Diaphragm, spherical-shell diaphragm and electroacoustic transducer, and method of manufacturing electroacoustic transducer Number:7,438,156 from the United States Patent and Trademark Office (PTO) owispatent A diaphragm in one mode of the present invention comprises an outer shape section having a circle with one diameter, or a shape of a polygon to be inscribed in a circle with the one diameter; an inner shape section protruding in one direction with regard to a plane including the outer shape section, wherein a shape formed by projecting the inner shape section on the plane is rotationally symmetric about the central axis of the circle; and a vibrating face section linking the outer shape section and the inner shape section and having an inclined face inclined to the central axis, wherein any one of cross-sectional shapes of the vibrating face section is rotationally symmetric about an eccentric axis which is eccentric with regard to the central axis, the cross-sectional shapes being defined by a plane intersecting perpendicularly to the central axis. An electroacoustic transducer uses the above diaphragm.<H electroacoustic, manufacturing, Diaphragm, spher, 7438156.html, Patent, pto, 7438156

Title: Diaphragm, spherical-shell diaphragm and electroacoustic transducer, and method of manufacturing electroacoustic transducer

Abstract: A diaphragm in one mode of the present invention comprises an outer shape section having a circle with one diameter, or a shape of a polygon to be inscribed in a circle with the one diameter; an inner shape section protruding in one direction with regard to a plane including the outer shape section, wherein a shape formed by projecting the inner shape section on the plane is rotationally symmetric about the central axis of the circle; and a vibrating face section linking the outer shape section and the inner shape section and having an inclined face inclined to the central axis, wherein any one of cross-sectional shapes of the vibrating face section is rotationally symmetric about an eccentric axis which is eccentric with regard to the central axis, the cross-sectional shapes being defined by a plane intersecting perpendicularly to the central axis. An electroacoustic transducer uses the above diaphragm.

Patent Number: 7,438,156 Issued on 10/21/2008 to Inagaki, et al.

Inventors: Inagaki; Kazuyuki (Ayase, JP), Nakaso; Jiro (Sagamihara, JP), Omoda; Manabu (Sagamihara, JP)
Assignee: Victor Company of Japan, Limited (Yokohama, JP)

Appl. No.: 11/332,488

Filed: January 17, 2006

Foreign Application Priority Data


Jan 20, 2005 [JP]			P2005-013378
Jan 20, 2005 [JP]			P2005-013380
Jan 20, 2005 [JP]			P2005-013383
Dec 28, 2005 [JP]			P2005-378001

Current U.S. Class: 181/173 ; 181/164; 181/165; 381/423

Current International Class: G10K 13/00 (20060101); H04R 7/06 (20060101)

Field of Search: 181/164,165,173 381/423

References Cited [Referenced By]

U.S. Patent Documents


1748990	March 1930	Nilson
1859629	May 1932	Nilson
3940576	February 1976	Schultz

Foreign Patent Documents


09-284886	Oct., 1997	JP
2000-078686	Mar., 2000	JP
2001-095088	Apr., 2001	JP

Primary Examiner: Donovan; Lincoln
Assistant Examiner: Luks; Jeremy
Attorney, Agent or Firm: The Nath Law Group Nath; Gary M. Meyer; Jerald L.

Claims

What is claimed is:

1. A diaphragm, comprising: an outer shape section with a shape of a circle having one diameter, or a shape of a polygon which is inscribed in a circle with the one diameter; an inner shape section which protrudes in one direction with regard to a plane including said outer shape section, wherein a shape formed by projecting said inner shape section on said plane is rotationally symmetric about the central axis of said circle with the one diameter; and a vibrating face section that links said outer shape section and said inner shape section and has an inclined face inclined to said central axis, wherein any one of cross-sectional shapes of said vibrating face section is rotationally symmetric about an eccentric axis which is eccentric with regard to said central axis, said cross-sectional shapes being defined by a plane intersecting perpendicularly to said central axis.

2. An electroacoustic transducer, comprising: the diaphragm according to claim 1; a flexible connecting member connected with the outer shape section of said diaphragm; a frame supporting said diaphragm through said connecting member in such a way that said diaphragm is freely vibrated; and a driving section which has a voice coil bobbin linked to one surface of said inner shape section in said diaphragm, and vibrates said diaphragm.

3. A diaphragm, comprising: an outer shape section with a shape of a circle having one diameter, or a shape of a polygon which is inscribed in a circle with the one diameter; an inner shape section which protrudes in one direction with regard to a plane including said outer shape section, wherein a shape formed by projecting said inner shape section on said plane is rotationally symmetric about the central axis of said circle with the one diameter; and a vibrating face section that links said outer shape section and said inner shape section and has an inclined face inclined to said central axis, wherein said vibrating face section includes a rotationally symmetric orbiting line about an eccentric axis which is eccentric with regard to said central axis; and a curvature of or an inclination angle of said vibrating face inside of said orbiting line and a curvature of or an inclination angle of said vibrating face outside of said orbiting line are discontinuous at said orbiting line.

4. An electroacoustic transducer, comprising: the diaphragm according to claim 3; a flexible connecting member connected with the outer shape section of said diaphragm; a frame supporting said diaphragm through said connecting member in such a way that said diaphragm is freely vibrated; and a driving section which has a voice coil bobbin linked to one surface of said inner shape section in said diaphragm, and vibrates said diaphragm.

5. A spherical shell diaphragm, comprising: a plurality of diaphragms with a regular n-gonal shape (n: an integer of 4 or more) which is inscribed in a circle with one diameter, said plurality of diaphragms being formed into a nearly spherical shape by linking together outer shape sections of said plurality of diaphragms, wherein each of said plurality of diaphragms includes; an inner shape section which protrudes in an outer direction with regard to a plane including an outer shape section of said diaphragm, wherein a shape formed by projecting said inner shape section on said plane is rotationally symmetric about the central axis of said circle with the one diameter; and a vibrating face section that links said outer shape section and said inner shape section and has an inclined face inclined to said central axis, wherein any one of cross-sectional shapes of said vibrating face section is rotationally symmetric about an eccentric axis which is eccentric with regard to said central axis, said cross-sectional shapes being defined by a plane intersecting perpendicularly to said central axis.

6. The spherical shell diaphragm according to claim 5, wherein the outer shape sections of said plurality of diaphragms are connected with one another through flexible linking members.

7. The spherical shell diaphragm according to claim 5, wherein said nearly spherical shell shape is a regular dodecahedron.

