Patent Publication Number: US-2019191251-A1

Title: Diaphragm and electroacoustic transducer

Description:
TECHNICAL FIELD 
     The present invention relates to a diaphragm and an electroacoustic transducer. 
     BACKGROUND ART 
     Electroacoustic transducers which interconvert between electric signals and sound waves are incorporated into electroacoustic transducer apparatuses such as headphones, microphones, and speakers. The electroacoustic transducer generates the sound waves in response to the electric signals by vibration of a diaphragm based on the electric signals or generates the electric signals in response to the sound waves by vibration of the diaphragm based on the sound waves. 
     The conversion types of the electroacoustic transducers include a dynamic type using a magnetic field and a condenser type using an electric field. 
     A dynamic electroacoustic transducer includes a magnetic circuit, a voice coil, and a diaphragm. The magnetic circuit generates a magnetic field. The voice coil is a conductor disposed in the magnetic field of the magnetic circuit and is attached to the diaphragm. The diaphragm generates sound waves by being vibrated by a driving force generated when flowing electric signals (currents) in the voice coil, or generates an electric signal in the voice coil by vibrating with the voice coil when receiving sound waves. 
     The diaphragm includes a vibrating portion and an attaching portion. The diaphragm is formed by pressurizing or heating of thin films such as polymer films. The vibrating portion includes a main dome and an auxiliary dome. The main dome has a circular dome shape in plan view. The auxiliary dome has an annular shape and a dome shape in plan view. The auxiliary dome continues to an outer peripheral edge of the main dome. The attaching portion continues to an outer peripheral edge of the auxiliary dome. That is, the main dome, the auxiliary dome, and the attaching portion are integrally formed. 
     In general, the diaphragm includes a thin film to reduce stiffness of the diaphragm. Thus, the mechanical strength of the diaphragm is likely to be low. As a result, the main dome can be readily deformed by an applied acoustic pressure or the driving force of the voice coil. If the mechanical strength of the diaphragm is low, the quality of sound output from the diaphragm decreases. 
     With respect to methods of enhancing the mechanical strength of the diaphragm, methods have been proposed to adhere a reinforcing film (reinforcing member) onto one face of the diaphragm (for example, refer to Japanese Unexamined Patent Application Publication No. 1980-137797), and to increase the thickness of the diaphragm (for example, refer to Japanese Unexamined Patent Application Publication No. 2008-85985). 
     SUMMARY OF INVENTION 
     Technical Problem 
     The lowest resonant frequency (f 0 ) of the diaphragm is varied by the influence of adhering the reinforcing member to the entire vibrating portion, in particular, along the outer peripheral edge of the auxiliary dome or increasing the thickness of the diaphragm in order to enhance the mechanical strength of the diaphragm. If the lowest resonant frequency is varied, the characteristics of the diaphragm in the low frequency range are deteriorated. 
     An object of the present invention is to solve the problem described above and provide a diaphragm and an electroacoustic transducer that suppress the influence to the lowest resonant frequency and enhance the mechanical strength. 
     Solution to Problem 
     A diaphragm according to the present invention includes a main dome, an auxiliary dome continuing to the outer peripheral edge of the main dome, and a reinforcing member disposed on a boundary between the main dome and the auxiliary dome. The reinforcing member is disposed so as not to reach the outer peripheral edge of the auxiliary dome. 
     Advantageous Effect of Problem 
     According to the present invention, the influence to the lowest resonant frequency can be suppressed and the mechanical strength can be enhanced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
         FIG. 1  is a perspective view of an exemplary electroacoustic transducer apparatus including an electroacoustic transducer according to the present invention. 
         FIG. 2  is a left side view of the electroacoustic transducer apparatus in  FIG. 1 . 
         FIG. 3  is a cross-sectional view of the electroacoustic transducer apparatus taken along line A-A in  FIG. 2 . 
         FIG. 4  represents a plan view illustrating an embodiment of a diaphragm according to the present invention, and a cross-sectional view of the diaphragm taken along line B-B in the plan view of  FIG. 4 . 
         FIG. 5  is a graph illustrating frequency characteristics of the electroacoustic transducer according to the present invention. 
         FIG. 6  is a cross-sectional view of a diaphragm illustrating another aspect of a reinforcing member included in the diaphragm according to the present invention. 
         FIG. 7  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
         FIG. 8  represents a plan view illustrating another embodiment of a diaphragm according to the present invention, and a cross-sectional view of the diaphragm taken along line C-C in the plan view of  FIG. 8 . 
         FIG. 9  is a cross-sectional view of a diaphragm illustrating another aspect of the reinforcing member. 
         FIG. 10  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
         FIG. 11  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
         FIG. 12  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
         FIG. 13  represents a plan view illustrating still another embodiment of a diaphragm according to the present invention, a cross-sectional view of the diaphragm taken along line D-D in the plan view of  FIG. 13 , and a bottom view of the diaphragm. 
         FIG. 14  is a cross-sectional view of a diaphragm illustrating another aspect of the reinforcing member. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of a diaphragm and an electroacoustic transducer will now be described with reference to the attached drawings. 
     Electroacoustic Transducer Apparatus ( 1 ) 
     An electroacoustic transducer apparatus including an electroacoustic transducer according to the present invention (hereinafter referred to as “present apparatus”) will now be described. 
