Abstract:
A sound production device for a vehicle includes: a speaker that causes a diaphragm to vibrate thereby producing sound; and a housing receiving the speaker and having a sound passage through which the sound produced by the speaker passes and a sound emission hole that causes the sound passed through the sound passage to externally emit. Plural resonant chambers having different resonant frequencies are defined in the sound passage, such that the sound passage has a labyrinth structure that is able to prevent a foreign substance form entering the diaphragm from the sound emission hole.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on Japanese Patent Application No. 2014-149748 filed on Jul. 23, 2014, the disclosure of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a sound production device for a vehicle alarm apparatus or a vehicle approach alert apparatus. 
       BACKGROUND ART 
       [0003]    Patent Literature 1 describes a sound production device for a vehicle. In the sound production device described in Patent Literature 1, a front surface of a speaker is covered by a cover having a sound emission hole. In a case where a sound production device is mounted inside of, for example, a front bumper of a vehicle, there is a concern that a flow of water may pass through the sound emission hole and impact a diaphragm of the speaker during high-pressure car washing or snow may enter the sound emission hole. Therefore, a shielding wall is provided on the cover to receive the flow of water or snow oriented from the sound emission hole to a sound-production member. In addition, the shielding wall is disposed to face the diaphragm. 
       PRIOR ART LITERATURES 
     Patent T Literature 
       [0004]    Patent Literature 1: JP 2013-29814 A 
       SUMMARY OF INVENTION 
       [0005]    While a space that is formed between the shielding wall and the diaphragm amplifies a sound pressure of a specific frequency by a resonance effect, there is a concern that the sound pressure is lowered in a frequency region which is higher than the resonant frequency. 
         [0006]    In addition, in a sound production device including a speaker having a large diameter, it is necessary to secure a large sound emission area, in order that sound characteristics of the speaker having the large diameter do not deteriorate. However, if a sound emission hole is made larger, water or snow is likely to enter the sound emission hole. 
         [0007]    The present disclosure is made in view of the above points and an object of the present disclosure is to provide a sound production device for a vehicle which can achieve both acoustic performance and prevention of entrance of water or snow. 
         [0008]    To achieve the above-described object, according to an aspect of the present disclosure, a sound production device for a vehicle includes: a speaker that causes a diaphragm to vibrate thereby producing sound; and a housing receiving the speaker and having a sound passage through which the sound produced by the speaker passes and a sound emission hole that causes the sound passed through the sound passage to externally emit. A plurality of resonant chambers having different resonant frequencies are defined in the sound passage, and the sound passage has a labyrinth structure that is able to prevent a foreign substance form entering the diaphragm from the sound emission hole. 
         [0009]    A large sound pressure can be obtained in a wide frequency band using multiple resonant chambers having different resonant frequencies. In addition, entrance of water or snow into the speaker portion can be prevented by the labyrinth structure. 
         [0010]    The housing may include a cylindrical base that receives the speaker and a cover that is disposed on one end of the base. The base includes a shielding wall disposed to face the diaphragm, and a first resonant chamber that is one of the plurality of resonant chambers is defined between the diaphragm and the shielding wall. 
         [0011]    A resonant frequency of the first resonant chamber can be adjusted using a volume of the first resonant chamber by appropriately setting a shape of the shielding wall. However, in the sound production device described in Patent Literature 1, since the shielding wall is provided in the cover, it is difficult to make the shielding wall into arbitrary shape other than a flat plate due to the constraints of a mold. In addition, in the sound production device described in Patent Literature 1, since a configuration of the cover is complicated, the shielding wall is formed using a slide mold. 
         [0012]    In contrast, when the shielding wall is provided in the base, the shape of the shielding wall can be appropriately set and the shielding wall can be formed without using a slide mold. 
         [0013]    The base includes: a base first wall having a cylindrical shape that extends from an outer peripheral edge portion of the shielding wall in a direction away from the diaphragm along an axial direction of the base; and a base second wall having a cylindrical shape that is disposed on an outer periphery side of the base first wall and that extends from an outer peripheral edge portion of the diaphragm along the axial direction of the base. The cover includes a cover plate portion that covers an opening of a space between the base first wall and the base second wall opposite to the diaphragm. A second resonant chamber, which is one of the plurality of resonant chambers and is positioned on a downstream side from the first resonant chamber in a sound flow direction, is defined by the base first wall, the base second wall, and the cover plate portion. A first clearance configuring the sound passage may be formed between the base first wall and the cover plate portion, and a second clearance configuring the sound passage may be formed between the base second wall and the cover plate portion. 
         [0014]    In this case, the cover plate portion may cover the first clearance. 