8. The spherical shell diaphragm according to claim 5, wherein when there is set a dividing line that separates said spherical shell diaphragm into two portions along said outer shape sections in such a way that each of said two portions has the same number of said diaphragms having an outer shape section along said dividing line, said eccentric axis of said diaphragm having the outer shape section along the dividing line is eccentric in a direction toward the vertex of said outer shape section along said dividing line.

9. The spherical shell diaphragm according to claim 5, wherein any one of said plurality of diaphragms has an opening.

10. An electroacoustic transducer using the spherical shell diaphragm according to claim 5.

11. The electroacoustic transducer according to claim 10, further comprising: a plurality of voice coil bobbins connected respectively with the inside surfaces of said plurality of diaphragms; and a plurality of driving sections which respectively include one of said voice coil bobbins, and vibrate said plurality of diaphragms.

12. An electroacoustic transducer using the spherical shell diaphragm according to claim 7, wherein said plurality of diaphragms are linked together in such a way that said plurality of diaphragms form eleven surfaces of said regular dodecahedron.

13. The electroacoustic transducer according to claim 12, comprising: a plurality of voice coil bobbins connected respectively with the inside surfaces of said plurality of diaphragms; and a plurality of driving sections which respectively include one of said voice coil bobbins, and vibrate said plurality of diaphragms, respectively.

14. A spherical shell diaphragm, comprising: a plurality of diaphragms with a regular n-gonal shape (n: an integer of 4 or more) which is inscribed in a circle with one diameter, said plurality of diaphragms being formed into a nearly spherical shape by linking together outer shape sections of said plurality of diaphragms, wherein each of said plurality of diaphragms includes; an inner shape section which protrudes in an outer direction with regard to a plane including an outer shape section of said diaphragm, wherein a shape formed by projecting said inner shape section on said plane is rotationally symmetric about the central axis of said circle with the one diameter; and a vibrating face section that links said outer shape section and said inner shape section and has an inclined face inclined to said central axis, wherein said vibrating face section includes a rotationally symmetric orbiting line about an eccentric axis which is eccentric with regard to said central axis; and a curvature of or an inclination angle of said vibrating face inside of said orbiting line and a curvature of or an inclination angle of said vibrating face outside of said orbiting line are discontinuous at said orbiting line.

15. The spherical shell diaphragm according to claim 14, wherein the outer shape sections of said plurality of diaphragms are connected with one another through flexible linking members.

16. The spherical shell diaphragm according to claim 14, wherein said nearly spherical shell shape is a regular dodecahedron.

17. The spherical shell diaphragm according to claim 14, wherein when there is set a dividing line separates said spherical shell diaphragm into two portions along said outer shape sections in such a way that each of said two portions has the same number of said diaphragms having an outer shape section along said dividing line, said eccentric axis of said diaphragm having the outer shape section along the dividing line is eccentric in a direction toward the vertex of said outer shape section along said dividing line.

18. The spherical shell diaphragm according to claim 14, wherein any one of said plurality of diaphragms has an opening.

19. An electroacoustic transducer using the spherical shell diaphragm according to claim 14.

20. The electroacoustic transducer according to claim 19, comprising: a plurality of voice coil bobbins connected respectively with the inside surfaces of said plurality of diaphragms; and a plurality of driving sections which respectively include one of said voice coil bobbins, and vibrate said plurality of diaphragms, respectively.

21. An electroacoustic transducer using the spherical shell diaphragm according to claim 16, wherein said plurality of diaphragms are linked together in such a way that said plurality of diaphragms form eleven surfaces of said regular dodecahedron.

22. The electroacoustic transducer according to claim 21, comprising: a plurality of voice coil bobbins connected respectively with the inside surfaces of said plurality of diaphragms; and a plurality of driving sections which respectively include one of said voice coil bobbins, and vibrate said plurality of diaphragms, respectively.

Description

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a diaphragm, a spherical-shell diaphragm and an electroacoustic transducer, and a method of manufacturing an electroacoustic transducer.

2. Description of the Related Art

An electroacoustic transducer, which is provided with a diaphragm, a frame supporting the periphery of the diaphragm, and a driving section with a magnetic circuit which vibrates the diaphragm in a uniaxial direction, and emits a sound, has been generally called a speaker. Such a diaphragm has had quite often a shape of a cone.

Generally, the surface profile of this cone shape is a nearly circular truncated cone, wherein the cone is obtained by cutting off the top portion of a nearly circular cone (right circular cone) with rotational symmetry about a central axis, and has inner and outer peripheries and an inclined portion inclined to the central axis which is in the vibrating direction.

Incidentally, it has been known that, in the case of the diaphragm with a shape of the nearly circular truncated cone, standing waves are generated in the radius direction all around the diaphragm, and there are easily caused a peak and a dip in frequency--sound pressure characteristics.

Then, in order to hinder such a peak and dip from being caused, there has been proposed a circular truncated cone that is configured in a way that the central axis of the inner periphery is eccentric from that of the outer one.

In the truncated circular cone having such eccentricity, a distance between the inner periphery end and the outer periphery end, the distance being measured along a line passing through the center axis of the inner periphery, is not constant along their circumferential direction.

Accordingly, the wavelength of a standing wave generated in the diaphragm is changed according to the circumferential positions, and a peak and a dip in the frequency--sound pressure characteristics are smoothened out.

As described above, the diaphragm with eccentricity may control the generation of a peak and a dip in the frequency--sound pressure characteristics. However, it is somewhat disadvantageous in that a general-purpose frame or a component for a magnetic circuit cannot be used for such a diaphragm, because such a frame or a component has an outer shape that is not eccentric with regard to the central axis of the inner periphery.

Thereupon, a structure without the above-described disadvantage has been described in Japanese Patent Application Laid-Open Publication No. H09-284886. According to this structure, the above-described diaphragm with eccentricity is installed in a frame or a component for a magnetic circuit, the outer shape of the component or the frame being not eccentric.

On the other hand, there has been known an electroacoustic transducer, which is provided with a diaphragm with a nearly spherical shape, and one driving section (magnetic circuit section) vibrating the diaphragm in the radial direction, and emits a sound in all directions from the center of the diaphragm.

This electroacoustic transducer is called a spherical speaker, a pulsating sphere speaker, or the like, and, has been disclosed in, for example, Japanese Patent Application Laid-Open Publications Nos. 2000-78686, and 2001-95088.

These publications have described, as one example of the diaphragm of this electroacoustic transducer, a diaphragm obtained by combining a plurality of diaphragms with a predetermined shape of approximately a plane into a shape of a nearly sphere.