     The present apparatus is an electroacoustic transducer apparatus, for example, headphones, ear phones, and speakers, that outputs sound waves based on sound signals from sound sources such as portable music players. In the following description, the present apparatus will be described by taking a headphone as an example. 
     Configuration of Electroacoustic Transducer Apparatus ( 1 ) 
       FIG. 1  is a perspective view of a present apparatus. 
       FIG. 2  is a left side view of a present apparatus. 
     A present apparatus  1  is worn on the head of a user and outputs sound waves based on the sound signals from a sound source. The present apparatus  1  is, for example, a wired headphone that receives sound signals from a sound source via cables (not shown). 
     The present apparatus may be a wireless headphone that receives sound signals from a sound source via wireless transmission such as Bluetooth (registered trademark). 
     In the following description, the top, bottom, right, left, front, and rear directions of the present apparatus  1  are the same as the top, bottom, right, left, front, and rear directions of the user wearing the present apparatus  1 . 
     The present apparatus  1  includes a first sound emission unit  10 , a second sound emission unit  20 , and a connection member  30 . 
       FIG. 3  is a cross-sectional view of the first sound emission unit  10  taken along line A-A in  FIG. 2 . 
     The first sound emission unit  10  is worn over the left ear of the user and outputs sound waves based on the sound signals from a sound source. The first sound emission unit  10  includes a housing  11 , an ear pad  12 , a circuit board  13 , and an electroacoustic transducer  14 A. 
     The housing  11  accommodates the circuit board  13  and the electroacoustic transducer  14 A. The housing  11  includes a baffle plate  111 , a first housing  112 , and a second housing  113 . 
     The baffle plate  111  holds the electroacoustic transducer  14 A. The first housing  112  defines a first housing chamber S 1  accommodating the electroacoustic transducer  14 A together with the baffle plate  111 . The second housing  113  defines a second housing chamber S 2  accommodating the circuit board  13  together with the first housing  112 . 
     The ear pad  12  is a buffer disposed between the housing  11  and the head of the user. The ear pad  12  defines a closed space S 3  between the housing  11  and the head of the user (hereinafter referred to as “front air chamber”) when the present apparatus  1  is worn on the head of the user. 
     The circuit board  13  is provided with such as a circuit for receiving the sound signals and a circuit for noise cancellation. The circuit board  13  is disposed in the second housing chamber S 2 . 
     The circuit board is not an essential configuration in the present invention. The first sound emission unit may not include the circuit board. In that case, the second chamber is not required. 
     The electroacoustic transducer  14 A generates sound waves based on electric signals (sound signals) from a sound source and outputs the sound waves to the front air chamber S 3 . The electroacoustic transducer  14 A is attached to the baffle plate  111  and is disposed in the first housing chamber S 1 . The configuration of the electroacoustic transducer  14 A will be described below. 
     Referring back to  FIG. 1 , the second sound emission unit  20  is worn over the right ear of the user and outputs sound waves based on the sound signals from a sound source. The second sound emission unit  20  has the same configuration as the configuration of the first sound emission unit  10 . That is, the second sound emission unit  20  includes a housing  21 , an ear pad  22 , a circuit board (not shown), and an electroacoustic transducer (not shown). 
     The connection member  30  connects the first sound emission unit  10  and the second sound emission unit  20 . 
     Configuration of Electroacoustic Transducer ( 1 ) 
     An electroacoustic transducer according to the present invention will now be described. The electroacoustic transducer (not shown) included in the second sound emission unit  20  has the same configuration as the configuration of the electroacoustic transducer  14 A included in the first sound emission unit  10 . An exemplary configuration of the electroacoustic transducer  14 A of the first sound emission unit  10  will be described below. 
     The electroacoustic transducer  14 A includes a unit case  141 , a magnetic circuit  142 , a voice coil  143 , and a diaphragm  144 A. 
     The unit case  141  accommodates the magnetic circuit  142 , the voice coil  143 , and the diaphragm  144 A. The unit case  141  is attached to the baffle plate  111 . 
     The magnetic circuit  142  generates a magnetic field. The magnetic circuit  142  includes a magnetic gap G through which a magnetic flux with a uniform density passes. 
     The voice coil  143  is configured to drive (vibrate) in response to the sound signals. The voice coil  143  is attached to the rear face of the diaphragm  144 A (the left face in  FIG. 3 ). The voice coil  143  is disposed in the magnetic gap G so as to traverse the magnetic flux. 
     The diaphragm  144 A is configured to vibrate in response to driving (vibration) of the voice coil  143  and to output sound waves. The diaphragm  144 A is a thin circular film in plan view. The diaphragm  144 A is a film composed of a synthetic resin such as polypropylene or polyethylene, for example. The configuration of the diaphragm  144 A will be described below. 
     Configuration of Diaphragm ( 1 ) 
     The diaphragm according to the present invention will now be described. 
       FIG. 4  illustrates an embodiment of the diaphragm according to the present invention.  FIG. 4  represents a plan view of the diaphragm, and a cross-sectional view of the diaphragm taken along line B-B in the plan view of  FIG. 4 . 
     The diaphragm  144 A includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 A. The main dome  1441 , the auxiliary dome  1442 , the attaching portion  1443 , the boundary  1444 , and the boundary  1445  are integrally formed by heat pressing. The diaphragm  144 A includes the boundary  1444  between the main dome  1441  and the auxiliary dome  1442 , and includes the boundary  1445  between the auxiliary dome  1442  and the attaching portion  1443 . 
