Patent Publication Number: US-8126188-B2

Title: Speaker and method of producing the same

Description:
This Application is a U.S. National Phase Application of PCT International Application PCT/JP2006/302936. 
     TECHNICAL FIELD 
     The present invention relates to loudspeakers to be used in various audio devices and communications devices, more specifically to small, thin and rectangular loudspeakers for use in mobile phones where loudspeaker mounting space is limited, and to manufacturing method of the loudspeakers. 
     BACKGROUND ART 
     Along with the trend toward miniaturization and multi-functioning of various audio devices and communications devices, miniaturization of loudspeakers to be used in these devices is increasingly accelerated. Especially for loudspeakers to be used in mobile phones, not only miniaturization but also high-quality sound is required. Under such circumstances, emphasis of loudspeaker development is placed on rectangular loudspeakers rather than more general circular loudspeakers to enable more efficient use of limited space available in mobile phones where loudspeaker mounting space is limited. 
       FIG. 6  is a cross-sectional view showing structure of a conventional loudspeaker of this type.  FIG. 7  is a perspective view showing structure of a yoke used in the loudspeaker. In  FIG. 6  and  FIG. 7 , by providing four folding portions  11   a  on a previously blanked sheet of a magnetic metallic material and folding them up, yoke  11  is formed into a shape of a bottomed rectangular frame. With this, reduction in material loss and improvement in productivity of yoke  11  can be achieved. Also, by stacking and joining rectangular magnet  12  and rectangular top plate  13  inside yoke  11 , a magnetic circuit having rectangular magnetic gap  14  is constructed. 
     The magnetic circuit and frame  15  in which yoke  11  is press fit are joined with an adhesive. Voice coil  16  is provided in a manner fitting in magnetic gap  14 . Central portion of diaphragm  17  couples with voice coil  16  while its peripheral border couples with the peripheral border of frame  15 . 
     In a conventional loudspeaker configured in this way, when an audio signal is input into voice coil  16  fit inside magnetic gap  14 , voice coil  16  vertically vibrates due to a magnetic field generated by magnetic gap  14 . This further causes vertical vibration of diaphragm  17  to which voice coil  16  is coupled thereby reproducing sound. 
     As a prior art technical literature related to the invention of this application, Unexamined Japanese Patent Publication 2003-37892, for example, is known. 
     However, as the above-mentioned conventional loudspeaker is fabricated by a method of preparing yoke  11  that configures a magnetic circuit by bending a sheet of a magnetic metallic material, a clearance is caused at each corner of yoke  11  formed into a rectangular configuration. Accordingly, magnetic flux leakage takes place from the clearances resulting in performance degradation such as reduction in the sound pressure due to reduction in magnetic flux density. There is also a fear of an adverse effect being caused by leakage magnetic flux on other electronic components densely mounted in the vicinity of the loudspeaker. 
     SUMMARY OF THE INVENTION 
     The present invention provides loudspeakers excellent in both quality and performance by solving such existing problems by eliminating magnetic flux leakage, and provides manufacturing method of such loudspeakers. 
     The loudspeaker in accordance with the present invention comprises a magnetic circuit having a magnetic gap, a frame made of a resin material and coupled to the magnetic circuit and, and a diaphragm having a voice coil that can be driven by a magnetic field generated by the magnetic gap and coupled to the center with its peripheral border coupled to the outer circumference of the frame. The magnetic circuit has a yoke formed in the shape of a rectangular dish and a magnet fixed inside the yoke. The magnetic circuit also has a tongue-like flange provided at each corner section that projects outwardly at a position below the top end of the yoke by a predetermined distance. The yoke is insert-molded in the frame in a manner covering the flanges. 
     Also, the method of manufacturing loudspeakers in accordance with the present invention comprises the steps of: drawing a planar magnetic metallic material into a rectangular dish and subsequently making a yoke having integrally provided tongue-like flanges that outwardly project at a position below the top end of the yoke by a predetermined distance by downwardly press working the peripheral border of the top end of each corner; insert molding the yoke into a resin frame in a manner such that the tongue-like flanges formed on the yoke are covered; making a magnetic circuit in which a magnetic gap is formed by joining a magnet inside the yoke; joining a voice coil to be driven by a magnetic field generated by the magnetic gap to a diaphragm; and joining the diaphragm joined with the voice coil to the frame. 
     According to the present invention as described above, by providing at each corner a tongue-like flange that outwardly projects at a position below the top end of the yoke by a predetermined distance and insert molding the yoke into a resin frame in a manner covering the tongue-like flanges, it becomes possible not only to greatly enhance the bonding strength between the yoke and frame but also to obtain a low profile. Also, by making the rectangular yoke in the shape of a dish, clearance at each corner is eliminated thus removing magnetic flux leakage and giving the advantage of stably providing loudspeakers which are excellent both in quality and performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing the construction of a loudspeaker obtained by the loudspeaker manufacturing method in the first preferred embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of a frame having an insert molded yoke to be used in the loudspeaker. 
         FIG. 3A  is a plan view of the yoke used in the loudspeaker. 
         FIG. 3B  is a front sectional view of the yoke used in the loudspeaker. 
         FIG. 3C  is a side sectional view of the yoke used in the loudspeaker. 
         FIG. 4A  is a diagram showing the method of manufacturing a yoke to be used in the loudspeaker. 
         FIG. 4B  is a diagram showing the method of manufacturing a yoke to be used in the loudspeaker. 
         FIG. 4C  is a diagram showing the method of manufacturing a yoke to be used in the loudspeaker. 
         FIG. 4D  is a diagram showing the method of manufacturing a yoke to be used in the loudspeaker. 
         FIG. 4E  is a diagram showing the method of manufacturing a yoke to be used in the loudspeaker. 
         FIG. 4F  is a diagram showing the method of manufacturing a yoke to be used in the loudspeaker. 
         FIG. 5  is a cross-sectional view showing the construction of a loudspeaker obtained by a loudspeaker manufacturing method in the second preferred embodiment of the present invention. 
         FIG. 6  is a cross-sectional view showing the construction of a conventional loudspeaker. 
         FIG. 7  is a perspective view of a yoke used in the loudspeaker. 
     
