[0001]    This application claims the benefit of Japanese Application No. 09-90302, filed in Japan on Mar. 25, 1997, which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to a speaker apparatus and a manufacturing method thereof.  
           [0004]    2. Discussion of the Related Art  
           [0005]    In a speaker apparatus for converting electric signals to acoustic energy, a so-called electrokinetic cone type speaker unit has conventionally been used.  
           [0006]    [0006]FIG. 11 shows an example of such a speaker unit. Referring to FIG. 11 , a cylindrical voice coil bobbin  103 , around which voice coil  102  is wound, is provided at the center of a diaphragm  101  (cone) of the cone type speaker unit.  
           [0007]    The diaphragm  101  and the voice coil bobbin  103  are fixed to one end of a ring-shaped edge  108  and a damper  109  having appropriate compliance and stiffness. The other ends of the edge  108  and damper  109  are fixed to a frame  112  equipped with a magnetic circuit  107 , so that the frame  112  elastically supports the diaphragm  101  and voice coil bobbin  103 .  
           [0008]    The edge  108  and damper  109  support the voice coil  102  and voice coil bobbin  103  at respective predetermined positions in a magnetic gap of the magnetic circuit  107 , which is constituted of a magnet  104 , a plate  105 , a pole yoke  106 , and the like. With this structure, the diaphragm  101  is elastically supported without contacting the magnetic circuit  107  so as to be capable of vibrating like a piston in a predetermined direction within a predetermined amplitude range.  
           [0009]    The leads of the voice coil  102  are connected to the respective ends of a pair of conductive lead wires  111 . The other ends of the paired lead wires  111  are connected to a pair of terminals  110  provided on the frame  112 .  
           [0010]    Thus, when an electric current carrying acoustic signals is supplied from the terminals  110  to the voice coil  102  through the lead wires  111 , the voice coil  102  is driven in the magnetic gap of the magnetic circuit  107  along the piston vibration direction of the diaphragm  101 . As a result, the diaphragm  101  vibrates together with the voice coil  102  and voice coil bobbin  103 , and converts the electric signals to acoustic energy, thereby producing acoustic waves.  
           [0011]    A center cap  113  is fixed on the diaphragm  101  to cover a center hole at the center of the diaphragm  101 , and moves integrally with the diaphragm  101 . With this structure, the structural strength between the diaphragm  101  and voice coil  102  is intensified, thereby minimizing undesirable separate vibrations of diaphragm  101  and voice coil  102 .  
           [0012]    Further, because the center cap  113  vibrates integrally with the diaphragm  101 , the center cap  113  also contributes to the generation of acoustic radiation power (mainly high frequency range) and also to phase correction of acoustic wave interference due to the shape of the diaphragm  101  by changing acoustic characteristics. Thus, the influences of the center hole of the diaphragm  101  on the acoustic characteristics can be corrected as desired.  
           [0013]    The conventional electrokinetic cone speaker unit is constructed in the above manner and is manufactured by the manufacturing method shown in FIGS.  12 A- 12 C and  13 A- 13 D.  
           [0014]    FIGS.  13 A- 13 D show the manufacturing steps of the cone type speaker unit of FIG. 11. FIGS.  12 A- 12 C show a preparatory process therefor.  
           [0015]    First, the preparatory process will be described with reference to FIGS.  12 A- 12 C FIG. 12A is a cross-sectional view showing a structure of a coil gauge  114  with the preparatory process in which the coil gauge  114  is set in a frame assembly including the frame  112  and the magnetic circuit  107 .  
           [0016]    Referring to FIG. 12A, the coil gauge  114  is formed by bonding a cylindrical coil holding portion  114   b,  made of a resin film or the like and having a predetermined thickness, to a cylindrical surface of a main unit  114   a,  made of metal or the like.  
           [0017]    The outer diameter D 1  of the cylindrical surface of the main unit  114   a  (or inner diameter of the coil holding portion  114   b ) is substantially equal to the diameter of the center pole located at the center of the pole yoke  106 . Accordingly, the coil gauge  114  is designed such that the coil holding portion  114   b  is removably fitted to the center pole of the pole yoke  106 , as shown in FIG. 12C.  
