct configured to connect the resonance chamber and the acoustic emission aperture. 
     The band-pass amplifier may include a resonance chamber configured to communicate with the front slit spaces and the acoustic emission aperture; and a passive radiator installed in the acoustic emission aperture. 
     The plurality of speaker units may be arranged in a non-coaxial force-moment compensation arrangement. 
     The loudspeaker may further include an attenuator arranged in a plurality of communication apertures connecting the front slit spaces and the resonance chamber and configured to apply an acoustic resistance. 
     At least two back chambers from among back chambers of the plurality of speaker units may communicate with each other. 
     The enclosure may further include an additional chamber configured to communicate with back chambers of the plurality of speaker units. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals refer to like elements, and wherein: 
         FIG. 1  is a perspective view illustrating an example loudspeaker; 
         FIG. 2  is a cross-sectional view of  FIG. 1 , taken along line A-A′; 
         FIG. 3  is a cross-sectional view of  FIG. 2 , taken along line B-B′; 
         FIG. 4  is a cross-sectional view of  FIG. 2 , taken along line C-C′; 
         FIG. 5  is a perspective view illustrating an example loudspeaker; 
         FIG. 6  is a cross-sectional view of  FIG. 5 , taken along line D-D′; 
         FIG. 7  is a graph illustrating an example frequency response based on a variation in a quality factor; 
         FIGS. 8 and 9  are cross-sectional views illustrating an example loudspeaker; 
         FIG. 10  is a partial cross-sectional view illustrating an example loudspeaker; 
         FIG. 11  is a partial cross-sectional view illustrating an example loudspeaker; 
         FIG. 12  is a cross-sectional view illustrating an example loudspeaker; 
         FIG. 13  is a perspective view illustrating an example loudspeaker; 
         FIG. 14  is a cross-sectional view of  FIG. 13 , taken along line G-G′; 
         FIG. 15  is a cross-sectional view of  FIG. 14 , taken along line H-H′; 
         FIG. 16  is a cross-sectional view of  FIG. 14 , taken along line I-I′; 
         FIG. 17  is a cross-sectional view illustrating an example loudspeaker; 
         FIG. 18  is a cross-sectional view illustrating an example loudspeaker; 
         FIG. 19  is a cross-sectional view illustrating an example loudspeaker; 
         FIG. 20  is a schematic configuration diagram illustrating an example loudspeaker; 
         FIG. 21  is a schematic configuration diagram illustrating an example loudspeaker; 
         FIG. 22  is a schematic configuration diagram illustrating an example loudspeaker with three speaker units; 
         FIG. 23  is a schematic configuration diagram illustrating an example loudspeaker; 
         FIG. 24  is a schematic perspective view illustrating an example loudspeaker; 
         FIG. 25  is a cross-sectional view of  FIG. 24 , taken along line M-M′; 
         FIG. 26  illustrates an example display apparatus employing an example loudspeaker; and 
         FIG. 27  illustrates an example display apparatus employing an example loudspeaker. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, loudspeakers according to example embodiments will be described in greater detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements throughout and the sizes or thicknesses of components may be exaggerated for clarity. As used herein, expressions such as ‘at least one of,’ when preceding a list of elements, modify the entire list of elements and do not necessarily modify the individual elements of the list. 
       FIG. 1  is a perspective view illustrating an example loudspeaker  1 .  FIG. 2  is a cross-sectional view of  FIG. 1 , taken along line A-A′.  FIG. 3  is a cross-sectional view of  FIG. 2 , taken along line B-B′.  FIG. 4  is a cross-sectional view of  FIG. 2 , taken along line C-C′. 
     Referring to  FIGS. 1 to 4 , the loudspeaker  1  includes an enclosure  10  and four speaker units  31  to  34  arranged in the enclosure  10 . An acoustic emission aperture  20  may be provided in the enclosure  10 . The position and direction of the acoustic emission aperture  20  are not limited. In the example embodiment, the acoustic emission aperture  20  is provided in an upper wall  11  of the enclosure  10 . The loudspeaker  1  according to the example embodiment may include a band-pass amplifier  25  configured to band-pass amplify the sound emitted from the four speaker units  31  to  34  and emit the sound via the acoustic emission aperture  20 . According to an example embodiment, the band-pass amplifier  25  may include a resonance chamber  90 , and a duct  91  connecting the resonance chamber  90  and the acoustic emission aperture  20  to each other. 
     Each of the speaker units  31  to  34  includes a diaphragm  31   a  and a motor  31   b  for driving the diaphragm  31   a . Although not shown, the motor  31   b  may, for example, include a stator and an oscillator. The motor  31   b  may, for example, employ either a moving coil manner using a magnet as a stator and a coil as an oscillator or a moving magnetic manner using a coil as a stator and a magnet as an oscillator. The shape of the diaphragm  31   a  is not limited to those illustrated in  FIGS. 2 to 4 . The diaphragm  31   a  may have various shapes provided that an area sufficient to obtain a desired acoustic power level can be secured. For example, the diaphragm  31   a  may have a round, oval, quadrangle shape, etc. Although a structure in which one diaphragm  31   a  is driven using two motors  31   b  is illustrated in the example embodiments of  FIGS. 2 to 4 , the number of the motors  31   b  is not limited and one or three or more motors  31   b  may be used in some cases. 
