Abstract:
Provided is a dynamic headphone that has a small size but makes a larger-diameter headphone unit mountable thereon, the dynamic headphone including a highly reliable acoustic channel that acoustically connects a front air chamber and a back air chamber to each other. A headphone case  20  houses a headphone unit  50  therein, and includes a back air chamber C 2  on a back side of the headphone unit  50.  The headphone case  20  includes: a back air chamber forming portion  40  that forms the back air chamber C 2;  and a mount portion  30  integrally provided to an opening end of the back air chamber forming portion  40,  the headphone unit  50  being mounted in the mount portion  30.  An acoustic channel  70  is provided between the mount portion  30  and the headphone unit  50.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is based on, and claims priority from, Japanese Application Serial Number JP2013-223427, filed Oct. 28, 2013, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an over-the-head type dynamic headphone that is fitted to a head side part so as to cover an ear, and, more specifically, to a dynamic headphone on which a large-diameter headphone unit is mountable without an increase in size of a headphone case. 
       BACKGROUND ART 
       [0003]    Headphones are classified broadly into three types, that is, an over-the-head type in which a headphone is held by a headband, an ear-hook type in which a headphone is held by being hooked on an ear, and an ear-insertion type in which a headphone is held by being directly inserted into an ear. 
         [0004]    Among these types, the over-the-head type headphone is popular for the following reasons: high sound quality is obtained because of the use of a headphone case large enough to cover the entire ear; and even long-time fitting puts a low load on the ear. 
         [0005]    According to a first conventional example of the over-the-head type headphone, as illustrated in  FIG. 3A , an over-the-head type headphone  1 A includes a headphone band (not illustrated) that is fitted along a head H in an arch-like manner, and a headphone case  2  is suspended at each end of the headband. 
         [0006]    A headphone unit  3  is housed in the headphone case  2  while being supported by a baffle plate  4 . A doughnut-shaped ear pad  5  to be placed around an ear E at the time of fitting of the headphone is integrally attached to a sound emitting surface of the headphone case  2 . In many cases, a dynamic electro-acoustic transducer is adopted for the headphone unit  3 . 
         [0007]    In the headphone case  2 , a back air chamber C 2  having a predetermined volume is formed by the baffle plate  4  on a back side of the headphone unit  3 , and a substantially hermetically sealed front air chamber C 1  is formed by the ear pad  5  also on a front side of the headphone unit  3  at the time of fitting of the headphone. 
         [0008]    In the headphone  1 A of this type, the following is a common practice to attenuate in-head localization of sound images and improve sound quality and frequency response. That is, an acoustic channel  6  is provided to part of the baffle plate  4 , an acoustic resistance material  6   a  such as non-woven fabric is attached to the acoustic channel  6 , and the front air chamber C 1  and the back air chamber C 2  are acoustically connected to each other. 
         [0009]    Meanwhile, in order to obtain a headphone having excellent sound quality, it is preferable to increase the diameter of the headphone unit  3  as much as possible. If a large-diameter headphone unit  3  is mounted as it is on the headphone  1 A having the configuration illustrated in  FIG. 3A , however, the size of the headphone case  2  increases accordingly, and the portability thereof is impaired. 
         [0010]    For the purpose of avoiding the portability thereof from being impaired, in order to mount the large-diameter headphone unit  3  without such an increase in size of the headphone case  2 , the acoustic channel  6  provided to the baffle plate  4  needs to be placed in the vicinity of the lower side of the ear pad  5  (the side of the ear pad  5  opposed to the baffle plate  4 ). 
         [0011]    If such a design is adopted, however, the acoustic channel  6  may be closed by the ear pad  5 , depending on a lateral pressure applied when the headphone is fitted to the head H. 
         [0012]    In view of the above, in a headphone  1 B (second conventional example) according to an invention described in Japanese Patent Application Publication No. 2013-42382, which is illustrated in  FIG. 3B , in order to make a larger-diameter headphone unit  3  mountable, a communication groove  4   a  is formed in the baffle plate  4  in the case where the acoustic channel  6  provided to the baffle plate  4  is placed on the lower side of the ear pad  5 . The communication groove  4   a  is communicated with the acoustic channel  6 , and is deep enough not to be closed by the ear pad  5 . 
         [0013]    According to Japanese Patent Application Publication No. 2013-42382, it is possible to provide a headphone that has a small size but includes the large-diameter headphone unit  3 , in which the acoustic channel  6  is hardly closed by the ear pad  5 . However, because the headphone still includes the baffle plate  4 , there is a limit to an increase in diameter of the headphone unit  3 . Moreover, because it is necessary to form, in the baffle plate  4 , the communication groove  4   a  that is deep enough not to be closed by the ear pad  5 , production costs become higher accordingly. 
         [0014]    Under the circumstances, the present invention has an object to provide a dynamic headphone that has a small size but makes a larger-diameter headphone unit mountable thereon, the dynamic headphone including a highly reliable acoustic channel that acoustically connects a front air chamber and a back air chamber to each other. 