           [0018]    The outer diameter D 2  of the coil holding portion  114   b  is substantially equal to the inner diameter D 3  of the voice coil bobbin  103 , as shown in FIG. 12B. Accordingly, the coil holding portion  114   b  is designed to hold the voice coil bobbin  103  in such a manner that the voice coil bobbin  103  can be removably fitted to the coil holding portion  114   b.    
           [0019]    As shown in FIG. 12B, the voice coil bobbin  103 , having the voice coil  102  wound thereon, is fitted to the coil gauge  114 . As shown in FIG. 12C, this coil gauge  114  is fitted to the center pole of the magnetic circuit  107 . This completes the preparatory process.  
           [0020]    As a result of the preparatory process above, voice coil bobbin  103  and voice coil  102  are held in the magnetic gap of the magnetic circuit  107  without contacting the center pole of the pole yoke  106  or the plate  105 . Also, the positions of the voice coil bobbin  103  and the voice coil  102  relative to the pole yoke  106  and plate  105  are determined.  
           [0021]    The next stage of the manufacturing process will be explained with reference to FIG. 13A to FIG. 13D First, as shown in FIG. 13A, the damper  109  is placed at a predetermined position in the frame assembly. Then, the coil gauge  114 , on which the voice coil bobbin  103  and voice coil  102  have been mounted in the preparatory process explained above is inserted into the center hole of the damper  109  and fitted to the center pole of the pole yoke  106 .  
           [0022]    Next, the inner circumference and the outer circumference of the damper  109  are fixed to the voice coil bobbin  103  and the frame assembly, respectively, with an adhesive agent. Here, the leads of the voice coil  102  are extracted to the upper side of the damper  109 .  
           [0023]    As shown in FIG. 13B, the diaphragm  101  having the edge  108  attached thereto is placed on the frame assembly, and the position of the diaphragm  101 , relative to the voice coil  102 , is fixed. Then, the outer circumference of the edge  108  is fixed to the frame assembly and the inner circumference of the diaphragm  101  is fixed to the voice coil bobbin  103  with an adhesive agent or the like. Because the motion of the voice coil bobbin  103  is restricted by the coil gauge  114 , the relative positional relationship between the voice coil  102  and diaphragm  101  remains fixed during the attachment of the diaphragm  101 .  
           [0024]    As shown in FIG. 13C, each lead of the voice coil  102  is soldered to an eyelet on the diaphragm  101 . The coil gauge  114  is then removed from the voice coil bobbin  103 .  
           [0025]    Next, the center cap  113  is fixed at the center of the diaphragm  101  with an adhesive agent, as shown in FIG. 13D. On the back side of the diaphragm  101 , the ends of the voice coil  102  are connected to a pair of terminals  110  through the paired lead wires  111 . The cone type speaker unit is thus completed.  
           [0026]    As described above, during the manufacture of the cone type speaker unit, the relative positions of the diaphragm  101 , damper  109 , and voice coil bobbin  103  need to be fixed with high precision. Therefore, until the diaphragm  101  and damper  109  are fixed to the voice coil bobbin  103  with an adhesive agent, the coil gauge  114  is necessary. For this reason, a center hole slightly larger than the maximum diameter of the coil gauge  114  at the center of the diaphragm  101  must be created.  
           [0027]    Because the structural strength of the diaphragm  101  is reduced by this center hole, the center cap  113  normally is used to reinforce the structure. However, to form the diaphragm  101  having high stiffness with a predetermined thickness, it is preferable to form the diaphragm  101  and the center cap  113  as one piece.  
           [0028]    The diaphragm  101  needs to have a high stiffness and to radiate acoustic waves with the same or equivalent phases throughout its entire vibrating regions without interference. To satisfy this requirement, a single-piece integrated diaphragm, such as a flat diaphragm formed of high stiffness material, has been used.  
           [0029]    FIGS.  14 A- 14 C show part of the manufacturing process for such a flat speaker unit using the flat diaphragm. In the figures, the same reference numerals as in FIGS.  11 - 13 D correspond to the same or like components.  
           [0030]    As shown in FIG. 14A, a frame  115  for the flat speaker unit is installed on the magnetic circuit  107  to constitute a frame assembly. The damper  109  is placed at a predetermined position of the frame assembly. Then, the coil gauge  114 , on which the voice coil bobbin  103  and voice coil  102  have been fitted in the preparatory process illustrated in FIGS.  12 A- 12 C, is inserted into the center hole of the damper  109  and fitted to the center pole of pole yoke  106 .  