     The main dome  1441 , the auxiliary dome  1442 , and the boundary  1444  constitute a vibrating portion vibrating based on driving of the voice coil  143 . The main dome  1441  has a circular shape in plan view and a dome shape convex to the right (the right in  FIG. 3 ) in cross-sectional view. The auxiliary dome  1442  has an annular shape in plan view and an arcuate shape convex to the right in cross-sectional view. The auxiliary dome  1442  continues to the outer peripheral edge of the main dome. That is, the auxiliary dome  1442  is disposed along the outer peripheral edge of the main dome  1441 . A line connecting boundary  1444  between the main dome  1441  and the auxiliary dome  1442  (an imaginary line) has a circular shape in plan view. The auxiliary dome  1442  has a top part P. The top part P is the top of the auxiliary dome  1442 . 
     The width of the boundary (in the horizontal direction in the cross-sectional view of  FIG. 4 ) is appropriately determined according to the application and the size of the diaphragm. 
     The attaching portion  1443  is attached to the unit case  141 . The diaphragm  144 A can vibrate relative to the unit case  141 . The attaching portion  1443  has an annular shape in plan view and a flat plate shape in cross-sectional view. The attaching portion  1443  continues to an outer peripheral edge of the auxiliary dome  1442 . That is, the attaching portion  1443  is disposed along the outer peripheral edge of the auxiliary dome  1442 . A line connecting the boundary  1445  between the auxiliary dome  1442  and the attaching portion  1443  (an imaginary line) has a circular shape in plan view. 
     The reinforcing member  1446 A reinforces the vibrating portion to enhance (increase) the mechanical strength of the vibrating portion. 
     The reinforcing member  1446 A covers the entirety of the front face of the main dome  1441  (the upper face in the cross-sectional view of  FIG. 4 ), the boundary  1444 , and part of the front face of the auxiliary dome  1442 . The reinforcing member  1446 A has a circular shape in plan view. The reinforcing member  1446 A is a thin film composed of a thermoplastic resin such as polycarbonate, for example. That is, a material of the reinforcing member  1446 A is different from a material of the vibrating portion. 
     The material of the reinforcing member may be the same as the material of the vibrating portion as long as the material that can reinforce the vibrating portion. 
     The reinforcing member  1446 A is adhered to a front face of the vibrating portion (the upper face in the cross-sectional view of  FIG. 4 ) with an adhesive (not shown). The adhesive is an ultraviolet (UV) curing-type adhesive, for example. 
     The adhesive is not limited to an UV curing-type adhesive as long as an adhesive which can adhere the reinforcing member to the vibrating portion. 
     The configuration of the reinforcing member is not limited to the embodiment. That is, the reinforcing member may have a configuration including a mesh for the entire or only part of the reinforcing member, and/or may include a groove, hole, or opening for flowing out an excessive adhesive. 
     As shown in the cross-sectional view of  FIG. 4 , the reinforcing member  1446 A is disposed on the front face of the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442  (on the upper face in the cross-sectional view of  FIG. 4 ). The reinforcing member  1446 A is disposed so as not to reach the outer peripheral edge of the auxiliary dome  1442 . That is, the reinforcing member  1446 A is not disposed along the boundary  1445 . In other words, the reinforcing member  1446 A is not disposed along the outer peripheral edge of the auxiliary dome  1442 . Thus, the reinforcing member  1446 A is adhered to the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442  with an adhesive (not shown). 
     The expression “the reinforcing member  1446 A is disposed so as not to reach the outer peripheral edge of the auxiliary dome  1442 ” indicates that an outer peripheral edge of the reinforcing member  1446 A having a circular shape in plan view are disposed in the auxiliary dome  1442  more inwardly (the boundary  1444  side) than the boundary  1445 . That is, the outer peripheral edge of the reinforcing member  1446 A is disposed on the auxiliary dome  1442  disposed between the boundary  1444  and the boundary  1445 . 
     As shown in the cross-sectional view of  FIG. 4 , the outer peripheral edge of the reinforcing member  1446 A is disposed so as to extend to the top part P of the auxiliary dome  1442 . That is, the reinforcing member  1446 A is disposed on the main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442 . 
     The outer peripheral edge of the reinforcing member is preferably disposed near the top part P of the auxiliary dome  1442 , for example. The phrase “near the top part P” is the area from “the intermediary position between the top part P and the boundary  1444 ” of the auxiliary dome  1442  to “the intermediary position between the top part P and the boundary  1445 ”. In other words, “near the peak P” includes an area extending inwardly from the top part P (the intermediary position side between the top part P and the boundary  1444 ) and an area extending outwardly from the top part P (the intermediary position side between the top part P and the boundary  1445 ). 
     Operation of Electroacoustic Transducer ( 1 ) 
     The operation of the electroacoustic transducer according to the present invention will now be described. 
     The diaphragm  144 A is configured to vibrate in response to driving (vibration) of the voice coil  143  and to output sound waves. The reinforcing member  1446 A is disposed on the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442 . Thus, the mechanical strength of the diaphragm  144 A is enhanced. Furthermore, the reinforcing member  1446 A is disposed so as not to reach the outer peripheral edge of the auxiliary dome  1442 . Thus, the influence to the lowest resonant frequency of the diaphragm  144 A (for example, an increase in the lowest resonant frequency) is suppressed. 
