VIBRATING BODY FOR ACOUSTIC TRANSDUCER AND SPEAKER DEVICE

Abstract

An example vibrating body for the acoustic transducer may include a diaphragm including a first vibrating part and a second vibrating part located at an outer circumference of the first vibrating part. A coil is configured to vibrate the diaphragm. An edge portion is located at an outer circumference of the diaphragm. A plurality of ribs are provided outside of the coil on the second vibrating part formed integrally with the second vibrating part. A plurality of ribs is provided on the edge portion formed integrally with the edge portion. None of the integrally formed ribs is provided inside of the coil on the first vibrating part. The ribs provided on the second vibrating part are formed in an inner circumferential side of regions of the edge portion, the regions being located between the ribs provided on the edge portion next to each other.

Claims

1. A vibrating body for an acoustic transducer comprising: a diaphragm including a first vibrating part and a second vibrating part located at an outer circumference of the first vibrating part; a coil configured to vibrate the diaphragm; an edge portion located at an outer circumference of the diaphragm; a plurality of ribs provided outside of the coil on the second vibrating part formed integrally with the second vibrating part; and a plurality of ribs provided on the edge portion formed integrally with the edge portion, wherein: none of the integrally formed ribs is provided inside of the coil on the first vibrating part; and the ribs provided on the second vibrating part are formed in an inner circumferential side of regions of the edge portion, the regions being located between the ribs provided on the edge portion next to each other.

2. The vibrating body for an acoustic transducer according to claim 1, wherein the ribs provided on the second vibrating part and the ribs provided on the edge portion extend in a radial direction of the edge portion and the diaphragm.

3. The vibrating body for an acoustic transducer according to claim 1, wherein an area of the first vibrating part is substantially smaller than a sum of an area of the second vibrating part and an area of the edge portion.

4. The vibrating body for an acoustic transducer according to claim 1, wherein an apex of the second vibrating part is formed so as to be lower than an apex of the edge portion.

5. The vibrating body for an acoustic transducer according to claim 1, wherein the ribs provided on the second vibrating part and the ribs provided on the edge portion are formed so as to be convex in directions different from each other.

6. The vibrating body for an acoustic transducer according to claim 1, wherein the first vibration part is provided inside of the coil, and the second vibrating part is provided outside of the coil.

7. The vibrating body for an acoustic transducer according to claim 1, wherein a bent part being bent substantially perpendicularly to an outer circumference of the edge portion in an acoustic radiation direction is formed on the outer circumference of the edge portion.

8. A vibrating body for an acoustic transducer comprising: a diaphragm; an edge portion located at an outer circumference of the diaphragm; a first pattern having concave and convex portions and formed on the diaphragm in a circumferential direction of the diaphragm; and a second pattern having concave and convex portions formed on the edge portion in a circumferential direction of the edge portion, wherein the concave and convex portions of the first pattern are formed alternating with the concave and convex portions of the second pattern.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 is a set of schematic diagrams illustrating the structure of a vibrating body for an acoustic transducer according to Embodiment 1 of the present invention, FIG. 1(a) being a plan view, FIG. 1(b) being a cross-partial view taken along the line A-A in FIG. 1(a).

[0018] FIG. 2 is a perspective view illustrating the schematic structure of the vibrating body for an acoustic transducer shown in FIG. 1.

[0019] FIG. 3 is a set of cross-partial views taken along the line B-B in FIG. 1(a), FIG. 3(a) showing an example in which each first reinforcing portion has a substantially triangular cross-partial shape, FIG. 3(b) showing an example in which each first reinforcing portion has a substantially dome-like cross-partial shape.

[0020] FIG. 4 is a cross-partial view illustrating the schematic structure of a speaker device according to Embodiment 2 of the present invention.

[0021] FIG. 5 is a set of schematic diagrams illustrating the structure of a magnetic circuit included in the speaker device shown in FIG. 4, FIG. 5(a) being a plan view, FIG. 5(b) being a front view, FIG. 5(c) being a cross-partial view taken along the line B-B in FIG. 5(a).

[0022] FIG. 6 is a cross-partial view illustrating the schematic structure of a speaker device according to Embodiment 3 of the present invention.

[0023] FIG. 7 is a set of schematic diagrams illustrating the structure of a magnetic circuit included in the speaker device shown in FIG. 6, FIG. 7(a) being a plan view, FIG. 7(b) being a front view, FIG. 7(c) being a cross-partial view taken along the line C-C in FIG. 7(a).