           [0031]    The inner circumference and the outer circumference of the damper  109  are fixed to the voice coil bobbin  103  and the frame assembly, respectively, with an adhesive agent. Here, the leads of the voice coil  102  are extracted to the upper side of the damper  109 .  
           [0032]    As shown in FIG. 14B, the leads of the voice coil  102  are connected to a pair of the terminals  110  through paired lead wires  111 . The coil gauge  114  is then removed from the voice coil bobbin  103  having the damper  109  fixed thereto.  
           [0033]    Next, as shown in FIG. 14C, a flat diaphragm  117  having an edge  116  attached thereto is placed on the frame assembly and is placed at a predetermined position relative to the voice coil  102 . Then, the outer circumference of the edge  116  is attached to the frame assembly with an adhesive agent, and the back side of the diaphragm  117  is attached to the voice coil bobbin  103 .  
           [0034]    Unlike the cone type speaker unit described above in this case, the flat diaphragm  117  is used, and thus, it is not necessary to reinforce the diaphragm with the center cap  113 .  
           [0035]    As described above, connection of the lead wires  111  in the flat speaker unit is carried out before the diaphragm  117  installed. In the case of the cone type speaker unit above, because the diaphragm  101  is formed to be cone-shaped, a sufficient space is provided to allow connection work of the lead wires  11  in the back of the diaphragm  101  even after the diaphragm  101  is fixed. However, if the flat speaker unit is manufactured using the same method, the diaphragm  117  is flat shaped. Therefore, a gap between the diaphragm  117  and damper  109  is much narrower, and connection work of the lead wires  111  is difficult.  
           [0036]    However, in this type of speaker unit, as described above, the coil gauge  114  is removed and the diaphragm  117  is positioned and fixed to the voice coil bobbin  103  that is floatably supported by the damper  109  in the installation process. Thus, the voice coil bobbin  103  and diaphragm  117  can move during the installation work of the diaphragm. Therefore, they may not be fixed with a desired positional relationship.  
           [0037]    As a result, the relative position between the voice coil  102  of the speaker unit and magnetic circuit  107  may change and/or the voice coil  102  and voice coil bobbin  103  may contact the pole yoke in a gap of the magnetic circuit  107 . In such cases, electric signals supplied to the voice coil  102  cannot be efficiently converted into acoustic energy to reproduce sound.  
           [0038]    Therefore, in the manufacture of the conventional flat speaker units, the compliances of the damper  109  and edge  116  should be limited within an appropriate range to facilitate the installation process of the voice coil bobbin  103  and diaphragm  117 .  
           [0039]    However, the compliances of the damper  109  and edge  116  need to have larger values when the low frequency reproduction range is to be expanded by lowering the minimum resonance frequency (ƒ 0 ) of the flat speaker unit. Also, damper  109  and edge  116  need to have large compliances in order to raise the acoustic pressure of the diaphragm  117  by enlarging the vibration range (amplitude) of the voice coil  102 . That is, the larger compliances are necessary to improve acoustic characteristics, such as reproduction frequency range of the flat speaker unit, maximum acoustic pressure, and the like. However, as long as the above-mentioned manufacturing method is used, there is a limit in setting of the compliances of the damper  109  and edge  116 , and therefore, it is difficult to improve the acoustic characteristics of the speaker unit.  
         SUMMARY OF THE INVENTION  
         [0040]    Accordingly, present invention is directed to a speaker apparatus and a manufacturing method thereof that substantially obviate the problems due to limitations and disadvantages of the related art.  
           [0041]    An object of the present invention is to provide a speaker apparatus having excellent acoustic characteristics and a simpler manufacturing method therefor.  
           [0042]    Additional features and advantages of the invention will be set forth in the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings  
           [0043]    To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a speaker apparatus including a diaphragm and a magnetic circuit, wherein the diaphragm has a positioning portion for positioning the diaphragm relative to the magnetic circuit.  
           [0044]    In another aspect, the present invention provides a speaker apparatus including a diaphragm; a magnetic circuit; and a positioning member fixed to the diaphragm for positioning the diaphragm relative to the magnetic circuit.  