    
    
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           1  Yoke 
           1   a  Flange 
           2  Frame 
           2   a  Air vent 
           3  Magnet 
           4  Top plate 
           5  Magnetic gap 
           6 ,  10  Diaphragm 
           6   a ,  10   a  Edge 
           7 ,  9  Voice coil 
           8  Cover 
       
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First Preferred Embodiment 
     A description of the present invention is given below in terms of the first preferred embodiment. 
       FIG. 1  is a cross-sectional view showing the structure of a loudspeaker obtained by the method of manufacturing loudspeakers in accordance with the first preferred embodiment of the present invention.  FIG. 2  is a cross-sectional view showing a frame in which a yoke used in the loudspeaker is insert-molded.  FIG. 3A ,  FIG. 3B , and  FIG. 3C  are, respectively, plan view, front cross-sectional view, and side cross-sectional view of the yoke used in the loudspeaker. In  FIG. 1 ,  FIG. 2 ,  FIG. 3A ,  FIG. 3B , and  FIG. 3C , yoke  1  is formed into the shape of a rectangular dish using a magnetic metallic material. Also, tongue-like flange la that projects outwardly from a position below the top end surface of yoke  1  by a predetermined distance is symmetrically provided at each corner and on the long sides. By providing the flanges at a position lowered by a predetermined distance, yoke  1  can be secured to frame  2 . 
     Air vents  2   a  are provided on resin-made frame  2 . When forming frame  2 , yoke  1  is inserted molded in a manner covering tongue-like flanges  1   a  provided on yoke  1 . Furthermore, the loudspeaker is so structured that the bottom of yoke  1  will project from the bottom surface of frame  2  after insert molding, thus making it easy to print or stamp indication marking of part number or lot number on the bottom of yoke  1 . 
     Magnet  3  fixed inside yoke  1  and top plate  4  joined on top of magnet  3  form a magnetic circuit that has magnetic gap  5 . 
     Voice coil  7  is joined to the central portion of diaphragm  6  that has integrally formed edge  6   a  on the outer circumference. Voice coil  7  is arranged in a manner fitting inside magnetic gap  5  formed in the magnetic circuit. And, by inputting an audio signal to voice coil  7 , a magnetic field is generated by magnetic gap  5  thus causing voice coil  7  to vertically vibrate. Diaphragm  6  joined to voice coil  7  is also caused to vertically vibrate thus reproducing the audio signal. Cover  8  protects diaphragm  6 . 
       FIG. 4A  to  FIG. 4F  are diagrams showing manufacturing method of yoke  1 . A description of this manufacturing method will be given in the following. 
     First, as shown in  FIG. 4A , a plate of magnetic metallic material is punched to a rectangular shape of predetermined dimensions. Subsequently, the rectangular plate is drawn by press working to the shape of a dish having a concave cross-section as shown in  FIG. 4B . 
     Subsequently, as shown in  FIG. 4C , a flange that outwardly projects from a position a predetermined distance below the top end surface is integrally formed by downward press working of the peripheral border of the top end surface of a rectangular dish-like molded body. Then, as shown in  FIG. 4D , leaving only those flanges that are formed at corners, other unnecessary parts are removed by punching. 
     Next, the remaining flanges are pressed again to a predetermined thickness as shown in  FIG. 4E . Finally, as shown in  FIG. 4F , unnecessary outer portions of the flanges are removed by punching thereby providing yoke  1  on which tongue-like flanges  1   a  are integrally provided. 
