Vehicle-mounted speaker

Abstract

To provide an on-vehicle speaker capable of reducing a load mass acting on a diaphragm even when the volume of a back space of a case is decreased.SOLUTION: In the in-vehicle speaker 1, the case 10 has the flat area 16a and the tapered area 17a around the flat area LA. The centroid Oc of the flat area 16a is set at a position closer to the duct 20 than the vibration center line Oz of the diaphragm. The widths W1 to W4 of the tapered area 17a when viewed in a plane orthogonal to the vibration center line are large at a position away from the duct 20, and become narrower toward the duct 20 along the circumferential trajectories C1 and C2. As a result, a back space between the internal wall surface of the case and the diaphragm in the case 10 is gradually widened along the circumferential loci C1 and C2 from a position away from the duct 20 toward the duct 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an in-vehicle speaker in which a diaphragm and a magnetic drive unit are housed in a case having a duct. [Background technology]

[0002] Patent Documents 1 and 2 describe in-vehicle speakers used as so-called subwoofers, etc. These in-vehicle speakers have a sound-generating unit inside a case, which is comprised of a diaphragm and a magnetic drive unit. The case is integrally formed with a duct that directs sound pressure generated when the diaphragm vibrates to the outside of the case, and the duct has a sound-generating port. The case with the diaphragm is installed in the exterior space of the vehicle, and the duct is attached to a hole in a bulkhead of the vehicle. Sound pressure generated inside the case by vibration of the diaphragm is output as reproduced sound from the sound-generating port of the duct into the interior space of the vehicle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-118585 [Patent Document 2] Japanese Patent Application Publication No. 2019-125962 Summary of the Invention [Problem to be solved by the invention]

[0004] In both the in-vehicle speakers described in Patent Documents 1 and 2, sound pressure is applied to the vehicle interior from the sound output port of the duct, but depending on the structure and size of the vehicle, an in-vehicle speaker with approximately the same structure as those described in Patent Documents 1 and 2 can be used, with the case installed in the vehicle interior and the duct opening to the outside space, and sound pressure being applied from the diaphragm inside the case toward the vehicle interior. In this case, the vibration characteristics of the diaphragm directly affect the acoustic output sensitivity.

[0005] The case with the duct functions as a Helmholtz resonator. However, near the resonant frequency of the Helmholtz resonator, the air inside the duct resonates, increasing the internal pressure of the case, significantly limiting the amplitude of the diaphragm. While sound pressure continues to be output from the duct toward the exterior, the suppression of the diaphragm's amplitude significantly reduces the sound pressure output from the diaphragm into the vehicle cabin. This type of car speaker is used as a woofer, operating at a frequency band of at most 150 Hz. To increase the output sensitivity of the diaphragm within the operating frequency band, the resonant frequency of the Helmholtz resonator must be set higher than 150 Hz. While the resonant frequency can be increased by making the duct wider and shorter, the duct opening diameter cannot be increased unconditionally due to vehicle-specific constraints. Furthermore, making the duct wider and shorter raises the risk of foreign objects and dust entering the vehicle.

[0006] Therefore, in order to increase the resonant frequency of the Helmholtz resonator, it is necessary to reduce the size of the case and the internal volume of the back space between the inner wall surface of the case and the diaphragm. However, reducing this internal volume shortens the opposing distance between the inner wall surface of the case and the diaphragm. This increases the load resistance (local pressure), which is the resistance to the airflow from the back space to the duct when the diaphragm vibrates. This load resistance effectively increases the acoustic load resistance within the duct. As a result, the load acting on the diaphragm increases, suppressing its movement in the operating frequency range and reducing the bass output sensitivity.

[0007] The present invention solves the above-mentioned conventional problems, and aims to provide an in-vehicle speaker with a structure that can reduce the acoustic load resistance from the back space between the inner wall surface of the case and the diaphragm toward the duct when the diaphragm vibrates. [Means for solving the problem]

[0008] The present invention provides an in-vehicle speaker having a case with a duct, a diaphragm installed inside the case, and a magnetic drive unit that drives the diaphragm, the diaphragm has an outer surface that applies sound pressure to the outside of the case and an inner surface that faces the inside of the case, the diaphragm includes a tapered portion that faces the inside of the case as it approaches a vibration center line that passes through the center line of the diaphragm and extends in the vibration direction, and a back space that is surrounded by the inner surface of the diaphragm and the inner wall surface of the case and leads to the inside of the duct is formed inside the case, When a cross section including the vibration center line and the opening center of the duct is defined as a longitudinal cross section, and a cross section including the vibration center line and perpendicular to the longitudinal cross section is defined as a transverse cross section, The area when viewed in the transverse cross section is larger than the area of ​​the opposing space between the tapered portion and the inner wall surface at a position on the opposite side of the vibration center line from where the duct exists when viewed in the longitudinal cross section.

[0009] In the in-vehicle speaker of the present invention, it is preferable that the area when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line gradually increases from the position of the longitudinal cross section to the position of the transverse cross section.