       FIG. 5  is a graph illustrating frequency characteristics of the electroacoustic transducer according to the present invention. 
       FIG. 5  shows a results of comparison between the frequency characteristics of a conventional electroacoustic transducer (hereinafter referred to as “conventional product”) and the frequency characteristics of the electroacoustic transducer according to the present invention. 
     In  FIG. 5 , the solid line indicates the frequency characteristics of the electroacoustic transducer  14 A according to the present invention whereas the dotted line indicates the frequency characteristics of the conventional product. As shown in  FIG. 5 , the frequency characteristics of the electroacoustic transducer  14 A and the frequency characteristics of the conventional product are almost comparable in the low frequency range. That is, although the electroacoustic transducer  14 A includes the reinforcing member  1446 A, the influence to the lowest resonant frequency of the diaphragm  144 A is suppressed. In the frequency characteristics of the electroacoustic transducer  14 A, the acoustic pressure outputted from the diaphragm is reduced in the middle and high frequency ranges compared to the frequency characteristics of the conventional product. In other words, the electroacoustic transducer  14 A has the excellent frequency characteristics because the resonance of the diaphragm  144 A is avoided and the frequency characteristics in the middle and high frequency ranges are improved compared to the conventional product. 
     Synopsis ( 1 ) 
     According to the embodiment described above, the diaphragm  144 A of the electroacoustic transducer  14 A includes the reinforcing member  1446 A on the vibrating portion. Thus, the mechanical strength of the diaphragm  144 A is enhanced. The reinforcing member  1446 A is disposed so as not to reach the outer peripheral edge of the auxiliary dome  1442 . Thus, the influence to the lowest resonant frequency of the diaphragm  144 A is suppressed. That is, the diaphragm  144 A can suppress the influence to the lowest resonant frequency and enhance the mechanical strength of the diaphragm  144 A. 
     The reinforcing member may have a configuration adhered to the rear face of the vibrating portion (the left face in  FIG. 3 ) with an adhesive instead of the front face of the vibrating portion. 
       FIG. 6  is a cross-sectional view of a diaphragm illustrating another aspect of the reinforcing member. 
       FIG. 6  shows an embodiment where a reinforcing member is adhered to the rear face of the vibrating portion (the lower face in  FIG. 6 ). 
     A diaphragm  144 B includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 B. 
     As shown in  FIG. 6 , the reinforcing member  1446 B is disposed on the rear faces of the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442 . The reinforcing member  1446 B is disposed so as not to reach the outer peripheral edge of the auxiliary dome  1442 . That is, the reinforcing member  1446 B is not disposed along the boundary  1445 . In other words, the reinforcing member  1446 B is not disposed along the outer peripheral edge of the auxiliary dome  1442 . Thus, the reinforcing member  1446 B is adhered to the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442  with an adhesive (not shown). The reinforcing member  1446 B has a circular shape in plan view, similar to the reinforcing member  1446 A described above. 
     The diaphragm  144 B including such a reinforcing member  1446 B also achieves the same effect as the diaphragm  144 A described above. 
     The reinforcing member may have a configuration adhered to the front face of the vibrating portion and the rear face of the vibrating portion with an adhesive. 
       FIG. 7  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
       FIG. 7  shows a reinforcing member adhered to the front face of the vibrating portion (the upper face in  FIG. 7 ) and the rear face of the vibrating portion (the lower face in  FIG. 7 ). That is,  FIG. 7  shows a first reinforcing member adhered to the front face of the vibrating portion and a second reinforcing member adhered to the rear face of the vibrating portion. 
     A diaphragm  144 C includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 C. 
     The reinforcing member  1446 C includes a first reinforcing member  1446 C 1  and a second reinforcing member  1446 C 2 . The shape of the first reinforcing member  1446 C 1  is the same as the shape of the second reinforcing member  1446 C 2 . The position of the outer peripheral edge (outer end portion) of the first reinforcing member  1446 C 1  is coincident with the position of the outer peripheral edge (outer end portion) of the second reinforcing member  1446 C 2 . 
     The position of the outer peripheral edge (outer end portion) of the first reinforcing member may not be coincident with the position of the outer peripheral edge (outer end portion) of the second reinforcing member. That is, as long as the outer peripheral edge (outer end portion) of the first reinforcing member and the outer peripheral edge (outer end portion) of the second reinforcing member are respectively disposed near the top part of the auxiliary dome, the outer peripheral edge (outer end portion) of the first reinforcing member may be disposed more outwardly than the outer peripheral edge (outer end portion) of the second reinforcing member, or the outer peripheral edge (outer end portion) of the first reinforcing member may be disposed more inwardly than the outer peripheral edge (outer end portion) of the second reinforcing member, for example. 
