Loudspeaker diaphragm, methods for its manufacture and loudspeakers using it

Abstract

Loudspeaker diaphragm (1A, 1B), comprising: a tissue (10) formed into a membrane shape, wherein the tissue (10) has a first surface (10A) and a second surface (10B) on a back side of the tissue (10) to the first surface (10A); a sealing layer (13A, 13B) arranged on the first surface (10A) of the fabric (10), wherein the sealing layer (13A, 13B) seals a mesh opening (10a) which is bounded by warp threads (11) and weft threads (12) of the fabric (10); and a coating (17A) formed from a first composite material (16A) which is a mixture of a plurality of first short nanofibers (14A) and a first plastic (15A), wherein the coating (17A) penetrates the fabric (10) from the second surface (10B) of the fabric (10) to the sealing layer (13A, 13B).

Description

Technical area

[0001] The present disclosure relates to a loudspeaker, a diaphragm included in the loudspeaker, and a method for manufacturing the diaphragm. Technical background

[0002] Loudspeaker diaphragms must be lightweight and not easily permeable. Patent Document 1 discloses a diaphragm comprising a fabric as the base element, microfibers as short fibers layered on the fabric, and a coating. The short microfibers are layered on the fabric using a wet-layering process to seal the structure (mesh openings) of the fabric. The coating covers the surfaces of the short fibers layered on the fabric.

[0003] Patent Document 2 describes a method for manufacturing a speaker diaphragm, comprising the steps of forming a plurality of virtual concentric circles between the center of a circle having a predetermined size and a circumference thereof; dividing each concentric circle at a predetermined angle; forming divided points on the circumference of each concentric circle; and arranging a plurality of threads from one point on the circumference of the circle to another point thereof so as to come into tangential contact with the divided points, thereby forming an omnidirectional pseudo-fabric; thermosetting the pseudo-fabric; and removing a gap formed on the pseudo-fabric using a resin, a film, or a sheet.

[0004] Patent Document 3 describes an acoustic membrane for converting electrical signals into mechanical signals to generate sounds. The acoustic membrane comprises carbon nanotubes or graphite nanofibers as a reinforcing material. Preferably, the carbon nanotubes or graphite nanofibers are contained within the acoustic membrane, dispersed, or coated onto the surface of the acoustic membrane.

[0005] The patent describes a loudspeaker diaphragm consisting of a film of textile fabric or nonwoven fabric made of a thermosetting resin, and a cardboard bonded to the film. Because the cardboard has a layer mixed with thermosetting resin on the film side, there is hardly any gap at the interface between the film and the cardboard.

[0006] Patent Document 5 describes an article on whose surface a relatively thin layer of a compatible polymer is formed, comprising closely spaced, short carbon nanotubes which are more or less uniformly distributed throughout the layer and oriented normal to the article surface.

[0007] Patent Document 6 describes a multilayer composite material comprising a base and a polymer coating layer. The plate-shaped base has a plurality of holes connected in the thickness direction, allowing air to flow through the holes in the thickness direction. The polymer coating layer is laminated to at least one of the top and bottom surfaces of the base body and formed into a nanofiber nonwoven structure. The nanofiber nonwoven structure is provided with irregular micro-holes formed by a plurality of nanofibers interwoven in a mesh. The powder is arranged along the inner side of the nanofibers along the longitudinal direction, forming protrusions.

