Electroacoustic transducer

Information

  • Patent Grant
  • 6654478
  • Patent Number
    6,654,478
  • Date Filed
    Wednesday, December 12, 2001
    22 years ago
  • Date Issued
    Tuesday, November 25, 2003
    20 years ago
Abstract
A pole piece 31 is placed on a lower case 21. A pole piece 31 has a core 32 and a base 33. The bobbin portion 24 extends from the lower case 21 toward the internal space of a case 1 so as to surround the outer periphery of the core 32. The bobbin portion 24 is divided into a plurality of portions along the circumferential direction of the core 32. The bobbin portion 24 has basal parts 26 and elongated parts 27. The pole piece 31 is pressed from the above of the lower case 21 in a state where the bobbin portion 24 is passed through holes 35 of the base 33, to be positioned on the outer periphery of the core 32, so that the pole piece is fitted and placed into the lower case 21. A coil 41 is configured by winding a conductor wire 42 around the elongated parts 27 of the bobbin portion 24.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to an electroacoustic transducer which transduces an electrical signal into a sound.




2. Description of the Related Art




JP-A-8-6558 discloses an electroacoustic transducer which comprises a case in which a pole piece is mounted. The pole piece comprises a base and a core fixed integrally to each other. A coil is placed on the side of the outer periphery of the core. A magnet is placed around the coil with a gap formed therebetween. The coil is placed by directly winding a conductor wire around the core, or by mounting a prewound coil to the core.




However, the following problems arise in the electroacoustic transducer during a step of placing the coil. When the conductor wire is directly wound around the core, there is a possibility that the conductor wire (insulating layer thereof) is damaged by the core which is made of a metal. Also, when a prewound coil is attached to the core, there is a possibility that the core rubs against the conductive wire, damaging the wire, particularly the insulating layer thereof. When the conductor wire (insulating layer thereof) is damaged in this way, the conductor wire may be in contact with a metal portion such as the core to cause a short circuit, thereby lowering the reliability and durability of the electroacoustic transducer.




It may be contemplated to provide an additional part around which a conductor wire is to be wound. In this case, the production cost is increased by the additional part, and a step of attaching the additional part is additionally required.




Moreover, the additional part reduces the capacity of the back space of the electroacoustic transducer. Accordingly, the sound pressure characteristic, particularly that in the bass region is lowered.




SUMMARY OF THE INVENTION




The invention has been made in view of these problems. It is an object of the invention to provide an electroacoustic transducer in which, during a step of placing a coil, a conductor wire can be prevented from being damaged without increasing the production cost and the manufacturing steps and reductions in reliability and durability can be suppressed.




According to an aspect of the invention, there is provided an electroacoustic transducer comprising:




a pole piece having a base and a core;




a coil disposed around the core;




a magnet disposed around the coil; and




a case made of a resin material, the case accommodating the pole piece, the coil, and the magnet in an internal space thereof,




wherein a bobbin portion is formed integrally with the case, the bobbin portion elongating toward the internal space of the case; and




the coil is configured by winding a conductor wire around the bobbin portion.




In the electroacoustic transducer of the invention, the bobbin portion is formed integrally with the case which is made of a resin material, and the conductor wire is wound around the bobbin portion to configure the coil. Since the bobbin portion is made of the same resin material as the case, it is possible to prevent the conductor wire (covering layer thereof) from being damaged during a step of winding the conductor wire around the bobbin portion. This configuration prevents a short circuit possibly caused by a damaged conductor wire (coil) being in contact with a metal portion such as the core, and hence it is possible to suppress reductions of the reliability and durability of the electroacoustic transducer.




In the electroacoustic transducer of the invention, since the bobbin portion is formed integrally with the case, another member for winding the conductor wire is not additionally required. Therefore, it is possible to realize simply and at a low cost a configuration in which the bobbin portion can be provided without increasing the production cost and the manufacturing steps, and the conductor wire (covering layer thereof) can be prevented from being damaged.




Preferably, the case comprises an upper case, and a lower case having a coil terminal portion to which an end of the conductor wire is electrically connected, and the bobbin portion is formed integrally with the lower case.




Since the case is configured in this way, the bobbin portion which extends into the internal space of the case can be easily formed.




Preferably, the bobbin portion extends from the lower case to surround the outer periphery of the core, and the base is placed on the lower case, and has a hole through which the bobbin portion is passed.




Since the bobbin portion is formed in this way, it is possible to realize very simply a configuration in which the base can be easily placed on the lower case without interfering with the bobbin portion.