Incidentally, Japanese Patent Application Laid-Open Publication No. H09-284886 has disclosed that a speaker having an edge member to be connected with the outer periphery of the diaphragm, the edge member having different widths in the radial direction, and a speaker having an edge member and a diaphragm installing member, wherein the edge member has a constant width in the radial direction whereas the diaphragm installing member connecting the above edge member and a frame has different widths in the radial direction, in order to install the diaphragm of which outer shape is eccentric with regard to the center in a frame in which a magnetic circuit is fixed at the center.

However, the above-described configurations have had a problem that, since neither the edge portion nor the diaphragm installing member are a diaphragm, and contribute to radiation of a voice, the projected area of the diaphragm becomes small to the size of the outer shape of the frame, and it is difficult, considering the size of the frame, to obtain a high sound-pressure in a range of low-pitched sound, and also to perform electroacoustic conversion of an input signal with a high efficiency.

Moreover, there has been a problem that, since the outer shape of the diaphragm is eccentric to the center of the magnetic circuit, the radiating axis of a voice does not intersect perpendicularly to the installed surface of the speaker, and it is difficult to specify a reference direction for a radiated voice and also to have a uniform directivity in the circumferential direction.

SUMMARY OF THE INVENTION

Then, the present invention has been made in order to solve the above-described problems, and its object is to provide a diaphragm and an electroacoustic transducer that are capable of reducing generation of standing waves, obtaining a high sound-pressure even in a range of low-pitched sound, realizing highly efficient electroacoustic conversion of an input signal, specifying a reference direction for a radiated voice, and obtaining a uniform directivity in the circumferential direction.

Moreover, another object thereof is to provide a spherical shell diaphragm and an electroacoustic transducer that are capable of reducing generation of standing waves, reducing the number of peaks and dips, even if the diaphragm has a shape of a nearly spherical shell; unneccesitating a special bonding member; positioning easily in assembling; realizing especially high sound pressure even in a range of low-pitched sounds; and realizing a highly efficient electro-acoustic conversion of input signals.

Furthermore, yet another object is to provide a method of manufacturing an electroacoustic transducer configured by joining a plurality of polygonal segments with an elastic material to produce a polyhedron spherical shell diaphragm, the respective polygonal segment being to be driven by an individual driving section, the method being able to facilitate positioning of each section so that easy assembling is realized and to reduce characteristics variation.

In order to realize the above-described objects, the present invention has the following configurations [1] through [6] as a solution.

[1] A diaphragm (10, 10R), comprising an outer shape section (14) with a shape of a circle having one diameter (D2), or a shape of a polygon which is inscribed in a circle with the one diameter (D2); an inner shape section (13) which protrudes in one direction with regard to a plane (PO) including the outer shape section (14), wherein a shape formed by projecting the inner shape section (13) on the plane (P0) is rotationally symmetric about the central axis (O) of the circle with the one diameter (D2); and a vibrating face section (12) that links the outer shape section (14) and the inner shape section (13) and has an inclined face inclined to the central axis (O), wherein any one of cross-sectional shapes of the vibrating face section (12) is rotationally symmetric about an eccentric axis (O2) which is eccentric with regard to the central axis (O), the cross-sectional shapes being defined by a plane (SS) intersecting perpendicularly to the central axis (O).

[2] A diaphragm (10, 10R), comprising an outer shape section (14) with a shape of a circle having one diameter (D2), or a shape of a polygon which is inscribed in a circle with the one diameter (D2); an inner shape section (13) which protrudes in one direction with regard to a plane (PO) including the outer shape section (14), wherein a shape formed by projecting the inner shape section (13) on the plane (PO) is rotationally symmetric about the central axis (O) of the circle with the one diameter (D2); and a vibrating face section (12) that links the outer shape section (14) and the inner shape section (13) and has an inclined face inclined to the central axis (O), wherein the vibrating face section (12) includes a rotationally symmetric orbiting line (15) about an eccentric axis (O2) which is eccentric with regard to the central axis (O); and a curvature (R) of or an inclination angle of the vibrating face (12a) inside of the orbiting line (15) and a curvature (R) of or an inclination angle of the vibrating face (12b) outside of the orbiting line (15) are discontinuous at the orbiting line (15), the orbiting line (15) being sandwiched between the both faces (12a, 12b).

[3] A diaphragm (100), comprising an outer shape section (14) with a regular n-gonal shape (n: an integer of 4 or more) which is inscribed in a circle with one diameter (D2); and n number of top portions (TP1 through TPn) that are provided respectively within n number of triangles (TR1 through TRn) obtained by dividing the regular n-gonal shape with line segments (T1G through TnG) connecting the center (GO) of the regular n-gonal shape and the vertices (T1 through Tn) of the regular n-gonal shape, wherein each line segment obtained by connecting the top portions (TP1 through TPn) with vertices (T1 through Tn) and the center (GO) is formed to be a ridge line; wherein the n-number of top portions (TP1 through TPn) are on an outer periphery line (C2) which is rotationally symmetric about an eccentric axis (O3) which is eccentric with regard to the central axis (GO) of the regular n-gonal shape.

[4] The diaphragm (100) according to claim 3, wherein the n-number of top portions (TP1 through TPn) and the center (GO) of the regular n-gonal shape are positioned so as to be protruded in one direction with regard to a plane (P0) including the vertices (T1 through Tn).

[5] The diaphragm (100) according to claim 4, wherein the center (GO) of and the vertices (T1 through Tn) of the regular n-gonal shape, and the n-number of top portions (TP1 through TPn) are on the same spherical surface (CF).

[6] An electroacoustic transducer (50, 50A), comprising the diaphragm (10, 10R, 100) according to claim 1; a flexible connecting member (30) connected with the outer shape section (14) of the diaphragm (10, 10R, 100); a frame (31) supporting the diaphragm (10, 10R, 100) through the connecting member (30) in such a way that the diaphragm (10, 10R, 100) is freely vibrated; and a driving section (32) which has a voice coil bobbin (21) linked to one surface of the inner shape section (13) in the diaphragm, and vibrates the diaphragm (10, 10R, 100).

[7] An electroacoustic transducer (50, 50A), comprising the diaphragm (10, 10R, 100) according to claim 2; a flexible connecting member (30) connected with the outer shape section (14) of the diaphragm (10, 10R, 100); a frame (31) supporting the diaphragm (10, 10R, 100) through the connecting member (30) in such a way that the diaphragm (10, 10R, 100) is freely vibrated; and a driving section (32) which has a voice coil bobbin (21) linked to one surface of the inner shape section (13) in the diaphragm (10, 10R, 100), and vibrates the diaphragm (10, 10R, 100).