       SUMMARY OF THE INVENTION 
       [0015]    In order to achieve the above-mentioned object, the present invention provides a dynamic headphone including: a headphone unit including: a diaphragm including a voice coil; a magnetic circuit portion including a magnetic gap in which the voice coil is placed; and a unit frame that supports the diaphragm and the magnetic circuit portion; a headphone case that houses the headphone unit therein while securing a back air chamber having a predetermined volume on a back side of the headphone unit; an ear pad that is provided to an outer peripheral edge part of the headphone case so as to: surround an ear on a sound emitting surface side of the headphone unit; and form a front air chamber having a predetermined volume on a front side of the headphone unit, when the dynamic headphone is fitted to a head side part of a human body; and an acoustic channel that acoustically connects the front air chamber and the back air chamber to each other. The headphone case includes: a back air chamber forming portion that forms the back air chamber; and a mount portion integrally provided to an opening end of the back air chamber forming portion, the headphone unit being mounted in the mount portion. The acoustic channel is provided between the mount portion and the headphone unit. 
         [0016]    According to a preferable aspect of the present invention, the mount portion includes: a cylindrical portion having a diameter larger than that of the unit frame; and an engagement portion that is bent inward from a front end of the cylindrical portion so as to be opposed to a peripheral edge part of the unit frame, and the acoustic channel is placed along inner surfaces of the engagement portion and the cylindrical portion. 
         [0017]    Moreover, the present invention includes, as preferable aspects: an aspect in which a predetermined acoustic resistance material is provided in the acoustic channel; and an aspect in which the ear pad is provided on an outer surface side of the engagement portion. 
         [0018]    According to the present invention, the headphone case includes: the dome portion that substantially forms the back air chamber; and the mount portion integrally provided to the opening end of the dome portion, the headphone unit being mounted in the mount portion. Hence, the headphone unit is directly mounted in the mount portion, and a baffle plate is not necessary, whereby a larger-diameter headphone unit can be mounted. Moreover, because the acoustic channel is provided between the mount portion and the headphone unit, the acoustic channel is not closed by the ear pad and the like, and thus has high reliability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a main part cross-sectional view illustrating a dynamic headphone according to an embodiment of the present invention; 
           [0020]      FIG. 2  is an exploded perspective view schematically illustrating a structure of the dynamic headphone; 
           [0021]      FIG. 3A  is a main part cross-sectional view illustrating a first conventional example; and 
           [0022]      FIG. 3B  is a main part cross-sectional view illustrating a second conventional example. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    An embodiment of the present invention is described with reference to  FIG. 1  and  FIG. 2 , and the present invention is not limited to the embodiment. 
         [0024]    As illustrated in  FIG. 1 , a dynamic headphone  10  according to the present embodiment is of over-the-head type, and includes a headphone case  20  that is suspended at each end of a headband (not illustrated) with the intermediation of a universal-joint-like hanger member (not illustrated). The headband is fitted along a head H of a user from a head top part to each head side part. Note that a pair of right and left headphone cases  20  is supported by the headband, and only one thereof is illustrated in  FIG. 1 , because the right and left headphone cases  20  have the same configuration as each other. 
         [0025]    The headband may be a general U-shaped headband that is fitted along the head H from the head top part to each head side part, and may also be, for example, of behind-the-head type in which the headphone is held by fitting the headband along a head back part. 
         [0026]    In the present embodiment, the headphone case  20  includes: a mount portion  30  in which a headphone unit  50  is mounted; and a dome portion  40  formed in a substantially cup shape, the dome portion  40  corresponding to a back air chamber forming portion that forms a back air chamber C 2  having a predetermined volume on a back side of the headphone unit  50 . The mount portion  30  is integrally attached to an opening end of the dome portion  40 . The material of each of the mount portion  30  and the dome portion  40  may be selected from synthetic resin materials, metal materials, and wood materials. 
         [0027]    The headphone unit  50  is a dynamic electro-acoustic transducer, and includes a diaphragm  51 , a magnetic circuit portion  52  for driving, and a unit frame  53  that supports the diaphragm  51  and the magnetic circuit portion  52 . 
         [0028]    The diaphragm  51  includes a center dome  511  and a sub-dome (also referred to as edge portion)  512  that is integrally provided in a continuous manner around the center dome  511 . A voice coil  513  is integrally attached using an adhesive or the like to a joint part between the center dome  511  and the sub-dome  512 , on a back side of the diaphragm  51 . 
         [0029]    The magnetic circuit portion  52  includes: a dish-like yoke  521  formed in a substantially U-shape in cross-section; and a discoid permanent magnet  522  that is placed in a bottom part of the yoke  521  and is magnetized in a plate thickness direction. A pole piece  523  is provided on the permanent magnet  522 , and the pole piece  523  forms a magnetic gap G having a predetermined width between the pole piece  523  and an inner peripheral surface of the yoke  521 . 
         [0030]    The entire unit frame  53  is formed in a discoid shape. The unit frame  53  includes, in the center thereof, an opening portion  531  that houses and supports the magnetic circuit portion  52  and is made of a cylindrical sleeve. A peripheral edge part of the sub-dome  512  of the diaphragm  51  is supported by a peripheral edge part of the unit frame  53  such that the voice coil  513  can vibrate in the magnetic gap G of the magnetic circuit portion  52 . 