     As shown in  FIG. 7 , the first reinforcing member  1446 C 1  is disposed on the front faces of the entire main dome  1441 , the boundary  1444  and part of the auxiliary dome  1442 . The first reinforcing member  1446 C 1  is disposed so as not to reach the outer peripheral edge on the front face of the auxiliary dome  1442 . As shown in  FIG. 7 , the second reinforcing member  1446 C 2  is disposed on the rear faces of the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442 . The second reinforcing member  1446 C 2  is disposed so as not to reach the outer peripheral edge on the rear face of the auxiliary dome  1442 . That is, neither the first reinforcing member  1446 C 1  nor the second reinforcing member  1446 C 2  are disposed along the boundary  1445 . In other words, neither the first reinforcing member  1446 C 1  nor the second reinforcing member  1446 C 2  are disposed along the outer peripheral edge of the auxiliary dome  1442 . The first reinforcing member  1446 C 1  is adhered to the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442  with an adhesive (not shown). The second reinforcing member  1446 C 2  is adhered to the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442  with an adhesive (not shown). Both of the first reinforcing member  1446 C 1  and the second reinforcing member  1446 C 2  have a circular shape in plan view, similar to the reinforcing member  1446 A described above. 
     The diaphragm  144 C including such a reinforcing member  1446 C achieves the same effect as the diaphragm  144 A as described above. 
     As described above, the reinforcing member included in the diaphragm according to the present invention includes one reinforcing member (the first reinforcing member) disposed on the front face of the boundary  1444  and another reinforcing member (the second reinforcing member) disposed on the rear face of the boundary  1444 . 
     Electroacoustic Transducer Apparatus, Electroacoustic Transducer, and Diaphragm ( 2 ) 
     Another embodiment of the electroacoustic transducer and the diaphragm according to the present invention (hereinafter referred to as “second embodiment”) will now be described, focusing on differences from the embodiment (hereinafter referred to as “first embodiment”) described above. The electroacoustic transducer in the second embodiment differs from the first embodiment in the shape and position of the reinforcing member of the diaphragm. 
     The electroacoustic transducer apparatus of the second embodiment includes an electroacoustic transducer of the second embodiment. The electroacoustic transducer of the second embodiment includes a diaphragm of the second embodiment. That is, the electroacoustic transducer apparatus of the second embodiment has an electroacoustic transducer including the diaphragm of the second embodiment. 
     In the second embodiment, the diaphragm has a different configuration from the diaphragm of the first embodiment, whereas the electroacoustic transducer apparatus and the electroacoustic transducer have the same configurations as the electroacoustic transducer apparatus and the electroacoustic transducer of the first embodiment. 
     The reinforcing member included in the diaphragm of the second embodiment is disposed only on the boundary between the main dome and the auxiliary dome, part of the main dome, and part of the auxiliary dome. Meanwhile, the reinforcing member, which the diaphragm of the first embodiment includes, is disposed not only on the boundary between the main dome and the auxiliary dome, but also on the entire main dome and part of the auxiliary dome. 
     Configuration of Diaphragm ( 2 ) 
       FIG. 8  illustrates another embodiment of a diaphragm according to the present invention.  FIG. 8  represents a plan view, and a cross-sectional view taken along line C-C in the plan view of  FIG. 8 . 
     In  FIG. 8 , components denoted by the same reference numerals as the components of the first embodiment include the same functions as the components of the first embodiment. 
     A diaphragm  144 D includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 D. 
     As shown in the cross-sectional view of  FIG. 8 , the reinforcing member  1446 D is disposed on the front faces (the upper faces in the cross-sectional view of  FIG. 8 ) of the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween. The reinforcing member  1446 D is disposed so as not to reach the outer peripheral edge of the auxiliary dome  1442 , and is disposed not near a top part Q of the main dome  1441 . That is, the reinforcing member  1446 D is disposed only on the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween, and is disposed not on the boundary  1445 . In other words, the reinforcing member  1446 D is not disposed on the outer peripheral edge of the auxiliary dome  1442 . The top part Q is the top of the main dome  1441 . 
     The reinforcing member  1446 D is adhered to the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween with an adhesive (not shown). That is, the reinforcing member  1446 D is adhered to part of the front face of the vibrating portion. As shown in the plan view of  FIG. 8 , the reinforcing member  1446 D has an annular shape in plan view. 
     The expression “a reinforcing member  1446 D is not disposed on a top part Q of the main dome  1441 ” indicates that the inner peripheral edge of the reinforcing member  1446 D having an annular shape in plan view is disposed between the top part Q of the main dome  1441  and the boundary  1444 . “Part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween” is referred to as a position near the top part Q rather than the intermediary position between the top part Q and the boundary  1444 , and a position near the top part P rather than the intermediary position between the top part P and the boundary  1444 . That is, “part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween” is referred to as an area from near the boundary  1444  rather than the top part P to near the boundary  1444  rather than the top part Q. 
     Synopsis ( 2 ) 
     According to the second embodiment described above, the diaphragm  144 D can suppress the influence to the lowest resonant frequency and enhance the mechanical strength of the diaphragm  144 D, similar to the first embodiment. 
     In the second embodiment, the reinforcing member may have a configuration adhered to the rear face of the vibrating portion instead of the front face of the vibrating portion with an adhesive. 
       FIG. 9  is a cross-sectional view of a diaphragm illustrating another aspect of the reinforcing member. 
       FIG. 9  shows an embodiment where a reinforcing member is adhered to the rear face of a vibrating portion (the lower face in  FIG. 9 ). 
     A diaphragm  144 E includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 E. 
