Patent Publication Number: US-2007121994-A1

Title: Speaker apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based on and claims the benefit of priority from the prior Japanese Patent Application No. 2005-336355, on Nov. 21, 2005; the entire contents of which are incorporated herein by reference.  
     BACKGROUND  
      1. Technical Field  
      The present invention relates to a speaker apparatus, particularly relates to a speaker apparatus integrated with an inner magnet type magnetic circuit as a magnetic circuit for driving a voice coil connected to a vibrating plate.  
      2. Related Art  
      In recent years, in accordance with space saving formation of acoustic apparatus or the like, also according to a speaker apparatus mounted thereto, a request for small-sized light-weighted formation has been increased. For the small-sized light-weighted formation of the speaker apparatus, small-sized formation of a magnetic circuit for driving a vibrating plate is effective.  
      Magnetic circuits integrated to a speaker apparatus can roughly be classified into an outer magnet type for arranging a magnet on an outer side of a yoke and an inner magnet type for arranging a magnet on an inner side of a yoke. According to a magnetic circuit of an inner magnet type, in comparison with a magnetic circuit of an outer magnet type, leakage of magnetic flux to the outside can be restrained. Therefore, an efficiency thereof is excellent. The inner magnet type is advantageous for small-sized light-weighted formation.  
      According to related arts, a speaker apparatus further improves such an inner magnet type magnetic circuit shown by  FIGS. 1 and 2 .  
      JP-A-2003-199189 discloses a speaker apparatus  10  mentioned below. In a related-art speaker apparatus  10 , a voice coil  4  is wound around an outer periphery of a voice coil bobbin  3  connected to an outer peripheral edge of a vibrating plate  2  of a dome type.  
      An inner magnet type magnetic circuit  6  for driving the voice coil  4  includes a pot yoke  8  (hereinafter, referred to as “a yoke  8 ”), a magnet  9 , and a pole piece  11 . The yoke  8  is made of a magnetic member formed in a pot type shape. The magnetic member includes a bottom plate portion  8   a  in a shape of a circular plate and a cylinder portion  8   b  extending an outer periphery of the bottom plate portion  8   a  in an axial direction of the vibrating plate  2 . The magnet  9  is formed in a circular-plate shape. Both faces of the magnet  9  are magnetized, one magnetized face of the magnet  9  is closely attached to the bottom plate portion  8   a.  The pole piece  11  is made of a magnetic member, and has a circular-plate shape. The pole piece  11  is closely attached to other magnetizing face of the magnet  9 . Magnetic gap s is formed between an outer peripheral portion of the pole piece  11  and the cylinder portion  8   b  of the yoke  8 . The voice coil  4  is inserted into the magnetic gap s.  
      In the inner magnet type magnetic circuit  6 , a short-circuit ring  13  formed by a metal of copper, aluminum or the like is fitted to be mounted to an outer peripheral portion of the pole piece  11  facing the magnetic gap s as an improvement measure for reducing magnetic distortion by nonlinearlity of a permeability.  
      JP-A-2002-78081 a speaker apparatus  20  as shown in  FIG. 2 , as mentioned below. A voice coil  24  is wound around an outer periphery of a voice coil bobbin  23  connected to an inner peripheral edge of a vibrating plate  22  of a cone type. An outer peripheral edge of the vibrating plate  22  is fixed to a speaker frame  26  by way of an edge  25 . The voice coil bobbin  23  is connected to the speaker frame  26  movably in an axial direction of the vibrating plate  22  by a corrugation damper  27 .  