     The speaker units  31  to  34  are accommodated in the enclosure  10 . In the enclosure  10 , baffles  41  to  44  in which the speaker units  31  to  34  are respectively disposed are provided. The speaker units  31  and  32  (e.g., including a first speaker unit  30   a ) are installed in the baffles (first baffle)  41  and  42  in a first direction Z 1 , e.g., to face a front wall  13  of the enclosure  10 . A front slit space  51  is provided between the front wall  13  of the enclosure  10  and the baffle  41 . A front slit space  52  is provided between the front wall  13  of the enclosure  10  and the baffle  42 . Back chambers  61  and  62  are disposed opposite to the front slit spaces  51  and  52  with respect to the baffles  41  and  42 . The back chambers  61  and  62  are sealed enclosure structures that are isolated from the resonance chamber  90  and the front slit spaces  51  and  52 . The front slit spaces  51  and  52  are connected to the resonance chamber  90  via communication apertures  71  and  72 . The speaker units  33  and  34  (e.g., including a second speaker unit  30   b ) are installed in the baffles (second baffles)  43  and  44  in a second direction Z 2  opposite the first direction Z 1 , e.g., to face a back wall  14  of the enclosure  10 . A front slit space  53  is provided between the back wall  14  of the enclosure  10  and the baffle  43 . A front slit space  54  is provided between the back wall  14  of the enclosure  10  and the baffle  44 . Back chambers  63  and  64  are disposed opposite to the front slit spaces  53  and  54  with respect to the baffles  43  and  44 . The back chambers  63  and  64  are isolated from the resonance chamber  90  and the front slit spaces  53  and  54 . The front slit spaces  53  and  54  of the speaker units  33  and  34  are connected to the resonance chamber  90  via communication apertures  73  and  74 . The resonance chamber  90  is separated from the front slit spaces  51  to  54  and the back chambers  61  to  64  by partitions  15  and  16 . The communication apertures  71  to  74  that communicate the front slit spaces  51  to  54  with the resonance chamber  90  are provided in the partitions  15  and  16 . The first baffles  41  and  42  and the second baffles  43  and  44  are located to make a step in the first direction Z 1 . The speaker units  31  to  34  and the resonance chamber  90  are arranged in a direction perpendicular to the first direction Z 1 . Due to the above structure, the speaker units  31  to  34  may be arranged in a non-coaxial structure. 
     The thicknesses of the front slit spaces  51  to  54  are determined to be as thin as possible within a range in which an excursion of the diaphragm  31   a  is acceptable and unnecessary resonance is not generated in the front slit spaces  51  to  54 . Thus, the thickness of the loudspeaker  1  may be decreased. 
     The speaker units  31  to  34  may be arranged in a non-coaxial force-moment compensation structure. For example, the speaker units  31  to  34  are spaced apart the same distance from the center of gravity CP of the loudspeaker  1 . The speaker units  31  and  32  are located to be symmetrical to the center of gravity CP. The speaker units  33  and  34  are located to be symmetrical to the center of gravity CP. When the speaker units  31  to  34  are driven by the same driving signal, a driving force F generated by the speaker units  31  and  32  in the first direction Z 1  and a driving force F generated by the speaker units  33  and  34  in the second direction Z 2  are offset by each other and thus the sum of the driving forces F generated by the speaker units  31  to  34  becomes ‘0’. Also, since the distances from the speaker units  31  to  34  to the center of gravity CP are the same, the sum of moments generated by the driving forces F generated by the speaker units  31  to  34  also becomes ‘0’. Due to this structure, the non-coaxial force-moment compensation structure may be realized. 
     The sum of the numbers of the first speaker unit  30   a  and the second speaker unit  30   b  realized in the non-coaxial force-moment compensation structure is ‘3’ or more. When a driving force generated by the first speaker unit  30   a  and a driving force generated by the second speaker unit  30   b  are the same, the sum of the numbers of the first speaker unit  30   a  and the second speaker unit  30   b  is an even number. When the sum of the numbers of the first speaker unit  30   a  and the second speaker unit  30   b  is an odd number, the driving force generated by the first speaker unit  30   a  and the driving force generated by second speaker unit  30   b  may be different. For example, when the sum of the numbers of the first speaker unit  30   a  and the second speaker unit  30   b  is ‘3’, one first speaker unit  30   a  having a driving force of 2F may be arranged at the center of gravity CP of the loudspeaker  1 , and two second speaker units  30   b  each having a driving force of F may be arranged to be symmetrical to the first speaker unit  30   a . The number, driving force, and geometric arrangement of each of the first speaker unit  30   a  and the second speaker unit  30   b  may be appropriately determined to satisfy the non-coaxial force-moment compensation structure. If the non-coaxial force-moment compensation structure is satisfied, the baffles  41  to  44  of the first speaker unit  30   a  and the second speaker unit  30   b  need not be disposed on the same plane. However, as described above, the thickness of the enclosure  10  may be decreased when the first baffles  41  and  42  and the second baffles  43  and  44  are arranged to make a step in the first direction Z 1 . 
     When the sum of the numbers of the first speaker unit  30   a  and the second speaker unit  30   b  is an even number, the first speaker unit  30   a  and the second speaker unit  30   b  are arranged to be symmetrical to the center of gravity CP. Thus, the resonance chamber  90  that communicates with the front slit spaces  51  to  54  of the first speaker unit  30   a  and the second speaker unit  30   b  may be easily employed. 
     The acoustic power of the loudspeaker  1  depends on the volume velocity of an acoustic medium, i.e., air, which is vibrated by the diaphragm  31   a . In order to increase the acoustic power, the excursion or area of the diaphragm  31   a  may be increased. It is difficult to increase the excursion of the diaphragm  31   a  when there is a restriction to increasing the thickness of the loudspeaker  1 , for example, when the loudspeaker  1  is applied to a slim type electronic device such as a flat panel television (TV) or when a slim type stand-alone loudspeaker is to be realized. Driving forces of a plurality of speaker units and moments accompanied by the driving forces may cause the loudspeaker  1  to vibrate. 
     According to the example embodiment, an acoustic emission area of the loudspeaker  1  is equal to the sum of the areas of the diaphragms  31   a  of the speaker units  31  to  34 . Thus a large acoustic emission area may be secured. Because the first speaker unit  30   a  and the second speaker unit  30   b  having different acoustic emission directions are arranged in the non-coaxial structure, a slim type loudspeaker  1  having a thin thickness may be manufactured. 
     Since the first speaker unit  30   a  and the second speaker unit  30   b  are operated in opposite directions, driving forces of the first speaker unit  30   a  and the second speaker unit  30   b  and moments generated by the driving forces may be partially offset. The sum of the driving forces and the sum of the moments may be less than those in a structure in which the loudspeakers  31  to  34  are operated in the same direction and thus vibration of the loudspeaker  1  may be decreased. Furthermore, the first speaker unit  30   a  and the second speaker unit  30   b  may be arranged in the non-coaxial force-moment compensation structure so that both of the sum of the driving forces and the sum of the moments may be ‘0’. Thus, the loudspeaker  1  that hardly vibrates and that has high acoustic power may be manufactured. 