           [0045]    In another aspect, the present invention provides a method for manufacturing a speaker apparatus including the steps of fixing a magnetic circuit to a frame; positioning a coil with respect to a center pole of the magnetic circuit; connecting a damper to the coil and the frame; projecting a jig from a center hole of the center pole; engaging a positioning portion provided on a diaphragm with the jig to position the diaphragm at a predetermined position with respect to the center pole; and connecting the positioned diaphragm to the coil and the frame.  
           [0046]    In another aspect, the present invention provides a method for manufacturing a speaker apparatus including the steps of fixing a magnetic circuit to a frame; positioning a coil with respect to a center pole of the magnetic circuit; connecting a damper to the coil and the frame; projecting a jig from a center hole of the center pole; engaging a positioning member with the jig for positioning the diaphragm at a predetermined position with respect to the center pole; fixing the diaphragm to the positioning member; and connecting the diaphragm fixed in the step of fixing to the coil and the frame.  
           [0047]    In another aspect, the present invention provides a speaker apparatus including a frame having a magnetic circuit; a voice coil bobbin installed in the frame to be magnetically coupled to the magnetic circuit, and a diaphragm movably installed in the frame and fixed to the voice coil bobbin so as to be driven by activating the magnetic circuit, the diaphragm further having a positioning portion used for securing the diaphragm relative to the magnetic circuit during an installation of the diaphragm in the frame.  
           [0048]    In a further aspect, the present invention provides a speaker apparatus including a frame having a magnetic circuit, a voice coil bobbin installed in the frame to be magnetically coupled to the magnetic circuit of the frame; and a diaphragm movably installed in the frame; and a support member connecting the diaphragm to the voice coil bobbin, the support member having a positioning portion used for securing a predetermined position of the diaphragm relative to the magnetic circuit during an installation of the diaphragm in the frame.  
           [0049]    Because the present invention is so constructed as described above, the diaphragm can be securely positioned relative to the magnetic circuit. Further, the installation process of the coil and diaphragm can be carried out while the diaphragm is positioned at a predetermined position relative to the coil.  
           [0050]    Thus, a speaker apparatus, in which the coil and diaphragm are positioned with respect to the magnetic circuit with high accuracy, can be produced easily. As compared with the conventional speaker apparatus, in which the entire diaphragm is integrally formed, the speaker apparatus of the present invention has superior acoustic characteristics.  
           [0051]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0052]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0053]    [0053]FIG. 1 schematically shows an example of a speaker apparatus according to a preferred embodiment of the present invention;  
         [0054]    [0054]FIGS. 2A, 2B are cross-sectional views showing an example of a diaphragm according to the present invention;  
         [0055]    FIGS.  3 A- 3 D schematically shows an example of a holder according to the present invention;  
         [0056]    [0056]FIG. 4 shows a state in which a diaphragm and a jig are engaged with a holder according to the present invention;  
         [0057]    [0057]FIGS. 5A and 5B schematically show an example of a damper according to the present invention;  
         [0058]    FIGS.  6 A- 6 C show an example of a method for manufacturing the cone type speaker unit according to a preferred embodiment of the present invention (preparatory process for the steps shown in FIGS.  7 A- 7 C);  
         [0059]    FIGS.  7 A- 7 C show an example of a method for manufacturing the cone type speaker unit according to a preferred embodiment of the present invention;  
         [0060]    [0060]FIG. 8 is a schematic cross-sectional view of a jig for use in the manufacture of the cone type speaker unit according to a preferred embodiment of the present invention;  
         [0061]    [0061]FIGS. 9A and 9B schematically show another example of the damper for use in the speaker apparatus of the present invention;  
         [0062]    [0062]FIG. 10 schematically shows a state in which a holder and a jig of the cone type speaker unit according to another preferred embodiment of the present invention are engaged with each other, FIG. 11 is a diagram showing an example of a conventional electrokinetic cone type speaker unit;  
         [0063]    FIGS.  12 A- 12 C show a method of manufacturing the conventional electrokinetic cone type speaker unit (preparatory process for the steps shown in FIGS.  13 A- 13 D);  
         [0064]    FIGS.  13 A- 13 D show a method for manufacturing the conventional electrokinetic cone type speaker unit; and  
         [0065]    FIGS.  14 A- 14 C show an example of a conventional flat speaker unit using a flat diaphragm and part of the manufacturing process thereof. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0066]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0067]    [0067]FIG. 1 is a cross-sectional view of main portions of an electrokinetic cone type speaker unit according to a preferred embodiment of the present invention Referring to FIG. 1, a diaphragm  1  is formed by integral formation of paper or resin into a parabolic shape having a substantially uniform thickness.  