According to another aspect of the present invention, there is provided an electroacoustic transducer comprising:




a pole piece having a base and a core;




a bobbin portion placed to surround an outer periphery of the core;




a coil formed of a conductor wire wound around the bobbin portion; and




a magnet placed around the coil,




wherein the bobbin portion is divided into a plurality of portions along a circumferential direction of the core.




In the electroacoustic transducer of the invention, since the coil is configured by winding the conductor wire around the bobbin portion, it is possible to prevent the conductor wire (covering layer thereof) from being damaged during a step of winding the conductor wire. This configuration prevents a short circuit possibly caused by a damaged conductor wire (coil) being in contact with the core. As a result, it is possible to suppress reductions of the reliability and durability of the electroacoustic transducer.




In the electroacoustic transducer of the invention, since the bobbin portion is divided into plural parts along the circumferential direction of the core, the bobbin portion is intermittently placed as viewed along the circumferential direction of the core, and hence the capacity of the bobbin portion can be reduced. Therefore, a reduction of the capacity of the back space of the electroacoustic transducer can be suppressed as far as possible, so that the sound pressure characteristic can be prevented from being lowered.




Preferably, the transducer further comprises a case comprising: an upper case; and a lower case having a coil terminal portion to which an end of the conductor wire is electrically connected, and the bobbin portion is formed integrally with the lower case.




Since the transducer further comprises a case configured in this way, another part for winding the conductor wire is not additionally required. Therefore, it is possible to realize simply and at a low cost a configuration in which the bobbin portion can be disposed without increasing the production cost and the manufacturing steps, and the conductor wire (covering layer thereof) can be prevented from being damaged.




Preferably, the bobbin portion extends from the lower case to surround the outer periphery of the core, and the core is pressed against the bobbin portion. Since the bobbin portion is formed in this way, the pole piece can be prevented from being detached from the lower case.




Preferably the base is placed on the lower case, and has a hole through which the bobbin portion is passed. Accordingly, it is possible to realize very simply a configuration in which the base can be easily placed on the lower case without interfering with the bobbin portion.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a perspective view showing the whole appearance of an electroacoustic transducer according to an embodiment of the invention.





FIG. 2

is a section view showing the electroacoustic transducer according to the embodiment of the invention.





FIG. 3

is an exploded perspective view showing the configuration of the electroacoustic transducer according to the embodiment of the invention.





FIG. 4

is a plan view of a pole piece included in the electroacoustic transducer according to the embodiment of the invention.





FIG. 5

is a perspective view of the pole piece included in the electroacoustic transducer according to the embodiment of the invention.





FIG. 6

is a plan view of a lower case included in the electroacoustic transducer according to the embodiment of the invention.





FIG. 7

is a perspective view of the lower case included in the electroacoustic transducer according to the embodiment of the invention.





FIG. 8

is a plan view showing a state where electroacoustic transducer where a conductor wire is wound around a bobbin portion to constitute a coil.





FIG. 9

is a perspective view showing the state where the conductor wire is wound around the bobbin portion to constitute the coil.











DETAILED DESCRIPTION OF THE PRESENT INVENTION




The present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the identical components are denoted by the same reference numerals, and duplicated description is omitted.





FIG. 1

is a perspective view showing the whole appearance of an electroacoustic transducer of the embodiment of the invention.

FIG. 2

is a section view showing the electroacoustic transducer.

FIG. 3

is an exploded perspective view showing the configuration of the electroacoustic transducer.




The electroacoustic transducer T has a case


1


made of a thermoplastic resin. The case


1


includes an upper case


11


and a lower case


21


which are bonded and fixed to each other by using the ultrasonic welding technique. The upper case


11


has a substantially box-like shape in which the lower face is opened. The upper case


11


has a sound release opening


12


in the upper face thereof and a sound release tube


13


extending toward the inside thereof. The upper case


11


has a stepped portion


14


against which an ultrasonic welder is to abut. A pole piece


31


, a coil


41


, a magnet


51


, a diaphragm


61


, and others are housed in the internal space defined by the upper case


11


and the lower case


21


.




The pole piece


31


is placed on the lower case


21


. As shown in

FIGS. 4 and 5

, the pole piece


31


has a core


32


having a substantially columnar shape, and a base


33


made of a metal material (for example, permalloy). The core


32


is caulked and integrally fixed to the center position of the base


33


. A cutaway portion


34


is formed in a predetermined position of the edge of the base


33


. A plurality of holes


35


(three in the embodiment) are formed in the base


33


so as to surround the portion to which the core


32


is fixed. A bobbin portion


24


that will be described later is to be passed through the plurality of holes


35


. In the embodiment, the base


33


is set to have a thickness of about 0.6 mm, and the length (the height) of the core


32


from the upper face of the base


33


is set to be about 3.8 mm.