[0010] Furthermore, in the in-car speaker of the present invention, it is preferable that the area when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line gradually increases from the position of the transverse cross section toward the boundary between the case and the duct.

[0011] The in-vehicle speaker of the present invention can be configured so that the opening angle when viewed in the transverse cross section is larger than the opening angle between the inner surface of the tapered portion and the inner wall surface of the case at a position on the opposite side of the vibration center line from where the duct is located when viewed in the longitudinal cross section.

[0012] In the in-vehicle speaker of the present invention, when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line, it is preferable that the opening angle gradually increases from the position of the longitudinal cross section to the position of the transverse cross section.

[0013] Furthermore, in the in-vehicle speaker of the present invention, when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line, it is preferable that the opening angle gradually increases from the position of the transverse cross section toward the boundary between the case and the duct.

[0014] In the in-vehicle speaker of the present invention, the inner wall surface of the case has a flat inner wall surface that is perpendicular to the vibration center line and faces the inner surface of the diaphragm, and a tapered inner wall surface that is located on the outer periphery of the flat inner wall surface and inclined in the same direction as the tapered portion of the diaphragm, The width dimension of the tapered inner wall surface when viewed in a plane perpendicular to the vibration center line can be configured to be narrower at the position of the transverse cross section than at the position of the longitudinal cross section.

[0015] In the in-vehicle speaker of the present invention, it is preferable that the width dimension gradually narrows from the position of the longitudinal cross section to the position of the transverse cross section along a circumferential path centered on the vibration center line.

[0016] Furthermore, in the in-vehicle speaker of the present invention, it is preferable that the width dimension gradually narrows along the circumferential path from the position of the cross section toward a boundary between the case and the duct.

[0017] The in-vehicle speaker of the present invention can be configured such that the centroid of the flat inner wall surface when viewed in the plane is closer to the duct than the vibration center line.

[0018] For example, in the in-vehicle speaker of the present invention, the duct opens into an outer space bounded by a partition wall, and sound pressure is applied from the diaphragm to an inner space bounded by the partition wall. [Effects of the Invention]

[0019] In car speakers that use a case with a duct, the air moving within the duct when the diaphragm vibrates becomes the load mass. However, because the back space is connected to a duct with a smaller internal volume, when the diaphragm vibrates, the resistance to the airflow from the farthest point from the duct in the back space toward the duct is also effectively added to the load mass of the duct. As the load mass increases, the vibration of the diaphragm is suppressed and output decreases. Therefore, the present invention reduces the resistance (local pressure) caused by the airflow toward the duct within the back space by increasing the area (volume) of each cross section of the back space along a circumferential path from the farthest point from the duct.

[0020] When a case with a duct is used, vibration of the diaphragm is suppressed near the Helmholtz resonance frequency. Therefore, in a speaker in which a duct opens into an outer space bounded by a partition wall and sound pressure is applied from the diaphragm to an inner space bounded by the partition wall, the sound pressure applied from the diaphragm to the vehicle interior space decreases near the Helmholtz resonance frequency. Therefore, in this speaker, it is desirable to set the Helmholtz resonance frequency higher than the operating frequency band. Although the Helmholtz resonance frequency can be set in a higher range by reducing the internal volume of the back space, even in this case, the in-vehicle speaker of the present invention can reduce the load resistance when air flows through the back space, thereby minimizing the decrease in sound pressure from the diaphragm caused by reducing the back space. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a plan view of an in-vehicle speaker according to an embodiment of the present invention; [Figure 2] 1 is a front view of an in-vehicle speaker according to an embodiment of the present invention; [Figure 3] FIG. 3 is a longitudinal cross-sectional view of the in-vehicle speaker shown in FIG. 1 taken along line III-III; [Figure 4] FIG. 4 is a cross-sectional view of the in-vehicle speaker shown in FIG. 1 taken along line IV-IV; [Figure 5]1 is a diagram comparing the sound pressure output and impedance of the diaphragm of a speaker according to an embodiment of the present invention with a speaker according to a comparative example; DETAILED DESCRIPTION OF THE INVENTION

[0022] <Structure of car speaker 1> An in-vehicle speaker 1 according to an embodiment of the present invention is shown in Figures 1 to 4. Figures 1 to 3 show a partition wall 2 of a vehicle such as an automobile, with a fitting hole 3 opening in the partition wall 2. The space on the right side of the partition wall 2 is the inner space, which is the vehicle interior space S1 that communicates with the passenger compartment of the vehicle. The space on the left side of the partition wall 2 is the outer space, which is the vehicle exterior space S2 that leads to the outside of the vehicle. The in-vehicle speaker 1 has a case 10 with an integrated duct 20. The case 10 is installed in the vehicle interior space S1, and sound pressure is applied to the vehicle interior space S1 when a diaphragm provided inside the case 10 vibrates. The end of the duct 20 is attached to the fitting hole 3 formed in the partition wall 2, and an opening 21 opens outside the partition wall 2 to the vehicle exterior space S2.