         [0068]    As a result, the diaphragm  1  has a closed form having a substantially circular region, to the circumference of which a ring-like edge  2  having appropriate compliance and stiffness is attached. That is, unlike conventional types, the diaphragm  1  has no opening portion through which a voice coil bobbin is to be inserted.  
         [0069]    A holder  3  formed of ABS resin or the like is fixed to the diaphragm  1  near the center at the back side of the diaphragm  1 . The holder  3  is fixed to a voice coil assembly (hereinafter referred to as coil) in which a voice coil  4  is wound around a cylindrical voice coil bobbin  5 . Thus, the holder  3  is integrally constructed with the diaphragm  1 , voice coil  4 , and voice coil bobbin  5 .  
         [0070]    The holder  3  and the voice coil bobbin  5  are fixed to the inner circumference of a ring-like damper  6  having appropriate compliance and stiffness. The outer circumferences of the edge  2  and damper  6  are respectively fixed to a frame  11  equipped with a magnetic circuit  10  including a magnet  7 , a plate  8 , and a pole yoke  9 , etc.  
         [0071]    The pole yoke  9 , part of the magnetic circuit  10 , has a substantially cylindrical center pole in the center of a circular plate on which the magnet  7  is placed. A cylindrical center hole  9   a,  coaxial with the center pole, is formed in the center pole.  
         [0072]    The edge  2  and the damper  6  have respective cross-sections suitable for obtaining a predetermined amplitude and for elastically supporting the diaphragm  1 , holder  3 , voice coil  4  and voice coil bobbin  5 . Thus, the edge  2  and the damper  6  position the voice coil  4  and voice coil bobbin  5  at respective predetermined positions in a magnetic gap of the magnetic circuit  10  so as not to contact the magnetic circuit  10 . The edge  2  and the damper  6  also elastically support the diaphragm  1  so that the diaphragm  1  can vibrate in a predetermined direction within a predetermined amplitude range like a piston.  
         [0073]    The leads of the voice coil are connected to the respective ends of a pair of supply lines (not shown in FIG. 1) provided on the damper  6 , and the other ends of the paired supply lines are electrically connected to a pair of terminals  12  on the frame  11 .  
         [0074]    Thus, when an electric current carrying acoustic signals is supplied from the terminals  12  to the voice coil  4  through the supply lines, the voice coil  4  is driven along the piston vibration direction within a magnetic gap of the magnetic circuit  10 . As a result, the diaphragm  1  vibrates together with the holder  3 , voice coil  4 , and voice coil bobbin  5  to convert the electric signals to acoustic energy, thereby producing acoustic waves.  
         [0075]    A detailed structure of the cone type speaker unit will now be described. First, the diaphragm  1  is described in more detail. FIGS. 2A and 2B are cross-sectional views showing an example of the diaphragm  1  with the edge  2  attached. FIG. 2B shows an enlarged view of a portion of FIG. 2A indicated by the arrow A. As shown in FIG. 2B, holder mounting portions  1   a,    1   b,  each shaped into a ring-like protrusion, are provided on the back side of the diaphragm  1 . The holder mounting portions  1   a,    1   b  are coaxial with the center axis X of the diaphragm  1 .  
         [0076]    The holder  3  will be described in more detail. FIGS.  3 A- 3 D are structural diagrams showing an example of the holder  3 . FIG. 3A is a top view, FIG. 3B is a side view, FIG. 3C is a bottom view, and FIG. 3D is a side sectional view.  
         [0077]    As shown in FIGS.  3 A- 3 D, ring-like protruding guides  3   a,    3   b  and a circular guide hole  3   c  are provided coaxially with the center axis Y at the back side of the holder  3 . The inner surface of the guide  3   a  is designed such that a jig  14  for use in a subsequent manufacturing process (which will be described later) can be removably attached to the guide  3   a.    