BEST MODE FOR CARRYING OUT TEE INVENTION

Embodiment 1

[0024] FIG. 1 is a set of schematic diagrams illustrating the structure of a vibrating body 1 for an acoustic transducer, according to Embodiment 1 of the present invention. FIG. 1(a) is a plan view, and FIG. 1(b) is a cross-partial view taken along the line A-A in FIG. 1(a). FIG. 2 is a perspective view illustrating the schematic structure of the vibrating body 1 for an acoustic transducer shown in FIG. 1. For example, the vibrating body 1 for an acoustic transducer is used for a speaker device mounted on a portable electronic device such as a mobile phone, a portable radio, and a PDA. The shorter diameter of such a speaker device is, for example, about 2 to 4 cm.

[0025] The vibrating body 1 for an acoustic transducer has, in plan view, a substantially track-like shape formed of two circular arcs and a rectangle interposed therebetween. The vibrating body 1 for an acoustic transducer includes a diaphragm 2 and an edge portion 3 that is formed integrally with the diaphragm 2. The diaphragm 2 includes a first vibrating part 2a having a substantially track-like shape in plan view and a second vibrating part 2b having a substantially hollow track-like shape in plan view. The first and second vibrating parts 2a and 2b are formed integrally, and a pocket 2c is interposed therebetween.

[0026] Herein, the substantially hollow track-like shape in plan view is a shape formed of two circular arc-shaped parts and two rectangles that have the similar to the circular arc-shaped parts in width and connect the ends of the circular arc-shaped parts thereof. The substantially hollow track-like shape is a shape that the first vibrating part 2a having the above substantially track-like shape and disposed substantially at the center thereof is hollowed out of. The vertical cross-part shape of the first vibrating part 2a is a substantially dome-like shape protruding toward the front side (in an acoustic radiation direction). The second vibrating part 2b includes two circular arc-shaped parts (first regions) 2ba and 2bb and two rectangular parts (second regions) 2bc and 2bd that have the similar to the circular arc-shaped parts 2ba and 2bb in width and connect with both ends of two rectangular parts, and the circular arc-shaped parts 2ba and 2bb are formed integrally with the rectangular parts 2bc and 2bd. The vertical cross-partial shape of the second vibrating part 2b is a substantially curved shape protruding toward the front side (in the acoustic radiation direction).

[0027] The pocket 2c has a substantially track ring-like shape in plan view. The substantially track ring-like shape is a substantially hollow track-like shape with a width extremely narrower than the entire circumferential length. The pocket 2c is configured to accommodate a voice coil (not shown) having a substantially track ring-like shape, and the voice coil is secured using an adhesive. Therefore, the pocket 2c has a depth enough to prevent the upper end of the accommodated voice coil from projecting from the connection portion with the first vibrating part 2a. The vibrating body 1 for an acoustic transducer having such a structure is referred to a pocket-type diaphragm.

[0028] The edge portion 3 is formed on the outer circumferential edge of the second vibrating part 2b so as to be integral with the diaphragm 2. The edge portion 3 has a substantially hollow track-like shape in plan view. More specifically, the edge portion 3 includes two circular arc-shaped parts (first regions) 3a and 3b and two rectangular parts (second regions) 3c and 3d that have the similar to the circular arc-shaped parts 3a and 3d in width and connect the both ends of the circular arc-shaped parts thereof, and the circular arc-shaped parts 3a and 3b are formed integrally with the rectangular parts 3c and 3d. The vertical cross-partial shape of the edge portion 3 is a substantially roll-like shape protruding toward the front side.

[0029] The area of the first vibrating part 2a is substantially equal to or less than the sum of the area of the second vibrating part 2b and the area of the edge portion 3. In the example shown in FIGS. 1 and 2, the sum of the area of the second vibrating part 2b and the area of the edge portion 3 is about 3.5 times larger than the area of the first vibrating part 2a.

[0030] The first vibrating part 2a has a substantially dome-like vertical cross-sectional shape protruding toward the front side (in the acoustic radiation direction), and the second vibrating part 2b has a substantially curved vertical cross partial shape protruding toward the front side (in the acoustic radiation direction). The edge portion 3 has a substantially roll-like vertical cross-partial shape protruding toward the front side. More specifically, all the first vibrating part 2a, the second vibrating part 2b, and the edge portion 3 have substantially curved vertical cross-sectional shapes protruding toward the front side (in the acoustic radiation direction). As shown in FIG. 1(b), the apex of the second vibrating part 2b is formed so as to be lower than the apex of the first vibrating part 2a or the apex 9 of the edge portion 3.

