Abstract:
A speaker structure having a simple configuration while maintaining good sound quality is disclosed. The speaker structure comprises a first speaker ( 20 ) having a first vibration plate ( 21 ), a first frame ( 22 ) for fixing the perimeter of the first vibration plate and a first magnetic circuit ( 24 ) for converting a signal into the vibration of the first vibration plate, a second speaker ( 30 ) having a second vibration plate ( 31 ), a second frame ( 32 ) for fixing the perimeter of the second vibration plate and a second magnetic circuit ( 34 ) for converting a signal into the vibration of the second vibration plate, and a fixing unit ( 50 ) for fixing the first magnetic circuit and the second magnetic circuit at their backs.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a speaker structure.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 7 is a section view of a prior art speaker structure. In FIG. 7, the reference numeral  100  denotes a box-style cabinet which is equipped with a speaker  200 . The speaker  200  comprises a cone  201 , a frame  202 , a voice coil  203 , a magnetic circuit  204 , etc. The magnetic circuit  204  comprises a plate  205 , a magnet  206 , a yoke  207 , etc. The speaker  200  is fixed at the front face of the cabinet  100  with screws  101 .  
           [0005]    In this prior art structure, vibration of the speaker is easily transmitted to the cabinet, and thereby an out-of-phase sound is generated by the cabinet. This is a cause of muddiness of the sound which is output from the speaker structure. In addition, when a sound is generated at the cone  201 , reaction to the movement of the cone  201  arises on the yoke  207 . Since the yoke  207  is apt to vibrate, the efficiency of energy transmission from the corn to air is low. This causes a bad transient characteristic of the sound (feeling of the sound speed) which is output from the speaker structure.  
           [0006]    In order to solve such problems, speaker structures wherein a speaker is fixed at the front face of a cabinet, and a yoke of the speaker is supported directly by a supporting rod of the speaker structure, have been proposed in the patent applications of publications (Kokai) No. 11-146471 and No. 5-153680. However, due to low structural strength of these speaker structures, there has been such a problem that the speaker structure mounted in a car is broken due to the vibration of the car in motion. Increasing the strength of the speaker structure brings new problems such as increasing its weight and making its structure more complex.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to provide a speaker structure with a simple configuration while maintaining good sound quality to solve the problems stated above.  
           [0008]    In order to achieve the above object, the speaker structure comprises a first vibration plate, a first frame for fixing the perimeter of the first vibration plate, a first speaker having a first magnetic circuit for converting a signal to the vibration of the first vibration plate, a second vibration plate, a second frame for fixing the perimeter of the second vibration plate, and a second speaker having a second magnetic circuit for converting a signal to the vibration of the second vibration plate, and a fixing unit for fixing the first magnetic circuit and the second magnetic circuit at their backs.  
           [0009]    In addition, it is preferable that the speaker structure has a means for supplying the same signals in phase to the first and the second magnetic circuits.  
           [0010]    It is also preferable that the speaker structure has a cabinet for covering the first and second speakers, a supporting means for supporting the fixing unit, a shock absorber placed between the first frame and the cabinet, a shock absorber placed between the second frame and the cabinet, and a shock absorber placed between the supporting means and the cabinet, and thereby the cabinet is kept in floating state compared to the first and second speakers and the supporting means.  
           [0011]    It is also preferable that the speaker structure has guides to be engaged with the edges of the cabinet, provided on the backs of the first and second frames.  
           [0012]    It is also preferable that the speaker structure has a door unit provided on the cabinet.  
           [0013]    It is also preferable that the fixing unit has a first rib fixed at the first magnetic circuit, a second rib fixed at the second magnetic circuit, and a connecting unit for connecting the first and the second ribs.  
           [0014]    It is also preferable that the speaker structure has a intermediate supporter which is fixed at the fixing unit and has contact with the inner surface of the cabinet, and it is also preferable that the intermediate supporter is in contact with the inner surface of the cabinet via a shock absorber, and that a sound absorber is mounted on the intermediate supporter.  
           [0015]    It is also preferable that the cabinet has an opening for air discharging. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a drawing showing a speaker structure according to the first embodiment of the present invention.  
         [0017]    [0017]FIG. 2 is a drawing showing a speaker structure in which a plurality of the speaker structures shown in FIG. 1 are arranged in a single cabinet.  