[0023] As shown in FIGS. 3 and 4, the in-vehicle speaker 1 includes a diaphragm 30 disposed within a case 10. A virtual line passing through the center of the diaphragm 30 and extending in the vibration direction of the diaphragm 30 is a vibration center line Oz. The Z1-Z2 direction is a vertical direction parallel to the vibration center line Oz and is the vibration direction of the diaphragm 30. The Z1 direction is the upward direction, and the Z2 direction is the downward direction. The Z2 direction is the sound generation direction toward the vehicle interior space S1 when the diaphragm 30 vibrates. FIG. 1 shows a vertical center line Ox that is perpendicular to the vibration center line Oz and includes the vibration center line Oz and the opening center Od of the opening 21 of the duct 20. The X1 direction is forward along the vertical center line Ox and is the exhaust direction of rear sound pressure from the opening 21 of the duct 20 toward the vehicle exterior space S2. The X2 direction is rearward, facing toward the interior of the case 10. 1 shows a horizontal center line Oy that intersects with the vertical center line Ox at a vibration center line Oz and is perpendicular to the vertical center line Ox. The Y1 direction along the horizontal center line Oy is the leftward direction, and the Y2 direction is the rightward direction.

[0024] A plane including the vibration center line Oz, the opening center Od of the duct 20, and the vertical center line Ox is a vertical cross section, and Fig. 3 is a vertical cross section of the case 10 and the duct 20 cut at the vertical cross section. A plane including the vibration center line Oz and the horizontal center line Oy and perpendicular to the vertical cross section is a horizontal cross section. Fig. 4 is a horizontal cross section of the case cut at the horizontal cross section.

[0025] The case 10 of the car speaker 1 shown in FIGS. 1 to 4 is die-cast from a metal material or injection-molded from reinforced plastic. The case 10 is composed of an upper case 11 and a lower case 12 assembled vertically. A duct 20 is provided in front of the upper case 11 (in the X1 direction). The duct 20 is molded integrally with the upper case 11. Alternatively, the duct 20 may be molded separately from the upper case 11 and joined to the upper case 11. The duct 20 has a uniform opening cross-sectional area in the front-to-rear direction (X direction). However, the duct 20 may have a shape in which the opening cross-sectional area gradually decreases toward the opening 21 (in the X1 direction). As shown in FIGS. 3 and 4, the lower case 12 has multiple sound-generating holes 13. A support frame 14 is provided inside the case 10. The outer periphery 14a of the support frame 14 is sandwiched between the upper case 11 and the lower case 12 from above and below.

[0026] As shown in Figures 3 and 4, a diaphragm 30 is provided inside the case 10. The diaphragm 30 has a circular (perfect circle or ellipse) shape when viewed in a plane perpendicular to the vibration center line Oz (when projected onto a plane), and has a tapered portion (cone portion) 31 that tapers inward toward the interior of the case 10 (toward the ceiling of the upper case 10) as it approaches the vibration center line Oz. The surface of the diaphragm 30 facing downward (in the Z2 direction) is the outer surface 38, and when the diaphragm 30 vibrates, sound pressure that becomes sound is applied from the outer surface 38 to the vehicle interior space S1 through the sound-generating holes 13 in the lower case 12. The surface of the diaphragm 30 facing upward (in the Z1 direction) is the inner surface 39, which faces toward the interior of the case 10.

[0027] An edge member 32 is joined to the outer periphery of diaphragm 30. Edge member 32 has a semicircular cross section and a ring-like shape when projected onto a plane. An inner periphery 32a of edge member 32 is adhered and fixed to the outer periphery of diaphragm 30, and an outer periphery 32b of edge member 32, together with an outer periphery 14a of support frame 14, is sandwiched between the outer peripheries of upper case 11 and lower case 12, and upper case 11 and lower case 12 are fixed together with screws.

[0028] As shown in FIGS. 3 and 4 , a central hole 30a is formed in the center of the diaphragm 30, and a cylindrical bobbin 33 is fixed inside the central hole 30a. A voice coil 34 is wound around and fixed to the outer periphery of the lower part of the bobbin 33. The opening at the top of the bobbin 33 is closed with a cap 35. Damper members 36 and 37 are provided inside the case 10. Each of the damper members 36 and 37 has a ring shape when projected onto a plane and a corrugated shape when viewed in vertical cross section as shown in FIG. 3. The outer peripheries of the damper members 36 and 37 are bonded and fixed to the upper support portion 14b of the support frame 14, and the inner peripheries of the damper members 36 and 37 are bonded and fixed to the outer periphery of the bobbin 33. The diaphragm 30 is supported by the edge member 32 and the damper members 36 and 37, and can vibrate up and down along the vibration center line Oz due to elastic deformation of the edge member 32 and the damper members 36 and 37.