As shown in

FIGS. 6 and 7

, integrally formed on the upper face of the lower case


21


are a wall


22


for defining the placement position of the pole piece


31


, a projection


23


engageable with the cutaway portion


34


of the base


33


, and the bobbin portion


24


for configuring the coil


41


. Formed at the wall


22


are projections


25


being engageable with a projection


15


formed on the upper case


11


. When the projections


25


and


15


are engaged with each other, the upper case


11


is positioned with respect to the lower case


21


. Each of the wall


22


and the projection


23


is set to have a height larger than the thickness of the base


33


. In the embodiment, the height of the wall


22


is set to be about 1.2 mm, and that of the projection


23


to be about 0.8 mm.




The bobbin portion


24


extends from the upper face of the lower case


21


toward the internal space of the case


1


so as to surround the outer periphery of the core


32


. The bobbin portion is divided into plural parts (three in the embodiment) along the circumferential direction of the core


32


. The bobbin portion


24


is configured by basal parts


26


and elongated parts


27


. The basal parts


26


are set to have a height (in the embodiment, about 0.85 mm) larger than the thickness of the base


33


. The length of each elongated part


27


is set to have a value (in the embodiment, about 2.95 mm) at which the top of the core


32


protrudes from the end of the elongated part


27


in a state where the pole piece


31


is placed on the lower case


21


. The inner diameter of the bobbin portion


24


(the basal parts


26


) is set to have a value (in the embodiment, about 2.2 mm) approximately equal to the outer diameter of the core


32


.




The face of each basal part


26


on the side of the core


32


is curved so as to extend along the outer periphery of the core


32


. In each elongated part


27


, also both the face on the side of the core


32


, and the rear face (the face on the side where a conductor wire


42


is to be wound) are curved so as to extend along the outer periphery of the core


32


. The sectional area of the basal parts


26


is set to be larger than that of the elongated parts


27


. According to this configuration, it is possible to ensure the mechanical strength of the bobbin portion


24


, so that the bobbin portion


24


is prevented from being detached from the lower case


21


.




The pole piece


31


(the base


33


) is pressed from the above of the lower case


21


in a state where the bobbin portion


24


(the elongated parts


27


) is passed through the holes


35


of the base


33


to be positioned on the outer periphery of the core


32


, whereby the pole piece is fitted and placed into the lower case


21


. At this time, the positioning of the pole piece


31


with respect to the lower case


21


is performed by engaging the cutaway portion


34


of the base


33


with the projection


23


of the lower case


21


. Under a state where the pole piece


31


is fitted into the lower case


21


, the core


32


is pressed against the bobbin portion


24


because the inner diameter of the bobbin portion


24


(the basal parts


26


) is set to have a value which is approximately equal to the outer diameter of the core


32


. As a result, the pole piece


31


is hardly detached from the lower case


21


.




As shown also in

FIGS. 8 and 9

, the coil


41


is configured by winding the conductor wire


42


around the elongated parts


27


of the bobbin portion


24


, and placed on the basal parts


26


. In the embodiment, a copper wire of a diameter of about 60 μm is used as the conductor wire


42


. An insulating layer is disposed on the outer periphery of the copper wire. The height of the coil is set to a value (in the embodiment, about 2.9 mm) smaller than the length of each elongated part


27


.




The basal parts


26


are set to have a height larger than the thickness of the base


33


so that the coil


41


does not abut against the base


33


(the pole piece


31


). The bobbin portion


24


(the elongated parts


27


) is divided into the plural parts along the circumferential direction of the core


32


so that the bobbin portion


24


(the elongated parts


27


) is intermittently placed as viewed along the circumferential direction of the core


32


. The conductor wire


42


is linearly wound between the divided parts of the bobbin portion


24


.




In the lower case


21


, lead terminals


28


and


29


serving as terminals of the coil


41


are disposed in an integral manner by so-called “insert molding”. As shown in

FIGS. 8 and 9

, the ends of the conductor wire


42


constituting the coil


41


are passed over the projection


23


formed on the lower case


21


, and then drawn out through a cutaway portion


30


formed in the wall


22


, onto lands


28




a


and


29




a


of the lead terminals


28


and


29


, respectively. Under this state, the ends are soldered to the lands


28




a


and


29




a.


The cutaway portion


30


formed in the wall


22


is sealed by a silicone material (not shown).