         [0078]    The guide  3   b  is designed such that the inner surface thereof can engage with the voice coil bobbin  5 . Further, the guide hole  3   c  is provided to engage with the holder mounting portion  1   a  of the diaphragm  1 . The maximum outer diameter of the holder  3  is designed such that the holder  3  can be mounted at a region of the diaphragm surrounded by the holder mounting portion  1   b.    
         [0079]    [0079]FIG. 4 shows a state in which diaphragm  1  and jig  14  are fitted to the holder  3 . As shown in FIG. 4, the contact surfaces between the diaphragm  1  and holder  3  are designed to be firmly fitted to each other when the guide hole  3   c  is engaged with the holder mounting portion  1   a.    
         [0080]    The diaphragm  1  and the holder  3  are bonded to each other with an adhesive agent. The holder mounting portion  1   b  also prevents leakage of the adhesive agent, and therefore, serves to suppress asymmetry in weight balance of the diaphragm  1  relative to the center axis X that may occur without it.  
         [0081]    When the diaphragm  1  and the holder  3  are bonded to each other as shown in FIG. 4, the center axis X of the diaphragm  1  should coincide with the center axis Y of the holder  3 , so that the diaphragm  1  and the holder  3  maintain the coaxial relation with high accuracy.  
         [0082]    Next, the damper  6  will be described in more detail. FIGS. 5A and 5B show an example of the damper  6 . FIG. 5A shows a top view and FIG. 5B shows a perspective view illustrating a part of damper  6 . The damper  6  has a ring-like shape and is a so-called corrugation damper. A pair of conductive supply lines  6   a,    6   b  made of copper foil or the like are attached to the surface of the damper  6 . To form the corrugation damper, resin or the like is immersed in cloth and coaxial corrugation is formed by heating the cloth, for example.  
         [0083]    The supply lines  6   a ,  6   b  may be disposed radially along the coaxial unevenness with an adhesive agent, damping agent, or the like, after resin is immersed in the cloth and the corrugation is formed by a heat treatment. The supply lines  6   a ,  6   b  also may be preliminarily attached to cloth before the corrugation is formed by heating. Further, a center hole  6   c  for allowing the coil to pass through is provided at the center of the damper  6 .  
         [0084]    A method for manufacturing the cone type speaker unit according to a preferred embodiment of the present invention will be described below.  
         [0085]    FIGS.  6 A- 6 B and FIGS.  7 A- 7 C show an example of a method for manufacturing the cone type speaker unit according to the preferred embodiment of the present invention. FIGS.  6 A- 6 C show a preparatory process for the subsequent process shown in FIGS.  7 A- 7 C.  
         [0086]    FIGS.  6 A- 6 C are cross-sectional views showing the structure of the coil gauge  13  and the preparatory process for installing the coil gauge  13  on a frame assembly constituted of the frame  11  and the magnetic circuit  10 .  
         [0087]    [0087]FIG. 6A shows a structure of the coil gauge  13 . Like the coil gauge  114  in FIGS.  12 A- 13 B, the coil gauge  13  has a cylindrical coil holding portion  13   b  made of resin or the like, having a predetermined thickness, and a main unit  13   a  made of metal, for example, having a cylindrical surface.  
         [0088]    The outer diameter D 4  of the cylindrical surface of the main unit  13   a  (or inner diameter of the coil holding portion  13   b ) is substantially equal to the diameter of the center pole located at the center of the pole yoke  9 . The coil gauge  13  is designed such that the coil holding portion  13   b  can be removably fitted to the center pole of the pole yoke  9 , as shown in FIG. 6C.  
         [0089]    The outer diameter D 5  of the holding portion  13   b  is substantially equal to the inner diameter D 6  of the voice coil bobbin  5 , as shown in FIG. 6B. When engaged, the voice coil bobbin  5  can be removably fitted to the coil holding portion  13   b.    
         [0090]    As shown in FIG. 6B, the voice coil bobbin  5  having the voice coil  4  wound thereon is fitted to the coil gauge  13 . Next, as shown in FIG. 6C, this coil gauge  13  is fitted to the center pole of the magnetic circuit  10  so that coil bobbin  5  is securely held. As a result, the voice coil bobbin  5  and voice coil  4  are held in the magnetic gap of the magnetic circuit  10  so as not to be in contact with the center pole of the pole yoke  9  or the plate  8 . The positions of the voice coil bobbin  5  and voice coil  4  relative to the pole yoke  9  and plate  8  are also fixed at respective predetermined positions. This completes the preparatory process.  