[0029] 3 and 4, a support hole 12a is formed in the center of the lower case 12, and a magnetic circuit unit 40 is fixed in the support hole 12a. The magnetic circuit unit 40 is composed of a lower yoke 41, a center yoke 42 fixed on the lower yoke 41 and positioned inside the bobbin 33, a ring-shaped magnet 43 fixed on the outer periphery of the lower yoke 41 and positioned outside the bobbin 33, and a ring-shaped upper yoke 44 fixed on the magnet 43. The lower yoke 41, the center yoke 42, and the upper yoke 44 are made of a magnetic material. A magnetic gap G is formed between the outer periphery of the center yoke 42 and the inner periphery of the upper yoke 44, and the voice coil 34, which is provided on the lower outer periphery of the bobbin 33, is positioned inside the magnetic gap G.

[0030] In the magnetic circuit section 40, a magnetic flux is generated that crosses the magnetic gap G. An electromagnetic force is generated by the voice current flowing through the voice coil 34 located in the magnetic gap G and the magnetic flux that crosses the voice coil 34 in the magnetic gap G, and a vertical vibration force is applied to the diaphragm 30 via the voice coil 34. The magnetic circuit section 40 and the voice coil 34 constitute a "magnetic drive section."

[0031] The interior of the case 10 is almost completely divided into upper and lower spaces by the diaphragm 30, edge member 32, and cap 35 that covers the top of the bobbin 33. The lower space divided by the diaphragm 30, edge member 32, and cap 35 is the outer space Vf, which communicates with the vehicle interior space S1 through the sound-generating hole 13 in the lower case 12. The upper space divided by the diaphragm 30, edge member 32, and cap 35 is the back space Vb. The back space Vb is a space surrounded by the diaphragm 30, edge member 32, and cap 35, as well as the inner surface of the upper case 11, i.e., the inner wall surface 15 of the case 10. The back space Vb is connected only to the internal space Vd of the duct 20.

[0032] 1 to 4, in-vehicle speaker 1, case 10 is disposed in vehicle interior space S1, and when diaphragm 30 vibrates, air vibrations are imparted from outer surface 38 of diaphragm 30 to outer space Vf, and the air vibrations become sound pressure that acts on vehicle interior space S1 through multiple sound-generating holes 13 formed in lower case 12, thereby providing reproduced sound to vehicle interior space S1. When diaphragm 30 vibrates, back pressure is applied from inner surface 39 of diaphragm 30 to back space Vb within case 10, in an opposite phase to the sound pressure acting on outer space Vf. This back pressure is imparted to outer space S2 through opening 21 of duct 20, and is not heard in vehicle interior space S1.

[0033] <Shape of the back space Vb> 3 and 4, the inner wall surface of case 10 facing diaphragm 30, i.e., inner wall surface 15 forming back space Vb, has a flat inner wall surface 16 that is perpendicular to vibration center line Oz and faces inner surface 39 of diaphragm 30, and a tapered inner wall surface 17 that is continuous with the outer periphery of flat inner wall surface 16 and slopes in the same direction as tapered portion 31 of diaphragm 30. As shown in Figures 3 and 4, upper case 11 is formed with a uniform thickness, so that in the appearance of case 10 when viewed from the top view of Figure 1, flat region 16a has approximately the same shape and area as flat inner wall surface 16 on its inner surface, and tapered region 17a has approximately the same shape and area as tapered inner wall surface 17 on its inner surface.

[0034] As shown in Fig. 1, the planar shape of the flat region 16a and the flat inner wall surface 16 is approximately circular, with its centroid Oc located on the longitudinal centerline Ox and closer to the duct 20 than the vibration centerline Oz. As a result, when viewed in the plan view of Fig. 1 (when projected onto a plane perpendicular to the vibration centerline Oz), the width dimension W of the tapered region 17a and the tapered inner wall surface 17 varies depending on the position. The width dimension W is the radial distance from the vibration centerline Oz between the outer circumferential edge 16e of the flat region 16a and the flat inner wall surface 16 and the outer circumferential edge 17e of the tapered region 17a and the tapered inner wall surface 17 when viewed in the plan view.

[0035] As shown in FIG. 1, the width dimension on the longitudinal centerline Ox, i.e., the width dimension on the longitudinal cross section shown in FIG. 3, is W1, and the width dimension on the transverse centerline Oy, i.e., the width dimension on the transverse cross section shown in FIG. 4, is W3. FIG. 1 shows a selected line A1 extending radially from the vibration centerline Oz at an angular position rearward of the transverse centerline Oy (in the X2 direction) and half the angle formed by the longitudinal centerline Ox and the transverse centerline Oy. The width dimension on the selected line A1, i.e., the width dimension on the selected cross section including the selected line A1 and the vibration centerline Oz, is W2. FIG. 1 shows a selected line A2 extending radially from the vibration centerline Oz at an angular position forward of the transverse centerline Oy (in the X1 direction) and half the angle formed by the longitudinal centerline Ox and the transverse centerline Oy. The width dimension on the selected line A2, i.e., the width dimension on the selected cross section including the selected line A1 and the vibration centerline Oz, is W4.