     Sound emitted from the speaker units  31  to  34  may be amplified, for example, by the band-pass amplifier  25  and is then emitted via the acoustic emission aperture  20 . The resonance chamber  90  and the duct  91  together form a Helmholtz resonator. The Helmholtz resonator is capable of amplifying sound corresponding to a resonance frequency and blocking sounds corresponding to frequencies higher than the resonance frequency. Thus, the Helmholtz resonator may act as a band-pass filter. If, for example, the volume of the resonance chamber  90  is V, a cross-sectional area of the duct  91  is A, the length of the duct  91  is d, and the velocity of sound in air is C, a resonance frequency f 0  of the Helmholtz resonator may be determined by the formula 
               f   0     =       C     2   ⁢   π       ⁢         A   dV       .             
Thus, the volume of the resonance chamber  90  and the cross-sectional area and length of the duct  91  may be appropriately determined such that sound of a desired frequency is amplified based on the resonance frequency f 0  and is then emitted via the acoustic emission aperture  20 .
 
     A loudspeaker having a force-moment offset compensation structure includes the first speaker unit  30   a  emitting sound in the first direction Z 1  and the second speaker unit  30   b  emitting sound in the second direction Z 2 . Sound is divided and emitted in two directions when an acoustic emission aperture is formed in front of each of the first and second speaker units  30   a  and  30   b , for example, when acoustic emission apertures for the first and second speaker units  30   a  and  30   b  are formed in the front wall  13  and the back wall  14  of  FIGS. 3 and 4 . When such a loudspeaker is applied to a slim type electronic device, for example, when the loudspeaker is applied as a woofer system for a flat panel TV, the front of the loudspeaker is blocked by a display and the back of the loudspeaker is blocked by a back panel. Thus, sound should be emitted via a very narrow acoustic duct according to a bottom, side, or top surface emission manner. In this case, sound may be lost in the acoustic duct and thus high acoustic power is difficult to obtain. Thus, in order to obtain high acoustic power, the size of the loudspeaker should be increased. 
     According to the example embodiment, sound emitted from the first and second speaker units  30   a  and  30   b  is collected in the resonance chamber  90  and then sound at a specific frequency band is amplified through, for example, a Helmholtz resonator action and emitted via the common acoustic emission aperture  20 . The position of the acoustic emission aperture  20  is not limited within a range in which the duct  91  may be connected to the resonance chamber  90 . For example, although the acoustic emission aperture  20  is formed in the upper wall  11  of the enclosure  10  in the example embodiments of  FIGS. 2 to 4 , the position of the acoustic emission aperture  20  is not limited thereto.  FIG. 5  is a perspective view illustrating an example loudspeaker  1 .  FIG. 6  is a cross-sectional view of the loudspeaker  1  of  FIG. 5 , taken along line D-D′. Referring to  FIGS. 5 and 6 , an acoustic emission aperture  20  is formed in a front wall  13  of an enclosure  10 . A duct  91  may connect a resonance chamber  90  and the acoustic emission aperture  20  such that sound of a desired frequency is amplified based on a resonance frequency and emitted via the acoustic emission aperture  20 . Although not shown, the acoustic emission aperture  20  may be formed in a back wall  14  or a lower wall  12  of the enclosure  10 . 
     As described above, the loudspeaker  1  according to the example embodiment is capable of collecting sound emitted from first and second speaker units  30   a  and  30   b  and emitting the sound via the acoustic emission aperture  20  which is commonly used. Thus, a sufficient acoustic emission area may be secured, and the loudspeaker  1  having the common acoustic emission aperture  20  may be realized in the non-coaxial structure or the non-coaxial force-moment compensation structure. Furthermore, the degrees of freedom of the position and an acoustic emission direction of the acoustic emission aperture  20  are large and thus the loudspeaker  1  employing the non-coaxial structure or the non-coaxial force-moment compensation structure is very effectively applicable to slim type electronic devices. 
     Since the resonance chamber  90  and front slit spaces  51  to  54  are arranged in a direction perpendicular to the first direction Z 1 , sound emitted from speaker units  31  to  34  in the first and second directions Z 1  and Z 2  propagates along a sound duct formed by the front slit spaces  51  to  54  and is then transferred the resonance chamber  90  via communication apertures  71  to  74 . The sound duct may be a factor that decreases acoustic power. In the loudspeaker  1  according to the example embodiment, a Helmholtz resonator is employed to amplify and output sound at a specific frequency band. Thus, a decrease in an output sound level may be compensated for while sound is collected. Also, when an output sound level is fixed, an excursion of a diaphragm  31   a  may be decreased to secure a high operating reliability. For example, when the loudspeaker  1  according to the example embodiment is applied to a woofer system, a band-pass enclosure type woofer system capable of performing bass boosting and having a remarkably reduced volume of a back chamber may be manufactured. 
       FIG. 7  is a graph illustrating an example frequency response according to a variation in a quality factor Q. In  FIG. 7 , a horizontal axis denotes a normalized frequency f/f c  obtained by normalizing a frequency f with a cutoff frequency f c , and a vertical axis denotes a sound pressure in dB. Referring to  FIG. 7 , as the quality factor Q increases, a sound pressure sharply rises while forming a knee near the cutoff frequency f c . As described above, when the quality factor Q is high, a transient time of a frequency response is long. Thus, the articulation of the whole speaker system is degraded. For example, in the case of a woofer system, a sound pressure sharply rises while forming a knee near a bass roll-off frequency. Such degradation in the articulation of the woofer system may be improved by reducing the quality factor Q. The quality factor Q may be reduced by applying acoustic resistance to a sound duct connected to a resonator. 
