Patent Publication Number: US-2016234586-A1

Title: Electroacoustic transducer

Description:
REFERENCE To RELATED APPLICATIONS 
     The Present Disclosure claims priority to prior-filed Japanese Patent Application No. 2013-215469, entitled “Electroacoustic Transducer,” filed on 16 Oct. 2013 with the Japanese Patent Office. The content of the aforementioned Patent Application is incorporated in its entirety herein. 
     BACKGROUND OF THE PRESENT DISCLOSURE 
     The Present Disclosure relates, generally, to a balanced armature electroacoustic transducer used in medical and audio devices, and, more particularly, to an electroacoustic transducer in which an external connection terminal is connected along the back surface of the housing to facilitate connection of the external connection terminal to a coil, while also reducing the number of connection points and improving connection reliability. 
     Electroacoustic transducers used in medical devices such as hearing aids and in audio devices such as earphones and headsets are known to include balance armature drive units. For example, the electroacoustic transducer described in UK Patent Application No. 9005574.0 (the content of which is incorporated in its entirety herein) includes a housing having an outlet for the acoustic waves on a front surface side, a balanced armature drive unit and a diaphragm arranged inside the housing, and external connection terminals arranged along a back surface side of the housing and connected electrically to a coil of the drive unit. Electrical signals inputted from the external connection terminal are converted to acoustic waves by the drive unit and the diaphragm, and the acoustic waves are outputted via the outlet. 
     Because the external connection terminal in this type of electroacoustic transducer is arranged along the back surface of the housing, the direction of sound emission remains centered on the nominal diameter and does not expand in the vertical and lateral directions. This allows the medical device or audio device incorporating the electroacoustic transducer to be more compact. 
     However, when an external connection terminal is arranged along the back surface of the housing in an electroacoustic transducer, the terminal base plate on which the external connection terminal has been mounted is fixed to the back surface portion of the housing and the terminal base plate and the coil are connected to each other electrically via a wire. As a result, it is difficult to connect the wire to the terminal base plate, and a disconnection may occur during the connection operation. Also, because a wire has to be connected at two points on a single external connection terminal, high connection reliability is difficult to obtain. 
     SUMMARY OF THE PRESENT DISCLOSURE 
     Therefore, it is an object of the Present Disclosure to solve this problem by providing electroacoustic transducer in which an external connection terminal is connected along the back surface of the housing to facilitate connection of the external connection terminal to a coil, while also reducing the number of connection points and improving connection 
     In order to achieve this object, the Present Disclosure provides an electroacoustic transducer for converting electric signals inputted from the outside into acoustic waves and outputting the acoustic waves. The electroacoustic transducer includes a housing having an outlet for the acoustic waves on a front surface side, a balanced armature drive unit and a diaphragm arranged inside the housing, and external connection terminals arranged along a back surface side of the housing and connected electrically to a coil of the drive unit. In this electroacoustic transducer, the external connection terminal has an external connection portion for receiving electric signals inputted from the outside, and a coil connecting portion connected to the coil and surrounded by a bobbin around which the coil has been wound. In addition, the coil connecting portion is connected to the coil and arranged so the external connection portion runs along the back surface of the housing. 
     The Present Disclosure is able to provide an electroacoustic transducer in which an external connection terminal is connected along the back surface of the housing to facilitate connection of the external connection terminal to a coil, while also reducing the number of connection points and improving connection reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The organization and manner of the structure and operation of the Present Disclosure, together with further objects and advantages thereof may best be understood by reference to the following Detailed Description, taken in connection with the accompanying Figures, wherein like reference numerals identify like elements, and in which: 
         FIG. 1  is a cross-sectional view of an earphone incorporating an electroacoustic transducer according to an embodiment of the Present Disclosure; 
         FIG. 2  is a cross-sectional view of the electroacoustic transducer of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of the electroacoustic transducer of  FIG. 2 ; 
         FIG. 4  is a perspective view of the external connection terminal and magnet strap prior to insertion molding of the electroacoustic transducer of  FIG. 2 ; 
         FIG. 5  is a perspective view of the external connection terminal, pad, bobbin and magnet strap after insertion molding of the electroacoustic transducer of Fig,  2 ; and 
         FIG. 6  is a perspective view of the completed drive unit in the electroacoustic transducer of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     While the Present Disclosure may be susceptible to embodiment in different forms, there is shown in the Figures, and will be described herein in detail, specific embodiments, with the understanding that the Present Disclosure is to be considered an exemplification of the principles of the Present Disclosure, and is not intended to limit the Present Disclosure to that as illustrated. 