[0036] The tapered region 17a and the tapered inner wall surface 17 have a width dimension W3 at the horizontal center line Oy that is narrower than a width dimension W1 on the vertical center line Ox and at a position farther from the duct 20 than the vibration center line Oz. The width dimension W2 at the selection line A1 is narrower than the width dimension W1 but wider than the width dimension W3. The width dimension W4 at the selection line A2 is narrower than the width dimension W3. The width dimension W gradually narrows along a counterclockwise circumferential locus C1 centered on the vibration center line Oz, from W1 at the vertical center line Ox to W2 at the selection line A1 to W3 at the horizontal center line Oy. Furthermore, the width dimension W gradually narrows along the circumferential locus C1 from W3 at the horizontal center line Oy to W4 at the selection line A2, toward the boundary 22 between the case 10 and the duct 20. In addition, in Figure 1, the shape of the case 10 is symmetrical in the horizontal direction (Y1-Y2 direction) with the vertical center line Ox as the boundary, and along the clockwise circumferential locus C2 centered on the vibration center line Oz, the width dimensions gradually narrow in the order W1, W2, W3, and W4, and gradually narrow toward the boundary 22 between the case 10 and the duct 20.

[0037] 3 and 4, the inclination angle α of the tapered portion 31 of the diaphragm 30 with respect to a plane perpendicular to the vibration center line Oz is uniform at any position on the tapered portion 31. However, because the width dimension W of the tapered region 17a and the tapered inner wall surface 17 of the case 10 when viewed in plan varies as described above, the inclination angle β3 of the tapered inner wall surface 17 with respect to the horizontal plane at the cross section shown in FIG. 4 is larger than the inclination angle β1 of the tapered inner wall surface 17 with respect to the horizontal plane at the vertical section shown in FIG. 3. Therefore, the opening angle (β3-α) between the inner surface 39 of the tapered portion 31 and the inner wall surface 15 of the case 10 (tapered inner wall surface 17) at the cross section is larger than the opening angle (β1-α) between the inner surface 39 of the tapered portion 31 and the inner wall surface 15 of the case 10 (tapered inner wall surface 17) at the vertical section. The opening angle at the selected cross section including the vibration center line Oz and the selected line A1 is larger than the opening angle at the longitudinal cross section and smaller than the opening angle at the transverse cross section. The opening angle at the selected cross section including the vibration center line Oz and the selected line A2 is larger than the opening angle at the transverse cross section. That is, the opening angle gradually increases from the longitudinal cross section toward the transverse cross section along the circumferential locus C1 and the circumferential locus C2, and further gradually increases from the transverse cross section toward the boundary 22 between the case 10 and the duct 20.

[0038] As shown in Fig. 1, width dimension W of tapered region 17a and tapered inner wall surface 17 varies along circumferential loci C1 and C2, and accordingly, the opening angle between inner surface 39 of tapered portion 31 and inner wall surface 15 (tapered inner wall surface 17) of case 10 at each cross-sectional position varies along circumferential loci C1 and C2. Therefore, the area of ​​the opposing space between inner surface 39 of tapered portion 31 of diaphragm 30 and inner wall surface 15 of case 10 in the vertical direction (Z1-Z2 direction) in the vertical cross-section shown in Fig. 3 is larger than the area of ​​the opposing space between inner surface 39 of tapered portion 31 of diaphragm 30 and inner wall surface 15 of case 10 in the vertical direction (Z1-Z2 direction). Fig. 3 shows an outer edge vertical line H1 extending in the vertical direction from the outer edge of diaphragm 30 and an inner edge vertical line H2 extending in the vertical direction from the inner edge of diaphragm 30. The area of ​​the opposing space in the vertical cross section is the area of ​​the opposing space surrounded by inner surface 39 of tapered portion 31 of diaphragm 30, tapered inner wall surface 17 of case 10, outer edge vertical line H1, and inner edge vertical line H2. The area of ​​the opposing space in the horizontal cross section is the area of ​​the opposing space surrounded by inner surface 39 of tapered portion 31 of diaphragm 30, tapered inner wall surface 17 of case 10, outer edge vertical line H3, and inner edge vertical line H4.

[0039] The area of ​​the opposing space in the selected cross section including the selected line A1 is larger than the area of ​​the opposing space in the longitudinal cross section and smaller than the area of ​​the opposing space in the transverse cross section, and the area of ​​the opposing space in the selected cross section including the selected line A2 is larger than the area of ​​the opposing space in the transverse cross section. The area (internal volume) of the back space Vb in each cross section including the vibration center line Oz is smallest at a position on the opposite side of the vibration center line Oz from where the duct 20 exists, and gradually increases from that position along the circumferential locus C1 and the circumferential locus C2 to the boundary 22 between the case 10 and the duct 20.