     As shown in  FIG. 9 , the reinforcing member  1446 E is disposed on the rear faces of the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween. The reinforcing member  1446 E is disposed so as not to reach the outer peripheral edge of the auxiliary dome  1442 , and is disposed not near the top part Q of the main dome  1441 . That is, the reinforcing member  1446 E is disposed only on the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween, and is disposed not on the boundary  1445 . In other words, the reinforcing member  1446 E is not disposed on the outer peripheral edge of the auxiliary dome  1442 . The reinforcing member  1446 E is adhered to the boundary  1444  and near the boundary  1444  with an adhesive (not shown). The reinforcing member  1446 E has an annular shape in plan view, similar to the reinforcing member  1446 D described above. 
     The diaphragm  144 E including such a reinforcing member  1446 E achieves the same effect as the diaphragm  144 A described above. 
     The reinforcing member may have a configuration adhered to the front face of the vibrating portion and the rear face of the vibrating portion with an adhesive. 
       FIG. 10  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
       FIG. 10  shows reinforcing members adhered to the front face of the vibrating portion (the upper face in  FIG. 10 ) and the rear face of the vibrating portion (the lower face in  FIG. 10 ). That is,  FIG. 10  indicates a first reinforcing member adhered to the front face of the vibrating portion and a second reinforcing member adhered to the rear face of the vibrating portion. 
     A diaphragm  144 F includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 F. 
     The reinforcing member  1446 F includes a first reinforcing member  1446 F 1  and a second reinforcing member  1446 F 2 . The shape of the first reinforcing member  1446 F 1  is the same as the shape of the second reinforcing member  1446 F 2 . The positions of an inner peripheral edge (inner end portion) and an outer peripheral edge (outer end portion) of the first reinforcing member  1446 F 1  are coincident with the positions of an inner peripheral edge (inner end portion) and an outer peripheral edge (outer end portion) of the second reinforcing member  1446 F 2 , respectively. 
     As shown in  FIG. 10 , the first reinforcing member  1446 F 1  is disposed on the front faces of the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween. The first reinforcing member  1446 F 1  is disposed so as not to reach the outer peripheral edge on the front face of the auxiliary dome  1442  and is disposed not near the top part Q of the main dome  1441 . As shown in  FIG. 10 , the second reinforcing member  1446 F 2  is disposed on the rear faces of the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween. The second reinforcing member  1446 F 2  is disposed so as not to reach the outer peripheral edge on the front face of the auxiliary dome  1442  and is disposed not near the top part Q of the main dome  1441 . That is, both the first reinforcing member  1446 F 1  and the second reinforcing member  1446 F 2  are disposed only on the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween, and are disposed not on the boundary  1445 . In other words, neither the first reinforcing member  1446 F 1  nor the second reinforcing member  1446 F 2  are disposed on the outer peripheral edge of the auxiliary dome  1442 . The first reinforcing member  1446 F 1  is adhered to the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween with an adhesive (not shown). The second reinforcing member  1446 F 2  is adhered to the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween with an adhesive (not shown). Both the first reinforcing member  1446 F 1  and the second reinforcing member  1446 F 2  have an annular shape in plan view, similar to the reinforcing member  1446 D described above. 
     The diaphragm  144 F including such a reinforcing member  1446 F achieves the same effect as the diaphragm  144 A. 
     The shape of the first reinforcing member may be different from the shape of the second reinforcing member. 
       FIG. 11  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
       FIG. 11  shows an embodiment where the shape of reinforcing members adhered to the front face (the upper face in  FIG. 11 ) of the vibrating portion is different from the shape of reinforcing members adhered to rear face (the lower face in  FIG. 11 ) of the vibrating portion. 
     A diaphragm  144 J includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 J. 
     The reinforcing member  1446 J includes a first reinforcing member  1446 J 1  and a second reinforcing member  1446 J 2 . The first reinforcing member  1446 J 1  has the same shape as the first reinforcing member  1446 F 1  in the second embodiment (see  FIG. 10 ) and is disposed at the same position on the diaphragm  144 J as the position of the reinforcing member  1446 F 1  on the diaphragm  144 F. 
     As shown in  FIG. 11 , the second reinforcing member  1446 J 2  is disposed on the rear faces of the boundary  1444 , the main dome  1441  and the auxiliary dome  1442  interposing the boundary  1444  therebetween. An outer peripheral edge of the second reinforcing member  1446 J 2  is disposed near the top part P rather than an outer peripheral edge of the first reinforcing member  1446 J 1 . The second reinforcing member  1446 J 2  is disposed so as not to reach the outer peripheral edge on the rear face of the auxiliary dome  1442 . Meanwhile, an inner peripheral edge of the second reinforcing member  1446 J 2  is disposed near the top part Q rather than an inner peripheral edge of the first reinforcing member  1446 J 1 . 
     The diaphragm  144 J including such a reinforcing member  1446 J achieves the same effect as the diaphragm  144 A. 
       FIG. 12  is a cross-sectional view of a diaphragm illustrating still another aspect of the reinforcing member. 
       FIG. 12  shows an embodiment where the shape of reinforcing members adhered to the front face (the upper face in  FIG. 12 ) of a vibrating portion is different from the shape of the reinforcing members adhered to the rear face (the lower face in  FIG. 12 ) of the vibrating portion. 
     A diaphragm  144 K includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 K. 
     The reinforcing member  1446 K includes a first reinforcing member  1446 K 1  and a second reinforcing member  1446 K 2 . The first reinforcing member  1446 K 1  will be described below. 
