Patent Publication Number: US-2022225017-A1

Title: Vehicle-mounted woofer device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the § 371 National Stage Entry of International Application No. PCT/JP2020/018032, filed on Apr. 27, 2020, which claims the benefit of Japanese Patent Application No. 2019-102557, filed on May 31, 2019, the contents of which applications are herein incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to a woofer system to be mainly mounted on a vehicle 
     BACKGROUND OF THE INVENTION 
     In recent years, in the environment of music reproduction in the vehicle cabin of an automobile, the spread of digital contents that make an occupant easily enjoy high-quality sound increasingly gives opportunities to reproduce even deep bass. 
     The location of an on-vehicle woofer system in an automobile is limited mainly to the inside of a door, a partition between a vehicle cabin and a luggage compartment (trunk), such as the back surface of a rear seat, or under a seat, for example. This is because there is a need to emit sound waves toward the inside of the vehicle cabin and to secure the space for placing the woofer system. 
     In particular, employing a speaker unit including a woofer for reproducing bass and a subwoofer for reproducing deep bass, an on-vehicle woofer system is generally in a large size. An idea is needed to mount such a large system in a limited space for placement. 
     For example, there is Patent Document 1 as a technique for reducing the size of an on-vehicle speaker system such as a woofer for reproducing bass. There is, for example, Patent Document 2 that provides an idea of the location of an on-vehicle woofer system. 
     Patent Document 1 describes a configuration of a speaker system including at least one Helmholtz resonator including a vent duct. 
     Patent Document 2 describes the following configuration of an on-vehicle speaker. A speaker box is housed in a wheel recess. A bolt is drawn out of the bottom of the housing recess and a nut is screwed onto the end of the bolt from the top of the speaker box to fix the speaker box into the wheel recess. 
     However, Patent Document 1 fails to disclose any structure for fixing the speaker system, for example, any structure for securing the airtightness of the part other than the duct of the Helmholtz resonator at the time of placing the speaker system in a spare tire housing as in Patent Document 2 
     On the other hand, Patent Document 2 fails to disclose any structure like a Helmholtz resonator, or any airtight structure such as a though-hole through which the bolt is inserted in the configuration of segmenting the inside of the speaker. 
     CITATION LIST 
     Patent Documents 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication (Published Japanese Translation of PCT Application) No. 2013-509049. 
         Patent Document 2: Japanese Unexamined Patent Publication No. H7-137581 
       