         [0015]    Thus, entrance of water or snow into the first clearance can be prevented. 
         [0016]    The cover plate portion may cover the second clearance. 
         [0017]    Thus, entrance of water or snow into the second clearance can be prevented. 
         [0018]    The cover may include a cylindrical cover erected wall to obstruct between the sound emission hole and the second clearance when the second clearance is viewed from the sound emission hole. 
         [0019]    Thus, entrance of water or snow into the second clearance can be prevented. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  is a perspective view of a sound production device according to an embodiment. 
           [0021]      FIG. 2( a )  is a front view of the sound production device,  FIG. 2( b )  is a left side view of the sound production device, and  FIG. 2( c )  is a bottom view of the sound production device. 
           [0022]      FIG. 3  is a cross-sectional view taken along a line III-III of  FIG. 2( a ) . 
           [0023]      FIG. 4  is a cross-sectional view taken along a line IV-IV of  FIG. 2( a ) . 
           [0024]      FIG. 5  is a front view of the sound production device from which a cover is removed. 
           [0025]      FIG. 6  is a perspective view of the sound production device from which a cover is removed. 
           [0026]      FIG. 7  is a graph illustrating a relationship between a sound pressure level and a frequency of the sound production device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    An embodiment will be described. An up-down direction illustrated in  FIG. 2  indicates a direction in a state where a sound production device is mounted on a vehicle. 
         [0028]    As illustrated in  FIGS. 1 to 6 , a base  1  is made of plastic, and includes a base cylinder portion  11  having a substantially rectangular cylindrical shape. A cover  2  is made of plastic, and has a based substantially rectangular cylindrical shape joined to an one-side opening of the base cylinder portion  11  so as to close the one side of the base cylinder portion  11 . A case  3  having a based substantially rectangular cylindrical is gas-tightly joined to the other end of the base cylinder portion  11  so as to close the other end of the base cylinder portion  11 . The base  1 , the cover  2 , and the case  3  configure a housing of the present disclosure. 
         [0029]    A speaker  4  is received in a space formed by the base cylinder portion  11  and the case  3 . The speaker  4  includes a conical diaphragm  41  producing a sound by vibrating and a diaphragm drive portion  42  that causes the diaphragm  41  to vibrate. 
         [0030]    The speaker  4  is joined in such a manner that the diaphragm drive portion  42  is fixed to the base  1  by screws and an outer peripheral edge portion of the diaphragm  41  is bonded to the base  1 . In addition, the diaphragm drive portion  42  is electrically connected to an external harness (not illustrated) via a wire line  43  and a connection terminal  44  that is press-fitted to the base  1 . 
         [0031]    The base  1  has a through hole (not illustrated) that causes a space formed by the base cylinder portion  11 , the case  3 , and the speaker  4  to communicate with the outside to suppress a pressure fluctuation of the space formed by the base cylinder portion  11 , the case  3 , and the speaker  4  due to a temperature change. The through hole is covered by a pressure adjusting film  5  that is made of fibers having characteristics of permeable to air but impermeable to water. 
         [0032]    The base  1  has a conical shielding wall  12  located between the cover  2  and the speaker  4  within the base cylinder portion  11 . The shielding wall  12  is disposed to face the diaphragm  41 , and a conical first resonant chamber  61  is formed between the shielding wall  12  and the diaphragm  41 . 
         [0033]    When the sound produced by the speaker  4  passes through the first resonant chamber  61 , a sound pressure of a specific frequency is amplified by a resonance effect of the first resonant chamber  61 . In the present embodiment, the resonant frequency of the first resonant chamber  61  is set to 2.7 kHz. 
         [0034]    The base  1  includes a cylindrical base first wall  13 , a cylindrical base second wall  14 , and a cylindrical base third wall  15 . The cylindrical base first wall  13  extends from an outer peripheral edge portion of the shielding wall  12  in a direction away from the diaphragm  41  along an axial direction (that is, an up-down direction of a paper surface of  FIG. 4 ) of the base  1 . The cylindrical base second wall  14  is coaxially disposed on an outer periphery side of the base first wall  13  and extends from a position of the outer peripheral edge portion of the diaphragm  41  along the axial direction of the base  1 . The cylindrical base third wall  15  is coaxially disposed on an inner periphery side of the base first wall  13  and extends from an intermediate portion of the shielding wall  12  in a radial direction in a direction away from the diaphragm  41  along the axial direction of the base  1 . 