         [0031]    Moreover, the unit frame  53  is provided with a plurality of communication holes  532  for communicating an air chamber on the back side of the diaphragm  51  with the back air chamber C 2 . An acoustic resistance material  533  such as non-woven fabric is attached to each communication hole  532 , whereby predetermined damping is applied to the diaphragm  51 . 
         [0032]    Further, a protector  54  having a large number of through-holes  541  for protecting the diaphragm  51  is provided on a front surface (in  FIG. 1 , a left surface) of the unit frame  53 . Perforated metal, metal mesh (guard mesh), and the like may be used for the protector  54 . In the present embodiment, a sleeve  534  into which the protector  54  is fitted is provided in a standing manner to the peripheral edge part of the unit frame  53 . 
         [0033]    Also with reference to  FIG. 2 , the mount portion  30  includes: a cylindrical portion  31  having a diameter larger than that of the unit frame  53 ; and an engagement portion  32  for receiving the unit frame  53 , the engagement portion  32  being bent inward (toward the center of the cylindrical portion  31 ) from a front end (in  FIG. 1  and  FIG. 2 , a left end) of the cylindrical portion  31  so as to be opposed to the peripheral edge part of the unit frame  53 . 
         [0034]    In the present embodiment, as illustrated in  FIG. 2 , the engagement portion  32  is formed in a circular plate (washer-like shape) having an opened central part, and may be made of a plurality of nail pieces that are bent inward at predetermined intervals from the front end of the cylindrical portion  31 . 
         [0035]    Moreover, although the engagement portion  32  is bent from the front end of the cylindrical portion  31  in the present embodiment, the engagement portion  32  may be formed as an independent member, and may be joined to the front end of the cylindrical portion  31  by using an adhesive, welding, or the like. 
         [0036]    In the present embodiment, an ear pad  60  is integrally attached to an outer surface of the engagement portion  32 . The ear pad  60  may be a pad obtained by covering a cushioned foam core  61  formed in an annular shape with, for example, a cover material  62  made of synthetic leather. 
         [0037]    At the time of fitting of the headphone, the ear pad  60  is pressed against the head side part at a predetermined lateral pressure applied by the headband so as to surround the ear E, whereby a substantially hermetically sealed front air chamber C 1  is formed on a front side of the headphone unit  50 . 
         [0038]    In the case where the headphone unit  50  is mounted in the mount portion  30 , in the present invention, a baffle plate is not necessary, and the headphone unit  50  is directly housed in the mount portion  30 . 
         [0039]    Moreover, an acoustic channel (an acoustic channel that acoustically connects the front air chamber C 1  and the back air chamber C 2  to each other)  70  for attenuating in-head localization of sound images and improving sound quality and frequency response is provided in the mount portion  30 . 
         [0040]    Accordingly, in the present embodiment, because the cylindrical portion  31  of the mount portion  30  has a diameter larger than that of the unit frame  53  of the headphone unit  50 , for example, an acoustic resistance material  71  that is made of felt or the like and has an L-shape in cross-section is provided in an annular shape to an inner surface of the cylindrical portion  31  and an inner surface of the engagement portion  32 , and the headphone unit  50  is then mounted (housed) in the mount portion  30 , whereby the acoustic channel  70  is formed. It is assumed that the respective widths of the annular parts of the ear pad  60  and the acoustic resistance material  71  and the width of the engagement portion  32  are the same as illustrated in  FIG. 1 . 
         [0041]    According to this configuration, the headphone unit  50  having a large diameter close to the outer diameter of the ear pad  60  can be mounted. Moreover, because the acoustic channel  70  is placed in the mount portion  30  that is not influenced by the ear pad  60 , the acoustic channel  70  having high reliability can be secured. 
         [0042]    In the above-mentioned embodiment, a gap serving as the acoustic channel  70  is provided between the mount portion  30  and the unit frame  53  by means of the acoustic resistance material  71 . Alternatively, according to another embodiment, for example, ribs each having a predetermined height may be formed on the inner surfaces of the cylindrical portion  31  and the engagement portion  32 , the acoustic channel  70  may be defined by a gap formed by the ribs, and the acoustic resistance material  71  having a predetermined acoustic resistance value may be placed in the acoustic channel  70 . Such an embodiment is also included in the present invention. 
         [0043]    Moreover, in the above-mentioned embodiment, the back air chamber C 2  is substantially formed by the cup-shaped dome portion  40 . Alternatively, according to another embodiment, the cylindrical portion  31  of the mount portion  30  may be extended in the axial direction by a predetermined length up to the back side of the headphone unit  50 , and a back end part of the cylindrical portion  31  may be included in an element for forming the back air chamber C 2 . 
         [0044]    According to the another embodiment, the back air chamber forming portion is constituted by the dome portion  40  and part of the mount portion  30 . Still alternatively, the back end part of the cylindrical portion  31  of the mount portion  30  may be closed by a cover plate or the like, whereby the back air chamber C 2  may be formed. In this case, the dome portion  40  is not necessary, and hence the back air chamber forming portion is constituted by the mount portion  30 .