    
     SUMMARY OF THE INVENTION 
     The present disclosure was made to solve such problems. It is an objective of the present disclosure to provide an on-vehicle woofer system that achieves miniaturization and bass reproduction and that can be efficiently placed in a spare tire housing, for example. 
     In order to achieve the objective, an on-vehicle woofer system according to the present disclosure includes: a speaker unit including a magnetic circuit and a diaphragm connected to the magnetic circuit, and capable of generating sound waves by electrically driving the magnetic circuit to vibrate the diaphragm; a Helmholtz resonator to which a first surface of the diaphragm is oriented, the Helmholtz resonator being connected to the speaker unit; a sealed container to which a second surface of the diaphragm that is a back surface of the first surface is oriented, the sealed container providing a sealed space connected to the speaker unit; and a tube penetrating the Helmholtz resonator, the speaker unit, and the sealed container. 
     The speaker unit includes a seal for connecting the Helmholtz resonator and the sealed container to form the tube, and separating an internal space of the Helmholtz resonator or an internal space of the sealed container from the internal space of the tube. 
     The on-vehicle woofer system further includes: an upper cover member connected to the speaker unit; and a duct in the upper cover member. The Helmholtz resonator includes: a chamber space defined by at least the speaker unit and the upper cover member; and an outer circumferential duct space connected to the chamber space and segmented along an outer circumference of the speaker unit, and the Helmholtz resonator is configured such that the outer circumferential duct space communicates with an outside via the duct. 
     The on-vehicle woofer system further includes; a base member connected to the speaker unit. The sealed container is defined by at least the speaker unit and the base member. 
     The magnetic circuit is connected to the second surface of the diaphragm. 
     The magnetic circuit is connected to the second surface of the diaphragm. 
     The Helmholtz resonator has a resonance frequency set higher than an upper limit of an operation band frequency of the speaker unit. 
     The on-vehicle woofer system has a substantially cylindrical outer shape. 
     The on-vehicle woofer system is placed in a spare tire housing of an automobile, and fixed to the spare tire housing using a fixing tool to be inserted through the tube. 
     The on-vehicle woofer system according to the present disclosure using the means described above achieves miniaturization and bass reproduction and that can be efficiently installed in a spare tire housing, for example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an on-vehicle woofer system according to an embodiment of the present disclosure. 
         FIG. 2  is a perspective cross-sectional view of an on-vehicle woofer system according to an embodiment of the present disclosure. 
         FIG. 3  is a perspective cross-sectional view of the on-vehicle woofer system according to the embodiment of the present disclosure. 
         FIG. 4  is a perspective view of the on-vehicle woofer system according to the embodiment of the present disclosure with an upper cover removed. 
         FIG. 5  is a cross-sectional view of the on-vehicle woofer system according to the embodiment of the present disclosure. 
         FIG. 6  is a comparison graph showing the frequency characteristics of a speaker system including a Helmholtz resonator according to the present disclosure, and the speaker system used in combination with a low-pass filter. 
         FIG. 7  is a perspective view showing a spare tire housing of an automobile. 
         FIG. 8  is a cross-sectional view where the on-vehicle woofer system according to the embodiment of the present disclosure is mounted in the spare tire housing. 
         FIG. 9  is a cross-sectional view of an automobile including an on-vehicle woofer system according to a variation of the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Now, an embodiment of the present disclosure will be described with reference to the drawings. 
     (Overall Structure of On-Vehicle Woofer System) 
     An on-vehicle woofer system  1  according to the embodiment of the present disclosure will be described with reference to  FIGS. 1 to 5 .  FIG. 1  is a perspective view of the on-vehicle woofer system  1  according to the embodiment of the present disclosure.  FIGS. 2 and 3  are perspective cross-sectional views of the on-vehicle woofer system according to the embodiment of the present disclosure.  FIG. 4  is a perspective view of the on-vehicle woofer system according to the embodiment of the present disclosure with an upper cover removed.  FIG. 5  is a cross-sectional view taken along the center axis O of the on-vehicle woofer system according to the embodiment of the present disclosure. 
     The on-vehicle woofer system  1  is a speaker system in a substantially cylindrical shape formed by joining an upper cover member  11  and a base member  12 . The on-vehicle woofer system  1  has a through-hole  19  coaxial with the center axis O of the substantially cylindrical shape. The on-vehicle woofer system  1  includes a duct  14  at an end. The on-vehicle woofer system  1  includes a speaker unit  20  inside. As shown in  FIG. 4 , the speaker unit  20  has a frame  29  that is fixed to an intermediate plate member  13  inside the on-vehicle woofer system  1 . The intermediate plate member  13  is fixed to the base member  12 . The intermediate plate member  13  and the base member  12  may be formed integrally. The intermediate plate member  13  may be fixed to the upper cover member  11  or may be formed integrally with the upper cover member  11 . 