      An inner magnet type magnetic circuit  28  for driving the voice coil  24  includes a pot yoke  29  (hereinafter, referred to as “a yoke  29 ”), a magnet  30 , and a pole piece  31 . The yoke  29  is made of a magnetic member formed by a pot substructure including a bottom plate portion  29   a  in a shape of a circular plate and a cylinder portion  29   b  configured by extending an outer periphery of the bottom plate portion  29   a  in an axial direction of the vibrating plate  22 . The magnet  30  is formed in a shape of a circular plate, and both faces of which are magnetized. One magnetized face of the magnet is closely attached to the bottom plate portion  29   a.  The magnet  30  is mounted to an inside of the yoke  29 . The pole piece  31  has a circular-plate shape by a magnetic member. The pole piece  31  is closely attached to other magnetized face of the magnet  30  at the inside of the yoke  29 . A magnetic gap s is formed between an outer peripheral portion thereof and the cylinder portion  29   b.  The voice coil  24  is inserted into the magnetic gap s.  
      A characteristic of the inner magnet type magnetic circuit  28  resides in mounting a repulsive magnet  33  both faces of which are magnetized in polarities reverse to those of the magnet  30  on a surface of the pole piece  31  on a side of the vibrating plate as an improvement measure for promoting an efficiency of the magnetic circuit by reducing a leakage magnetic flux from the magnet  30  to the side of the vibrating plate  22 .  
     SUMMARY  
      In the inner magnet type magnetic circuit, it is conceivable to mount the repulsive magnet described in JP-A-2002-78081 in addition to mounting the short-circuit ring described in JP-A-2003-199189 so as to increase the efficiency of the magnetic circuit not only by reducing the magnetic distortion by the nonlinearlity of the permeability but also reducing the leakage magnetic flux to the side of the vibrating plate.  
      However, according to a structure of mounting the short-circuit ring  13  to the outer peripheral portion of the pole piece  11  as in JP-A-2003-199189 mentioned above, a vacant space above the pole piece is reduced by mounting the short-circuit ring  13  and therefore, an outer diameter of the repulsive magnet  33  needs to be restricted to be small such that the repulsive magnet  33  does not interfere with the short-circuit ring  13 .  
      Further, when the outer diameter of the repulsive magnet  33  is reduced, a magnetic intensity in the side of the magnetic gap s by the repulsive magnet  33  is reduced and therefore, an inherent function of the repulsive magnet  33  of reducing the leakage magnetic flux to the side of the vibrating plate cannot sufficiently be achieved, as a result, there poses a problem that an initial object of increasing the efficiency of the magnetic circuit cannot be achieved.  
      There is a problem that when a reduction in the magnetic distortion is achieved by mounting the short-circuit ring, the outer diameter of the repulsive magnet mounted on the pole piece needs to be reduced, and an increase in the efficiency of the magnetic circuit by mounting the repulsive magnet cannot sufficiently be achieved.  
      The present invention has been made in view of the above circumstances and provides a speaker apparatus. According to an aspect of the present invention,  
      According an aspect of the invention, there is provided a speaker apparatus including: an inner magnet type magnetic circuit for driving a voice coil connected to a vibrating plate, the magnetic circuit comprising; a yoke being made of a magnetic member, the yoke comprising a bottom plate portion having a circular-plate shape and a cylinder portion extending an outer periphery of the bottom plate portion in an axial direction of the vibrating plate; a magnet at least partly mounted at an inside of the yoke, the magnet having a circular-plate shape, both faces of the magnet being magnetized, a magnetized face of the magnet being attached to the bottom plate portion of the yoke; and a pole piece having a circular-plate shape, the pole piece being formed of a magnetic member and attached to the other magnetized face of the magnet at an inside of the yoke, a magnetic gap being formed between an outer peripheral portion of the pole piece and the cylinder portion of the yoke, the voice coil inserted into the magnetic gap; a repulsive magnet both faces being magnetized to polarities reverse to a polarity of the magnet and attached on a surface thereof of a vibrating plate side of the pole piece; and a short-circuit ring made of copper, the short-circuit ring mounted and fitted to an inner peripheral portion of a front end of the cylinder portion of the yoke. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a vertical sectional view of a related-art speaker apparatus having an inner magnet type magnetic circuit.  
       FIG. 2  is a vertical sectional view of another related-art speaker apparatus having an inner magnet type magnetic circuit.  
       FIG. 3  is an exemplary vertical sectional view of a speaker apparatus according to a first embodiment.  