     Here, flanges  1   a  integrally provided on yoke  1  may be extended over the entire outer circumference of yoke  1 . However, it is difficult to provide an outwardly projecting flange over the entire circumference by pressing a very small dimension as fracture may occur on the way due to insufficient elongation of the flange material. A structure in which flanges are partially provided at each corner in a symmetrical way or on the long sides like the flanges described in the first preferred embodiment of the present invention is the most effective and productivity is also good. 
     In a loudspeaker that uses yoke  1  as manufactured in this way in accordance with the first preferred embodiment, tongue-like flange  1   a  that outwardly projects from a position a predetermined distance below the top surface of yoke  1  is provided. And, by insert-molding yoke  1  in frame  2  in a manner covering flange  1   a , not only the bonding strength between yoke  1  and frame  2  is greatly improved but also a low profile can be obtained. Furthermore, by forming rectangular yoke  1  into the shape of a dish, clearance at each corner can be eliminated thus eliminating magnetic flux leakage and enabling stable manufacture of loudspeakers that are excellent in both quality and performance. 
     Second Preferred Embodiment 
     A description of the present invention will be given below referring to the second preferred embodiment. 
     In the second preferred embodiment, the structure of the voice coil used in the loudspeaker is different from that used in the first preferred embodiment. As other structures are the same as those in the first preferred embodiment, elements similar to those in the first preferred embodiment are given the same reference numbers and detailed description of those elements are omitted, and description will be given only on the different elements referring to drawings. 
       FIG. 5  is a cross-sectional view showing the structure of a loudspeaker obtained by the method of manufacturing loudspeakers in the second preferred embodiment of the present invention. In  FIG. 5 , voice coil  9  is formed by forming a wound coil of a predetermined pattern on the top and rear sides of a resin base material. 
     The base material of voice coil  9  excluding the coil is joined to the center of diaphragm  10  that has an integrally formed edge  10   a  on the outer circumference in a manner such that voice coil  9  is disposed above magnetic gap  5  and close to magnetic gap  5  without touching. Voice coil  9  is disposed above magnetic gap  5  and opposite to magnetic gap  5 . 
     Base material of the central portion of diaphragm  10  has rigidity while edge  10   a  is made of a flexible material. Accordingly, the degree of freedom of motion of diaphragm  10  is high thus fully assuring the dynamic range of the sound coming out from the loudspeaker. 
     Similar to the loudspeaker in accordance with the first preferred embodiment, the loudspeaker configured in this way in accordance with the second preferred embodiment is free from magnetic flux leakage and is excellent both in quality and performance. As voice coil  9  can be made lightweight and its shape can be freely changed, it is possible to manufacture a loudspeaker that is adaptable to any shape even when the mounting space is limited. 
     INDUSTRIAL APPLICABILITY 
     The loudspeaker in accordance with the present invention is free from magnetic flux leakage and is excellent in both quality and performance. Also, the method of manufacturing loudspeakers in accordance with the present invention is useful for manufacturing loudspeakers for use in information-communication devices such as mobile phones.