Acoustic apparatus

Abstract

An acoustic apparatus may include a frame having an annular open portion that opens in an axial direction; a diaphragm supported by being attached to the annular open portion via a flexible edge member so as to be capable of vibrating in the axial direction; and a driving unit connected to the diaphragm at a center portion of the diaphragm, where the driving unit is configured to apply a driving force in the axial direction to the diaphragm. The diaphragm has a rotationally symmetric shape around an axis of the diaphragm when viewed in the axial direction. The diaphragm includes a sheet member having an orientation dispersion structure in which shape-anisotropic fillers are dispersed in a resin with long axes of the fillers oriented in one predetermined direction, and the diaphragm has mechanical characteristics having two-fold rotation symmetry around the axis.

Claims

1. An acoustic apparatus comprising: a frame having an annular open portion that opens in an axial direction; a diaphragm supported by being attached to the annular open portion via a flexible edge member so as to be capable of vibrating in the axial direction; and a driving unit connected to the diaphragm at a center portion of the diaphragm, where the driving unit is configured to apply a driving force in the axial direction to the diaphragm, wherein the diaphragm has a continuously rotationally symmetric shape around an axis of the diaphragm when viewed in the axial direction, wherein the diaphragm is formed of one seamless sheet member having an orientation dispersion structure in which shape-anisotropic fillers are dispersed in a resin with long axes of the fillers oriented in one predetermined direction; and wherein the diaphragm includes: a high-rigidity portion of the diaphragm in which the orientation direction of the fillers is parallel to a direction from a center portion to an outer circumferential portion of the diaphragm and flexural rigidity in the high-rigidity portion is greater than portions of the diaphragm where the orientation of the fillers is orthogonal to the direction from the center portion to the outer circumferential portion of the diaphragm when it is attempted to bend an area between the center portion and the outer circumferential portion of the diaphragm, a low-rigidity portion of the diaphragm in which the orientation direction of the fillers is orthogonal to the direction from the center portion to the outer circumferential portion of the diaphragm and flexural rigidity in the low-rigidity portion is less than portions of the diaphragm where the orientation of the fillers is parallel to the direction from a center portion to an outer circumferential portion of the diaphragm when it is attempted to bend an area between the center portion and the outer circumferential portion of the diaphragm, where flexural rigidity is continuously decreased from the high-rigidity portion to the low-rigidity portion, and the diaphragm has mechanical characteristics having two-fold rotation symmetry around the axis.

2. The acoustic apparatus according to claim 1, wherein the diaphragm is a vacuum-formed article or a pressure-formed article formed of a sheet member in which the fillers are dispersed in a thermoplastic resin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a conceptual sectional view illustrating a structure of a speaker according to one embodiment of the present disclosure;

(2) FIG. 1B is a partial plan view in the X1-X2 direction illustrating a structure of a diaphragm included in the speaker;

(3) FIG. 2A is a sectional perspective view illustrating the structure of the diaphragm of the speaker according to the embodiment;

(4) FIG. 2B is a plan view in the X1-X2 direction illustrating the structure of the diaphragm of the speaker according to one embodiment; and

(5) FIG. 3 is a graph showing frequency characteristics of a speaker according to a modification of one embodiment of the present disclosure, together with frequency characteristics of speakers having other structures.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) Embodiments and implementations of the present disclosure will be described below with reference to the drawings. FIG. 1A is a conceptual sectional view illustrating a structure of a speaker according to one embodiment of the present disclosure, and FIG. 1B is a partial plan view in the X1-X2 direction illustrating a structure of a diaphragm included in the speaker. In the plan view, a shape appearing on the Y1 side in the Y1-Y2 direction is the same as that appearing on the Y2 side in the Y1-Y2 direction; thus, the plan view illustrates only the Y2 side. FIG. 2A is a sectional perspective view illustrating the structure of the diaphragm of the speaker according to the embodiment, and FIG. 2B is a plan view in the X1-X2 direction illustrating the structure of the diaphragm of the speaker according to the embodiment. The sectional perspective view illustrates a section in which a sectional area of the diaphragm of the speaker is the maximum.