         [0091]    The next stage of the manufacturing process will be explained with reference to FIGS.  7 A- 7 C. First, the damper  6  is placed at a predetermined position of the frame assembly, as shown in FIG. 7A. Then, the coil gauge  13  on which the coil has been mounted in the preparatory process shown in FIGS.  6 A- 6 C is inserted into the center hole  6   c  of the damper  6 . The coil gauge  13  is fitted to the center pole of the pole yoke  9  so that the coil is secured at a predetermined position.  
         [0092]    Next, the inner circumference and the outer circumference of the damper  6  are bonded to the voice coil bobbin  5  and the frame assembly, respectively, with an adhesive agent. Here, the leads of the voice coil  4  are extracted to the upper side of the damper  6 .  
         [0093]    After the damper  6  is fixed to the voice coil bobbin  5  and the frame assembly, the supply lines  6   a ,  6   b  are electrically connected to the voice coil  4  near the center hole  6   c  of the damper  6 . The other ends (outer side of the damper  6 ) of the paired supply lines  6   a ,  6   b  are electrically connected to a pair of terminals  12  mounted on the frame  11 .  
         [0094]    In this condition, diaphragm  1  has not been installed yet. Therefore, unlike the conventional case described above, connection work of the supply lines  6   a ,  6   b  to the terminals  12  need not be carried out in a narrow space between the damper and the diaphragm. Further, this connection work can be done with the voice coil bobbin  5  fixed to the coil gauge  13 , and therefore the work can be executed easily, stably, and securely.  
         [0095]    After the supply lines  6   a ,  6   b  are connected to the voice coil  4  and the terminals  12 , the coil gauge  13  is removed from the voice coil bobbin  5 .  
         [0096]    Next, as shown in FIG. 7B, the jig  14  is inserted into the center hole  9   a  from the bottom of the pole yoke  9 , and the top of the jig  14  is projected from the center pole.  
         [0097]    [0097]FIG. 8 schematically shows the cross-section of jig  14 . The jig  14  is formed of material having excellent wear resistance, processing precision, and processability, such as “DERLIN.” A cylindrical standing portion  14   b  having a predetermined height is integrally provided at the center of a circular base  14   a.    
         [0098]    The diameter D 7  of the standing portion  14   b  near the base  14   a  is so designed as to allow the standing portion  14   b  to be detachably fitted to the center hole  9   a  of the pole yoke  9 . The diameter D 8  near the top of the standing portion  14   b  is so designed that the inner face of the guide  3   a  of the holder  3  (FIG. 4) can be detachably fitted to the top of the standing portion  14   b.    
         [0099]    The standing portion  14   b  has a step portion  14   c  having an edge parallel to the base  14   a.  As shown in FIG. 4, when the inner face of the guide  3   a  of the holder  3  engages with the standing portion  14   b,  the step portion  14   c  comes into contact with the bottom of the guide  3   a  to support the holder  3 .  
         [0100]    In FIG. 7B, the jig  14  protrudes from the center pole of the pole yoke  9 . An adhesive agent is applied to the inner circumference of the damper  6  and the side face of the voice coil bobbin  5  projecting from the damper  6 . Then, the guide  3   a  of the holder  3  is engaged with the standing portion  14   b  to be placed on the step portion  14   c.  As a result, while the coil is positioned at a predetermined position relative to the magnetic circuit  10  shown in FIG. 7A, the guide  3   a  is supported by the step portion  14   c  and the guide  3   b  is fixed to the damper  6  and coil.  
         [0101]    Referring to FIG. 7C, a portion of the frame assembly to which the edge  2  is to be attached and a portion of the surface of the holder  3  to which the diaphragm  1  is to be attached are coated with an adhesive agent. Then, the diaphragm  1  (see FIG. 2) having the edge  2  attached thereto is placed from above. The holder mounting portion  1   a  of the diaphragm  1  is engaged with the center hole  3   c  of the holder  3  to define the position of diaphragm  1  relative to the holder  3  (FIG. 4). The outer circumference of the edge  2  is fixed to the frame assembly. As a result, the diaphragm  1  is positioned at a predetermined position and fixed to the holder  3 . Then, the jig  14  is removed from the holder  3  and pulled out from the center hole  9   a . The cone type speaker unit of the present embodiment is thus completed.  