     As such, references to a feature or aspect are intended to describe a feature or aspect of an example of the Present Disclosure, not to imply that every embodiment thereof must have the described feature or aspect. Furthermore, it should be noted that the description illustrates a number of features. While certain features have been combined together to illustrate potential system designs, those features may also be used in other combinations not expressly disclosed. Thus, the depicted combinations are not intended to be limiting, unless otherwise noted. 
     In the embodiments illustrated in the Figures, representations of directions such as up, down, left, right, front and rear, forward and rearward, used for explaining the structure and movement of the various elements of the Present Disclosure, are not absolute, but relative. These representations are appropriate when the elements are in the position shown in the Figures. If the description of the position of the elements changes, however, these representations are to be changed accordingly. 
       FIG. 1  is a cross-sectional view of an earphone incorporating an electroacoustic transducer according to an embodiment of the Present Disclosure. Because the electroacoustic transducer converts electric signals into acoustic waves, it can be incorporated into an earphone  100 , as shown in  FIG. 1 , or into a headset or hearing aid. The earphone  100  has a bush  101  holding the electroacoustic transducer  1 , a cable  102  connected electrically to the electroacoustic transducer  1 , a body  103  covering the bush  101 , and an ear pad  104  attached to the leading end of the body  103 . The ear pad  104  is inserted into the ear. 
     The cable  102  is connected to audio equipment (not shown) such as a music player, television or radio via a connector (not shown) on the other end, and inputs electric signals outputted from the audio equipment to the electroacoustic transducer  1 . The electroacoustic transducer  1  converts the inputted electric signals into acoustic waves, and outputs the converted acoustic waves from the front end. The acoustic waves outputted from the electroacoustic transducer  1  propagate via the acoustic guide holes  103   a,    104   a  in the body  103  and the ear pad  104  towards the user&#39;s ear. 
     Referring to  FIGS. 2-3 , the electroacoustic transducer  1  has a housing  2 , a diaphragm unit  3 , and a drive unit  10 . The housing  2  is composed of a top housing  4  and a bottom housing  5 , The top housing  4  and the bottom housing  5  are connected to each other via a fixing means such as laser welding or an adhesive with the diaphragm unit  3  interposed between them. The bottom housing  5  has a box-like shape and an open upper surface. The upper surface opening in the bottom housing  5  is covered by the diaphragm  3 , and the drive unit  10  is arranged in the space covered by the bottom housing  5  and the diaphragm unit  3 . The drive unit  10  is fixed to the bottom portion of the bottom housing  5  via a spacer  6  in order to provide a magnetic shield. More specifically, after fixing the spacer  6  to the bottom portion of the bottom housing  5  via a fixing means such as laser welding or an adhesive, the drive unit  10  is fixed to the spacer  6  via a fixing means such as laser welding or an adhesive. 
     The upper surface of the diaphragm unit  3  is covered by the top housing  4 . A cutout portion is formed in a portion of the top housing  4  to serve as an outlet  4   a  for the acoustic waves, and the space covered by the diaphragm unit  3  and the top housing  4  communicates with the space outside of the housing  2  via the cutout portion. In the present specification, the outlet  4   a  is formed on the front surface side of the housing  2 . 