         [0018]    [0018]FIG. 3 is a drawing showing a speaker structure according to the second embodiment of the present invention.  
         [0019]    [0019]FIG. 4 is a drawing showing a speaker structure according to the third embodiment of the present invention.  
         [0020]    [0020]FIG. 5 is a plan view of the cabinet  13 .  
         [0021]    [0021]FIG. 6 is a perspective view of the speaker structure shown in FIG. 4.  
         [0022]    [0022]FIG. 7 is a drawing showing a prior art speaker structure. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring to the drawings, preferred embodiments of the present invention are described below.  
         [0024]    [0024]FIG. 1 is a section view showing a speaker structure according to the first embodiment of the present invention. In FIG. 1, reference numeral  10  denotes a cylindrical hollow cabinet, and reference numerals  20  and  30  denote a speaker. The speaker  20  comprises a cone  21  which is a vibration plate, a frame  22  for fixing the perimeter of the cone  21 , a voice coil  23  for vibrating the cone, a magnetic circuit  24 , a terminal  28 , etc. The magnetic circuit  24  comprises a plate  25 , a magnet  26 , yoke  27 , etc. The speaker  30  comprises a cone  31 , a frame  32 , a voice coil  33 , a magnetic circuit  34 , a terminal  38 , etc. The magnetic circuit  34  comprises a plate  35 , a magnet  36 , yoke  37 , etc. It is preferable that the speaker  20  and  30  are completely identical in configuration and shape but they may have, at least, a cone with the same diameter, and a magnetic circuit with the same shape.  
         [0025]    A rib  50  is fixed at a yoke  27  of the speaker  20  and a yoke  37  of the speaker  30  at their symmetrically opposed positions. Although the rib  50  is fixed at both yokes as shown in FIG. 1, the rib  50  may be fixed anywhere on the magnetic circuit. Thus the speaker  20  and the speaker  30  are coupled via the rib  50 . The rib  50  comprises a cylindrical metal, etc., and it is preferable that the rib  50  does not have a constant cross sectional area throughout its length so that the rib  50  itself does not resonate. In other word, a so-called barrel-style rib is preferable which has small cross sectional area at the both ends connected to the yoke  27  and yoke  37 , and large cross sectional area at the center part.  
         [0026]    A guide  29  ( 39 ) is provided at the back of the perimeter of the frame  22  ( 32 ) for the speaker  20  ( 30 ). The cabinet  10  is so configured that it is engaged with the guides  29  and  39  via shock absorbers  42  at the entirety of both edges and is thus positioned. The shock absorbers  42  are placed between the speakers  20 ,  30  and the cabinet  10  to secure airtightness of the cabinet  10 . The shock absorbers  42  also keep the speakers  20  and  30  in a floating state without fixing them to the cabinet. As stated above, the speakers  20  and  30  are kept in floating state compared to the cabinet  10 , and thereby the vibrations of the speakers  20  and  30  are not transmitted to the cabinet  10  directly.  
         [0027]    The shock absorbers  42  may be made of a material which at least has a cushion, keeps airtightness, and does not transmit the vibrations of the speakers  20  and  30  to the cabinet  10  directly. In addition, it is desired that the shock absorber is of a material which attenuates the signals of speakers  20  and  30  by 60 dB or more in their reproduction bandwidth. PEF is an example of such a material.  
         [0028]    Signals such as audio signals are supplied to each speaker through an input terminal  40 , a connecting wire  41 , and terminals  28  and  38 . It is preferable that the signals to be supplied to each speaker are the same signals in phase, and generate the same sound from each speaker at the same time. When the same signals in phase are supplied to each speaker, the reactions of each speaker, due to the vibrations of the yokes, are canceled out through the rib  50 .  
         [0029]    As stated above, two speakers are arranged back to back and connected via the rib, and thereby it is possible that the vibration of the yoke is suppressed efficiently and that the sound exchanging efficiency of the cone is increased. In addition, since each speaker is kept in floating state compared to the cabinet, it is possible that the vibration of the yoke is hardly transmitted to the cabinet, and that the ringing of the cabinet is reduced. It is also possible that the noise generated by the speakers is reduced.  