       FIGS. 8 and 9  are cross-sectional views illustrating an example loudspeaker  1 .  FIGS. 8 and 9  correspond generally to  FIGS. 3 and 4 , respectively. Referring to  FIGS. 8 and 9 , attenuators  71   a  to  74   a  configured to apply acoustic resistance are located in communication apertures  71  to  74 , respectively. For example, the attenuators  71   a  to  74   a  may be porous fabrics, punching plates, etc. The acoustic resistance depends on aperture ratios of the attenuators  71   a  to  74   a . Thus, a desired quality factor Q may be obtained by employing the attenuators  71   a  to  74   a  each having an appropriate aperture ratio. As described above, when the attenuators  71   a  to  74   a  are employed, the articulation of the loudspeaker  1  may be improved. 
     Although the back chambers  61  to  64  have a sealed enclosure structure isolated from the outside in the above examples, the structures of the back chambers  61  to  64  are not limited thereto. 
       FIG. 10  is a partial cross-sectional view illustrating an example loudspeaker  1 .  FIG. 10  illustrates only a back chamber  61  but back chambers  62  to  64  have the same structure as the back chamber  61 . Thus, the reference numerals assigned to the back chambers  62  to  64  and elements thereof are also illustrated in the form of parenthesis in  FIG. 10 . Referring to  FIG. 10 , the back chambers  61  to  64  have a vented enclosure structure. Referring to  FIG. 10 , the back chambers  61  to  64  communicate with the outside of an enclosure  10  via ducts  81  to  84 . The back chambers  61  to  64  and the ducts  81  to  84  act together as a Helmholtz resonator. The frequency of sound passing through the ducts  81  to  84  depends on the lengths and cross-sectional areas of the ducts  81  to  84 . In the vented enclosure structure, the phase of low-frequency energy formed in the back chambers  61  to  64  by speaker units  31  to  34  may be converted and then the phase-converted low-frequency energy may be emitted to the outside of the enclosure  10 . Thus, a low-frequency output of the loudspeaker  1  may be improved and acoustic energy of the back chambers  61  to  64  may be effectively used, thereby improving the efficiency of the loudspeaker  1 . Also, a small-sized and slim type loudspeaker  1  capable of obtaining the same output may be realized. 
       FIG. 11  is a partial cross-sectional view illustrating an example loudspeaker  1 .  FIG. 11  illustrates only a back chamber  61  but back chambers  62  to  64  have the same structure as the back chamber  61 . Thus, the reference numerals assigned to the back chambers  62  to  64  and elements thereof are also illustrated in the form of parenthesis in  FIG. 11 . Referring to  FIG. 11 , the back chambers  61  to  64  have a passive radiator type enclosure structure. Referring to  FIG. 11 , passive radiators  85  to  88  facing the outside of an enclosure  10  are installed in the back chambers  61  to  64 , respectively. The passive radiators  85  to  88  each include a diaphragm but do not include a motor. Thus, the passive radiators  85  to  88  are operated based on a change in pressure applied to the back chambers  61  to  64  when speaker units  31  to  34  are operated. Frequency tuning may be easily performed on the passive radiators  85  to  88  by controlling the mass of the diaphragm and the hardness of a suspension. Due to the above structure, acoustic energy of the back chambers  61  to  64  may be effectively used to improve the efficiency of the loudspeaker  1 . Also, a small-sized and slim type loudspeaker  1  capable of obtaining the same output may be realized. 
     Although the back chambers  61  to  64  are independent and isolated with each other in the example embodiments of  FIGS. 1 to 4 , at least one among the back chambers  61  to  64  may communicate with the other back chambers.  FIG. 12  is a cross-sectional view illustrating an example loudspeaker  1 .  FIG. 12  illustrates a modified example of the loudspeaker  1  illustrated in  FIGS. 1 to 4 .  FIG. 12  is a cross-sectional view of  FIG. 2 , taken along lines E-E′ and F-F′. In  FIG. 12 , reference numerals enclosed in a parenthesis belong to a cross-sectional view taken along line F-F′, and the other reference numerals that are not enclosed in a parenthesis belong to a cross-sectional view taken along line E-E′. Referring to  FIGS. 2 and 12 , the back chambers  61  and  63  of the speaker units (e.g., first speaker group)  31  and  33  located to one side of the resonance chamber  90  and the back chambers  62  and  64  of the speaker units (e.g., second speaker group)  32  and  34  located on another side of the resonance chamber  90  communicate with one another. For example, the first speaker unit  31  and the second speaker unit  33  make a pair and the back chambers  61  and  63  thereof communicate with each other. The first speaker unit  32  and the second speaker unit  34  make a pair and the back chambers  62  and  64  thereof communicate with each other. 
     Due to the above structure, effective capacities of these back chambers may be increased. Air in the back chambers  61  to  64  acts, for example, as a spring when the speaker units  31  to  34  are operated. A spring constant of a vibration system including these speaker units is equal to the sum of a spring constant of a suspension of the diaphragm and a spring constant provided by the air in the back chambers  61  to  64 . A resonant frequency of the vibration system is proportional to the square of the spring constant. When the volumes of the back chambers  61  to  64  increase, the spring constant provided by the air in the back chambers  61  to  64  decreases, thereby lowering the spring constant of the vibration system. Accordingly, the resonant frequency of the vibration gauge decreases and thus low-frequency characteristics of the loudspeaker  1  may be improved. 
     Although the first and second speaker units  30   a  and  30   b  are configured to communicate with one resonance chamber  90  in the above examples, the loudspeaker  1  may include two or more resonance chambers. 
       FIG. 13  is a perspective view illustrating an example loudspeaker  100 .  FIG. 14  is a cross-sectional view of  FIG. 13 , taken along line G-G′.  FIG. 15  is a cross-sectional view of  FIG. 14 , taken along line H-H′.  FIG. 16  is a cross-sectional view of  FIG. 14 , taken along line I-I′. 