[0040] <Sound Effects> In the in-vehicle speaker 1, the diaphragm 30 vibrates in the vertical direction (Z1-Z2 direction) due to electromagnetic force generated by the voice current flowing through the voice coil 34 and the magnetic field that crosses the voice coil 34 within the magnetic gap G of the magnetic circuit unit 40. The sound pressure applied from the outer surface 38 of the diaphragm 30 to the outer space Vf forms reproduced sound and is applied to the vehicle interior space S1 through the sound generation hole 13 in the lower case 12. When the diaphragm 30 vibrates, back pressure is applied from the inner surface 39 to the back space Vb, and this back pressure is applied to the vehicle exterior space S2 through the opening 21 of the duct 20. The sound pressure acting on the outer space Vf and the back pressure acting on the back space Vb are out of phase with each other, but the baffle function of the partition wall 2 prevents interference between the sound pressure applied to the vehicle interior space S1 and the back pressure.

[0041] Due to the structure of the frame that constitutes the vehicle, there is a limit to how large the fitting hole 3 in the bulkhead 2 can be made. Furthermore, if the fitting hole 3 is enlarged and the opening area of ​​the opening 21 of the duct 20 is increased, there is a risk that moisture, dust, etc. may enter the duct 20, so the opening area of ​​the opening 21 of the duct 20 cannot be made too large. Therefore, when the diaphragm 30 vibrates, the difficulty in the movement of air within the duct 20 becomes the load mass (md). Furthermore, when the diaphragm 30 vibrates, the back pressure acting on the back space Vb advances toward the internal space Vd of the duct 20, and the difficulty in the passage of air toward the duct 20 in the back space Vb also becomes the back pressure load mass (mb). Since the load mass (md) and back pressure load mass (mb) are added to the mass (mmv) of the vibration system consisting of the diaphragm 30, bobbin 33, voice coil 34, edge member 32, damper members 36, 37, etc., the presence of the load masses (md) and (mb) effectively increases the mass of the vibration part including the diaphragm 30.

[0042] 3, the back space Vb of the in-car speaker 1 of the embodiment is narrowest on the opposite side of the vibration center line Oz from where the duct 20 is located, i.e., the facing space between the outer edge vertical line H1 and the inner edge vertical line H2, and the area of ​​the facing space appearing in each cross section including the vibration center line Oz gradually increases along the circumferential loci C1 and C2. When the diaphragm 30 vibrates, a back pressure, in which the air density periodically varies, is generated in the facing space between the outer edge vertical line H1 and the inner edge vertical line H2 in the back space Vb, and this back pressure tries to move toward the duct 20 along the circumferential loci C1 and C2. 3, the area of ​​the opposing space at the cross section to which it moves becomes larger, and therefore, even if the air density at that cross section is added to the air density of the air moving from the vertical cross section, the increase in air pressure per unit area of ​​the opposing space appearing at the cross section can be made as small as possible. The back pressure moves toward duct 20 along circular locus C1 and circular locus C2, and the area of ​​the opposing space appearing at each cross section toward duct 20 gradually increases, so the cumulative pressure of the air density in the opposing space appearing at each cross section can be minimized, which acts to reduce the back pressure load mass (mb).

[0043] As a comparative example, a speaker is assumed in which the area of ​​the opposing space between tapered portion 31 of diaphragm 30 and inner wall surface 15 of case 10, which appears in cross sections at all positions along circumferential loci C1 and C2 toward duct 20, is uniform. In this comparative speaker, when back pressure, which is the density of air generated in the opposing space at the position farthest from duct 20, moves toward duct 20 along circumferential loci C1 and C2, the area of ​​the opposing space at the cross section to which it moves is the same, so conceptually the density of the back pressure doubles, and as it moves further, it becomes four or eight times as large, and the pressure movement load (local pressure) toward duct 20 within back space Vb accumulates and becomes very large.

[0044] In the in-car speaker 1 of the embodiment, the accumulation of the difficulty in air flowing (pressure movement) toward the duct 20 within the back space Vb (pressure movement) can be reduced, as in the comparative example. When the internal volumes of the back spaces Vb of the in-car speaker 1 of the embodiment and the comparative example are set to the same value, the in-car speaker 1 of the embodiment can reduce the back pressure load mass (mb), which represents the difficulty in air flowing toward the duct 20, more than the speaker of the comparative example, and can therefore reduce local pressure. Therefore, in the in-car speaker 1 of the embodiment, the vibration load on the diaphragm 30 can be reduced, and the sensitivity of the speaker output can be increased as much as possible.

[0045] The embodiment of the in-vehicle speaker 1 in which the area of ​​the opposing space of the back space Vb gradually increases toward the duct 20 can be particularly effective when the case 10 is installed in the vehicle interior space S1 and the opening 21 of the duct 20 is open to the vehicle exterior space S2, as shown in Figures 1 to 3.