         [0030]    If the two speakers are connected back to back without a rib, it is not possible to provide sufficient space in the cabinet, especially in the rear of each cone, and thereby there may be a problem that it is not possible to generate a good sound, and there may also be a problem that design flexibility is reduced. From the reasons stated above, it is important that the two speakers are fixed each other via a fixing unit comprising a rib, etc. allowing a space between the two speakers.  
         [0031]    [0031]FIG. 2 illustrates an example of a speaker apparatus wherein four sets of speaker structures according to the first embodiment stated above are arranged in a single box-style cabinet  11 . As illustrated in this figure, speakers  20   a ,  20   b ,  20   c  and  20   d  are arranged at the front side of the figure, and speakers  30   a ,  30   b ,  30   c  and  30   d  are arranged at the other side of the figure opposed to speakers  20   a ,  20   b ,  20   c  and  20   d  respectively. Each speaker illustrated in FIG. 2 is a small speaker having a cone diameter of 10 to 40 cm.  
         [0032]    As stated above, multiple sets of pairs of speakers, which are fixed via a rib on their magnetic circuit, are mounted in the single cabinet, and thereby it is possible to raise the volume of reproduced low frequency sound while capitalizing on the low distortion characteristics of small speakers.  
         [0033]    [0033]FIG. 3 is a section view of a speaker structure according to the second embodiment of the present invention.  
         [0034]    The second embodiment is a variation of the first embodiment, and only the shape of cabinet covering the two speakers  20  and  30  is different from the first embodiment. In the second embodiment, the cabinet comprises a cylindrical hollow body  12   a  similar to the cabinet  10  as shown in FIG. 1, and a cylindrical hollow projection part  12   b  projecting upward from the body  12   a . The top end of the projection part  12   b  is open to let the air escape.  
         [0035]    Regarding the dimensions of the projection part  12 , for example, C=12 cm and D=100 cm is preferable in case of A=12 cm and B=20 cm, where, A is the diameter of the cones  21  and  31  of the speakers  20  and  30 , B is the length of the body  12   a , C is the diameter of the projection part  12   b , and D is the length of the projection part  12   b.    
         [0036]    Since the top end of the projection part  12   b  is opened as shown in FIG. 3, the resonance frequency may be reduced by the opening, and thereby the ability for reproducing low frequency sound of the speaker may be improved.  
         [0037]    [0037]FIG. 4 is a section view of a speaker structure according to the third embodiment of the present invention.  
         [0038]    In FIG. 4, reference numeral  13  denotes a cylindrical hollow cabinet, and the reference numerals  20  and  30  denote a speaker similar to the speaker of the first embodiment.  
         [0039]    One end of the rib  51  is fixed at the yoke  27  of the speaker  20 . The other end of the rib  51  is threaded, thereby being connected to the connecting unit  54  by screwing. Likewise, one end of the rib  52  is fixed at the yoke  37  of the speaker  30 , and the other end of the rib  52  is threaded, thereby being connected to the connecting unit  54  by screwing.  
         [0040]    One end of the rib  51  and one end of the rib  52  are fixed at yokes  27  and  37  respectively as shown in FIG. 4, but may be fixed at any parts of the magnetic circuits  24  and  34  respectively. Thus, the speaker  20  and the speaker  30  are coupled via the rib  51 , the rib  52  and the connecting unit  54 . The ribs  51  and  52  comprises cylindrical metal, etc, and it is preferable that the ribs  51  and  52  do not have a constant cross sectional area throughout their length so that they do not resonate by themselves. The connecting unit  54  is fixed at a stand  60 . Furthermore, it is preferable that the ribs  51  and  52  are fixed, at the magnetic circuits  24  and  34  respectively, at their symmetrically opposed center positions, and thereby it is possible to reduce the resonance of the ribs  51  and  52 .  
         [0041]    [0041]FIG. 5 is a bottom view of the cabinet  13 . The speaker  20  is mounted at the lower part of the figure, and the speaker  30  is mounted at the upper part of the figure. An opening  15  for the stand  60  is provided at the bottom of the cabinet, and doors  14   a  and  14   b  are provided around the opening. The doors  14   a  and  14   b  are mounted on the cabinet  13  by means of hinges so as to be opened from side to side frontward in the figure. Opening the doors  14   a  and  14   b  makes mounting the stand  60  to the connecting unit  64  and wiring inside the cabinet easy.  