     The drive unit  10  includes an armature  11 , a bobbin  21 , a pair of external connection terminals  31 , a pad  41 , a coil  51 , a pair of magnets  61 , a magnet strap  71  and a drive pin  81 . The armature  11  is a metal plate that has been bent into a substantially E-shaped form when viewed from above, and has a base plate portion  12 , a pair of side plate portions  13  extending from both ends of the base plate portion  12 , and a vibrating portion  14  extending from the central portion of the base plate portion  12  between the side plate portions  13 . The pair of side plate portions  13  are fixed to the outside surface portion of the magnet strap  71  using a fixing means such as laser welding. The bobbin  21  has a coil winding portion  23  around which a coil  51  has been wound, and a magnet positioning portion  24  for positioning the pair of magnets  61 , The base portion  22 , the coil winding portion  23 , and the magnet positioning portion  24  are integrally molded using a resin material. 
     The base portion  22  has a surface which is substantially parallel to the base portion  12  of the armature  11 . A through-hole  25  is formed in the center of the base portion  22  through which the vibrating portion  14  of the armature  11  passes. A portion of the pair of external connection terminals  31  is embedded in the upper portion of the base portion  22 . Each external connection terminal  31  has an external connection portion  32  for receiving electric signals inputted from the outside, a coil connecting portion  33  connected to the coil  51 , an embedded portion  34  embedded in the bobbin  21 , and a linking portion  35  linking the coil connecting portion  33  (embedded portion  34 ) to the external connection portion  32 . The terminal has a reverse L-shape when viewed from the side after completion, and is integrated with the base portion  22  when the bobbin  21  is molded. 
     A pair of protruding portions  26  which protrude towards the back surface are integrally formed in the base portion  22 . The pair of protruding portions  26  are formed in positions corresponding to the pair of cutout portions  5   a.  formed in the back surface portion of the bottom housing  5 . When the drive unit  10  is incorporated into the bottom housing  5 , the protruding portions  26  are fitted into the cutout portions  5   a  of the bottom housing  5 , and position the drive unit  10  with respect to the bottom housing  5 . 
     The linking portion  35  of the external connection terminal  31  protrudes from the leading end surface of the protruding portion  26 , and is bent downward to link up with the external connection portion  32 . In this way, the external connection portion  32  of the external connection terminal  31  is arranged along the back surface of the housing  2  with the drive unit  10  fixed to the bottom housing  5 . 
     The coil winding portion  23  has a pair of arm portions  23   a,    23   b  extending parallel to each other at a predetermined interval so as to connect the space between the base portion  22  and the magnet positioning portion  24 . The coil  51  is formed by winding a coil wire  52  around the arm portions  23   a,    23   b.  The end portion of the coil wire  52  is tied to the coil connecting portion  33  of each external connection terminal  31 , and fixed to the coil connecting portion  33  using welding or soldering. 
     The magnet positioning portion  24  is formed so as to extend from the coil winding portion  23  to the front surface side of the housing  2 . Space remains on the coil winding portion  23  side for inserting the vibrating portion  14  of the armature  11 , and this covers the magnet strap  71 . The pair of magnets  61  are positioned relative to the bobbin  21  so that the magnets  61  are arranged vertically to leave space for inserting the vibrating portion  14  of the armature  11 . Each magnet  61  is pushed into the magnet strap  71  from the front, and is fixed to the magnet strap  71  to the outside of the magnet positioning portion  24  using a fixing means such as welding. 
     The magnet strap  71  is itself magnetic, and is integrated with the magnet positioning unit  24  (bobbin  21 ) when the bobbin  21  is integrally molded by arranging the strap to the outside of the section constituting the magnet positioning portion  24 . The magnet strap  71  may be fixed to the bobbin  21  in a separate step after the bobbin  21  has been completed. 