(7) As illustrated in FIG. 1A, a speaker 1 may include a frame 11 having a substantially truncated cone shape and various members attached to the frame 11. The frame 11 includes, at an outer circumferential edge thereof, an annular open portion 11a having a circular-ring shape and a spoke-like support 11c extending from the annular open portion 11a. In the drawing, the support 11c is indicated by a discontinuous line having cut-out holes 11b for convenience of understanding.

(8) A diaphragm 12 that generates a sound pressure in the speaker 1 includes a flexible edge member 12a at an outer circumferential edge of the diaphragm 12. The diaphragm 12 is supported by being attached to the annular open portion 11a via the flexible edge member 12a so as to be capable of vibrating in the axial direction (X1-X2 direction in FIG. 1A).

(9) The diaphragm 12 has a substantially truncated cone shape and has a circular outer shape when viewed in the axial direction (X1-X2 direction). The diaphragm 12 includes the flexible edge member 12a at the outer circumferential edge thereof and is attached to the annular open portion 11a of the frame 11 via the flexible edge member 12a. In the speaker 1 in FIG. 1A, specifically, the flexible edge member 12a is bonded to the annular open portion 11a of the frame 11 using an adhesive agent. Supported by the frame 11 as described above, the diaphragm 12 can vibrate in the X1-X2 direction. The diaphragm 12 includes an opening (diaphragm opening) 12b at a center portion when viewed in the axial direction (X1-X2 direction). The diaphragm 12 is connected to a bobbin 15 at an inner circumferential surface of the diaphragm opening 12b. The bobbin 15 is a part of a driving unit (described later).

(10) A dust cap 13 having a hemispherical-cap shape is disposed on the X2 side of the diaphragm 12 in the X1-X2 direction to cover the diaphragm opening 12b. The dust cap 13 is a member that suppresses unstable operation of the bobbin 15 because a foreign substance enters the diaphragm opening 12b toward the X1 side in the X1-X2 direction.

(11) The support 11c of the frame 11 has a truncated cone shape and has a top portion (magnetic circuit mount portion 11d) on which a magnetic circuit 14 is mounted. The magnetic circuit 14 includes a columnar center pole 14a. The center pole 14a has a central axis directed in a vibration direction (axial direction (X1-X2 direction)) of the diaphragm. Around the rear (the X1 side in the X1-X2 direction) of the center pole 14a, a bottom plate 14b is disposed so as to be integral with the center pole 14a. On the front side (the X2 side in the X1-X2 direction) of the bottom plate 14b, an annular magnet 14c is mounted. On the front side (the X2 side in the X1-X2 direction) of the magnet 14c, an annular top plate 14d is mounted. The provision of the magnet 14c forms an annular magnetic gap 14e between the center pole 14a and the top plate 14d. The bottom plate 14b and the top plate 14d form a yoke.

(12) On the rear side (the X1 side in the X1-X2 direction) of the diaphragm 12, the bobbin 15 having a cylindrical shape is secured. As illustrated in FIG. 1A, the bobbin 15 is inserted into the magnetic gap 14e of the magnetic circuit 14 positioned on the rear side (the X1 side in the X1-X2 direction) of the diaphragm 12. The bobbin 15 includes a portion inserted into the magnetic gap 14e, the portion having a side surface around which a voice coil 16 is wound. The bobbin 15 reciprocates in the axial direction (X1-X2 direction) in accordance with a current flowing through the voice coil 16 positioned inside the magnetic gap 14e, which causes the diaphragm 12 to vibrate and generate a sound pressure.

(13) A damper 17 is disposed between the diaphragm 12 and the magnetic circuit 14 in the axial direction (X1-X2 direction). The damper 17 is supported by the support 11c of the frame 11 at an outer circumference side of the damper 17, and supports the bobbin 15 at an inner circumference side of the damper 17. The damper 17, in addition to the diaphragm 12, also reciprocates in the axial direction (X1-X2 direction) along with the reciprocation of the bobbin 15. The damper 17 is formed of an elastic member. In a state in which no current flows through the voice coil 16, the damper 17 has a function of returning the bobbin 15 to a neutral position by using an elastic recovery force.