       FIG. 4  is an exemplary vertical sectional view enlarging a yoke and a short-circuit ring of an inner magnet type magnetic circuit shown in  FIG. 3 .  
       FIG. 5  is an exemplary enlarged view of portion A of  FIG. 3 .  
       FIG. 6  is an exemplary vertical sectional view of a speaker apparatus according to a second embodiment.  
       FIG. 7  is an enlarged view of portion B of  FIG. 6 . 
    
    
     DESCRIPTION OF THE EMBODIMENTS  
     First Embodiment  
      An explanation will be given of a speaker apparatus according to a first embodiment of the invention in reference to the drawings as follows.  
      A speaker apparatus  40  adopts a vibrating plate  42  of a dome type. A voice coil  44  is wound around an outer periphery of a voice coil bobbin  43  connected to an outer peripheral edge of the vibrating plate  42 . The outer peripheral edge of the vibrating plate  42  is bonded with an edge  45 . The outer peripheral edge of the edge  45  is fixed to a speaker frame  48  by being pinched by a ring holder  46  and an edge holder  47 .  
      The speaker frame  48  is configured by a bottom wall portion  48   a  disposed on a back side of the vibrating plate  42 , a peripheral wall portion  48   b  substantially in a cylindrical shape formed by being extended from an outer periphery of the bottom wall portion  48   a  to a front side (side of vibrating plate  42 ), and a flange portion  48   c  expanded to an outer side in a diameter direction from a front end of the peripheral wall portion  48   b.    
      The bottom wall portion  48   a  of the speaker frame  48  is fixed with an inner magnet type magnetic circuit  51  for driving the voice coil  44 .  
      The inner magnet type magnetic circuit  51  includes a pot yoke  52  (hereinafter, referred to as “a yoke  52 ”) made of a magnetic member, a magnet  55  arranged at an inside of the yoke  52 , a pole piece  56  arranged on the magnet  55  to be attached thereto, a repulsive magnet  57 , for promoting an efficiency of the magnetic circuit by reducing leakage magnetic flux to a side of the vibrating plate  42 , and a short-circuit ring  58  for reducing magnetic distortion by nonlinearlity of a permeability.  
      The yoke  52  is formed of a magnetic member. In the pot type structure of the yoke  52 , a bottom plate portion  52   a  in a shape of a circular plate, and a cylinder portion  52   b  formed by extending an outer periphery of the bottom plate portion  52   a  in an axial direction of the vibrating plate  42  (direction along a center axis  53 ), and the bottom plate portion  52   a  is fixed to the bottom wall portion  48   a  of the speaker frame  48  by adhering or the like. The bottom plate portion  52   a  of the yoke  52  is formed with an opening  52   c  for inserting a pole  48   d  formed to be raised at a center of the bottom wall portion  48   a  of the speaker frame  48 .  
      The magnet  55  has a circular-plate shape. A center of the magnet  55  is formed with an opening  55   a  for inserting the pole  48   d,  and both faces of the magnet  55  are magnetized. One of the magnetized faces is closely attached to the bottom plate portion  52   a  of the yoke  52 . The magnet  55  is fixed to an inside of the yoke  52  by adhering or the like.  
      The pole piece  56  has a circular-plate shape. The pole piece  56  is made of a magnetic member. The pole piece  56  is adhered to be fixed onto other magnetized face of the magnet  55  at the inside of the yoke  52 , and partitions a magnetic gap s into which the voice coil  44  is inserted between an outer peripheral portion thereof and the cylinder portion  52   b  and the yoke  52 . A center of the pole piece  56  is formed with an opening  56   a  for inserting the pole  48   d.    
      According to the first embodiment, although the repulsive-magnet  57  is constituted by a shape of a circular plate similar to the magnet  55 , both faces thereof are magnetized in polarities reverse to those of the magnet  55  and fixed to be mounted onto a surface of the pole piece  56  in a side of the vibrating plate  42  by adhering or the like.  