     The internal space of the on-vehicle woofer system  1  is divided into a sealed space  51  and a combined space with the speaker unit  20  as a boundary. The combined space is the combination of a chamber space  52  and an outer circumferential duct space  53  that constitute a Helmholtz resonator. Here, a diaphragm  21  constituting the speaker unit  20  has a first surface intersecting the vibration direction, and a second surface that is the back surface of the first surface. The sealed space  51  serves as a sealed container enclosed by the base member  12 , the intermediate plate member  13 , and the speaker unit  20 . Oriented to the sealed space  51  is the second surface of the diaphragm  21 . The chamber space  52  is defined by the upper cover member  11 , the intermediate plate member  13 , and the speaker until  20 . Oriented to the chamber space  52  is the first surface of the diaphragm  21 . The outer circumferential duct space  53  is defined by the upper cover member  11  and the base member  12 , and surrounds the circumference of the speaker until  20 . The outer circumferential duct space  53  is connected to a part of the chamber space  52 . The duct  14  is located in the upper cover member  11  so that the outer circumferential duct space  53  communicates with the outside via the duct  14 . Together with the chamber space  52 , the outer circumferential duct space  53 , and the opening of the duct  14 , the upper cover member  11  forms the Helmholtz resonator. As described above, the first surface of the diaphragm  21  constituting the speaker unit  20  is oriented to the chamber space  52  that forms the Helmholtz resonator, whereas the second surface of the diaphragm  21  is oriented to the sealed space  51 . The sound waves are emitted from the speaker unit  20  through the chamber space  52 , the outer circumferential duct space  53 , and the opening of the duct  14  to the outside. The Helmholtz resonator will be described later. 
     As shown in  FIG. 5 , the speaker unit  20  includes the diaphragm  21  and a magnetic circuit  22 . The speaker unit  20  is in a substantially concentric circular shape having the center axis passing through the center of the diaphragm  21  and parallel to the vibration direction. The center axis is coaxial with the enter axis O of the substantially cylindrical shape of the whole on-vehicle woofer system  1 . The diaphragm  21  includes a center edge  21   a  around the through-hole  19  at the center, a cone  21   b  extending radially outward from the center, and a circumferential edge  21   c  around the circumference of the cone  21   b . The center edge  21   a  is connected airtightly to a tubular first seal  30 . Connected air-tight to the lower end of the first seal  30  is a tubular second seal  31  which is connected airtightly to a column  24   b  of a yoke  24 , which will be described later, to constitute a part of a tube  18  serving as a part of the through-hole  19  at the center of the on-vehicle woofer system  1 . The center axis of the speaker until  20  and the center axis O of the substantially cylindrical shape of the whole on-vehicle woofer system  1  may shift from each other as long as a through-hole can be formed. 
     The center proximal end of the cone  21   b  is connected to a voice coil bobbin  23  wound with a coil of the magnetic circuit  22  to transmit the vibration of the voice coil bobbin  23 . That is, the axial direction of the speaker unit  20  coincides with the amplitude direction of the diaphragm  21 . 
     The magnetic circuit  22  includes the yoke  24  having a back surface serving as a disk-shaped flange  24   a , and the column  24   b  projecting from the center of the flange  24   a . Disposed on the outer circumference of the column  24   b  of the yoke  24  vibratably along the axis is the voice coil bobbin  23  which is provided with an annular magnet  25  on its outer circumference. The magnet  25  is sandwiched between the flange  24   a  of the yoke  24  and an annular plate  26 . 
     The magnetic circuit  22  mainly includes the voice coil bobbin  23 , the yoke  24 , the magnet  25 , and the plate  26 , and is what is called an “external magnetic circuit” having the magnet  25  on the outer side of the magnetic circuit 
     The region from the plate  26  to the circumferential edge  21   c  of the diaphragm  21  is covered with a frame  27 . Interposed between the inner surface of the frame  27  and the outer circumference of the voice coil bobbin  23  is a damper  28  which vibratably supports the voice coil bobbin  23 . 
     The voice coil bobbin  23  is wound with a voice coil which is connected to a signal transmission circuit. The voice coil bobbin  23  vibrates upon receipt of a signal from the signal transmission circuit. Incorporated into the signal transmission circuit may be a device, such as a low-pass filter or a band-pass filter, which limits the frequency band for driving the voice coil bobbin  23 . 
     Referring back to the overall structure of the on-vehicle woofer system  1 , the frame  29  of the speaker unit  20  and the intermediate plate member  13  that constitutes the Helmholtz resonator airtightly divide the chamber space  52  from the sealed space  51  at a close contact A. The first seal  30  and the upper cover member  11  that constitutes the Helmholtz resonator airtightly divide the chamber space  52  from the through hole  19  at a close contact B. The yoke  24  and the base member  12  that constitutes the sealed container airtightly divide the sealed space  51  from the through-hole  19  at a close contact C. In this manner, the tube  18  is formed which constitutes the through-hole  19  penetrating the Helmholtz resonator, the speaker unit  20 , and the sealed container. The internal space of the Helmholtz resonator, the internal space of the sealed container, and the through-hole  19 , which is the internal space of the tube  18 , can be separated from each other. 
     (Helmholtz Resonator). Next, the Helmholtz resonator will be described. The Helmholtz resonator is expressed by Equation 1 below where, as a structure constituting the Helmholtz resonator, L is the duct length, S p  is the cross-sectional area of the duct opening, V is the volume within the chamber, c is the speed of sound, and f p  is the port resonance frequency. 
     