     Referring to  FIGS. 13 to 16 , the loudspeaker  100  includes an enclosure  110 , four speaker units  131  to  134  located in the enclosure  110 , and first and second resonance chambers  190   a  and  190   b . In the enclosure  110 , a through-unit (e.g., aperture)  120  passing through at least one of a front wall  113  and a back wall  114  is provided. In the through-unit  120 , first and second acoustic emission apertures  120   a  and  120   b  are provided. The first and second acoustic emission apertures  120   a  and  120   b  communicate with the first and second resonance chambers  190   a  and  190   b  via first and second ducts  191   a  and  191   b , respectively. The through-unit  120  acts as an integrated acoustic emission aperture via which sound is emitted from the speaker units  131  to  134 . Each of the speaker units  131  to  134  includes a diaphragm  131   a  and a motor  131   b  for driving the diaphragm  131   a . The motor  131   b  may employ a moving coil manner or a moving magnet manner. In the example embodiment, the diaphragm  131   a  may have, for example, a round shape. 
     In the enclosure  110 , baffles  141  to  144  in which the speaker units  131  to  134  are respectively disposed are provided. The speaker units  131  and  132  (a first speaker unit  130   a ) are disposed in the baffles  141  and  142  in a first direction Z 1 , e.g., to face the front wall  113  of the enclosure  110 . Back chambers  161  and  162  of the speaker units  131  and  132  are isolated from the first and second resonance chambers  190   a  and  190   b  and front slit spaces  151  and  152 . The speaker units  133  and  134  (a second speaker unit  130   b ) are disposed in the baffles  143  and  144  in a second direction Z 2  opposite the first direction Z 1 , e.g., to face the back wall  114  of the enclosure  110 . The back chambers  163  and  164  of the speaker units  133  and  134  are isolated from the first and second resonance chambers  190   a  and  190   b  and front slit spaces  153  and  154 . The speaker units  131  to  134  and the first and second resonance chambers  190   a  and  190   b  are arranged in a direction perpendicular to the first direction Z 1 . 
     As described above, at least one among the speaker units  131  to  134  is arranged in a direction opposite the direction in which the other speaker units are arranged. Thus, the sum of driving forces of the speaker units  131  to  134  and the sum of moments generated by the driving forces may be reduced. 
     The speaker units  131  to  134  may be disposed in the enclosure  110  in the non-coaxial force-moment compensation structure. The speaker units  131  to  134  are spaced apart the same distance from a center of gravity CP of the loudspeaker  100 . The speaker units  131  and  132  are located to be symmetrical to the center of gravity CP. The speaker units  133  and  134  are located to be symmetrical to the center of gravity CP. Thus, when the speaker units  131  to  134  are driven by the same driving signal, driving forces F generated by the speaker units  131  and  132  in the first direction Z 1  and driving forces F generated by the speaker units  133  and  134  in the second direction Z 2  are offset by each other and thus the sum of the driving forces F generated by the speaker units  131  to  134  becomes ‘0’, Also, since the distances from the speaker units  131  to  134  to the center of gravity CP are the same, the sum of the moments generated by the driving forces F of the speaker units  131  to  134  also becomes ‘0’. Due to the above structure, the non-coaxial force-moment compensation structure may be realized. 
     The front slit spaces  151  and  153  of the speaker units (first speaker group)  131  and  133  are connected to the first resonance chamber  190   a  via first communication apertures  171  and  173 , respectively. The front slit spaces  152  and  154  of the speaker units (second speaker group)  132  and  134  are connected to the second resonance chamber  190   b  via second communication apertures  172  and  174 , respectively. 
     The first and second resonance chambers  190   a  and  190   b  form Helmholtz resonators acting as band-pass amplifiers  125   a  and  125   b , together with first and second ducts  191   a  and  191   b . By appropriately determining the volumes of the first and second resonance chambers  190   a  and  190   b  and the cross-sectional areas and lengths of the first and second ducts  191   a  and  191   b , sound at a desired frequency band may be amplified based on a resonance frequency and emitted via the first and second acoustic emission apertures  120   a  and  120   b.    
     The positions of the first and second acoustic emission apertures  120   a  and  120   b  are not limited within a range in which the first and second ducts  191   a  and  191   b  may be connected to the first and second resonance chambers  190   a  and  190   b . For example, although the first and second acoustic emission apertures  120   a  and  120   b  are formed in the through-unit  120  passing through the front wall  113  and the back wall  114  of the enclosure  110  in the example embodiments of  FIGS. 13 to 16 , the positions of the first and second acoustic emission apertures  120   a  and  120   b  are not limited thereto. For example,  FIGS. 17 and 18  are cross-sectional views illustrating another example loudspeaker  100 . The loudspeakers  100  illustrated in  FIGS. 17 and 18  are substantially the same as the loudspeaker  100  illustrated in  FIG. 14 , except for the positions of first and second acoustic emission apertures  120   a  and  120   b . Referring to  FIG. 17 , the first and second acoustic emission apertures  120   a  and  120   b  are formed in an upper wall  111  of an enclosure  110 . First and second ducts  191   a  and  191   b  extend to the upper wall  111  and respectively connect first and second resonance chambers  190   a  and  190   b  to the first and second acoustic emission apertures  120   a  and  120   b . Referring to  FIG. 18 , the first and second acoustic emission apertures  120   a  and  120   b  are respectively formed in sidewalls  116  and  117  of an enclosure  110 . The first and second ducts  191   a  and  191   b  extend to the sidewalls  116  and  117  and connect first and second resonance chambers  190   a  and  190   b  to the first and second acoustic emission apertures  120   a  and  120   b , respectively. 
     As described above, in the loudspeaker  100  according to the example embodiment, sound emitted from the speaker units  131  and  133  and sound emitted from the speaker units  132  and  134  are respectively collected in the first and second resonance chambers  190   a  and  190   b  and sound at a specific frequency band is then amplified through the Helmholtz resonance action and emitted via the first and second acoustic emission apertures  120   a  and  120   b . Thus, the loudspeaker  100  may be realized in the non-coaxial structure or the non-coaxial force-moment compensation structure having a high degree of freedom of an acoustic radiation direction. The loudspeaker  100  employing the non-coaxial structure or the non-coaxial force-moment compensation structure is effectively applicable to slim type electronic devices. 