[8] An electroacoustic transducer (50, 50A), comprising the diaphragm (10, 10R, 100) according to claim 3; a flexible connecting member (30) connected with the outer shape section (14) of the diaphragm (10, 10R, 100); a frame (31) supporting the diaphragm (10, 10R, 100) through the connecting member (30) in such a way that the diaphragm (10, 10R, 100) is freely vibrated; and a driving section (32) which has a voice coil bobbin (21) linked to one surface of the inner shape section (13) in the diaphragm (10, 10R, 100), and vibrates the diaphragm (10, 10R, 100).

[9] A spherical shell diaphragm (200), comprising a plurality of diaphragms (10, 10R) with a regular n-gonal shape (n: an integer of 4 or more) which is inscribed in a circle with one diameter (D2), the plurality of diaphragms (10, 10R) being formed into a nearly spherical shape by linking together outer shape sections (14) of the plurality of diaphragms (10, 10R), wherein each of the plurality of diaphragms (10, 10R) includes; an inner shape section (13) which protrudes in an outer direction with regard to a plane (PO) including an outer shape section (14) of the diaphragm (10, 10R), wherein a shape formed by projecting the inner shape section (13) on the plane (PO) is rotationally symmetric about the central axis (O) of the circle with the one diameter (D2); and a vibrating face section (12) that links the outer shape section (14) and the inner shape section (13) and has an inclined face inclined to the central axis (O), wherein any one of cross-sectional shapes of the vibrating face section (12) is rotationally symmetric about an eccentric axis (O2) which is eccentric with regard to the central axis (O), the cross-sectional shapes being defined by a plane (SS) intersecting perpendicularly to the central axis (O).

[10] The spherical shell diaphragm (200, 201) according to claim 9, wherein the outer shape sections (14) of the plurality of diaphragms (10, 10R, 100) are connected with one another through flexible linking members (102).

[11] The spherical shell diaphragm (200, 201) according to claim 9, wherein the nearly spherical shell shape is a regular dodecahedron.

[12] The spherical shell diaphragm (200, 201) according to claim 9, wherein when there is set a dividing line (EQ) that separates the spherical shell diaphragm into two portions along outer shape sections (14) in such a way that each of said two portions has the same number of the diaphragms (10, 10R, 100) having an outer shape section (14) along the dividing line (EQ), the eccentric axis (03) of the diaphragm (10, 10R, 100) having the outer shape section (14) along the dividing line (EQ) is eccentric in a direction toward the vertex of the outer shape section (14) along the dividing line (EQ).

[13] The spherical shell diaphragm (200, 201) according to claim 9, wherein any one of the plurality of diaphragms (10, 10R, 100) has an opening.

[14] A spherical shell diaphragm (200), comprising a plurality of diaphragms (10, 10R) having a regular n-gonal shape (n: an integer of 4 or more) which is inscribed in a circle with one diameter (D2), the plurality of diaphragms (10, 10R) being formed in to an early spherical shape by linking together outer shape sections (14) of the plurality of diaphragms (10, 10R), wherein each of the plurality of diaphragms (10, 10R) includes; an inner shape section (13) which protrudes in an outer direction with regard to a plane (PO) including an outer shape section (14) of the diaphragm, wherein a shape formed by projecting the inner shape section (13) on the plane (PO) is rotationally symmetric about the central axis (O) of the circle with the one diameter (D2); and a vibrating face section (12) that links the outer shape section (14) and the inner shape section (13) and has an inclined face inclined to the central axis (O), wherein the vibrating face section (12) includes a rotationally symmetric orbiting line (15) about an eccentric axis (O2) which is eccentric with regard to the central axis (O); and a curvature (R) of or an inclination angle of the vibrating face (12a) inside of the orbiting line (15) and a curvature (R) of or an inclination angle of the vibrating face (12b) outside of the orbiting line (15) are discontinuous at the orbiting line (15).

[15] The spherical shell diaphragm (200, 201) according to claim 14, wherein the outer shape sections (14) of the plurality of diaphragms (10, 10R, 100) are connected with one another through flexible linking members (102).

[16] The spherical shell diaphragm (200, 201) according to claim 14, wherein the nearly spherical shell shape is a regular dodecahedron.

[17] The spherical shell diaphragm (200, 201) according to claim 14, wherein when there is set a dividing line (EQ) separates the spherical shell diaphragm into two portions along the outer shape sections (14) in such a way that each of the two portions has the same number of the diaphragms (10, 10R, 100) having an outer shape section (14) along the dividing line (EQ), the eccentric axis of the diaphragm (10, 10R, 100) having an outer shape section (14) along the dividing line (EQ) is eccentric in a direction toward the vertex of the outer shape section (14) along the dividing line (EQ).

[18] The spherical shell diaphragm (200, 201) according to claim 14, wherein any one of the plurality of diaphragms (10, 10R, 100) has an opening.

[19] A spherical shell diaphragm (201), comprising a plurality of diaphragms (100) with a regular n-gonal shape (n: an integer of 4 or more) which is inscribed in a circle with one diameter (D2), the plurality of diaphragms (100) being formed into a nearly spherical shape by linking together outer shape sections (14) of the plurality of diaphragms (100), wherein each of the plurality of diaphragms (100) includes; n number of top portions (TP1 through TPn) that are provided respectively within n number of triangles (TR1 through TRn) obtained by dividing the regular n-gonal shape with line segments (T1G through TnG) connecting the center (GO) of the regular n-gonal shape and the vertices (T1 through Tn) of the regular n-gonal shape, wherein each line segment obtained by connecting the top portions (TP1 through TPn) with vertices (T1 through Tn) and the center (GO) is formed to be a ridge line; wherein the n-number of top portions (TP1 through TPn) are on an outer periphery line (C2) of a shape with rotational symmetry about the central axis (GO) of the regular n-gonal shape.

[20] The spherical shell diaphragm (201) according to claim 19, wherein the shape with rotational symmetry is rotationally symmetric about an eccentric axis (O3) which is eccentric with regard to the central axis (GO).

[21] The spherical shell diaphragm (201) according to claim 19, wherein, in the diaphragms (100), the n-number of top portions (TP1 through TPn) and the center (GO) of the regular n-gonal shape are positioned so as to be protruded into one direction with regard to a plane (PO) including the vertices (T1 through Tn).

[22] The spherical shell diaphragm (201) according to claim 21, wherein in each of the diaphragms (100), n-number of vertices (T1 through Tn) as vertices of the regular n-gonal shape in the outer shape section (14), the n-number of top portions (TP1 through TPn), and the center (GO) of the regular n-gonal shape are on the same spherical surface (CF).