[0031] As shown in FIG. 1(b), the apex 9 of the edge portion 3 is formed so as to be positioned near the outer circumferential side in respect with the center 10 between the inner and outer circumferences of the edge portion 3.

[0032] A plurality of first reinforcing portions 6a and 6b being convex toward the front side (in the acoustic radiation direction) are formed across the boundary between the edge portion 3 and the second vibrating part 2b. In the example shown in FIGS. 1 and 2, one reinforcing portion 6a is formed near the circular arc-shaped part 2ba side in respect with a boundary 4a between the circular arc-shaped part 2ba and the rectangular part 2bc of the second vibrating part 2b and near the rectangular part 3c side in respect with a boundary 5a between the circular arc-shaped part 3a and the rectangular part 3c of the edge portion 3. Another reinforcing portion 6a is formed near the circular arc-shaped part 2ba side in respect with a boundary 4b between the circular arc-shaped part 2ba and the rectangular part 2bd and near the rectangular part 3d side in respect with a boundary 5b between the circular arc-shaped part 3a and the rectangular part 3d. In addition, another reinforcing portion 6a is formed near the circular arc-shaped part 2bb side in respect with a boundary 4c between the circular arc-shaped part 2bb and the rectangular part 2bc and near the rectangular part 3c side in respect with a boundary 5c between the circular arc-shaped part 3b and the rectangular part 3c. Moreover, another reinforcing portion 6a is formed near the circular arc-shaped part 2bb side in respect with a boundary 4d between the circular arc-shaped part 2bb and the rectangular part 2bd and near the rectangular part 3d Side in respect with a boundary 5d between the circular arc-shaped part 3b and the rectangular part 3d. In other words, the first reinforcing portions 6a extend parallel to the shorter sides of the rectangular parts 2bc, 2bd, 3c, and 3d, respectively.

[0033] In the example shown in FIGS. 1 and 2, a plan view of an overall vibrating body 1 for an acoustic transducer including the edge portion 3 can be view as an ellipsoidal shape. First reinforcing portions 6b are formed on the long axis 7 of the ellipsoidal shape and substantially symmetrical positions with respect to the long axis 7 In other words, the first reinforcing portion 6b extends from the second vibrating part 2b to the edge portion 3 substantially in the radial direction of the circular arc-shaped part such as the circular arc-shaped part 2ba, 2bb, 3a, and 3b. The first reinforcing portion 6a and 6b are formed on the substantially symmetrical positions with respect to the short axis, when a plan view of an overall vibrating body 1 for an acoustic transducer including the edge portion 3 can be view as the ellipsoidal shape.

[0034] Preferably, the height h of the first reinforcing portion 6b shown in FIG. 1(b) is substantially equal to or less than the height defined as a distance from the outer circumference of the second vibrating part 2b to the apex of the edge portion 3. Although not shown in the figure, the same is applied to the height of the first reinforcing portion 6a. The reason for this setting will be described below. The higher the heights of the first reinforcing portions 6a and 6b are, the more the inverse resonance can be suppressed, and the more the movement (the rolling phenomenon) of the first vibrating part 2a or the second vibrating part 2b in a horizontal direction (a direction substantially perpendicular to the vibration direction of the voice coil) can be suppressed. However, as the heights of the first reinforcing portions 6a and 6b increase, the rigidity of the edge portion 3 increases, i.e., the edge portion 3 comes to resist bending in the radial direction. Therefore, the response of the edge portion 3 to the vibration of the first vibrating part 2a and to the vibration of the second vibrating part 2b can be impaired (e.g., the first vibrating part 2a or the second vibrating part 2b comes to resist vibrating). When the heights of the first reinforcing portions 6a and 6b are substantially equal to or less than the height defined as a distance from the outer circumference of the second vibrating part 2b to the apex of the edge portion 3, the response of the edge portion 3 to the vibration of the first vibrating part 2a and to the vibration of the second vibrating part 2b can be relatively large. When the heights of the first reinforcing portions 6a and 6b are set to be comparatively short, for example, to about one-half the height defined as a distance from the outer circumference of the second vibrating part 2b to the apex of the edge portion 3, comparatively large rigidity can be ensured, and the inverse resonance can also be suppressed.

[0035] Preferably, each of the first reinforcing portions 6a and 6b has a polygonal shape in plan view. In the example shown in FIGS. 1 and 2, each of the first reinforcing portions 6a and 6b has a substantially rhombic shape (substantially rectangular shape) in plan view. When each of the first reinforcing portions 6a and 6b has a polygonal shape in plan view, the first reinforcing portions 6a and 6b are allowed to bend in the radial or circumferential direction of the circular arc-shaped parts 3a and 3b, and the occurrence of unnecessary vibrations (for example, the inverse resonance and rolling phenomenon) can thereby be suppressed.