[0046] FIG. 5 compares the characteristics of speaker 1 according to the embodiment of the present invention with those of a comparative speaker. As mentioned above, the comparative speaker has a structure in which the area of ​​the opposing space between tapered portion 31 of diaphragm 30 and inner wall surface 15 of case 10, which appears in cross sections at all positions along circular loci C1 and C2 toward duct 20, is uniform. In FIG. 5, the horizontal axis represents frequency (Hz), the vertical axis on the left side represents sound pressure output (dB) from the diaphragm, and the vertical axis on the right side represents speaker impedance (Ω). In FIG. 5, (i) shows the frequency characteristics of the sound pressure output imparted from diaphragm 30 to outer space Vf within case 20 in speaker 1 according to the embodiment of the present invention, while (ii) shows the impedance characteristics of speaker 1 according to the embodiment. (iii) shows the frequency characteristics of the sound pressure output imparted from the diaphragm to outer space Vf within the case in the comparative speaker, and (iv) shows the impedance characteristics of the comparative speaker. "fo1" is the lowest resonance frequency of the vibration system of the speaker 1 according to the embodiment of the present invention, which is made up of the diaphragm 30, bobbin 33, voice coil 34, edge member 32, and damper members 36 and 37, and "fd1" is the resonance frequency of the Helmholtz resonator made up of the back space Vb and duct 20. "fo2" is the lowest resonance frequency of the vibration system in the comparative example, and "fd2" is the resonance frequency of the Helmholtz resonator made up of the back space and duct in the comparative example.

[0047] In the speaker 1 of the embodiment and the speaker of the comparative example, a Helmholtz resonator is configured by the case and duct, but a reduction in sound pressure output (r) occurs from the diaphragm in frequency bands approaching the resonance frequencies "fd1" and "fd2." This occurs because, near the resonance frequencies of the Helmholtz resonator, the air in the duct 20 resonates and vibrates with a large amplitude, increasing the internal pressure in the back space Vb and suppressing the amplitude of the diaphragm 30. The in-vehicle speaker 1 is used as a woofer, and its operating frequency band is approximately 150 Hz or lower. If a reduction in sound pressure output (r) occurs in or near this operating frequency band, the acoustic output delivered to the vehicle interior space S1 will be significantly reduced, for example, in the 80 Hz to 150 Hz band.

[0048] Therefore, by setting the resonant frequency of the Helmholtz resonator formed by the back space Vd inside the case and the internal space Vd of the duct 20 to a higher frequency band, the reduction in sound pressure output (r) can be shifted to a range higher than the frequency band used by the woofer. The resonant frequency can be increased by widening the opening area of ​​the duct and reducing the volume of the back space Vb. However, as mentioned above, in the case of in-car speakers, there is a limit to how large the opening area of ​​the duct can be, so in order to increase the resonant frequency, it is necessary to reduce the internal volume of the back space Vb. If the area of ​​the diaphragm is kept above a certain value and the internal volume of the back space Vb is reduced, the vertical distance between the diaphragm and the inner wall of the case must be narrowed. The speaker of the comparative example has a structure in which the area of ​​the opposing space in the vertical direction between the tapered portion of the diaphragm and the inner wall surface of the case, which appears in cross sections at all positions toward the duct along the circumferential loci C1 and C2, is uniform. As a result, the cumulative value of the back pressure load mass (mb), which expresses the difficulty of air passing toward the duct within the back space Vb, becomes very large, the acoustic output given from the diaphragm to the vehicle interior space S1 decreases, and the sensitivity as a speaker decreases significantly.

[0049] In the speaker of the comparative example, the volume of the back space Vb of the case cannot be reduced, so the resonant frequency "fd2" of the Helmholtz resonator cannot be set in a very high range, as shown in (iii) in Figure 5, and the reduction in sound pressure output (r) emitted from the diaphragm tends to approach the frequency band used as a woofer or to appear within the frequency band used. Furthermore, in the speaker of the comparative example, the cumulative value of the back pressure load mass (mb) becomes large, so as shown in (iii), the problem arises that the sound pressure output cannot be increased in the frequency band used lower than the frequency at which the reduction in sound pressure output (r) occurs.

[0050] In the in-vehicle speaker 1 of the embodiment, even if the internal volume of the back space Vb is reduced to set the resonance frequency "fd1" of the Helmholtz resonator in a high range, the area of ​​the back space Vb in each cross section including the vibration center line Oz is gradually increased along the circumferential loci C1 and C2 toward the duct 20, thereby making it possible to suppress the accumulation of the back pressure load mass (mb), which represents the difficulty of air passing through the back space Vb toward the duct. Therefore, as shown in (i) in Figure 5, by reducing the internal volume of the back space Vb within the case 20, the resonance frequency "fd1" of the Helmholtz resonator can be set to a higher frequency band than in the speaker of the comparative example, and the reduction in sound pressure output (r) can be shifted to a band higher than 150 Hz, which is the upper limit of the frequency band used as a woofer. In addition, since the cumulative value of the back pressure load mass (mb), which represents the difficulty of air passing through the back space Vb toward the duct, becomes smaller, it becomes possible to obtain sound pressure from the diaphragm 30 with good sensitivity over a wide frequency band below 150 Hz, as shown by line (i).

[0051] Furthermore, as shown in (i) of Figure 5, by setting the lowest resonance frequency "fo1" of the vibration system consisting of the diaphragm 30, bobbin 33, voice coil 34, edge member 32, damper members 36, 37, etc. to a frequency band lower than the resonance frequency "fd1" of the Helmholtz resonator and close to the frequency band used as a woofer, the diaphragm 30 becomes more likely to vibrate in the frequency band used, making it possible to increase the sound pressure output.