[23] The spherical shell diaphragm (201) according to claim 22, wherein the spherical shell diaphragm (201) include a plurality of diaphragms (100) with the same spherical surface (CF) as one another.

[24] The spherical shell diaphragm (200, 201) according to claim 19, wherein the outer shape sections (14) of the plurality of diaphragms (10, 10R, 100) are connected with one another through flexible linking members (102).

[25] The spherical shell diaphragm (200, 201) according to claim 19, wherein the nearly spherical shell shape is a regular dodecahedron.

[26] The spherical shell diaphragm (200, 201) according to claim 19, wherein when there is set a dividing line (EQ) separates the spherical shell diaphragm into two portions along the outer shape sections (14) in such a way that each of the two portions has the same number of the diaphragms (10, 10R, 100) having an outer shape section (14) along the dividing line (EQ), the eccentric axis (O3) of the diaphragm (10, 10R, 100) having an outer shape section (14) along the dividing line (EQ) is eccentric in a direction toward the vertex of the outer shape section along the dividing line (EQ).

[27] The spherical shell diaphragm (200, 201) according to claim 19, wherein any one of the plurality of diaphragms (10, 10R, 100) has an opening.

[28] An electroacoustic transducer (150) using the spherical shell diaphragm (200, 201) according to claim 9.

[29] The electroacoustic transducer (150) according to claim 28, further comprising a plurality of voice coil bobbins (221) connected respectively with the inside surfaces of the plurality of diaphragms (10, 10R, 100); and a plurality of driving sections (232) which respectively include one of the voice coil bobbins (221), and vibrate the plurality of diaphragms (10, 10R, 100).

[30] An electroacoustic transducer (150) using the spherical shell diaphragm according to claim 11, wherein the plurality of diaphragms (10, 10R, 100) are linked together in such a way that the plurality of diaphragms (10, 10R, 100) form eleven surfaces of the regular dodecahedron.

[31] The electroacoustic transducer (150) according to claim 30, comprising a plurality of voice coil bobbins (221) connected respectively with the inside surfaces of the plurality of diaphragms (10, 10R, 100); and a plurality of driving sections (232) which respectively include one of the voice coil bobbins (221), and vibrate the plurality of diaphragms (10, 10R, 100), respectively.

[32] An electroacoustic transducer (150) using the spherical shell diaphragm (200, 201) according to claim 14.

[33] The electroacoustic transducer (150) according to claim 32, comprising a plurality of voice coil bobbins (221) connected with the inside surfaces of the plurality of diaphragms (10, 10R, 100), respectively; and a plurality of driving sections (232) which respectively include one of the voice coil bobbins (221), and vibrate the plurality of diaphragms (10, 10R, 100), respectively.

[34] An electroacoustic transducer (150) using the spherical shell diaphragm (200, 201) according to claim 16, wherein the plurality of diaphragms (10, 10R, 100) are linked together in such a way that the plurality of diaphragms (10, 10R, 100) form eleven surfaces of the regular dodecahedron.

[35] The electroacoustic transducer (150) according to claim 34, comprising a plurality of voice coil bobbins (221) connected respectively with the inside surfaces of the plurality of diaphragms (10, 10R, 100); and a plurality of driving sections (232) which respectively include one of the voice coil bobbins (221), and vibrate the plurality of diaphragms (10, 10R, 100), respectively.

[36] An electroacoustic transducer (150) using the spherical shell diaphragm (200, 201) according to claim 19.

[37] The electroacoustic transducer (150) according to claim 36, comprising a plurality of voice coil bobbins (221) connected respectively with the inside surfaces of the plurality of diaphragms (10, 10R, 100); and a plurality of driving sections (232) which respectively include one of the voice coil bobbins (221), and vibrate the plurality of diaphragms (10, 10R, 100), respectively.

[38] An electroacoustic transducer (150) using the spherical shell diaphragm (200, 201) according to claim 25, wherein the plurality of diaphragms (10, 10R, 100) are linked together in such a way that the plurality of diaphragms (10, 10R, 100) form eleven surfaces of the regular dodecahedron.

[39] The electroacoustic transducer (150) according to claim 38, comprising a plurality of voice coil bobbins (221) connected respectively with the inside surfaces of the plurality of diaphragms (10, 10R, 100); and a plurality of driving sections (232) which respectively include one of the voice coil bobbin (221), and vibrate the plurality of diaphragms (10, 10R, 100), respectively.

[40] A method of manufacturing an electroacoustic transducer (150), comprising making, from a diaphragm material, a diaphragm segment (10, 10R, 100, 101) with an outer shape section (14) having a shape of a regular pentagon which is inscribed in a circle with one diameter (D2); arranging a plurality of the diaphragm segments (10, 10R, 100, 101) in plane, to bond, with an flexible linking member (102), sides which can be arranged in parallel with one another so as to oppose one another by positioning the vertices thereof; fastening a plurality of driving sections (232) which respectively have a voice coil bobbin (221), and vibrate the plurality of diaphragm segments (10, 10R, 100, 101), respectively, to each surface (132a) of a base (130) with an outer shape of a regular dodecahedron in such a way that each of the voice coil bobbins (221) extends in a direction intersecting perpendicularly to each of the surfaces (132a) of the regular dodecahedron; and fastening the plurality of voice coil bobbins (221) to the inside surfaces of the plurality of diaphragm segments (10, 10R, 100, 101), respectively.

[41] The method of manufacturing an electroacoustic transducer (150), according to claim 40, wherein the plurality of diaphragm segments (10, 10R, 101) comprise: an inner shape section (13) which protrudes in one direction with regard to a plane (PO) including the outer shape section (14), wherein a shape formed by projecting the inner shape section (13) on the plane (PO) is rotationally symmetric about the central axis (O) of the circle with the one diameter (D2); and a vibrating face section (12) that links the outer shape section (14) and the inner shape section (13) and has an inclined face inclined to the central axis (O), wherein any one of cross-sectional shapes of the vibrating face section (12) is rotationally symmetric about an eccentric axis (O2) which is eccentric with regard to the central axis (O), the cross-sectional shapes being defined by a plane (SS) intersecting perpendicularly to the central axis (O).