[0036] The cross-sectional shape of each of the first reinforcing portions 6a and 6b may be any of a substantially inverted V-shape, a substantially inverted U-shape, a substantially rectangular shape, a substantially sawtooth shape, and a substantially sinusoidal shape. FIG. 3 is a set of cress-sectional views taken along the line B-B in FIG. 1(a). FIG. 3(a) shows an example in which each first reinforcing portion 6b has a substantially inverted V-shaped cross-sectional shape, and FIG. 3(b) shows an example in which each first reinforcing portion 6b has a substantially inverted U-shaped cross-sectional shape. In the example shown in FIG. 3(a), the first reinforcing portion 6b includes straight inclined surfaces 41 and 42 that come in contact with each other to form an apex 43. In the example shown in FIG. 3(b), the first reinforcing portion 6b includes curved inclined surfaces 44 and 45 that come in contact with each other to form an apex 46.

[0037] A plurality of second reinforcing portions 8a and 8b being convex toward the rear side (in the direction opposite to the acoustic radiation direction) are formed in the circular arc-shaped parts 3a and 3b. The cross-sectional shape of each of the second reinforcing portions 8a and 8b may be any of a substantially inverted V-shape, a substantially inverted U-shape, a substantially rectangular shape, a substantially sawtooth shape, and a substantially sinusoidal shape.

[0038] The lengths of the second reinforcing portions 8a and 8b are slightly less than the widths of the circular arc-shaped parts 3a and 3b. The minimum resonance frequency f.sub.0 can be adjusted to the desired value by arranging the second reinforcing portions 8a and 8b. More specifically, when the length of the second reinforcing portions 8a and 8b is extremely long, it is difficult to adjust the minimum resonance frequency f.sub.0. When the length of the second reinforcing portions 8a and 8b is short, the second reinforcing portions 8a and 8b resist bending in the circular arc-shaped parts 3a and 3b, and the vibrations of the diaphragm 2 are thereby suppressed, so that the vibrations of the voice coil are not well transmitted to the diaphragm 2. In the example shown, the lengths of the second reinforcing portions 8a and 8b are slightly less than the widths of the circular arc-shaped parts 3a and 3b, and the minimum resonance frequency f.sub.0 can thereby be adjusted to the desired value.

[0039] In the example shown in FIGS. 1 and 2, three second reinforcing portions 8a are formed at predetermined intervals in a region extending from the boundary 4a between the circular arc-shaped part 3a and the rectangular part 3c to the long axis 7, and three second reinforcing portions 8a are formed at predetermined intervals in a region extending from the boundary 4b between the circular arc-shaped part 3a and the rectangular part 3d to the long axis 7. Similarly, in the example shown in FIGS. 1 and 2, three second reinforcing portions 8a are formed at predetermined intervals in a region extending from the boundary 4c between the circular arc-shaped part 3b and the rectangular part 3c to the long axis 7, and three second reinforcing portions 8a are formed at predetermined intervals in a region extending from the boundary 4d between the circular arc-shaped part 3b and the rectangular part 3d to the long axis 7. In the example shown in FIGS. 1 and 2, two second reinforcing portions 8b are formed in the circular arc-shaped part 3a in the substantially symmetric position with respect to the long axis 7. Similarly, two second reinforcing portions 8b are formed in the circular arc-shaped part 3b in the substantially symmetric position with respect to the long axis 7. In other words, the second reinforcing portions 8a and 8b extend in the radial directions of the circular arc-shaped parts 3a and 3b. The second reinforcing portions 8a and 8b described above are formed so as to be substantially symmetric with respect to the short axis (not shown) of the ellipsoidal shape, in plan view, of the vibrating body 1 for an acoustic transducer including the edge portion 3.

[0040] A bent part 3e being bent substantially perpendicularly in the front side (in the acoustic radiation direction) is formed on the outer circumference of the edge portion 3. Since the bent part 3e is formed, the vibrating body 1 for an acoustic transducer can be easily mounted on a frame (not shown) with high accuracy when a speaker device is assembled using the vibrating body 1 for an acoustic transducer. More specifically, the bent part 3e plays a role of positioning.