(14) The speaker 1 having such a structure can generate, as described above, a sound pressure in the axial direction X1 (X1-X2 direction) by causing a current to flow through the voice coil 16 to thereby cause the diaphragm 12 to vibrate. The proportionality coefficient between the magnitude of the current flowing through the voice coil 16 and the magnitude of a sound pressure to be generated is ideally the same at any frequency. However, in reality, for example, the resonant frequency of the speaker 1 influences the frequency dependence of the sound pressure to have a peak (a band in which the sound pressure is high) and a dip (a band in which the sound pressure is low) in a specific range. In particular, when the diaphragm 12 has a shape continuously rotationally symmetric around the axis (the line in the X1-X2 direction) like the speaker 1 illustrated in FIG. 1, that is, when the diaphragm has a shape which may be expressed with a plurality of coaxial circles, a resonance peak in a high range is likely sharpened when viewed in the X1-X2 direction.

(15) FIG. 3 is a graph showing frequency characteristics of a speaker according to a modification of one embodiment of the present disclosure, together with frequency characteristics of speakers having other structures. The graph indicated by a gray broken line in FIG. 3 is a graph showing frequency characteristics of a speaker (hereinafter, referred to as reference speaker) including a diaphragm having mechanical characteristics isotropic around the axis (the line in the X1-X2 direction), that is, a speaker with the shape and mechanical characteristics having continuous rotation symmetry around the axis (the line in the X1-X2 direction). As illustrated in FIG. 3, there is found a peak at which the sound pressure is locally high with frequencies around 5 kHz. This peak is based on the resonance of the diaphragm.

(16) In order to decrease the intensity of such a resonance peak, the diaphragm 12 of the speaker 1 is formed of a sheet member that has an orientation dispersion structure in which shape-anisotropic fillers FB are dispersed in a resin with the long axes thereof oriented in one predetermined direction (specifically, orientation direction D1 along the Y1-Y2 direction) as illustrated in FIGS. 2A and 2B.

(17) Using the sheet member having the orientation dispersion structure to form the diaphragm 12, as described above, improves the mechanical characteristics of the diaphragm when compared with a case in which the fillers FB are not contained. As a result, the mechanical characteristics of the diaphragm 12 can be improved.

(18) Examples of the shape-anisotropic fillers FB include carbon-based materials, such as carbon fiber and carbon nanotubes, and oxide-based materials, such as glass fiber. The length of each of the fillers FB may be any length. Non-limiting examples of the length are a length between 0.01 to 10 mm inclusive, or may be preferably a length between 0.1 mm to several millimeters inclusive from a viewpoint of ease of handling. The ratio of the length of the major axis of each filler FB to the length of the minor axis of the filler FB, what is called the aspect ratio, may be any ratio. The aspect ratio of each filler FB may be preferably 5 or higher. The type of the resin contained in the sheet member is not limited. Non-limiting examples of the resin are polyolefin, such as polyethylene and polypropylene; polyester, such as polyethylene terephthalate; polyamide, such as nylon 6,6; polyvinyl chloride; and polyimide.

(19) The method of manufacturing the sheet member may be any method, as long as the sheet member can have an appropriate orientation dispersion structure. Specific examples of the method of manufacturing the sheet member are extrusion forming, expansion, and blow forming. The sheet member may preferably contain a filler having high orientation dispersion properties, so as to have high in-plane uniformity. In such a case, the sheet member is preferably an extrusion-formed article. With such a sheet member being the extrusion-formed article, the uniformity of the material of the sheet member as a constituent material of the diaphragm 12 is increased, which may make it easy to realize the speaker 1 having excellent quality uniformity.

(20) The diaphragm 12 is formed of such a sheet member. The manufacturing method of the diaphragm 12 is not particularly limited. The manufacturing method of the diaphragm is typically vacuum forming or pressure forming of forming a sheet member with use of a mold having an exhaust hole. By heating the sheet member during vacuum forming etc., formability may be increased.