[42] The method of manufacturing an electroacoustic transducer (150), according to claim 40, wherein each of the plurality of diaphragm segments (100, 101) comprises: an outer shape section (14) with a regular n-gonal shape (n: an integer of 4 or more) which is inscribed in a circle with one diameter (D2), n-number of top portions (TP1 through TPn) that are provided respectively within n number of triangles (TR1 through TRn) obtained by dividing the regular n-gonal shape with line segments (T1G through TnG) connecting the center (GO) of the regular n-gonal shape and the vertices (T1 through Tn) of the regular n-gonal shape, wherein each line segment obtained by connecting the top portions (TP1 through TPn) with vertices (T1 through Tn) and the center (GO) is formed to be a ridge line; and the n-number of top portions (TP1 through TPn) are on an outer periphery line (C2) of a shape with rotational symmetry about an eccentric axis (G3) which is eccentric with regard to the central axis (GO) of the regular n-gonal shape.

According to the present invention, there may be provided an advantage that generation of standing waves is reduced, a high sound-pressure is obtained even in a range of low-pitched sound, a highly-efficient electroacoustic conversion of an input signal is enabled, a reference direction for a voice radiation is specified, and a uniform directivity in the circumferential direction is obtained.

According to the present invention, there may be brought about another advantage that generation of standing waves is reduced; a special bonding member is not required; positioning is easy upon assembling; high sound pressure may be obtained even in a range of low-pitched sounds; and a highly efficient electro-acoustic conversion of input signals may be enabled.

According to the present invention, there may be presented yet another advantage of simplified positioning of each section, easy assembling, and reduced variations in sound characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing a diaphragm according to a first example of the present invention;

FIG. 2A is a plan view showing the diaphragm according to the first example of the present invention;

FIG. 2B is a cross-sectional view showing the diaphragm according to the first example of the present invention;

FIG. 3 is a cross-sectional view showing an electroacoustic transducer according to the first example of the present invention;

FIG. 4 is a cross-sectional view showing another example of the electroacoustic transducer according to the first example of the present invention;

FIG. 5 is a schematic view explaining a distribution of standing waves in a conventional diaphragm;

FIG. 6 is a schematic view explaining a distribution of standing waves in the diaphragm according to the first example of the present invention;

FIG. 7 is a graph showing frequency--sound pressure characteristics according to the eccentricity amounts of the diaphragm;

FIGS. 8A through 8C are schematic cross-sectional views explaining the shapes of a diaphragm according to the first example of the present invention;

FIGS. 9A through 9C are schematic cross-sectional views explaining other shapes of diaphragm according to the first example of the present invention;

FIG. 10 is a plan view and a cross-sectional view explaining a variant of the diaphragm according to the first example of the present invention;

FIGS. 11A and 11B are comparative illustration, wherein FIG. 11A is a front view explaining a conventional diaphragm and FIG. 11B is a front view explaining a diaphragm according to a second example of the present invention;

FIG. 12 is a schematic cross-sectional view explaining an electroacoustic transducer according to the second example of the present invention;

FIG. 13 is a development view explaining a diaphragm according to an application example of the present invention;

FIG. 14 is an appearance view showing an electroacoustic transducer according to the application example of the present invention;

FIG. 15 is a perspective view explaining the structure of the electroacoustic transducer according to the application example of the present invention;

FIG. 16 is a partial cross-sectional view explaining the electroacoustic transducer according to the application example of the present invention;

FIG. 17 is a perspective view explaining the structure of another electroacoustic transducer according to an application example of the present invention;

FIG. 18A is a front view explaining a variant of the diaphragm according to the application example of the present invention;

FIG. 18B is a perspective view explaining the variant of the diaphragm according to the application example of the present invention; and

FIG. 19 is a front view explaining the electroacoustic transducer according to the application example of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to preferred examples, an embodiment according to the present invention will be explained, using FIG. 1 through FIG. 19.

In the following explanations, the rotational symmetry means at least twofold or more rotational symmetry.

First Example

The shape of a diaphragm according to a first example will be explained using FIGS. 1, 2A and 2B. In FIG. 1, a curvature of the curved surface of a diaphragm 10 is schematically shown with a plurality of solid lines 16 in the radial direction for the sake of easier understanding.

FIG. 1 is a perspective view showing an external appearance of the diaphragm 10; FIG. 2A is a plan view showing the diaphragm 10; and FIG. 2B is a sectional view taken along the S1-S1 line in FIG. 2A.

As shown in FIGS. 1, 2A, and 2B, the diaphragm 10 is formed like a nearly disc which includes a center section 11 ranging from a central axis O to an inner diameter section 13 with a diameter D1 [refer to FIG. 2A], and an inclined section 12 ranging from the inner section 13 to an outer diameter section 14 with a diameter D2 [refer to FIG. 2A].

The material of the diaphragm is not limited to a special one, but a sheet of paper, resin such as polypropylene (PP), metal such as aluminum, ceramics, or wood may be used.

The inner diameter section 13 is formed, protruding from a reference surface PO including the outer diameter section 14 by a maximum height h1 [refer to FIG. 2B], and the center section 11 within the inside of the inner diameter section 13 has a curved surface dented inward from the inner diameter section 13 of the most protruding part by a depth of h2 [refer to FIG. 2B].

Accordingly, the inner diameter section 13 forms a circular ridge line with a diameter D1.

The inclined section 12 is formed as a surface linking the inner diameter section 13 and the outer diameter section 14.

Moreover, an intermediate diameter section 15 (shown with a double dotted and dashed line) with a diameter D3 is formed between the inner diameter section 13 and the outer diameter section 14. The intermediate diameter section 15 corresponds to a location (inflection section) in which the curvature of the surface of the inclined section 12 is remarkably changed.

The diaphragm 10 is more specifically explained below. The surface (hereinafter, called an inside inclined-section 12a) of a region within the inside (in the side of the central axis O) of the intermediate diameter section 15 within the inclined section 12 is formed as a curved surface with a curvature in the denting direction, and the surface (hereinafter, called the outside inclined-section 12b) of a region outside (in a side opposite to that of the central axis O) from the intermediate diameter section 15 is formed as a plane surface without a curvature.

Moreover, the intermediate diameter section 15 has a central axis O2 which is eccentric with regard to the central axis O of the inner diameter section 13 and that of the outer diameter section 14 by a distance a (eccentricity amount a).

Accordingly, the intermediate diameter section 15 is a location at which the curvature of the surface at the side of the eccentric central axis O2 (the inside inclined-section 12a) and that of the surface (the outside inclined-section 12b) opposite to the surface at the side of the eccentric central axis O2 are discontinuous as a boundary therebetween, and is shown with a line circling around the eccentric central axis O2.

Moreover, the curvature R of the inside inclined-section 12a is not constant, and is continuously changed from a maximum Rmax to a minimum Rmin [refer to FIG. 2B] in the circumferential direction. The inside inclined-section 12a is formed, based on the changing curvatures R, and the eccentricity amount .alpha..