     The pad  41  is a resin member which holds the external connection portion  32  of each external connection terminal  31 , and which runs along the back surface of the housing  2  with the external connection portions  32  of the external connection terminals  31 . When the bobbin  21  is molded, the pad  41  in the present embodiment is integrally molded with the pair of external connection terminals  31  separately using a resin. However, the bobbin  21  may also be molded at a different time. 
     After the drive unit  10  has been incorporated into the housing  2 , the pad  41  is bonded. to the back surface of the housing  2  using an adhesive  91 . At this time, the linking portion  35  of the external connection terminals  31  exposed inside the housing is covered with adhesive  91 , and the space between the protruding portions  26  of the bobbin  21  and the housing  2  is also filled with adhesive  91 . 
     After the vibrating portion  14  of the armature  11  has been inserted between the coil  51  and the pair of magnets  61 , and the side plate portions  13  of the armature  11  have been fixed to the outside surface portion of the magnet strap  71 , the drive pin  81  is fixed to the leading end portion of the vibrating portion  14  using a fixing means such as laser welding. The drive pin  81  fixed to the vibrating portion  14  extends upward, and the upper end portion is fixed to the diaphragm  3   a  in the diaphragm unit  3  using a fixing means such as laser welding when the drive unit  10  is incorporated into the housing  2 . 
     In operation, a magnetic circuit is formed in the electroacoustic transducer  1  by the pair of magnets  61 , and a direct current magnetic field is generated between the magnets  61 . When electric signals are applied to the coil  51  via the pair of external connection terminals  31 , an alternating current is generated and the alternating current magnetic flux flows through a magnetic circuit composed of the vibrating portion  14  of the armature  11 , the magnets  61 , the magnetic strap  71 , and the side plate portions  13  and base plate portion  12  of the armature  11 . This generates an alternating current magnetic field between the magnets  61  and the vibrating portion  114  of the armature  11 . Superimposing an alternating current magnetic field over a direct current magnetic field causes the vibrating portion  14  of the armature  11  to vibrate. The vibration of the vibrating portion  14  is transmitted to the diaphragm  3   a  in the diaphragm unit  3  via the drive pin  81 , and the diaphragm  3   a  vibrates. When the diaphragm  3   a  vibrates, the pressure inside the space covered by the diaphragm unit  3  and the top housing  4  changes, and the change in pressure generates acoustic waves which are outputted from the housing  2  via the outlet  4   a.  The electroacoustic transducer  1  in the present embodiment includes a spout  7  with a cylindrical acoustic guide  7   a,  and this spout  7  is fixed using a fixing means such as laser welding or an adhesive to the upper portion of the front surface of the housing  2  in which the outlet  4   a  is formed in order to improve the directionality of the acoustic waves outputted from the outlet  4   a.    
     Referring to  FIGS. 4-6 , which illustrate the manufacture of the drive unit  10 , when the drive unit  10  is manufactured, insertion molding is used in which the pair of external connection terminals  31  and the magnet strap  71  are integrally molded in the same resin used to mold the pad  41  and the bobbin  21 . As shown in  FIG. 4 , the pair of external connection terminals  31  and the magnet strap  71  are arranged at predetermined positions in the mold when the bobbin  21 , the pair of external connection terminals  31 , the pad  41 , and the magnet strip  71  are integrally molded in the insertion molding process. 
     In this step, the pair of external connection terminals  31  are integrally linked via a carrier portion  36 , and the linking portion  35  is a flat plate prior to the bending process. In order to improve the integration of the pad  41 , a protruding portion  32   a  is molded three-dimensionally in the external connection portion  32  of each external connection terminal  31  to be embedded in the pad  41 . In order to improve the integration of the bobbin  21 , a linking hole  34   a  linking the front and back resin is formed in the embedded portion  34  of each external connection terminal  31 , and a bent portion  34   b  is formed to prevent detachment of the bobbin  21 . The linking hole  34   a  is a through-hole formed with half-die unevenness to secure the base portion  22  and the embedded portion  34 , It also maintains rigidity as a support portion when the linking portion  35  is bent at the notch  35   a.    