         [0035]    The base  1  includes a planar base plate portion  16  that extends from an outer periphery surface of the base second wall  14  outward in a direction perpendicular to the axis of the base  1  (that is a left-right direction of the paper surface of  FIG. 4 ). The base plate portion  16  is positioned between the diaphragm  41  and a tip portion (that is, an end portion adjacent to the cover  2 ) of the base second wall  14 . A cylindrical space is formed by the base cylinder portion  11 , the base second wall  14 , and the base plate portion  16 . 
         [0036]    The cover  2  includes a cover bottom wall portion  21  having a substantially rectangular plate shape, and a cover side wall portion  22  having a substantially rectangular cylindrical shape. The cover side wall portion  22  extends from an outer peripheral portion of the cover bottom wall portion  21  toward the base  1  along the axial direction of the base  1 . 
         [0037]    The cover  2  includes a cover plate portion  23  having a disc-shape that covers an opening of the cylindrical space formed between the base first wall  13  and the base second wall  14  opposite to the diaphragm  41 . 
         [0038]    A cylindrical second resonant chamber  62  is formed by the base first wall  13 , the base second wall  14 , and the cover plate portion  23 . The second resonant chamber  62  is positioned on a downstream side of the first resonant chamber  61  in a sound flow direction. The sound amplified by the first resonant chamber  61  is propagated to the second resonant chamber  62 . 
         [0039]    When the sound propagated to the second resonant chamber  62  passes through the second resonant chamber  62 , the sound pressure of the specific frequency is amplified by the resonance effect of the second resonant chamber  62 . In the present embodiment, the resonant frequency of the second resonant chamber  62  is set to 5 kHz. 
         [0040]    A first clearance  63  through which sound passes is formed between the base first wall  13  and the cover plate portion  23 , and a second clearance  64  through which sound passes is formed between the base second wall  14  and the cover plate portion  23 . The first clearance  63  and the second clearance  64  are positioned on a downstream side of the second resonant chamber  62  in the sound flow direction, and the sound amplified by the second resonant chamber  62  is further propagated on the downstream side via the first clearance  63  and the second clearance  64 . 
         [0041]    The cover plate portion  23  covers a part of the opening of the cylindrical space formed between the base first wall  13  and the base third wall  15  opposite to the shielding wall  12 . 
         [0042]    A third resonant chamber  65  is formed by the shielding wall  12 , the base first wall  13 , the base third wall  15 , and the cover plate portion  23 . The third resonant chamber  65  is positioned on a downstream side of the second resonant chamber  62  in the sound flow direction. A part of the sound amplified by the second resonant chamber  62  is propagated to the third resonant chamber  65  via the first clearance  63 . 
         [0043]    When the sound propagated to the third resonant chamber  65  passes through the third resonant chamber  65 , the sound pressure of the specific frequency is amplified by the resonance effect of the third resonant chamber  65 . In the present embodiment, the resonant frequency of the third resonant chamber  65  is set to 3.8 kHz. 
         [0044]    A circular first sound emission hole  24  is formed on an inner periphery side of the cover plate portion  23 . The sound amplified by the third resonant chamber  65  is emitted to the outside via the first sound emission hole  24 . 
         [0045]    Multiple second sound emission holes  25  are formed in the cover bottom wall portion  21 . Multiple third sound emission holes  26  are formed between the cover bottom wall portion  21  and the cover plate portion  23 . In order to clarify positions and ranges of the third sound emission holes  26  in  FIG. 1 , portions of the third sound emission holes  26  are conveniently illustrated in a twill pattern. 
         [0046]    Multiple third clearances  66  are formed between a tip surface of the cover side wall portion  22  and a surface of the base cylinder portion  11  facing the tip surface of the cover side wall portion  22 . The third clearances  66  function as the sound emission holes. Hereinafter, the third clearances  66  refer to as fourth sound emission holes  66 . 
         [0047]    A part of the sound amplified by the second resonant chamber  62  is propagated on the downstream side via the second clearance  64  and is emitted from the second sound emission holes  25 , the third sound emission holes  26 , and the fourth sound emission holes  66  to the outside. 
         [0048]    The first resonant chamber  61 , the second resonant chamber  62 , the third resonant chamber  65 , the first clearance  63 , and the second clearance  64  configure a sound passage of the present disclosure. 
         [0049]    The cover  2  includes a cover erected wall  27  having a cylindrical shape that extends from the cover bottom wall portion  21  toward the base plate portion  16  along the axial direction of the base  1 . The cover erected wall  27  is disposed on an outer periphery side of the base second wall  14  and the cover plate portion  23 , and on an inner periphery side of the fourth sound emission holes  66 . The second clearance  64  is obstructed by the cover erected wall  27  so as not to visible when the second clearance  64  is viewed from the fourth sound emission holes  66  and the second sound emission holes  25 . Therefore, water or snow does not enter the second clearance  64 . 