Then, an electroacoustic transducer 50 using the diaphragm 10 will be explained.

The electroacoustic transducer 50 is also called a speaker unit. As shown in, for example, FIG. 3, the electroacoustic transducer 50 is configured to include the diaphragm 10, a flexible edge 30 which is connected to the outer diameter section 14 of the diaphragm 10, a housing 31 to which the edge 30 is firmly fixed, and a magnetic circuit 34 which drives the diaphragm 10 fastened to the housing 31.

The magnetic circuit 34 is composed of a cup-type yoke 23 having a bottom 23a and a ring-type wall 23b, a magnet 24 fastened to the inside surface of the bottom 23a, and a cylinder-type pole piece 25 fastened to the magnet 24. The edge 30 as a linking member linking the diaphragm 10 and the housing 31 may be made of, for example, a rubber material and a resin material.

Moreover, a voice coil bobbin 21 and a voice coil 22, which is wound around the outer peripheral surface at one end of the voice coil bobbin 21, are inserted into a gap between the ring-type wall 23b of the yoke 23 and the pole piece 25. Electric power is supplied to the voice coil 22 from the outside through a lead wire 22a, which is taken out to the outside through a hole 31a provided in the housing 31.

Moreover, the outer peripheral surface of the voice coil bobbin 21 is connected to the housing 31 through an elastic damper 33. The housing 31 supports the bobbin 21 through the damper 33 so as to allow the bobbin 21 to vibrate freely in a direction (vibrating direction) parallel to the central axis O of the diaphragm 10.

A driving section 32 is configured to include the magnetic circuit 34, the voice coil bobbin 21, and the voice coil 22.

Further detailed explanation will be made, part of which will have been repeated. The ring-type edge 30 with elasticity is fixed to around the outer diameter section 14 of the diaphragm 10, and the outer periphery of the edge 30 is fastened to a ring-type frame 31b in the housing 31. In fastening, the diaphragm 10 is installed in such a way that the inner diameter section 13 is protruded in a direction away from the driving section 32.

One end of the voice coil bobbin 21 with a shape of a circular tube is fastened to the surface of the inner diameter section 13, wherein the surface is in the opposite side to the protruding side of the section 13 which is protruding like a circular ridge line.

The voice coil 22 is wound on the outer peripheral surface at the other end side of the voice coil bobbin 21.

Moreover, the cup-type yoke 23 is arranged in such a way that the inner wall of the ring-type wall 23b faces the voice coil 22 leaving a predetermined magnetic gap therebetween.

On the other hand, the outer peripheral surface of the disk-like pole piece 25 linked to the cylinder-type magnet 24 is arranged to face the inner surface of the voice coil bobbin 21 leaving a predetermined gap, the inner surface being opposite to the outer surface of the voice coil 21 around which the voice coil 22 is wound.

The voice coil bobbin 21 is supported through the damper 33 by the housing 31 in such a way that the bobbin 21 may be moved in the vibrating direction.

Since general-purpose components having their outer shape formed non-eccentric with regard to the central axis O are used without any modification to prepare the edge 30, the housing 31, and the driving section 32 which are to be used in the electroacoustic transducer 50, exclusive components are not necessary for the diaphragm 10, thereby preventing an increase in production costs.

The inner diameter section 13 of the diaphragm 10 may be protruded in relation to the driving section 32 in a direction opposing to the above-described direction shown in FIG. 3, that is, in a direction toward the driving section 32. In other words, this configuration is another form in which the inner diameter section 13 is dented as shown in FIG. 4.

In an electroacoustic transducer 50A shown in FIG. 4, the diaphragm 10 is protruded in a direction opposing to the protruding direction of the diaphragm 10 of the electroacoustic transducer 50 shown in FIG. 3, and one end of the voice coil bobbin 21 is fixed to a surface in the protruding side of the inner diameter section 13 in the diaphragm 10. Except this configuration, the electroacoustic transducer 50A has the same configuration as that of the electroacoustic transducer 50.

Accordingly, there can be used the voice coil bobbin 21 having the shorter length thereof in the direction of the central axis O than that of the electroacoustic transducer 50.

Since the electroacoustic transducer 50 in which the inner diameter section 13 is protruded outward as shown in FIG. 3 has a broader directivity than that of the electroacoustic transducer 50A with the inner diameter section 13 which is dented inward as shown in FIG. 4, the electroacoustic transducer 50 is preferably used as an electroacoustic transducer (so-called a tweeter) which emits sounds in a high-pitched range, though it is generally difficult for the transducer for high-pitched sounds to have a broad directivity.

Moreover, the electroacoustic transducer 50A in which the inner diameter section 13 is dented inward is preferable as an electroacoustic transducer (so-called a woofer) with a large diameter for low-pitched sounds because the diaphragm 10 does not protrude outward in the electroacoustic transducer 50A.

Subsequently, there will be explained as follows a characteristics comparison between the above-described case where the diaphragm 10 in which the central axis O2 of the intermediate diameter section 15 is eccentric with regard to the central axis O of the outer diameter section 14 is used and a case where a diaphragm in which the central axis O2 of the intermediate diameter section 15 is not eccentric is used.

FIG. 5 shows the vibrating state of a diaphragm 10a (a comparison example) with a configuration in which the intermediate diameter section 15 has a central axis O2 without an eccentricity with regard to the central axis O of the diaphragm 10, and FIG. 6 shows the vibrating state of the diaphragm 10 according to the present invention, wherein the intermediate diameter section 15 has the central axis O2 with an eccentricity from the central axis O of the diaphragm 10.

FIG. 5 and FIG. 6 show the distribution of standing waves in the direction of the central axis O of each diaphragm on each of sections taken along the A-A line under a condition for analysis of the vibration, in which force determined by the effective coil length and the number of turns of the voice coil 22 is applied as sine vibration to the voice coil 22 under an actual magnetic field strength by the magnetic circuit 34, and vibration of 12 kHz is caused.

In each drawing, the upper section thereof is a plan view of each diaphragm, and the lower section thereof represents an amount of displacement caused by the vibration, corresponding to its upper section.

Specifically, the dashed lines show the cross-sectional shape of each diaphragm and the solid lines schematically show the distribution of each standing waves in the lower sections representing the displacement amounts, which are rather exaggerated.

It is found by comparison between the drawings that, when the diaphragm 10 according to the present invention is used, the standing wave is clearly asymmetry with regard to the central axis O. Moreover, the number of remarkable maxima generated in the left side and the right side with regard to the central axis O is also different from each other.