     Although the back chambers  161  to  164  are independent and isolated from each other in the example embodiments of  FIGS. 13 to 18 , at least one among the back chambers  161  to  164  may communicate with the other chambers.  FIG. 19  is a cross-sectional view illustrating an example loudspeaker  100   t .  FIG. 19  is a modified example of the loudspeakers  100  illustrated in  FIGS. 13 to 18 .  FIG. 19  illustrates a cross-sectional view of  FIG. 14 , taken along lines J-J′ and K-K′. In  FIG. 19 , reference numerals enclosed in a parenthesis belong to a cross-sectional view taken along line K-K′, and the other reference numerals that are not enclosed in a parenthesis belong to a cross-sectional view taken along line J-J′. Referring to  FIGS. 14 and 19 , back chambers  161  and  163  of speaker units (a first speaker group)  131  and  133  adjacent to a first resonance chamber  190   a  communicate with each other, and back chambers  162  and  164  of speaker units (a second speaker group)  132  and  134  adjacent to a second resonance chamber  190   b  communicate with each other. For example, the first speaker unit  131  and the second speaker unit  133  make a pair and the back chambers  161  and  163  thereof communicate with each other. The first speaker units  132  and the second speaker unit  134  make a pair and the back chambers  162  and  164  communicate with each other. Otherwise, the back chambers  161  to  164  may communicate with one another. Due to the above structure, effective capacities of the back chambers  161  to  164  may be increased and low-frequency characteristics of the loudspeaker  100  may be improved. 
     In the enclosure  110 , an additional chamber  192  may be further provided. The additional chamber  192  may be arranged to balance the weight of the enclosure  110  with respect to the speaker units  131  to  134 . The additional chamber  192  may be isolated from the first and second resonance chambers  190   a  and  190   b  and front slit spaces  151  to  154 . As illustrated in  FIG. 19 , the back chambers  163  and  162  may be connected to the additional chamber  192  via communication apertures  175  and  176 . Due to the above structure, all of the back chambers  161  to  164  may communicate with the additional chamber  192 , thereby greatly increasing effective capacities of the back chambers  161  to  164 . 
     The attenuators  71   a  to  74   a  described above with reference to  FIGS. 8 and 9  are also applicable to the communication apertures  171  to  174  of the loudspeakers  100  illustrated in  FIGS. 13 to 19 . Due to the above structure, the attenuators  71   a  to  74   a  having appropriate aperture ratios may be disposed in the communication apertures  171  to  174  to achieve a desired quality factor Q and improve the articulation of the loudspeaker  100 . 
     The vented enclosure structure and the passive radiator type enclosure structure described above with reference to  FIGS. 10 and 11  are also applicable to the back chambers  161  to  164  of the loudspeakers  100  illustrated in  FIGS. 13 to 19 . Due to the above structure, acoustic energy of the back chambers  161  to  164  may be effectively used to improve the efficiency of the loudspeaker  100 . Also, a small-sized and slim type loudspeaker  100  capable of obtaining the same output may be manufactured. 
     Although the loudspeakers  1  and  100  in which four speaker units are arranged in the non-coaxial force-moment compensation structure are described in the above examples, the number of speaker units is not limited to four.  FIG. 20  is a schematic configuration diagram illustrating an example loudspeaker  400  including, for example, six speaker units  431  to  436 . Referring to  FIG. 20 , an enclosure  410  may, for example, be a disc type. Speaker units  431 ,  433 , and  435  are first speaker units emitting sound in a first direction. Speaker units  432 ,  434 , and  436  are second speaker units emitting sound in a second direction. The speaker units  431  and  436  make a pair and are arranged to be symmetrical to a center of gravity CP. The speaker units  432  and  435  make a pair and are arranged to be symmetrical to the center of gravity CP. The speaker units  433  and  434  make a pair and are arranged to be symmetrical to the center of gravity CP. Due to the above structure, a non-coaxial force-moment compensation structure in which both of the sum of driving forces and the sum of moments are ‘0’ is realized. Front slit spaces of the six speaker units  431  to  436  are connected to a resonance chamber  490  via a communication aperture (not shown). An acoustic emission aperture  420  is connected to the resonance chamber  490  via a duct  491 . The duct  491  and the resonance chamber  490  form a band-pass amplifier  425  together. Due to the above structure, the loudspeaker  400  having a slim type non-coaxial force-moment compensation structure may be realized, in which sound emitted from the speaker units  431  to  436  is collected in the resonance chamber  490  and sound at a specific frequency band is amplified through the Helmholtz resonance action and emitted via the acoustic emission aperture  420 . 
     The vented enclosure structure and the passive radiator type enclosure structure described above with reference to  FIGS. 10 and 11  are also applicable to the back chambers of the loudspeaker  400  of  FIG. 20 . Due to the above structure, acoustic energy of the back chambers may be effectively used to improve the efficiency of the loudspeaker  400 . Also, a small-sized and slim type loudspeaker  400  capable of obtaining the same output may be realized. To adjust the articulation of the loudspeaker  400 , an attenuator configured to apply acoustic resistance may be disposed in the communication aperture connecting the resonance chamber  490  and the speaker units  431  to  436 . Also, the back chambers of the speaker unit  431  to  433  may communicate with one another, and the back chambers of the speaker unit  434  to  436  may communicate with one another. 
       FIG. 21  is a schematic configuration diagram illustrating an example loudspeaker  500  including six speaker units  531  to  536 . Referring to  FIG. 21 , an enclosure  510  may, for example, be a disc type. Speaker units  531 ,  533 , and  535  are first speaker units emitting sound in a first direction. Speaker units  532 ,  534 , and  536  are second speaker units emitting sound in a second direction. The speaker units  531  and  536  make a pair and are arranged to be symmetrical to a center of gravity CP. The speaker units  532  and  535  make a pair and are arranged to be symmetrical to the center of gravity CP. The speaker units  533  and  534  make a pair and are arranged to be symmetrical to the center of gravity CP. Due to the above structure, a non-coaxial force-moment compensation structure in which both of the sum of driving forces and the sum of moments are ‘0’ is realized. 