(21) Since the sheet member has the orientation dispersion structure as described above, the sheet member has anisotropic mechanical characteristics. Specifically, the mechanical characteristics in the orientation direction D1 differ from the mechanical characteristics in a direction orthogonal to the orientation direction D1. The modulus of longitudinal elasticity and specific frequency are typically relatively high in the orientation direction D1, and the tensile elasticity is relatively high in the direction orthogonal to the orientation direction D1.

(22) As described above, since the sheet member has the orientation dispersion structure in the diaphragm 12 formed by including the sheet member, the mechanical characteristics, in particular, the modulus of longitudinal elasticity of the diaphragm 12 is increased as compared with a diaphragm formed of a sheet member in which fillers are not dispersed. Also, since the sheet member has the anisotropic mechanical characteristics, the mechanical characteristics of the diaphragm 12 in the orientation direction D1 of the sheet member differ from the mechanical characteristics of the diaphragm 12 in the direction orthogonal to the orientation direction D1. As a result, the mechanical characteristics of the diaphragm 12 have two-fold rotation symmetry with a rotation angle of 180 degrees around the axis (the line in the X1-X2 direction). Hence, the shape of the diaphragm 12 of the speaker 1 has continuous rotation symmetry around the axis (the line in the X1-X2 direction), and the mechanical characteristics of the diaphragm 12 have two-fold rotation symmetry. In terms of rotation symmetry, two-fold rotation symmetry has the lowest symmetry. Due to this, when the diaphragm 12 vibrates, a resonance peak in a high range is less likely sharpened in the frequency characteristics of the sound pressure.

(23) In other words, the diaphragm 12 includes a high-rigidity region and a low-rigidity region. In the high-rigidity region, the orientation direction of the fillers is parallel to a direction from a center portion to an outer circumferential portion of the diaphragm 12 and flexural rigidity there is high when it is attempted to bend an area between the center portion and the outer circumferential portion of the diaphragm 12. In the low-rigidity region, the orientation direction of the fillers is orthogonal to the direction from the center portion to the outer circumferential portion of the diaphragm 12 and flexural rigidity there is low when it is attempted to bend an area between the center portion and the outer circumferential portion of the diaphragm 12. Flexural rigidity is continuously decreased from the high-rigidity region to the low-rigidity region. This causes the resonance peak in the high range to be continuously dispersed.

(24) FIG. 3 shows the frequency characteristics of the speaker 1 according to an aspect of the present disclosure using a solid line. As shown in FIG. 3, there is no sharp peak in a band around 5 kHz whereas a peak is clearly found in the graph indicated by the gray broken line (the frequency characteristics of the reference speaker).

(25) FIG. 3 shows the frequency characteristics of a speaker including an oblique-cone diaphragm (black broken line), and the frequency characteristics of a speaker including a diaphragm with a modified sectional shape (black fine dotted line), although the basic shape of each of the speakers is common to the shape of the speaker 1. The outer shape of the diaphragm with the modified sectional shape has, for example, an S-shaped ridge line, the shape which has eight-fold rotation symmetry around the axis (the line in X1-X2 direction).

(26) In the case of the speaker including the oblique-cone diaphragm, a dip appears with frequencies around 5 kHz. This may be caused by rolling of the diaphragm having an eccentric shape. In the case of the speaker including the diaphragm with the modified sectional shape, a strong peak is found with frequencies around 5 kHz although the intensity thereof is slightly lower than that of the reference speaker. This may be because the diaphragm still has a highly symmetric shape around the axis (the line in the X1-X2 direction).

(27) Illustrative embodiments and implementations of the present disclosure have been described above. However, the present disclosure is not limited thereto. For example, a configuration realized through appropriate addition, omission, and design change of components by a person skilled in the art with respect to the aforementioned embodiments or application examples thereof and a configuration realized through an appropriate combination of the features in the embodiment are included in the scope of the present disclosure provided that such speakers realize the concept of the present invention.

(28) For example, the diaphragm 12 may be a formed article having a laminated structure including the sheet member having the above-described orientation dispersion structure and an exterior sheet. The provision of the exterior sheet improves the design of the diaphragm. However, the weight of the diaphragm is increased, and hence the acoustic characteristics may be decreased (for example, a sound pressure in a high range may be decreased).

(29) It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this disclosure.