       
         
           
             
               
                 
                   
                     f 
                     p 
                   
                   = 
                   
                     
                       c 
                       
                         2 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         π 
                       
                     
                     ⁢ 
                     
                       
                         
                           S 
                           p 
                         
                         
                           V 
                           ⁢ 
                           L 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Mathematical 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     It is found from Equation 1 that the port resonance frequency f p  decreases with a decrease in the cross-sectional area S p  of the duct opening, an increase in the duct length L, and an increase in the volume V within the chamber. For example, a speaker system in a predetermined size attached with the Helmholtz resonator will be described. According to Equation 1, the port resonance frequency f p  is about 110 Hz, where the volume V within the chamber, which is formed by the diaphragm  21  and a space in contact with the diaphragm  21  and a space in contact with the diaphragm  21 , is 2.0 liters, the cross sectional area S p  of the opening of the duct  14  is 3940 mm 2 , the duct length L is 500 mm, and the speed c of sound is 343.2 m/s at a temperature of 20° C. The operation band frequency to be reproduced can be equal to or lower than 80 Hz that is the port resonance frequency using a low-pass filter, for example. Accordingly, the sound waves can be efficiently emitted at a bass frequency range. 
       FIG. 6  shows the frequency characteristics of a speaker system (indicated by the solid line) obtained by attaching a Helmholtz resonator to the speaker unit  20 , and a speaker system (indicated by the dotted line) used in combination with a secondary low-pass filter (with calculated values) with a cutoff frequency of 80 Hz. In  FIG. 6 , the horizontal axis represents the frequency (unit: Hz), and the vertical axis represents the sound pressure level (unit: dB) of the speaker system measured under predetermined conditions. 
     As shown in  FIG. 6 , the speaker system attached with the Helmholtz resonator has the maximum value of the sound pressure level around 50 Hz. In the on-vehicle woofer system (i.e., a speaker system)  1  attached with the Helmholtz resonator according to the embodiment of the present disclosure, assume that the upper limit of the operation band frequency of the speaker unit is set to 80 Hz. At this time, the volume within the chamber is set small so that the resonance frequency of the Helmholtz resonator is higher than the operation band frequency. The air mass of the duct communicating with the chamber then affects the moving mass Mms of the diaphragm, which provides the effect of reducing the minimum resonance frequency f o  of the on-vehicle woofer system  1 . Specifically, with a decrease in the volume within the chamber, which is in contact with the diaphragm  21  extending to the Helmholtz resonator, to about two liters, for example, the air load mass increases with respect to the diaphragm  21 . This increases the moving mass Mms of the diaphragm  21  and decreases f o . 
     As described above, the speaker system attached with the Helmholtz resonator exhibits improved bass reproduction performance. Accordingly, the on-vehicle woofer system  1  according to the embodiment of the present disclosure also exhibits improved bass reproduction performance while being in a small size. 
     (Placement) 
       FIG. 7  is a perspective view showing that a spare tire  43  is placed in a spare tire housing  40  in the trunk of the automobile and is fixed using the fastening member  42  such as a nut. The on-vehicle woofer system  1  according to the embodiment of the present disclosure is placed in the spare tire housing  40  in place of the spare tire  43 . The spare tire housing  40  is formed as a recess in the trunk. 
       FIG. 8  is a cross-sectional view where the on-vehicle woofer system  1  according to the embodiment of the present disclosure is mounted in the spare tire housing  40 . The on-vehicle woofer system  1  is in a substantially cylindrical shape and placed in the spare tire housing  40  in place of a spare tire in a cylindrical shape as well, which allows efficient utilization of the spatial volume of the spare tire housing  40 . The on-vehicle woofer system  1  is fixed to the spare tire housing as follows. A bolt  41 , which is a fixing tool protruding from the spare tire housing  40 , is inserted through the through-hole  19  formed by the tube  18  of the on-vehicle woofer system  1 . The fastening member  42  such as the nut is screwed onto the bolt  41 . The on-vehicle woofer system  1  is directly fixed to the floor of the automobile, which corresponds to the bottom of the spare tire housing  40 . This configuration reduces unnecessary vibrations or other troubles in the on-vehicle woofer system  1  at the time of driving the speaker unit  20 . 