         [0042]    The entire edges of the cabinet  13  are positioned by the frames  22  and  32  of speakers, and the shock absorbers  42 . And also a shock absorber  42  is placed between the doors  14   a ,  14   b  of the cabinet  13  and the stand  60 . These shock absorbers  42  secure airtightness of the cabinet  10 , and keep the cabinet  13  in floating state compared to the speakers  20  and  30 , and also to the stand  60 . As stated above, the cabinet  13  is kept in floating state compared to the speakers  20  and  30  and to the stand  60 , and thereby vibrations of the speakers  20  and  30  are not transmitted to the cabinet  13  directly. The materials and so on of the shock absorbers  42  are similar to ones for the first embodiment aforementioned.  
         [0043]    Additionally, a intermediate supporter  70  is provided inside the cabinet  13  to stabilize the rib  51 . The intermediate supporter  70  comprises a ring  71 , a base  72  fixed at the rib  51 , columns  73  for fixing the ring  71  and the base  72 , and a shock absorber  74 . The intermediate supporter  70  is in contact with the inner wall of the cabinet  13  via the shock absorber  74 . FIG. 6 is a perspective view showing the inside of the cabinet. According to FIG. 6, it can be understood how the intermediate supporter  70  is fixed at the rib. Using this intermediate supporter  70 , the relative position of the rib  51  to the cabinet  13  may be kept constant, and the rib may be stabilized accordingly. Felt or the like is suitable for the material of the shock absorber  74 . In addition, it is preferable to wrap a sound absorber such as glass fiber around the columns  73 . The intermediate supporter  70  is fixed at only the rib  51  as shown in FIG. 4, but a similar intermediate supporter may be provided for the rib  52 .  
         [0044]    Signals such as audio signal are supplied to each speaker through a input terminal, a connecting wire, and terminals, as in the first embodiment, which are not shown in FIG. 4. It is preferable, as in the first embodiment, that signals to be supplied to each speaker are the same signals in phase, and generate the same sound from each speaker at the same time. When the same signals in phase are supplied to each speaker, reactions of each speaker due to the vibration of the cones are canceled out through the ribs  51  and  52 , and connecting unit  54 .  
         [0045]    An example of how to assemble the speaker structure according to the third embodiment is described below. First, the rib  51  fixed at the speaker  20  is fixed to the connecting unit  54  by screwing. Then, the guide  29  of the speaker  20  is engaged with a end of the cabinet  13  via the shock absorber  42 . After that, the speaker  30  and the rib  52  fixed at the speaker  30  are inserted from the other end of the cabinet  13  in such a way that the rib  52  is screwed into the connecting unit  54 . Then the rib  52  is fixed to the connecting unit  54  by screwing in such a way that the guide  39  of the speaker  30  is engaged with the other end of the cabinet  13  via the shock absorbers  42 . After the above procedures, the speakers  20  and  30  are secured by the ribs  51  and  52 , and the connecting unit  54 , and the cabinet  13  is positioned between the guides of the speakers  20  and  30 .  
         [0046]    After that, the doors  14   a  and  14   b  of the cabinet are opened, and the stand  60  is inserted through the opened the doors, and then connecting unit  54  is fixed to the stand  60 . Furthermore, predetermined wiring for each speaker is carried out. Lastly, the doors  14   a  and  14   b  are closed in such a way that the shock absorber  42  is positioned between the doors  14   a ,  14   b , and the stand  60 . According to the above procedures, the speaker structure of the third embodiment is assembled.  
         [0047]    As stated above, the two speakers are fixed to each other via fixing devices including ribs allowing spacing between the two speakers, and thereby it is possible that the vibration of the yoke is suppressed efficiently and the sound exchanging efficiency of the cone is increased.  
         [0048]    When the same signals in phase are supplied to the two speakers, the forces by which the yokes of the speakers push or pull each other are canceled out and, thereby, the vibration of the yoke is suppressed efficiently.  
         [0049]    In addition, when each speaker is kept in a floating state compared to the cabinet, the vibrations of the yokes are hardly transmitted to the cabinet and the abnormal sound of the cabinet is reduced. The noise generated by the speakers are is also reduced.  
         [0050]    Furthermore, the speaker structure is so configured that it is assembled while pulling both speakers by the connecting unit  54 , thereby may be steady regardless of the vibration during transportation.