[0052] <Modification> As shown in Figures 2 and 3, in the embodiment of the car speaker 1, the center line Od1 of the duct 20 extends in a direction perpendicular to the vibration center line Oz, but the center line Od1 of the duct 20 may extend in the vertical direction (Z1-Z2 direction) and be connected to the case 10 at a position away from the vibration center line Oz.

[0053] Furthermore, the in-vehicle speaker 1 may be used in such a manner that the case 10 is installed in the exterior space S2 of the vehicle, and sound pressure that forms the reproduced sound is applied to the interior space S1 of the vehicle through the opening 21 of the duct 20. In this case, too, by using the case 10 that forms the back space Vb of the embodiment, it is possible to reduce the back pressure load mass (mb), which expresses the difficulty of air passing through the back space Vb toward the duct 20, and it is possible to increase the vibration sensitivity of the diaphragm 30. [Explanation of symbols]

[0054] 1. Car speakers 2 Bulkhead 10 cases 11 Upper case 12 Lower case 13. Sound hole 15 Inner wall surface 16 Flat inner wall surface 16a flat area 17 Tapered inner wall surface 17a Tapered area 20 Duct 21 Opening 22 Boundary between case and duct 30 diaphragm 31 Tapered section 34 voice coil 38 Inner surface of diaphragm 39 Outer surface of diaphragm 40 Magnetic circuit section A1, A2 selection line C1,C2 circular locus G Magnetic gap H1 Outer vertical line H2 Inner vertical line H3 Outer vertical line H4 Inner vertical line Oc centroid Od opening center Ox vertical center line Oy horizontal center line Oz vibration center line S1 Vehicle interior space (inner space) S2 Vehicle exterior space (outside space) Vb back space Vf outer space W1, W2, W3, W4 Width dimensions of the tapered area and tapered inner wall surface

Claims

1. An in-vehicle speaker having a case with a duct, a diaphragm installed inside the case, and a magnetic drive unit that drives the diaphragm, the diaphragm has an outer surface that applies sound pressure to the outside of the case and an inner surface that faces the inside of the case, the diaphragm includes a tapered portion that faces the inside of the case as it approaches a vibration center line that passes through the center line of the diaphragm and extends in the vibration direction, and a back space that is surrounded by the inner surface of the diaphragm and the inner wall surface of the case and leads to the inside of the duct is formed inside the case, When a cross section including the vibration center line and the opening center of the duct is defined as a longitudinal cross section, and a cross section including the vibration center line and perpendicular to the longitudinal cross section is defined as a transverse cross section, An in-vehicle speaker characterized in that, when viewed in the vertical section, the area when viewed in the horizontal section is larger than the area of ​​the opposing space between the tapered portion and the inner wall surface at a position on the opposite side of the vibration center line from where the duct exists.

2. 2. The in-vehicle speaker according to claim 1, wherein the area when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line gradually increases from the position of the longitudinal cross section to the position of the transverse cross section.

3. 3. The in-vehicle speaker according to claim 2, wherein the area when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line gradually increases from the position of the cross section toward the boundary between the case and the duct.

4. 2. The in-vehicle speaker according to claim 1, wherein the opening angle when viewed in the transverse section is larger than the opening angle between the inner surface of the tapered portion and the inner wall surface of the case at a position on the opposite side of the vibration center line from where the duct is located when viewed in the longitudinal section.

5. 5. The in-vehicle speaker according to claim 4, wherein when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line, the opening angle gradually increases from the position of the longitudinal cross section to the position of the transverse cross section.

6. 6. The in-vehicle speaker according to claim 5, wherein when viewed in a cross section including the vibration center line at each position on a circumferential path centered on the vibration center line, the opening angle gradually increases from the position of the transverse cross section toward the boundary between the case and the duct.

7. the inner wall surface of the case has a flat inner wall surface that is perpendicular to the vibration center line and faces the inner surface of the diaphragm, and a tapered inner wall surface that is located on the outer periphery of the flat inner wall surface and is inclined in the same direction as the tapered portion of the diaphragm, 5. The car speaker according to claim 4, wherein the width of the tapered inner wall surface is narrower at the transverse cross section than at the longitudinal cross section when viewed in a plane perpendicular to the vibration center line.

8. 8. The vehicle speaker according to claim 7, wherein the width gradually narrows from the position of the longitudinal cross section to the position of the transverse cross section along a circumferential path centered on the vibration center line.

9. 9. The vehicle speaker according to claim 8, wherein the width gradually narrows along the circumferential path from the position of the cross section toward a boundary between the case and the duct.

10. 10. The vehicle speaker according to claim 7, wherein the centroid of the flat inner wall surface when viewed from above is located closer to the duct than the vibration center line.

11. 5. The car speaker according to claim 1, wherein the duct opens into an outer space bounded by a partition wall, and sound pressure is applied from the diaphragm to an inner space bounded by the partition wall.

Images