         [0102]    Although in this embodiment the diaphragm  1  is structured entirely in closed curvature within a substantially circular range to which the edge  2  is attached, the above-described method is not restricted to this example. That is, as long as the diaphragm  1  is provided with the guides  1   a ,  1   b , or the like, for positioning the diaphragm relative to the magnetic circuit during the manufacture of the speaker apparatus, the diaphragm  1  may have an even opening portion. Further, it is permissible to provide the diaphragm with an opening and then close the opening after assembly.  
         [0103]    Although in the embodiment described above the diaphragm  1  is fixed to the holder  3  after the damper  6  and voice the coil  4  are fixed to the holder  3 , it is permissible to first fix the diaphragm  1  to the holder  3  and then fix the damper  6  and the voice coil  4  to the holder  3 .  
         [0104]    Further, the holder  3  may be integrated with the diaphragm  1  with the guides  1   a,    1   b.  In this case, the step of fixing the holder  3  to the diaphragm  1  is omitted.  
         [0105]    Although in the embodiment described above the center cap is not provided, it is permissible to so construct with the center cap as in the prior art, if desired. In this case, the process for attaching the center cap may be provided any time after the step of installing the diaphragm.  
         [0106]    Although the paired supply lines  6   a ,  6   b  on the damper  6  of the cone type speaker unit are formed on the surface of the corrugation damper formed of cloth with a heat treatment, the present invention is not restricted to this example. FIGS. 9A, 9B show another example of damper  15  for use in the speaker apparatus according to the present invention. FIG. 9A shows a top view and FIG. 9B shows a perspective view showing a part of the damper. As shown in FIGS. 9A, 9B, the paired supply lines  15   a,    15   b  may be woven in the cloth.  
         [0107]    In the embodiments described above, holder  3  and jig  14  are designed such that the standing portion  14   b  is inserted into the interior of the guide  3   a  provided at the back side of the holder  3 . However, as shown in FIG. 10, holder  16  may be supported by jig  17  at a predetermined position by engaging an additional protrusion  16   a  of the holder  16  (fixed to the diaphragm  1 ) with a recessed portion  17   a  of the jig  17 , for example.  
         [0108]    In this case, the area of the engagement between the protrusion  16   a  and the recessed portion  17   a  can be increased as desired. Thus, the jig  17  is capable of supporting the holder  16  more stably. As shown in FIG. 10, the holder  16  is so constructed to have the protrusion  16   a  at the center instead of the guide hole  3   c  of the holder  3 . The jig  17  has the recessed portion  17   a,  which is not provided in the jig  14 .  
         [0109]    If the holder  16  and jig  17  are used in the manufacturing process of the speaker apparatus, the height of the guide (corresponding to the guide  3   b  of the holder  3 ) of the holder  16  that engages with the voice coil bobbin  5  need not be so large to support the holder. Therefore, the additional weight can be minimized, while the effective radiation area of the diaphragm of the speaker apparatus remains unchanged, thereby achieving a higher acoustic conversion efficiency.  
         [0110]    With the present invention described above, the diaphragm can be securely positioned relative to the magnetic circuit. Further, fixing work for the coil and diaphragm can be carried out without sacrificing accuracy of the designed positional relation between the coil and diaphragm. Thus, a speaker apparatus, in which the coil and diaphragm are excellently positioned with respect to the magnetic circuit, can easily be manufactured. Furthermore, when the one-piece diaphragm of the present invention is used, as compared with the conventional speaker apparatus in which the entire diaphragm is integrally formed, the speaker apparatus of the present invention provides much superior acoustic characteristics.  
         [0111]    It will be apparent to those skilled in the art that various modifications and variations can be made in the speaker apparatus and production method thereof of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
A speaker apparatus includes a frame having a magnetic circuit, a voice coil bobbin installed in the frame to be magnetically coupled to the magnetic circuit, and a diaphragm movably installed in the frame and fixed to the voice coil bobbin so as to be driven by activating the magnetic circuit. The diaphragm has a positioning portion that had been used for securing the diaphragm relative to the magnetic circuit during an installation of the diaphragm in the frame.