         [0050]    The cover plate portion  23  protrudes from the first clearance  63  to the inner periphery side and covers the first clearance  63 . Therefore, water or snow does not enter the first clearance  63 . 
         [0051]    The cover plate portion  23  is disposed adjacent to the third sound emission holes  26  with respect to the second clearance  64  and covers the second clearance  64 . Therefore, water or snow does not enter the second clearance  64  from the third sound emission holes  26 . 
         [0052]    From a viewpoint of preventing water or snow from entering, it is preferable that a dimension of the first clearance  63  or the second clearance  64  is set to 1 to 2mm. 
         [0053]    The sound production device having such a configuration described above is disposed, for example, within a front bumper of a vehicle. The sound produced by the speaker  4  passes through the first resonant chamber  61 , the second resonant chamber  62 , the third resonant chamber  65 , the first clearance  63 , and the second clearance  64 , and then is emitted from the first sound emission hole  24 , the second sound emission holes  25 , the third sound emission holes  26 , and the fourth sound emission holes  66  to the outside as an alarm sound. 
         [0054]    In  FIG. 7 , a solid line indicates characteristics of the sound production device of the present embodiment which includes the first resonant chamber  61 , the second resonant chamber  62 , and the third resonant chamber  65 , and a broken line indicates characteristics of a sound production device of a comparative example which does not include a resonant chamber. 
         [0055]    As clearly illustrated in  FIG. 7 , the sound production device of the present embodiment has a sound pressure level which increases in the vicinity of the resonant frequency of each of the resonant chambers  61 ,  62 , and  65  compared to the sound production device of the comparative example which does not include the resonant chamber. In other words, a large sound pressure is obtained in a wide frequency band by providing multiple resonant chambers  61 ,  62 , and  65  having different resonant frequencies. 
         [0056]    The sound production device of the present embodiment has the sound pressure level which decreases in a frequency region exceeding  5  kHz, but there is no problem on the use of the product that the sound pressure level is decreased in the frequency region. 
         [0057]    A sound passage from the speaker portion up to each of the sound emission holes  24 ,  25 ,  26 , and  66  is an intricate path, that is, a labyrinth structure, and thereby the flow of water during high-pressure car washing or snow is prevented from entering the sound passage. 
         [0058]    Water or snow entering the cylindrical space formed by the base cylinder portion  11 , the base second wall  14 , and the base plate portion  16  from the second sound emission holes  25 , the third sound emission holes  26 , and the fourth sound emission holes  66  is received by the base plate portion  16 , and then is moved to a portion of the cylindrical space on a lower side, and is emitted to the outside from the fourth sound emission hole  66  which is positioned on the lowermost portion of the fourth sound emission holes  66 . Therefore, water or snow does not arrive at the diaphragm  41  and damage of the speaker  4  due to adhesion of water is prevented. 
         [0059]    Water entering the third resonant chamber  65  from the first sound emission hole  24  is received by the shielding wall  12 , and then is moved to the lowermost portion of the third resonant chamber  65 , and is emitted to the outside from the first clearance  63  and the second clearance  64  which are positioned in the lowermost portion of among the first clearances  63  and the second clearances  64 . In addition, snow entering the third resonant chamber  65  from the first sound emission hole  24  is deposited on the shielding wall  12 . Therefore, water or snow does not arrive at the diaphragm  41  and damage of the speaker  4  due to adhesion of water is prevented. 
         [0060]    According to the present embodiment, since the multiple resonant chambers  61 ,  62 , and  65  having different resonant frequencies are provided, a large sound pressure can be obtained in a wide frequency range. 
         [0061]    Since the sound passage has the labyrinth structure, entrance of water or snow into the speaker  4  can be prevented. 
         [0062]    Furthermore, since the shielding wall  12  is provided in the base  1 , a shape of the shielding wall  12  can be appropriately set and the shielding wall  12  can be formed without using the slide mold. 
       Other Embodiment 
       [0063]    It should be appreciated that the present disclosure is not limited to the embodiments described above and can be modified appropriately within the scope of the appended claims. 
         [0064]    In the respective embodiments above, it goes without saying that elements forming the embodiments are not necessarily essential unless specified as being essential or deemed as being apparently essential in principle. 
         [0065]    In a case where a reference is made to the components of the respective embodiments as to numerical values, such as the number, values, amounts, and ranges, the components are not limited to the numerical values unless specified as being essential or deemed as being apparently essential in principle. 
         [0066]    Also, in a case where a reference is made to the components of the respective embodiments above as to shapes and positional relations, the components are not limited to the shapes and the positional relations unless explicitly specified or limited to particular shapes and positional relations in principle.