[0041] The diaphragm 2, the edge portion 3, the first reinforcing portions 6a and 6b, and the second reinforcing portions 8a and 8b described above are formed integrally by, for example, press forming. Examples of the material for the diaphragm 2 and the edge portion 3 include paper, woven fabrics including a fiber, knitted products including a fiber, non-woven fabrics, the woven fabrics impregnated with binding resin such as silicone resin, a metal material, a synthetic resin, an acrylic foam, and a hybrid material formed of a synthetic resin and a metal. Examples of the metal materials include aluminum, titanium, duralumin, beryllium, magnesium, and alloys thereof. Examples of the synthetic resin include polypropylene, polyethylene, polystyrene, polyethylene terephthalate, polyethylene naphthalate, polymethyl methacrylate, polycarbonate, polyallylate, epoxy resin, polysulfone, polyurethane having a urethane bond, and rubber. The acrylic foam, which is foamed resin, is formed using, for example, methyl methacrylate, methacrylic acid, styrene, maleic anhydride, and methacrylamide as raw materials. The vibrating body 2 and the edge portion 3 can be made of known foamed resins. The hybrid material is formed of, for example, a synthetic resin such as polypropylene and a metal such as tungsten.

[0042] As described above, in the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, the first reinforcing portions 6a and 6b are formed so as to extend from the second vibrating part 2b to the edge portion 3. This allows the high resonance frequency associated with the inverse resonance to be outside the audible range, and the acoustic characteristic of a speaker device including the vibrating body 1 for an acoustic transducer can thereby be improved. Moreover, since the first reinforcing portions 6a and 6b extend substantially in the radial directions of the circular arc-shaped parts 2ba, 2bb, 3a, and 3b, the rigidity at the boundary between the second vibrating part 2b and the edge portion 3 is large, and this allows the entire vibrating body 1 for an acoustic transducer to vibrate in substantially the same phase. Therefore, a speaker device including the vibrating body 1 for an acoustic transducer can have a flat frequency characteristic.

[0043] Moreover, since the first reinforcing portions 6a and 6b can bend in the radial or circumferential directions of the circular arc-shaped parts 3a and 3b, the occurrence of unnecessary vibration such as the inverse resonance can be suppressed. When the vibrating body 1 for an acoustic transducer vibrates, the first reinforcing portions 6a and 6b can bend, and this allows the edge portion 3 to vibrate in response to the vibration of the first vibrating part 2a and the vibration of the second vibrating part 2b.

[0044] A plurality of first reinforcing portions 6b (three in the example shown in FIGS. 1 and 2) are formed so as to extend from the circular arc-shaped part 2ba of the second vibrating part 2b to the circular arc-shaped part 3a of the edge portion 3, and from the circular arc-shaped part 2bb of the second vibrating part 2b to the circular arc-shaped part 3b of the edge portion 3. Therefore, the rigidity in the vicinity of the boundary (bonding portion) between the circular arc-shaped part 3a and the circular arc-shaped part 2ba can be relatively large, and accordingly, the stress can be prevented from concentrating in the vicinity of the boundary when driving the vibrating body 1 for an acoustic transducer. This can prevent the occurrence of unnecessary movement in the vibrating body 1 for an acoustic transducer.

[0045] In the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, the area of the first vibrating part 2a is substantially equal to or less than the sum of the area of the second vibrating part 2b and the area of the edge portion 3. With this configuration, when a speaker device is assembled using the vibrating body 1 for an acoustic transducer, a magnetic circuit of the external magnetic type can be used. When a magnetic circuit of the external magnetic type is used, the outer diameter of the magnet of the magnetic circuit can be greater than that when a magnetic circuit of the internal magnetic type is used. Therefore, the magnetic flux density of the magnetic field generated by the magnet can be large, and the sensitivity of the speaker device can thereby be increased. When a magnetic circuit of the internal magnetic type is used, on the other hand, the width of the edge portion (the difference between the outer and inner diameters) is small, and accordingly, it is difficult to increase the rigidity of the edge portion.

[0046] In the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, vertical cross-sectional shapes of the first vibrating part 2a, the second vibrating part 2b, and the edge portion 3 have substantially curved shapes protruding toward the front side (in the acoustic radiation direction). The apex of the second vibrating part 2b is formed so as to be lower than the apex of the first vibrating part 2a or the apex of the edge portion 3. Moreover, the height of the outer circumference of the second vibrating part 2b is substantially equal to the height of the outer circumference of the first vibrating part 2a. With this configuration, the phase of the acoustic wave emitted from the second vibrating part 2b is substantially the same as the phase of the acoustic wave emitted from the first vibrating part 2a. In particular, when the height of the apex of the first vibrating part 2a is substantially the same as the height of the apex of the second vibrating part 2b and the height of the outer circumference of the first vibrating part 2a is substantially the same as the height of the outer circumference of the second vibrating part 2b, the difference in phase between the acoustic waves emitted from the first and second vibrating parts 2a and 2b can be comparatively small.