     The second reinforcing member  1446 K 2  has the same shape as the second reinforcing member  1446 F 2  in the second embodiment (see  FIG. 10 ) and is disposed at the same position on the diaphragm  144 K as the position of the reinforcing member  1446 F 2  on the diaphragm  144 F. 
     As shown in  FIG. 12 , the first reinforcing member  1446 K 1  is disposed on the front faces of the boundary  1444 , the main dome  1441  and the auxiliary dome  1442  interposing the boundary  1444  therebetween. An outer peripheral edge of the first reinforcing member  1446 K 1  is disposed near the top part P rather than an outer peripheral edge of the second reinforcing member  1446 K 2 . The first reinforcing member  1446 K 1  is disposed so as not to reach the outer peripheral edge on the front face of the auxiliary dome  1442 . Meanwhile, an inner peripheral edge of the first reinforcing member  1446 K 1  are disposed near the top part Q rather than an inner peripheral edge of the second reinforcing member  1446 K 2 . 
     Electroacoustic Transducer Apparatus, Electroacoustic Transducer, and Diaphragm ( 3 ) 
     The other embodiment of the electroacoustic transducer and diaphragm according to the present invention (hereinafter referred to as “third embodiment”) will now be described, focusing on differences from the first embodiment and the second embodiment described above. 
     The electroacoustic transducer apparatus of the third embodiment includes an electroacoustic transducer of the third embodiment. The electroacoustic transducer of the third embodiment includes a diaphragm of the third embodiment. That is, the electroacoustic transducer apparatus of the third embodiment has the electroacoustic transducer including the diaphragm of the third embodiment. 
     In the third embodiment, the diaphragm has a different configuration from the diaphragms in the first embodiment and the second embodiment, while the electroacoustic transducer apparatus and the electroacoustic transducer have the same configurations as the electroacoustic transducer apparatuses and the electroacoustic transducer in the first embodiment and the second embodiment. 
     The reinforcing member included in the diaphragm of the third embodiment includes a first reinforcing member disposed on the front faces of the entire main dome, the boundary, and part of the auxiliary dome and a second reinforcing member disposed on the rear faces of the boundary, part of the main dome and part of the auxiliary dome interposing the boundary therebetween. The diaphragm of the third embodiment differs from the diaphragms of the first embodiment and the second embodiment in that the shape of the first reinforcing member is different from the shape of the second reinforcing member. 
     Configuration of Diaphragm ( 3 ) 
       FIG. 13  illustrates still another embodiment of a diaphragm according to the present invention.  FIG. 13  represents a plan view, a cross-sectional view taken along line D-D in the plan view of  FIG. 13 , and a bottom view. 
     In  FIG. 13 , components denoted by the same reference numerals as the components of the first embodiment include the same functions as the components of the first embodiment. 
     The diaphragm  144 G includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 G. 
     The reinforcing member  1446 G includes a first reinforcing member  1446 G 1  and a second reinforcing member  1446 G 2 . The shape of the first reinforcing member  1446 G 1  is a different from the shape of the second reinforcing member  1446 G 2 . The first reinforcing member  1446 G 1  has the same shape as the first reinforcing member  1446 C 1  in the first embodiment (see  FIG. 7 ), and is disposed at the same position on the diaphragm  144 G as the position of the reinforcing member  1446 C 1  on the diaphragm  144 C. The second reinforcing member  1446 G 2  has the same shape as the second reinforcing member  1446 F 2  in the second embodiment (see  FIG. 10 ) and is disposed at the same position on the diaphragm  144 G as the position of the reinforcing member  1446 F 2  on the diaphragm  144 F. 
     As shown in the cross-sectional view of  FIG. 13 , the first reinforcing member  1446 G 1  is disposed on the front faces (the upper faces in the cross-sectional view of  FIG. 13 ) of the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442 . As shown in the cross-sectional view of  FIG. 13 , the second reinforcing member  1446 G 2  is disposed on the rear faces (the lower faces in the cross-sectional view of  FIG. 13 ) of the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween. That is, the reinforcing member  1446 G is disposed on the front face and the rear face of the vibrating portion. 
     Synopsis ( 3 ) 
     According to the embodiments described above, the diaphragm  144 G of the third embodiment can suppress the influence to the resonant frequency and enhance the mechanical strength of the diaphragm  144 G, similar to the first embodiment and the second embodiment. 
     The reinforcing member may have a configuration that the first reinforcing member and the second reinforcing member are disposed with their positions reversed in the third embodiment. 
       FIG. 14  is a cross-sectional view of a diaphragm illustrating another aspect of the reinforcing member. 
       FIG. 14  shows an embodiment where reinforcing members are adhered to the front face of a vibrating portion (the upper face in  FIG. 14 ) and the rear face of the vibrating portion (the lower face in  FIG. 14 ). 
     A diaphragm  144 H includes a main dome  1441 , an auxiliary dome  1442 , an attaching portion  1443 , a boundary  1444 , a boundary  1445 , and a reinforcing member  1446 H. 
     The reinforcing member  1446 H includes a first reinforcing member  1446 H 1  and a second reinforcing member  1446 H 2 . The first reinforcing member  1446 H 1  has the same shape as the first reinforcing member  1446 F 1  in the second embodiment (see  FIG. 10 ), and is disposed at the same position on the diaphragm  144 H as the position of the reinforcing member  1446 F 1  on the diaphragm  144 F. The second reinforcing member  1446 H 2  has the same shape as the second reinforcing member  1446 C 2  in the first embodiment (see  FIG. 8 ), and is disposed at the same position on the diaphragm  144 H as the position of the reinforcing member  1446 C 2  on the diaphragm  144 C. 