Referring again

FIGS. 2 and 3

, the magnet


51


is configured by an annular plastic magnet, and placed on the side of the outer periphery of the coil


41


with a gap provided between the magnet and the coil


41


. The magnet


51


is placed against the base


33


of the pole piece


31


, and against the wall


22


of the lower case


21


, thereby restricting the placement position of the magnet.




A stepped portion


52


is formed in the magnet


51


. The diaphragm


61


is placed on the stepped portion


52


. In the embodiment, the magnet


51


functions also as a support member which supports the diaphragm


61


. A magnetic piece


62


, serving as an additional mass, is disposed in a center portion of the diaphragm


61


. The diaphragm


61


is caused to be attracted toward the magnet


51


by function of the static magnetic field of the magnet


51


. The upward movement of the diaphragm


61


is restricted by the stepped portion


14


of the upper case


11


.




A back space A is formed on the side of the back face of the diaphragm


61


. A resonant space B surrounded by the upper case


11


is formed on the side of the upper face of the diaphragm


61


. The resonant space B is opened to the outside through the sound release tube


13


formed on the upper case


11


, i.e., the sound release opening


12


.




Then, the operation of the electroacoustic transducer T of the invention will be described. In the electroacoustic transducer T, the base


33


, the core,


32


, the diaphragm


61


, and the magnet


51


constitute a magnetic circuit, and the static magnetic field generated by the magnet


51


acts on the diaphragm


61


, so that the magnetized diaphragm


61


is attracted toward the core


32


. The magnet


51


functions so as to generate a bias magnetic field for the diaphragm


61


.




In contrast to the unidirectional magnetic field due to the static magnetic field, when an electric signal in the form of AC, pulses or the like is applied between the lead terminals


28


and


29


, the signal current flows through the coil


41


, and an oscillating magnetic field corresponding to the electric signal is generated in the core


32


. When the direction of the oscillating magnetic field is opposite to that of the static magnetic field of the magnet


51


, the diaphragm


61


swings in the direction away from the core


32


. When the direction of the oscillating magnetic field coincides with that of the static magnetic field, the diaphragm is attracted toward the core


32


. Such mechanical vertical movements depend on the frequency of the electric signal, with the result that the diaphragm


61


vibrates to cause air to oscillate. This oscillation is amplified as a resonant sound by the resonant space B. This sound is released mainly through the sound release opening


12


to the outside.




In the embodiment, as described above, the bobbin portion


24


(the basal parts


26


and the elongated parts


27


) is formed integrally with the lower case


21


(the case


1


) made of a resin material (thermoplastic resin), and the conductor wire


42


is wound around the bobbin portion


24


(the elongated parts


27


), whereby the coil


41


is configured. It is possible to prevent the conductor wire


42


, particularly the covering layer (insulating layer) thereof from being damaged during a step of winding the conductor wire


42


around the bobbin portion


24


(the elongated parts


27


), since the bobbin portion


24


(the elongated parts


27


) is made of the same resin material as the lower case


21


(the case


1


). As a result, this prevents a short circuit possibly caused by a damaged conductor wire


42


(coil


41


) being in contact with a metal portion such as the core


32


. It is possible to suppress reductions in reliability and durability of the electroacoustic transducer T.




The bobbin portion


24


(the basal parts


26


and the elongated parts


27


) and the lower case


21


(the case


1


) can be molded at one time because the bobbin portion


24


(the basal parts


26


and the elongated parts


27


) is formed integrally with the lower case


21


(the case


1


). Accordingly, Another part for winding the conductor wire


42


is not additionally required. Therefore, it is possible to realize simply and at a low cost a configuration in which the bobbin portion


24


can be disposed without increasing the production cost and the manufacturing steps, and the conductor wire


42


(covering layer thereof) can be prevented from being damaged.




Since the bobbin portion


24


(the basal parts


26


and the elongated parts


27


) is divided into plural parts along the circumferential direction of the core


32


, the bobbin portion


24


(the basal parts


26


and the elongated parts


27


) is intermittently placed as viewed along the circumferential direction of the core


32


, and hence the capacity of the bobbin portion


24


can be reduced. Therefore, a reduction of the capacity of the back space A of the electroacoustic transducer T can be suppressed as far as possible, so that the sound pressure characteristic can be prevented from being lowered.




Moreover, the conductor wire


42


is linearly wound between the divided parts of the bobbin portion


24


(the elongated parts


27


). According to this configuration, even when vibrations of any kind are transmitted to the coil


41


as in the case where the upper case


11


and the lower case


21


are ultrasonic welded together, movement of the coil


41


around the bobbin portion


24


is restricted, including a movement of the coil


41


toward the center axis of the core


32


. As a result, it is possible to prevent the conductor wire


42


constituting the coil


41


, from being damaged or broken.