      Further, the magnetized face of the repulsive magnet  57  on the side of the vibrating plate  42  is adhered with a top plate  59  formed in a shape of a circular plate as a sound absorbing member.  
      As shown by  FIG. 4 , the short-circuit ring  58  is integrally formed with a cylindrical portion  58   a  fitted to an inner periphery of the cylinder portion  52   b  of the yoke  52 , and a fold back portion  58   b  in a flange-like shape expanded from a front end of the cylindrical portion  58   a  to an outer side in a diameter direction by pressing a copper plate or the like, and is fitted to be mounted to an inner peripheral portion of the front end of the cylinder portion  52   b  of the yoke  52 .  
      When the short-circuit ring  58  is fitted to be mounted to the inner peripheral portion of the front end of the cylinder portion  52   b  of the yoke  52 , as shown by  FIG. 5 , the fold back portion  58   b  is mounted onto a front end face of the cylinder portion  52 , so that the short-circuit ring  58  is positioned in an axial direction.  
      As shown by  FIG. 5 , the ring holder  46  includes a cylinder portion  46   a  fitted to an outer periphery of the cylinder portion  52   b  of the yoke  52 , a hold piece  46   b  extended to an inner side in a diameter direction from an upper end of the cylinder portion  46   a,  and an edge supporting portion  46   c  extended to an outer side in a diameter direction from the upper end of the cylinder portion  46   a  and is formed by being integrally molded by a resin material or the like.  
      When the ring holder  46  is fitted to be mounted onto the cylinder portion  52   b,  the ring holder  46  pinches the fold back portion  58   b  of the short-circuit ring  58  mounted onto the front end face of the cylinder portion  52   b  to fix the short-circuit ring  58 .  
      As shown by  FIG. 3 , an outer peripheral edge of the edge  45  is mounted onto the edge supporting portion  46   c  of the ring holder  46 . The edge  45  is fixed by being pinched by the edge holder  47  in a ring-like shape mounted onto an outer peripheral edge thereof and the edge supporting portion  46   c.    
      As shown by  FIG. 3 , an inner peripheral portion of the flange portion  48   c  disposed on a front end side of the speaker frame  48  is coupled with a diffuser  61  extended to a front side of the vibrating plate  42 , protecting the vibrating plate  42  against an external force, at the same time, improving an acoustic property.  
      According to the inner magnet type magnetic circuit  51  of the speaker apparatus  40  explained above, the short-circuit ring  58  is arranged not on the pole piece  56  but at the inner peripheral portion of the front end of the cylinder portion  52   b  of the yoke  52  and therefore, the short-circuit ring  58  does not prevent the repulsive magnet  57  from being mounted onto the pole piece  56 . Therefore, when the short-circuit ring  58  is mounted, a diameter of the repulsive magnet  57  can be enlarged until an outer diameter thereof becomes substantially equal to an outer diameter of the pole piece  56 .  
      As a result, according to the inner magnet type magnetic circuit  51  of the speaker apparatus  40  of the first embodiment, the magnetic distortion can be reduced by mounting the short-circuit ring  58 , at the same time, an effect of the repulsive magnet  57  of increasing the efficiency of the magnetic circuit by reducing the leakage magnetic flux in the side of the vibrating plate  42  can maximally be achieved, and both of high efficiency formation and high quality formation of the speaker apparatus  40  can be achieved.  
      Further, according to the inner magnet type magnetic circuit  51  of the first embodiment, the short-circuit ring  58  includes the cylindrical portion  58   a  fitted to the inner periphery of the cylinder portion  52   b  of the yoke  52 , and the fold back portion  58   b  expanded from the front end of the cylindrical portion  58   a  to the outer side in the diameter direction, the short-circuit ring  58  is positioned in the axial direction by mounting the fold back portion  58   b  to the front end face of the cylinder portion  52   b  of the yoke  52 .  
      Therefore, in assembling the inner magnet type magnetic circuit  51 , the short-circuit ring  58  can easily be positioned to promote a performance of assembling the inner magnet type magnetic circuit  51 .  