     As shown in  FIG. 5 , an assembly A is produced by the insertion molding process which consists of the integrated bobbin  21 , the pair of external connection terminals  31 , the pad  41 , and the magnet strap  71 . After insertion molding, the carrier portion  36  of the external connection terminals  31  is severed. 
     After the assembly A has been molded, the pair of magnets  61  are incorporated into the magnet positioning portion  24  of the bobbin  21  and fixed. A coil wire  52  is also wound around the coil winding portion  23  of the bobbin  21  to form a coil  51 . The end portion of the coil wire  52  is tied to the coil connecting portions  33  of the external connection terminals  31 , and is fixed to the coil connecting portions  33  using, for example, arc welding or soldering. 
     The external connection terminals  31  and the coil  51  are wired and connected on the assembly A composed of the integrated bobbin  21  around which the coil  51  is wound, and the external terminal connection terminals  31 . This makes it easier to connect the coil  51  and the external connection terminal  31 , and can prevent disconnection during the connection process. Because the wiring and connection process is performed at only one spot on each external connection terminal  31 , the number of connection spots can be reduced and the reliability of the connection can be improved. In the present embodiment, each external connection terminal  31  has a projecting portion  33   a  at the leading end of the coil connecting portion  33  to keep the coil wire  52  tied to the coil connecting portion  33  from coming off. As shown in  FIG. 4 , the coil connecting portion  33  prior to the bending process is flush with an external connection terminal  31 , extends to one side of the base portion  22 , and is positioned above the side plate portions  13  of the armature  11 . This makes the process easier when the coil connecting portion  33  is formed, and eliminates the need for additional space for arranging the coil connecting portion  33 . This makes the overall device more compact. 
     Next, the armature  11  is incorporated into the assembly A. In this step, the vibrating portion  14  of the armature  11  is inserted into the through-hole  25  in the bobbin  21 , and the side plate portions  13  of the armature  11  are fixed to the outer surface of the magnet strap  71  using a fixing means such as laser welding. 
     After the armature  11  has been incorporated into the assembly A, as shown in  FIG. 6 , the linking portion  35  of the external connection terminals  31  is bent so that the external connection portion  32  of the external connection terminals  31  and the pad  41  run along the back surface of the housing  2 . A notch  35   a  is formed on both sides of the linking portion  35 , and the linking portion  35  is bent using the notches  35   a  as the starting point. Finally, the drive pin  81  is fixed to the vibrating portion  14  of the armature  11  passing through the assembly A using a fixing means such as laser welding to complete the drive unit  10 . 
     Referring to  FIGS. 2-3 , when the drive unit  10  is incorporated into the housing  2 , the drive unit  10  is first placed inside the bottom housing  5 . At this time, the protruding portions  26  formed in the bobbin  21  of the drive unit  10  are fitted into the cutout portions  5   a  of the bottom housing  5  to position the drive unit  10  inside the bottom housing  5 . Next, the drive unit  10  is positioned relative to the bottom housing  5 , and the bottom portion of the drive unit  10  is fixed to the spacer  6  secured to the bottom portion of the bottom housing  5  using a fixing means such as laser welding or an adhesive. 
     Next, the opening in the upper surface of the bottom housing  5  is covered by the diaphragm unit  3 . At this time, the upper end of the drive pin  81  is fixed to the diaphragm  3   a  in the diaphragm unit  3  using a fixing means such as laser welding or an adhesive, and the bottom housing  5  and the diaphragm unit  3  are fixed using a fixing means such as laser welding or an adhesive. 
     Next, the diaphragm unit  3  is covered by the top housing  4 . At this time, the top housing  4  is fixed to the bottom housing  5  using a fixing means such as laser welding or an adhesive with the diaphragm unit  3  interposed between the top housing  4  and the bottom housing  5  in order to form the housing  2 . After the housing  2  has been formed, the spout  7  is fixed to the upper portion of the front surface of the housing  2  using a fixing means such as laser welding or an adhesive. 