     As shown in  FIG. 14 , the first reinforcing member  1446 H 1  is disposed on the front faces of the boundary  1444 , part of the main dome  1441  and part of the auxiliary dome  1442  interposing the boundary  1444  therebetween. As shown in  FIG. 14 , the second reinforcing member  1446 H 2  is disposed on the rear faces of the entire main dome  1441 , the boundary  1444 , and part of the auxiliary dome  1442 . That is, the reinforcing member  1446 H is disposed on the front face and the rear face of the vibrating portion. 
     The diaphragm  144 H including such a reinforcing member  1446 H achieves the same effect as the diaphragm  144 A described above. 
     Synopsis (Miscellaneous) 
     In the diaphragm according to the present invention, the reinforcing member may have a configuration stacking thin films on at least one of the front face or rear face of the vibrating portion. That is, the thin films include a first thin film and a second thin film stacked on the first thin film, for example. In this case, the first thin film and the second thin film are bonded with an adhesive. As long as reinforcing the vibrating portion can enhance the mechanical strength of the vibrating portion, a material of the first thin film may be the same as or different from a material of the second thin film. Stacking the thin films is referred to as stacking “a thin film disposed remote from the vibrating portion (the second thin film)” on “a thin film disposed near the vibrating portion (the first thin film)”. 
     In the reinforcing member having a configuration of stacking thin films, the material of the second thin film is preferably tougher than the material of the first thin film. Such a configuration can more robustly reinforce the vibrating portion. 
     In the configuration including the first reinforcing member and the second reinforcing member, the material of the first reinforcing member may be different from the material of the second reinforcing member. 
     The embodiments described above are examples of the case when diaphragms according to the present invention are applied to headphones converting electric signals to sound waves. However, the diaphragms according to the present invention may be applied to electroacoustic transducers converting sound waves to electric signals. That is, the diaphragms according to the present invention are applicable to driver units used in microphone units, for example. In other words, the driver units vibrate the diaphragms according to the present invention in response to sound waves and generate electric signals based on this vibration. In this case, a driver unit is an example of the electroacoustic transducer according to the present invention. A microphone unit including this driver unit is an example of the present apparatus. 
     Synopsis of Diaphragm and Electroacoustic Transducer According to the Present Invention 
     Configurational features of the diaphragm and electroacoustic transducer according to the present invention, and the electroacoustic transduction apparatus including the diaphragm and the electroacoustic transducer according to the present invention described above will be summarized below. 
     (Feature 1) 
     A diaphragm comprising: 
     a main dome; 
     an auxiliary dome extending from an outer peripheral edge of the main dome; and 
     a reinforcing member disposed on a boundary between the main dome and the auxiliary dome, wherein 
     the reinforcing member is disposed so as not to reach an outer peripheral edge of the auxiliary dome. 
     (Feature 2) 
     The diaphragm according to feature 1, wherein the outer peripheral edge of the reinforcing member is disposed near a top part of the auxiliary dome. 
     (Feature 3) 
     The diaphragm according to feature 1, wherein the boundary has a circular shape, and the reinforcing member has an annular shape. 
     (Feature 4) 
     The diaphragm according to feature 1, wherein the reinforcing member is not disposed on a top part of the main dome. 
     (Feature 5) 
     The diaphragm according to feature 1, wherein the reinforcing member is or includes a mesh part. 
     (Feature 6) 
     The diaphragm according to feature 1, wherein a material of the reinforcing member is different from a material of the auxiliary dome. 
     (Feature 7) 
     The diaphragm according to feature 1, wherein the reinforcing member includes at least one of; 
     a first reinforcing member disposed on a front face of the boundary; and 
     a second reinforcing member disposed on a rear face of the boundary. 
     (Feature 8) 
     The diaphragm according to feature 7, wherein 
     the reinforcing member comprises both the first reinforcing member and the second reinforcing member, and 
     wherein a material of the first reinforcing member is different from a material of the second reinforcing member. 
     (Feature 9) 
     The diaphragm according to feature 7, wherein 
     the reinforcing member comprises both the first reinforcing member and the second reinforcing member, and 
     wherein a shape of the first reinforcing member is a different from a shape of the second reinforcing member. 
     (Feature 10) 
     The diaphragm according to claim  7 , wherein 
     one or more of the first reinforcing member and the second reinforcing member is not disposed near the top part of the main dome. 
     (Feature 11) 
     The diaphragm according to feature 1, wherein the reinforcing member includes a first thin film and a second thin film stacked on the first thin film. 
     (Feature 12) 
     The diaphragm according to feature 11, wherein a material of the first thin film is different from a material of the second thin film. 
     (Feature 13) 
     An electroacoustic transducer converting electric signals to sound waves or converting sound waves to electric signals, comprising: 
     a diaphragm configured to vibrate in response to the electric signals or to vibrate in response to the sound waves, wherein 
     the diaphragm is the diaphragm according to feature 1. 
     (Feature 14) 
     An electroacoustic transducer apparatus comprising: 
     an electroacoustic transducer converting electric signals to sound waves or converting sound waves to electric signals, wherein 
     the electroacoustic transducer is the electroacoustic transducer according to feature 13.