     As described above, the Helmholtz resonator to which the first surface of the diaphragm  21  is oriented, the Helmholtz resonator being connected to the speaker unit  20 ; the sealed container to which the second surface of the diaphragm that is the back surface of the first surface is oriented, the sealed container providing the sealed space connected to the speaker unit  20 ; and the tube  18  penetrating the Helmholtz resonator, the speaker unit  20 , and the sealed container. This configuration allows fixing of the on-vehicle woofer system  1  using a bolt, for example, inserted through the tube  18 , and secures the airtightness of the part other than the opening formed by the duct  14  of the Helmholtz resonator. Accordingly, the Helmholtz resonator allows the on-vehicle woofer system  1  to have a lower minimum resonance frequency F o  and to reproduce lower bass (i.e., at a lower frequency) even using a speaker unit with a small aperture. As a result, the on-vehicle woofer system  1  reproduces even bass, while being in a small size. 
     In addition, the second surface of the diaphragm  21  is oriented to the sealed container so that the sound waves radiated from the first surface of the diaphragm  21  and the sound waves radiated from the second surface neither interfere nor cancel each other. This configuration provides stable bass reproduction performance. 
     The outer circumferential duct space  53  is segmented along the outer circumference of the speaker unit  20 . The outer circumferential duct space  53  has thus a great length, without increasing the size of the on-vehicle woofer system  1 . Accordingly, the port resonance frequency decreases, which improves the bass reproduction performance. 
     While an embodiment of the present disclosure has been described above, the present disclosure is not limited to this embodiment. 
     For example, as shown in  FIG. 9 , a pipe  46  connected to the duct  14  of the on-vehicle woofer system  1  in a trunk space  44  may lead to a vehicle interior space  45  so that an occupant efficiently hears the sound emitted from the on-vehicle woofer system  1  in the vehicle interior space  45 . In this case, the pipe  46  substantially extends the outer circumferential duct space, which decreases the port resonance frequency and improves the bass reproduction performance. 
     The following configuration has been described above in the embodiment. The Helmholtz resonator is located on the first surface of the diaphragm  21 . The sealed container providing the sealed space is located on the second surface of the diaphragm  21  which is the back surface of the first surface. The magnetic circuit  22  is connected to the second surface of the diaphragm  21 . That is, the sealed container is located on the magnetic circuit  22 . Alternatively, the present disclosure may have the following configuration. The magnetic circuit  22  is connected to the first surface of the diaphragm  21 , that is, the Helmholtz resonator may be located on the magnetic circuit  22 . 
     The upper cover member  11  and the base member  12  are fastened to each other by a screw or welding. The joint between the upper cover member  11  and the base member  12  may be fastened with a seal interposed therebetween to ensure the airtightness. 
     The speaker unit  20  according to the embodiment described above is a speaker in the shape of a concentric ring as viewed from the front. The speaker shape is not limited thereto and may be, for example, a rectangular or like a track as viewed from the front. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
         
           
               1  On-Vehicle Woofer System 
               11  Upper Cover Member 
               12  Base Member 
               13  Intermediate Plate Member 
               14  Duct 
               18  Tube 
               19  Through-Hole 
               20  Speaker Unit 
               21  Diaphragm 
               21   a  Center Edge 
               21   b  Cone 
               21   c  Circumferential Edge 
               22  Magnetic Circuit 
               23  Voice Coil Bobbin 
               24  Yoke 
               24   a  Flange 
               24   b  Column 
               25  Magnet 
               26  Plate 
               27  Frame 
               28  Damper 
               29  Frame 
               30  First Seal 
               31  Second Seal 
               40  Spare Tire Housing 
               41  Bolt 
               42  Fastening Member 
               43  Spare Tire 
               44  Trunk Space 
               45  Vehicle Interior Space 
               46  Pipe 
               51  Sealed Space 
               52  Chamber Space 
               53  Outer Circumferential Duct Space