The case


1


comprises the upper case


11


; and the lower case


21


in which the lead terminals


28


and


29


are disposed. The bobbin portion


24


(the basal parts


26


and the elongated parts


27


) is formed integrally with the lower case


21


, the bobbin portion


24


(the basal parts


26


and the elongated parts


27


) and the lower case


21


(the case


1


) can be molded at one time, and hence another part for winding the conductor wire


42


is not additionally required. Therefore, it is possible to realize simply and at a low cost a configuration in which the bobbin portion


24


can be provided without increasing the production cost and the manufacturing steps, and the conductor wire


42


(covering layer thereof) can be prevented from being damaged.




The bobbin portion


24


(the basal parts


26


and the elongated parts


27


) is extends from the lower case


21


so as to surround the outer periphery of the core


32


, and the core


32


is pressed against the bobbin portion


24


. Therefore, the pole piece


31


can be prevented from being detached from the lower case


21


, by the simple configuration.




The base


33


of the pole piece


31


has the holes


35


through which the bobbin portion


24


(the basal parts


26


and the elongated parts


27


) is to be passed. When the pole piece


31


is fitted and placed into the lower case


21


, therefore, the bobbin portion


24


(the basal parts


26


and the elongated parts


27


) does not interfere with the base


33


. As a result, it is possible to realize very simply a configuration in which the pole piece


31


can be easily placed on the lower case


21


.




The invention is not restricted to the embodiment described above. The above-mentioned values, and the shape of each component, and the like (for example, the shape and number of divisions of the bobbin portion


24


) can be set with being suitably changed. In the embodiment, the bobbin portion


24


is configured by the basal parts


26


and the elongated parts


27


. The configuration of the bobbin portion is not limited thereto. Alternatively, the bobbin portion may be configured by only parts corresponding to the elongated parts


27


.




In the embodiment, the bobbin portion


24


is formed integrally with the lower case


21


(the case


1


). The invention is not restricted thereto. For example, the bobbin portion


24


may be formed separately from the lower case


21


(the case


1


), and then attached and fixed to the lower case


21


by bonding or the like.




In the embodiment, the pole piece


31


is placed on the lower case


21


by means of fitting. The manner of the placement is not restricted thereto. For example, the pole piece


31


may be disposed integrally on the lower case


21


by the insert molding in the same manner as the lead terminals


28


and


29


. In this case, the bobbin portion


24


is formed so as to cover the outer periphery of the core


32


of the pole piece


31


.




As described above in detail, according to the invention, it is possible to provide an electroacoustic transducer in which, during a step of placing a coil, a conductor wire can be prevented from being damaged, without increasing the production cost and the manufacturing steps, and reductions in reliability and durability can be suppressed.



Claims
  • 1. An electroacoustic transducer comprising:a pole piece having a base and a core; a bobbin portion placed to surround an outer periphery of the core; a coil formed of a conductor wire wound around the bobbin portion; and a magnet placed around the coil, wherein the bobbin portion is divided into a plurality of unattached individual portions along a circumferential direction of the core.
  • 2. The electroacoustic transducer according to claim 1, wherein the transducer further comprises a case comprising:an upper case; and a lower case having a coil terminal portion to which an end of the conductor wire is electrically connected, and the bobbin portions are formed integrally with the lower case.
  • 3. The electroacoustic transducer according to claim 2, wherein the bobbin portions extend from the lower case to surround the outer periphery of the core, andthe core is pressed against the bobbin portions.
  • 4. The electroacoustic transducer according to claim 3, wherein the base is placed on the lower case, and has holes through which the bobbin portions are passed.
  • 5. The electroacoustic transducer according to claim 2, wherein the base is placed on the lower case, and has holes through which the bobbin portions are passed.
Priority Claims (2)
Number Date Country Kind
P. 2000-382286 Dec 2000 JP
P. 2000-382297 Dec 2000 JP
US Referenced Citations (4)
Number Name Date Kind
2271525 Seabert Feb 1942 A
2699472 Olson et al. Jan 1955 A
5394479 Ishigaya et al. Feb 1995 A
5894263 Shimakawa et al. Apr 1999 A
Foreign Referenced Citations (5)
Number Date Country
0 706 300 Apr 1996 EP
3-240399 Oct 1991 JP
8-6558 Jan 1996 JP
8-186895 Jul 1996 JP
9-179562 Jul 1997 JP