     The loudspeaker  500  includes first and second resonance chambers  590   a  and  590   b . In the enclosure  510 , first and second acoustic emission apertures  520   a  and  520   b  communicating with an integrated acoustic emission aperture  520  are provided. First and second ducts  591   a  and  591   b  connect the first and second resonance chambers  590   a  and  590   b  to the first and second acoustic emission apertures  520   a  and  520   b , respectively. The first duct  591   a  and the first resonance chamber  590   a  form a band-pass amplifier  525   a  together. The second duct  591   b  and the second resonance chamber  590   b  together form a band-pass amplifier  525   b.    
     Front slit spaces of the speaker units  531  to  533  are connected to the first resonance chamber  590   a  via a communication aperture (not shown). Front slit spaces of the speaker units  534  to  536  are connected to the second resonance chamber  590   b  via a communication aperture (not shown). Due to the above structure, the loudspeaker  500  having a slim type non-coaxial force-moment compensation structure may be realized, in which sound emitted from the speaker units  531  to  533  is collected in the first resonance chamber  590   a  and sound at a specific frequency band is amplified through the Helmholtz resonance action and emitted via the first acoustic emission aperture  520   a , and sound emitted from the speaker units  534  to  536  is collected in the second resonance chamber  590   b  and sound at a specific frequency band is amplified through the Helmholtz resonance action and emitted via the second acoustic emission aperture  520   b.    
     The vented enclosure structure and the passive radiator type enclosure structure described above with reference to  FIGS. 10 and 11  are also applicable to back chambers of the loudspeaker  500  of  FIG. 21 . Due to the above structure, acoustic energy of the back chambers may be effectively used to improve the efficiency of the loudspeaker  500 . Also, a small-sized and slim type loudspeaker  500  capable of obtaining the same output may be realized. In order to control the articulation of the loudspeaker  500 , an attenuator configured to apply acoustic resistance may be located in each of the communication aperture connecting the resonance chamber  590   a  and the front slit spaces of the speaker units  531  to  533  and the communication aperture connecting the resonance chamber  590   b  and the front slit spaces of the speaker units  534  to  536 . The back chambers of the speaker units  531  to  533  may communicate with one another. The back chambers of the speaker units  534  to  536  may communicate with one another. Otherwise, the back chambers of the speaker units  531  to  536  may communicate with an additional chamber  592 . 
     The number of the resonance chambers is not limited to one or two. In the enclosure  510 , three or more resonance chambers communicating with the front slit spaces of two or more speaker units may, for example, be provided. 
     The non-coaxial force-moment compensation structure may be realized with an odd number of speaker units.  FIG. 22  is a schematic configuration diagram illustrating an example loudspeaker  600  with three speaker units  631  to  633 . Referring to  FIG. 22 , the speaker unit  631  is a first speaker unit emitting sound in the first direction Z 1 , and the speaker units  632  and  633  are second speaker units emitting sound in the second direction Z 2 . The speaker unit  631  is located at a center of gravity CP of the loudspeaker  600 . The speaker units  632  and  633  are arranged to be symmetrical to the center of gravity CP. The speaker unit  631  has a driving force of 2F. The speaker units  632  and  633  each have a driving force of F. Due to the above structure, a non-coaxial force-moment compensation structure in which both of the sum of the driving forces and the sum of moments are ‘0’ may be realized. Front slit spaces of the speaker units  631  to  633  are connected to a resonance chamber  690  via a communication aperture (not shown). An acoustic emission aperture  620  is connected to the resonance chamber  690  via a duct  691 . The duct  691  and the resonance chamber  690  together form a band-pass amplifier  625 . 
     Due to the above structure, a slim type non-coaxial force-moment compensation structure loudspeaker  600  may be realized, in which sound emitted from the speaker units  631  to  633  is collected in the resonance chamber  690  and sound at a specific frequency band is amplified through the Helmholtz resonance action and emitted via the acoustic emission aperture  620 . In addition, an odd number of speaker units, e.g., five, seven, or more speaker units, may be arranged in the force-moment compensation structure. 
     The vented enclosure structure and the passive radiator type enclosure structure described above with reference to  FIGS. 10 and 11  are also applicable to the back chambers of the loudspeaker  600  of  FIG. 22 . In order to control the articulation of the loudspeaker  600 , an attenuator configured to apply acoustic resistance may be disposed in the communication aperture connecting the resonance chamber  690  and the front slit spaces of the speaker units  631  to  633 . The back chambers of the speaker units  631  to  633  may communicate with one another. The back chambers of the speaker units  631  to  633  may communicate with an additional chamber  692 . 
     Although as a band-pass amplifier to prevent a decrease in a sound output, a Helmholtz resonator in which an acoustic emission aperture is connected to a resonance chamber via a duct is disclosed in the above examples, a structure preventing a decrease in a sound output is not limited thereto. 
       FIG. 23  is a schematic configuration diagram illustrating an example loudspeaker  700 . The loudspeaker  700  according to the present example is substantially the same as the loudspeaker  1  of  FIG. 2 , except that a passive radiator  701  that replaces the above duct  91  forms a band-pass amplifier  26  together with a resonance chamber  90 . The resonance chamber  90  and the passive radiator  701  together form a resonator. The bandwidth of sound emitted from speaker units  31  to  34  is amplified and the sound is emitted via an acoustic emission aperture  20 . 
     If the mass of a diaphragm of the passive radiator  701  is m and the sum of a spring constant of a suspension supporting the diaphragm and a spring constant provided by air in the resonance chamber  90  is K, a resonance frequency fi of the resonator formed by the resonance chamber  90  and the passive radiator  701  may be determined using the formula 
               f   1     =       1     2   ⁢   π       ⁢         k   m       .             
Thus, by appropriately determining the volume of the resonance chamber  90 , the mass of the diaphragm of the passive radiator  701 , and the spring constant of the suspension, sound at a desired frequency band may be amplified based on the resonant frequency fi and emitted via the acoustic emission aperture  20 . Thus, an effect obtained when a Helmholtz resonator is used may be achieved. The ducts of  FIGS. 14, 17, 18, 20, 21, and 22  may be also replaced with the passive radiator  701 .