[0047] In the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, the apex of the edge portion 3 is formed so as to be located on the outer circumferential side in respect with the center between the inner and outer circumferences of the edge portion 3. With this configuration, the effective vibrating area of the vibrating body 1 for an acoustic transducer can be large, and the sound pressure can thereby be increased.

[0048] In the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, the first reinforcing portions 6a and 6b are formed so as to be convex toward the front side (in the acoustic radiation direction). Therefore, the occurrence of such inverse resonance that the first vibrating part 2a and the second vibrating part 2b vibrate in mutually opposite directions can be suppressed.

[0049] In the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, the second reinforcing portions 8a and 8b are formed so as to be convex toward the rear side (in the direction opposite to the acoustic radiation direction). Therefore, the edge portion 3 can have relatively large rigidity, and the response of the edge portion 3 to the vibration of the first vibrating part 2a and to the vibration of the second vibrating part 2b can be comparatively high.

[0050] In the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, the second reinforcing portions 8a and 8b extend in the radial directions of the circular arc-shaped parts 3a and 3b. Therefore, the rigidity of the edge portion 3 can be adjusted, i.e., the rigidity of the vibrating body 1 can be adjusted. This enables the adjustment of the minimum resonance frequency f.sub.0. By forming the second reinforcing portions 8a and 8b, unnecessary movement, such as a vibration in a circumferential direction, in the vibrating body 1 for an acoustic transducer can be more suppressed as compared to the case where the second reinforcing portions 8a and 8b are not formed. For example, when a vibration in a circumferential direction is transmitted to the second vibrating part 2b and the edge portion 3 during the vibrations of the vibrating body 1 for an acoustic transducer, the widths of the second reinforcing portions 8a and 8b are reduced or increased in the circumferential direction, i.e., the second reinforcing portions 8a and 8b are expanded or contracted. This can suppress the occurrence of circumferential vibrations.

[0051] The reason that no second reinforcing portions 8a and 8b are provided in the rectangular parts 3c and 3d is described below. If second reinforcing portions 8a and 8b are provided also in the rectangular parts 3c and 3d, the rigidity of the rectangular parts 3c and 3d (in the short axis direction) provided with the second reinforcing portions 8a and 8b is greater than the rigidity of the circular arc-shaped parts 3a and 3b (in the major axis direction) provided with the second reinforcing portions 8a and 8b. Therefore, unnecessary movement such as the rolling phenomenon is more likely to occur in the vibrating body 1 for an acoustic transducer. This mechanism may be supposed as follows. The second reinforcing portions 8a and 8b have grooves having a V-shaped cross-sectional shape, and the taps of the grooves of the second reinforcing portions 8a and 8b are opened and closed in the circumferential direction by the vibrations propagating in the circumferential direction. When the taps of the grooves are opened and closed, the rigidity of the circular arc-shaped parts 3a and 3b becomes comparatively small. Accordingly, the vibration is easily transmitted in the long axis direction or amplified, so that unnecessary movement such as the rolling phenomenon may be more likely to occur in the vibrating body 1 for an acoustic transducer. This is the reason why no second reinforcing portions 8a and 8b are provided in the rectangular parts 3c and 3d.

[0052] In the vibrating body 1 for an acoustic transducer according to Embodiment 1 of the present invention, three first reinforcing portions 6b and two second reinforcing portions 8b are disposed alternately so that one portion is sandwiched between other portions. With this configuration, each of the first reinforcing portions 6b and the second reinforcing portions 8b can be formed to have a size large enough to exert its intended function. However, when the first reinforcing portion 6b and the second reinforcing portion 8b are formed continuously with each other, the first reinforcing portions 6b or the second reinforcing portions 8b must be formed to have a small size when the sizes and other factors of the second vibrating part 2b and the edge portion 3 are taken into consideration. For example, when the first reinforcing portion 6b is formed to have a small size, or a speaker device is constructed with the vibrating body 1 for an acoustic transducer, resonance or inverse resonance occurs and a peak-dip in the high tune range become large. This may result in deterioration in acoustic characteristic. When the convex first reinforcing portion 6b and the concave second reinforcing portion 8b are formed continuously with each other, a bending point is formed on the boundary between the first reinforcing portion 6b and the second reinforcing portion 8b. Therefore, stress acts on this bending point, and this may result in damage to the diaphragm 2.