     Second Embodiment  
      As shown by  FIG. 7 , a speaker apparatus  60  of a second embodiment which differs from the speaker apparatus  40  of the first embodiment in a following configuration. The inner periphery of the front end side of the cylinder portion  52   b  of the yoke  52  is formed with a step portion (hereinafter, referred to as “a stepped difference”)  52   d  for butting an end face of the short-circuit ring  58  fitted to the cylinder portion  52   b.  By butting the end face of the short-circuit ring  58  to the stepped difference  52   d,  the short-circuit ring  58  is positioned in the axial direction.  
      Any part of the short-circuit ring  58  other than the stepped difference  52   d  may be common to the first embodiment. In the second embodiment the common constitution is attached with the same numeral and an explanation thereof will be omitted.  
      According to the structure of positioning the short-circuit ring  58  in the second embodiment, the short-circuit ring  58  can be configured by a simple cylindrical structure which is not mounted with the fold back portion  58   b  shown in the first embodiment, and the short-circuit ring  58  is easy to be worked and produced.  
      Although the speaker apparatus shown in the above-descried respective embodiments use the vibrating plate of the dome type. However, the embodiments are applicable to a speaker apparatus using a vibrating plate of a cone type.  
      Further, the embodiments are applicable to a speaker apparatus for a speaker apparatus for vehicle-mounted use, a household use, or for a theater or the like.  
      According to the above-embodiments, the short-circuit ring  58  does not constitute any hindrance in mounting the repulsive magnet  57  onto the pole piece  56 . Therefore, even in the constitution of mounting the short-circuit ring  58 , the diameter of the repulsive magnet  57  can be enlarged until the outer diameter becomes substantially equal to the outer diameter of the pole piece  56 .  
      As a result, according to the inner magnet type magnetic circuit  51  of the speaker apparatus  40  of the embodiment, the magnetic distortion can be reduced by mounting the short-circuit ring  58 , at the same time, the effect of the repulsive magnet  57  of increasing the efficiency of the magnetic circuit by reducing the leakage magnetic flux to the side of the vibrating plate  42  can maximally be achieved, and both of high efficiency formation and high quality formation of the speaker apparatus  40  can be achieved.  
      According to the above-embodiments, the short-circuit ring is arranged not on the pole piece but at the inner peripheral portion of the front end of the cylinder portion of the yoke and therefore, the short-circuit ring does not constitute any hindrance in mounting the repulsive magnet onto the pole piece. Therefore, even in a constitution of being mounted with the short-circuit ring, a diameter of the repulsive magnet can be enlarged until an outer diameter thereof becomes substantially equal to an outer diameter of the pole piece.  
      As a result, according to the inner magnet type magnetic circuit of the speaker apparatus of the embodiments, magnetic distortion can be reduced by mounting the short-circuit ring. At the same time, the effect of the repulsive magnet of increasing an efficiency of the magnetic circuit by reducing leakage magnetic flux to a side of the vibrating plate can maximally be achieved, and both of high efficiency formation and high quality formation of the speaker apparatus can be achieved.  
      According to the above-embodiments, the short-circuit ring may include a cylindrical portion fitted to an inner periphery of the cylinder portion of the yoke, and a fold back portion extended from a front end of the cylindrical portion to an outer side in a diameter direction and is positioned in the axial direction by being mounted onto a front end face of the cylinder portion.  
      Thereby, the short-circuit ring is positioned easily and a performance of integrating the inner magnet type magnetic circuit is promoted.  
      According to the above-embodiments, an inner periphery on the front end side of the cylinder portion of the yoke may be formed with a stepped difference for butting an end face of the short-circuit ring fitted to the cylinder portion, and the short-circuit ring is positioned in the axial direction by butting the end face to the stepped difference.  
      When such a constitution is constructed the short-circuit ring can be constituted by a simple cylinder structure which is not mounted with the fold back portion or the like and the short-circuit ring is easily worked and produced.