 
     As described above, even if a plurality of speaker units are arranged in the non-coaxial structure, vibration occurs during an operation of a loudspeaker when both of the sum of driving forces and the sum of moments are not ‘0’. An electronic device in which the loudspeaker is installed may be negatively influenced by the vibration. In order to decrease the vibration, a vibration isolation structure may be provided in the loudspeaker.  FIG. 24  is a schematic perspective view illustrating an example loudspeaker  800 .  FIG. 25  is a cross-sectional view of  FIG. 24 , taken along line M-M′. The loudspeaker  800  of  FIG. 24  is substantially the same as the loudspeaker  1  of FIG.  1 , except that a structure configured to decrease vibration is employed. Referring to  FIGS. 24 and 25 , in an enclosure  10 , a coupling unit  810  configured to couple the loudspeaker  800  to an electronic device (not shown) is provided. For example, the coupling unit  810  may be extended to the outside of the enclosure  10 . In the coupling unit  810 , for example, an engagement hole  811  configured to be engaged with a screw may be provided. The loudspeaker  800  may include a vibration isolation member  820  interposed between the coupling unit  810  and the electronic device. The vibration isolation member  820  may be formed of a material having a vibration isolation property, e.g., rubber, felt, sponge, etc. The vibration isolation member  820  may be interposed between the loudspeaker  800  and the electronic device to decrease vibration to be transferred from the loudspeaker  800  to the electronic device. The vibration isolation member  820  is also applicable to a loudspeaker having the non-coaxial force-moment compensation structure. 
     The loudspeaker  800  according to the example embodiment is applicable to various types of electronic devices. For example, the loudspeaker  800  is applicable to display apparatuses such as flat panel TVs, monitors, etc. and slim type or small-sized electronic devices such as sound bars, etc. For example, the loudspeaker  800  may be employed as a woofer system for an electronic device. 
       FIG. 26  illustrates an example display apparatus  3  employing a loudspeaker. Referring to  FIG. 26 , the display apparatus  3  includes a housing  302  configured to accommodate a flat panel display  301 . In the housing  302 , an acoustic emission aperture  303  is provided. In the housing  302 , the loudspeaker  1  of  FIG. 1  may be disposed. 
     As illustrated in  FIG. 26 , when a space between edges of the housing  302  and the display  301 , e.g., the frame of the display apparatus  3 , is thin, the acoustic emission aperture  303  may be provided in a lower or side surface of the housing  302 . In the example embodiment, the acoustic emission aperture  303  is provided in the lower surface of the housing  302 . The loudspeaker  1  is disposed in the housing  302  such that the upper wall  11  faces downward and the acoustic emission aperture  20  faces the acoustic emission aperture  303 . 
     Although not shown, the acoustic emission aperture  303  may be provided in a side surface of the housing  302 . In this case, the loudspeaker  1  of  FIG. 1  is disposed in the housing  302  such that the upper wall  11  faces the side surface of the housing  302  and the acoustic emission aperture  20  faces the acoustic emission aperture  303 . 
     Due to the above structure, sound may be emitted directly from the loudspeaker  1  via the acoustic emission aperture  303  without any change in a sound direction. Thus, a sound duct having a complicated structure need not be installed in the housing  302 . Furthermore, the display apparatus  3  may be manufactured to have a slim structure with a smooth design, in which no aperture is formed in the front and back surfaces of the housing  303 . 
       FIG. 27  illustrates the display apparatus  3  employing a loudspeaker according to another example embodiment. Referring to  FIG. 27 , the display apparatus  3  includes a housing  302  configured to accommodate a flat panel display  301 . An acoustic emission aperture  303  may be provided in the housing  302 . An acoustic emission aperture  303  may be formed in a front surface of the housing  302 . The loudspeaker  1  of  FIG. 5  or the loudspeaker  100  of  FIG. 13  may be disposed in the housing  302  such that the front wall  13  or  113  faces the front surface of the housing  302  and the acoustic emission aperture  20  or the acoustic emission apertures  120   a  and  120   b  may face the acoustic emission aperture  303 . 
     Although not shown, the acoustic emission aperture  303  is provided in a back surface of the housing  302 , and the loudspeaker  1  of  FIG. 5  or the loudspeaker  100  of  FIG. 13  may be disposed in the housing  302  such that the front wall  13  or  113  faces the back surface of the housing  302  and the acoustic emission aperture  20  or the acoustic emission apertures  120   a  and  120   b  face the acoustic emission aperture  303 . 
     Due to the above structure, sound may be emitted directly from the loudspeaker  1   100  via the acoustic emission aperture  303  without any change in a sound direction. Thus, the display apparatus  3  may be manufactured to have a slim structure not including a sound duct having a complicated structure and installed in the housing  302 . 
     In the loudspeakers according to the above example embodiments, a plurality of speaker units may be employed to secure a large acoustic emission area. Since sound emitted from the plurality of speaker units are collected and emitted to the outside of an enclosure, a degree of freedom of an acoustic emission direction may be increased. The bandwidth of sound emitted from the plurality of speaker units may be band-pass amplified and the sound may be emitted to the outside of the enclosure, thereby reducing degradation in an acoustic power level. The plurality of speaker units may be arranged in the non-coaxial structure or the non-coaxial force-moment compensation structure in order to reduce vibration of the loudspeaker. Furthermore, an attenuator may be employed to improve the articulation of sound. 
     The loudspeakers illustrated in  FIGS. 1 to 25  may function as a slim type stand-along woofer system. 
     Although a display apparatus is described as an example of an electronic device in the above examples, examples of the electronic device may include a personal computer (PC), a notebook computer, a mobile phone, a tablet PC, a navigation terminal, a smart phone, a personal digital assistant (PDA), a portable multimedia player (PMP), and a digital broadcasting receiver, or the like. In addition, the electronic device may be understood to include various types of apparatuses having a communication function that have been developed and put on the market or that will be developed in near future. 
     It should be understood that example embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each example embodiment should typically be considered as available for other similar features or aspects in other example embodiments. 
     While one or more example embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.