Embodiment 2

[0053] FIG. 4 is a cross-partial view illustrating the schematic structure of a speaker device according to Embodiment 2 of the present invention. FIG. 5 is a set of schematic diagrams illustrating the structure of a magnetic circuit included in the speaker device shown in FIG. 4. FIG. 5(a) is a plan view, FIG. 5(b) is a front view, and FIG. 5(c) is a cross-partial view taken along the line B-B in FIG. 5(a). The speaker device according to Embodiment 2 is mounted on a portable electronic device such as a mobile phone, a portable radio, or a PDA. The short diameter of the speaker device is, for example, about 2 to 4 cm. The speaker device according to Embodiment 2 includes the vibrating body 1 for an acoustic transducer according to Embodiment 1 described above, a magnetic circuit 11, and a frame 12. In FIGS. 4 and 5, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted.

[0054] The pocket 2c of the vibrating body 1 for an acoustic transducer accommodates a voice coil 13 having a substantially track ring-like shape, and the voice coil 13 is fixed with an adhesive. The magnetic circuit 11 is of the internal and external magnetic type. More specifically, a magnetic gap g is formed between an external magnet 21 and an internal magnet 22, and the external magnet 21 and the internal magnet 22 are sandwiched between a yoke 25 and corresponding external and internal plates 23 and 24.

[0055] The external magnet 21 and the internal magnet 22 are each, for example, a permanent magnet such as a neodymium, samarium-cobalt, alnico, or ferrite magnet. Both the external magnet 21 and the internal magnet 22 have substantially hollow track-like shapes in plan view. A through hole 21a having a substantially track-like shape is formed on the inner side of the external magnet 21. A through hole 22a having a substantially cylindrical shape is formed on the inner side of the internal magnet 22.

[0056] The external plate 23 and the internal plate 24 are formed of a magnetic material such as iron. The external plate 23 and the internal plate 24 have a substantially hollow track-like shape in plan view. The shape of the external plate 23 in plan view is geometrically similar to the shape of the external magnet 21 in plan view, and the shape of the internal plate 24 in plan view is geometrically similar to the shape of the internal magnet 22 in plan view. More specifically, the external plate 23 is slightly shorter than the external magnet 21 in both the long and short axis directions, while, the internal plate 24 is slightly longer than the internal magnet 22 in both the long and short axis directions.

[0057] A through hole 23a having a substantially track-like shape is formed substantially at the center of the external plate 23. The outer long and short diameters of the through hole 23a are slightly smaller than those of the through hole 21a. A through hole 24a having a substantially cylindrical shape is formed on the inner side of the internal plate 24. The outer long and short diameters of the through hole 24a are slightly larger than those of the through hole 22a. The external plate 23 is fixed on the upper surface of the external magnet 21 using, for example, an adhesive. Similarly, the internal plate 24 is fixed on the upper surface of the internal magnet 22 using, for example, an adhesive.

[0058] The yoke 25 is formed of a magnetic material such as pure iron, oxygen-free steel, or silicon steel. The yoke 25 has a substantially track-like shape in plan view. More specifically, the outer circumferential shape of the yoke 25 in plan view is geometrically similar to the outer circumferential shape of the external magnet 21 in plan view and is slightly smaller than the outer circumferential shape of the external magnet 21 in plan view in both the long and short axis directions. A through hole 25a having a substantially cylindrical shape is formed on the inner side of the yoke 25. The outer diameter of the through hole 25a is slightly greater than the outer diameter of the through hole 22a. The yoke 25 is fixed on the upper surfaces of the external magnet 21 and the internal magnet 22 through, for example, an adhesive.

[0059] The frame 12 is formed of, for example, an iron-series metal, anon-ferrous metal, an alloy thereof, or a synthetic resin. Examples of the iron-based metal include pure iron, oxygen-free steel, and silicon steel. Examples of the non-ferrous metal include aluminum, magnesium, and zinc. Examples of the synthetic resin include an olefin-series thermoplastic resin such as polypropylene, ABS (acrylonitrile-butadiene-styrene) resin, and polyethylene terephthalate-series thermoplastic resin, and other thermoplastic resins. The frame 12 is formed by, for example, draw molding of an iron-series metal, die-casting of a non-ferrous metal or an alloy thereof, or injection molding of a synthetic resin.

[0060] The frame 12 has a substantially track-like overall shape in plan view. The frame 12 has: a step part 12a to which the outer circumferential edge of the external magnet 21 is secured; and a step part 12b to which the bent part 3e formed on the outer circumference part of the edge portion 3 of the vibrating body 1 for an acoustic transducer is attached. The outer circumferential edge of the external magnet 21 of the magnetic circuit 11 is secured to the step part 12a, and the bent part 3e of the edge portion 3 is attached to the step part 12b. As shown in FIG. 4, the lower portion of the pocket 2c in which the voice coil 13 is accommodated is inserted into the magnetic gap g.