     Next, the external connection portions  32  of the external connection terminals  31  and the pad  41  running along the back surface of the housing  2  are bonded to the back surface of the housing  2  using an adhesive  91 . At this time, the linking portion  35  of the external connection terminals  31  exposed to the outside in the housing  2  are covered with the adhesive  91 , and the spaces between the protruding portions  26  of the bobbin  21  and the housing  2  are filled in with the adhesive  91 . When this step has been finished, the drive unit  10  has been incorporated into the housing  2 , and the electroacoustic transducer  1  is complete. 
     In the embodiment described above, the electroacoustic transducer  1  includes a housing  2  having an outlet  4   a  for the acoustic waves on a front surface side, a balanced armature drive unit  10  and a diaphragm  3   a  arranged inside the housing  2 , and external connection terminals arranged along a back surface side of the housing  2  and connected electrically to a coil  51  of the drive unit  10 . The external connection terminals  31  have an external connection portion  32  for receiving electric signals inputted from the outside, and a coil connecting portion  33  connected to the coil  51 , a pad  41  holding the external connection portion  32 , and a bobbin  21  around which the coil  51  has been wound. These are integrally molded with the external connection terminals  31  using a resin. The coil  51  wound around the bobbin  21  is connected directly to the coil connecting portion  33 , and the external connection portion  32  and the pad  41  run along the back surface of the housing  2 . The external connection terminals  31  also run along the back surface of the housing  2 . In this electroacoustic transducer  1 , the external connection terminals  31  and coil  51  are wired and. connected on an assembly A in which the bobbin  21  around which the coil  51  is wound and the external connection terminals  31  have been integrated. As a result, the coil  51  and the external connection terminals  31  are easy to connect, and disconnections are prevented during the connection process. Because coil  51  is connected directly to the coil connecting portion  33  of the external connection terminals  31 , and the wiring and connection process for the coil  51  is performed at only one spot on each external connection terminal  31 , the number of connection spots can be reduced and the reliability of the connection can be improved. Because the pad  41  and the bobbin  21  are molded separately from resin and are integrally linked via the external connection terminals  31 , there is a greater degree of freedom in determining the shape and arrangement of the pad  41  and the bobbin  21  compared to a situation in which the pad  41  and the bobbin  21  are integrally molded. 
     By bending the linking portion  35  linking the pad  41  and the bobbin  21  in the external connection terminals  31 , the external connection portion  32  and the pad  41  run along the back surface of the housing  2 . For example, by bending the linking portion  35  after incorporation of the armature  11 , the external connection portions  32  and the pad  41  can run along the back surface of the housing  2  without obstructing the process of incorporating the armature  11 . Because the linking portion  35  of the external connection terminals  31  is covered with an adhesive  91  when the pad  41  is bonded to the back surface of the housing  2 , the linking portion  35  of the external connection terminals  31  is prevented from establishing a short with the housing  2  or another component, and the manufacturing process can be simplified compared to a situation in which the linking portion  35  is coated in another step. 
     A preferred embodiment of the Present Disclosure was described in detail above. However, the Present Disclosure is not limited to the embodiment described above. Various modifications and improvements are possible within the spirit of Present Disclosure described in the claims. For example, when assembly A is formed, a pad  41  does not have to be formed for the external connection terminals  31 , and the external connection portions  32  can run along the back surface alone. In this embodiment, shorts can be prevented between the back surface of the housing  2  and the external connection portions  32  running along the back surface by providing a thin, insulating resin sheet between the back surface of the housing  2  and the external connection portions  32 . This also allows for a more compact device. Further, the electroacoustic transducer  1  in the present embodiment has a pair of external connection terminals, but the number of external connection terminals is not limited to a pair. For example, the Present Disclosure can be advantageously embodied in an electroacoustic transducer with three terminals including a GND connection.