FIG. 7 shows frequency--sound pressure characteristics for three kinds of electroacoustic transducers: one using the diaphragm 10a as the comparison example shown in FIG. 5 in which the central axis O2 of the intermediate diameter section 15 and the central axis O of the inner diameter section 13 are in agreement with each other (that is, the eccentricity amount is zero); and the other two using the diaphragm 10 with an .alpha. of 1.5 mm, and the diaphragm 10 with an .alpha. of 3.0 mm, respectively, as examples according to the present invention, wherein .alpha. is assumed to be an eccentricity amount of the central axis O2 of the intermediate diameter section 15 from the central axis O of the inner diameter section 13.

It is found that, a deep dip is seen at nearly 8 kHz (referred to by the arrow in the drawing) when the diaphragm 10a as the comparison example is used. However, when there is eccentricity, the dip becomes shallow and, furthermore, when the eccentricity amount becomes larger, the dip becomes more leveled off.

Moreover, it is found that other peaks and dips become flat by the eccentricity, and the larger eccentricity amount a causes the peaks and dips to be more leveled.

Incidentally, the inside inclined-section 12a between the inner diameter section 13 and the intermediate diameter section 15 may have a curved surface shown in, for example, FIG. 8A through FIG. 8C as a cross-sectional shape in a plane passing through the central axis O. [FIG. 8A through FIG. 8C are schematic views, showing that the intermediate diameter section 15 has the central axis O2 which is eccentric to the left in the drawing, with regard to the central axis O of the outer diameter section 14.]

Concretely, FIG. 8A and FIG. 8C are examples in which the inside inclined-section 12a is an inclined curved surface having a curvature in such a way that the surface is dented inward as the cross-sectional shape.

Moreover, FIG. 8B is an example in which the inside inclined-section 12a is an inclined curved surface having a curvature in such a way that the surface is dented inward as the cross-sectional shape, and, at the same time, the outer diameter section 14 is an inclined plane without a curvature as the cross-sectional shape.

On the other hand, the outside inclined-section 12b between the intermediate diameter section 15 in the inclined section 12 and the outer diameter section 14 may be a curved surface shown in, for example, FIG. 8A through FIG. 8C.

Concretely, the outside inclined-section 12b may be a plane without an inclination as shown in FIG. 8A, or an inclined plane which is continuous from the adjacent inside inclined-section 12a as shown in FIG. 8B.

Moreover, the section 12b may be an inclined curved surface with an inclination in the opposite direction to that of the inside inclined-section 12a as shown in FIG. 8C, or an inclined plane 12b1 as shown with a dotted line in FIG. 8C.

Moreover, the inside inclined-section 12a may be an inclined plane without a curvature in a cross-sectional shape as shown in FIG. 9A through FIG. 9C. (FIG. 9A through FIG. 9C also are schematic views, showing that the intermediate diameter section 15 has the central axis O2 which is eccentric to the left in the drawing, with regard to the central axis O of the outer diameter section 14.)

Moreover, the outside inclined-section 12b may be a plane without an inclination as shown in FIG. 9A, or an inclined plane with an inclination in the same direction as that of the inside inclined-section 12a as shown in FIG. 9B. Furthermore, the section 12b may be an inclined plane with an inclination in the opposite direction to that of the inside inclined-section 12a as shown in FIG. 9C.

Obviously, the shape of the inclined section 12 may be a combination of those shown in FIG. 8A through FIG. 8C and FIG. 9A through FIG. 9C, and the shape is not limited to the combinations.

As shown in FIG. 8A through FIG. 8C and FIG. 9A through FIG. 9C, a cross-sectional shape taken along the S-S line has a central axis O5 eccentric from the central axis O by .alpha.2, the cross-sectional shape intersecting perpendicularly to the central axis O, and is rotationally symmetric about the eccentric central-axis O5, in the diaphragm 10 according to the present example.

Moreover, the shape of a diaphragm is not limited to a shape with rotational symmetry about the central axis O5 which is eccentric at all the positions in the direction of the central axis O from a position d1 (a position at which the central axis O and the reference plane PO intersect with each other) in the reference plane PO, which includes the outer diameter section 14, to a position d2 (a position at which the central axis O and a plane P13 including the inner diameter section 13 intersect with each other) in the inner diameter section 13, and may be a shape in which the inclined section 12 partially includes positions d at which a shape with rotational symmetry about the eccentric central-axis O5 is obtained as an eccentric surface section.

Moreover, the intermediate diameter section 15 is set as a location at which the angle of inclination angle, excluding the example shown in, for example, FIG. 8B, or a curvature of the surface of the inclined section 12 is suddenly changed, in other words, as a location as a boundary at which curvatures or angles of inclination of the two surfaces which are connected with each other are discontinuous.

Furthermore, the intermediate diameter section 15 is a location that is visually identified as a boundary line in which the reflection of light is visually different when light is irradiated from one direction.

The intermediate diameter section 15 is not limited to a complete circle, and may be a shape which has the central axis O2 with an eccentricity with regard to the central axis O and is rotationally symmetric about the eccentric central axis O2.

Similarly, the inner diameter section 13 is not limited to a complete circle, and may be a rotationally symmetric shape, for example, an ellipse.

Though the diaphragm 10 with a dented surface at the center section 11 has been explained in the above-described examples, the center section 11 may be a plane, or a protruded surface.

Moreover, the size of the center section 11, in other words, the size of the inner diameter section 13 in the radial direction may be arbitrarily set.

Accordingly, for example, when the inner diameter section 13 is assumed to be a complete circle, the size of the diameter D1 is arbitrary.

Though the example in which the outer shape of the above-described diaphragm 10 is a circle has been explained, the outer shape may be assumed to be a polygon (for example, a regular pentagon) which is inscribed in a circle. In this case, the dimensions of the polygon and the intermediate-diameter section may be set in such a way that interference does not occur between the outer shape of the polygon and the intermediate section 15.

Moreover, the outside inclined-section 12b may be assumed to be a curved surface with a center of curvature O4 in the opposite side to the protruding side of the inner diameter section 13 as shown in FIG. 10.

FIG. 10 shows the cross-sectional shape of a diaphragm 10R in which, as one example, the outside inclined-section 12b is formed with a curved surface along a spherical surface CF with a radius R1.

This diaphragm 10R has a similar shape, except the outside inclined-section 12b, to that of the diaphragm 10 shown in FIG. 2A and FIG. 2B.

Since the shape of the inner diameter section 13, the outer diameter section 14 and the intermediate diameter