[0061] As described above, in Embodiment 2 of the present invention, the vibrating body 1 for an acoustic transducer according to Embodiment 1 described above and the magnetic circuit 11 of the internal and external magnetic type constitutes the speaker device. In the vibrating body 1 for an acoustic transducer, the second vibrating part 2b is larger than the first vibrating part 2a, and the plurality of first reinforcing portions 6a and 6b are formed so as to extend from the second vibrating part 2b to the edge portion 3. In addition, the plurality of second reinforcing portions 8a and 8b are formed in the edge portion 3. Therefore, according to Embodiment 2 of the present invention, the sensitivity of the speaker device can be increased, and deterioration in the acoustic characteristic of the speaker device can be suppressed. Moreover, the occurrence of unnecessary movement (such as the rolling phenomenon) in the pocket 2c in which the voice coil 13 is accommodated can be suppressed.

Embodiment 3

[0062] FIG. 6 is a cross-sectional view illustrating the schematic structure of a speaker device according to Embodiment 3 of the present invention. FIG. 7 is a set of schematic diagrams illustrating the structure of a magnetic circuit included in the speaker device shown in FIG. 6. FIG. 7(a) is a plan view, FIG. 7(b) is a front view, and FIG. 7(c) is a cross-sectional view taken along the line C-C in FIG. 7(a). The speaker device according to Embodiment 3 is mounted on a portable electronic device such as a mobile phone, a portable radio, or a PDA. The short diameter of the speaker device is, for example, about 2 to 4 cm. The speaker device according to Embodiment 3 includes the vibrating body 1 for an acoustic transducer according to Embodiment 1 above, a magnetic circuit 31, and the frame 12. In FIGS. 6 and 7, parts corresponding to those in FIGS. 1, 2, 4, and 5 are denoted by the same reference numerals, and the description thereof is omitted.

[0063] The magnetic circuit 31 shown in FIGS. 6 and 7 is different from the magnetic circuit 11 shown in FIGS. 4 and 5 in that a yoke 32 is newly provided instead of the internal magnet 22 and the yoke 25. More specifically, the magnetic circuit 31 is of the external magnetic type in which the external magnet 21 is sandwiched between the external plate 23 and the yoke 32.

[0064] As with the yoke 25, the yoke 32 is formed of a magnetic material such as pure iron, oxygen-free steel, or silicon steel. The yoke 32 has a substantially track-like shape in plan view. More specifically, the outer circumferential shape of the yoke 32 in plan view is geometrically similar to the outer circumferential shape of the external magnet 21 in plan view and is slightly smaller than the outer circumferential shape of the external magnet 21 in plan view in both the long and short axis directions. The yoke 32 includes a bottom plate part 32a having a substantially track-like shape in plan view and a pillar part 32b that is provided substantially at the center of the bottom plate part 32a and has a substantially track-like shape in plan view. The bottom plate part 32a is formed integrally with the pillar part 32b. A through hole 32c having a substantially cylindrical shape is formed substantially at the center (on the inner side) of the pillar part 32b. The yoke 32 is fixed on the upper surface of the external magnet 21 using, for example, an adhesive.

[0065] As described above, in Embodiment 3 of the present invention, the vibrating body 1 for an acoustic transducer according to Embodiment 1 described above and the magnetic circuit 31 of the external magnetic type constitutes the speaker device. In the vibrating body 1 for an acoustic transducer, the second vibrating part 2b is larger than the first vibrating part 2a, and the plurality of first reinforcing portions 6a and 6b are formed so as to extend from the second vibrating part 2b to the edge portion 3. In addition, the plurality of second reinforcing portions 8a and 8b are formed in the edge portion 3. Therefore, according to Embodiment 3 of the present invention, the sensitivity of the speaker device can be increased, and deterioration in the acoustic characteristic of the speaker device can be suppressed. Moreover, the occurrence of unnecessary movement (such as the rolling phenomenon) in the pocket 2c in which the voice coil 13 is accommodated can be suppressed.

[0066] The embodiments of the present invention have been described with reference to the drawings, but the specific configuration is not limited to these embodiments. Design modifications and other modifications are included in the present invention so long as they do not depart from the subject-matter of the present invention.

[0067] The technological features in each embodiment described above can be applied to other embodiments so long as their objects, configurations, and the like do not cause a contradiction and a problem.