[0008] With this design, even when a fabric made of stiff fibers with large mesh openings is used as a base element, only the mesh openings on the surface of the fabric can be sealed by the short fibers. Accordingly, it is possible to produce a membrane that is light and resistant to air permeation. BibliographyPatent literature Patent Document 1: Unexamined Japanese Patent Publication No. 2015-43548 A Patent specification 2: US 6,039,146 A Patent specification 3: US 2009 / 0045005 A1 Patent Document 4: JP 2009-027309 A Patent specification 5: DE 10 2012 212 944 A1 Patent specification 7: KR 101292088 B1 Summary of the invention

[0009] To laminate short fibers on a fabric by a wet-lamination process, a laminated material solution in which short fibers are mixed with water at a specific concentration is used. Then, only the water in the laminated material solution is expelled through the mesh openings of the fabric, leaving the short fibers in the fabric. Therefore, Patent Document 1 uses microfibers with an average length of at least one time and at most ten times the average mesh opening of the fabric and an average diameter of 1 μm to 100 μm. Therefore, the short fibers remain on the surface of the fabric during the wet-lamination process, allowing the short fibers to be laminated on the fabric.

[0010] Furthermore, in Patent Document 1, after the short fibers are stacked on the fabric, the surfaces of the short fibers stacked on the fabric are covered with the coating to seal the mesh openings of the fabric more reliably.

[0011] In order to improve the high-frequency characteristics of the loudspeaker, to improve the distortion characteristics by increasing stiffness or to reduce the weight of the loudspeaker, the mesh openings of the fabric as the basic element must be sealed by short fibers with an average diameter of less than 1 µm.

[0012] The present disclosure provides a membrane having a configuration such that when the short fibers having an average diameter of less than 1 µm are stacked on the fabric as a base member, the short fibers are not washed out through the mesh openings of the fabric.

[0013] A first diaphragm according to the present disclosure includes a fabric that is a base member, a sealing layer, and a coating. The fabric has a first surface and a second surface located on a back side of the fabric to the first surface, and is formed into a speaker diaphragm shape. The sealing layer is disposed on the first surface of the fabric and seals mesh openings defined by warp threads and weft threads of the fabric. The coating is formed from a first composite material that is a mixture of a plurality of first short nanofibers and a first plastic. The coating permeates the fabric from the second surface of the fabric to the sealing layer.

[0014] It should be noted that the short nanofibers are short fibers with an average diameter of less than 1 µm.

[0015] A second diaphragm according to the present disclosure includes a fabric, which is a base member, and a sealing layer. The fabric has a first surface and a second surface located on a back side of the fabric relative to the first surface, and is formed into the shape of a loudspeaker diaphragm. The sealing layer is disposed on the first surface of the fabric and seals mesh openings defined by warp and weft threads of the fabric. The sealing layer is formed from a first composite material that is a mixture of the plurality of first short nanofibers and a first plastic.

[0016] In a method for manufacturing the first membrane, the sealing layer is formed on the first surface of the fabric so as to seal the mesh openings defined by the warp and weft threads of the fabric. The fabric is a basic element, and the sealing layer is formed before or after the fabric is formed into the shape of a membrane. In the case where the sealing layer is formed before or after the fabric is formed into the shape of a membrane, the first composite material, which is a mixture of first short nanofibers and the first plastic, is first applied or sprayed onto the second surface of the fabric, which is located on the back side of the fabric to the first surface, so that the first composite material penetrates the sealing layer. Subsequently, the fabric is formed into the shape of a membrane, and the first composite material is dried.Alternatively, after the fabric with the waterproofing layer is formed into a membrane shape, the first composite material is applied or sprayed onto the second surface of the fabric so that the first composite material penetrates the waterproofing layer, and the first composite material is dried. On the other hand, in the case where the fabric with the waterproofing layer is formed into a membrane shape, the first composite material is applied or sprayed onto the second surface of the fabric so that the first composite material penetrates the waterproofing layer, and the first composite material is dried.

[0017] In a method for manufacturing the second membrane, the sealing layer is formed on the first surface of the fabric so as to seal the mesh openings defined by the warp and weft threads of the fabric. The fabric is a base member, and the sealing layer is formed before or after the fabric is formed into the shape of a membrane. To form the sealing layer, a composite material that is a mixture of a plurality of short nanofibers and a first plastic is applied or sprayed onto the first surface of the fabric. Then, in the case where the sealing layer is formed before the fabric is formed into the shape of a membrane, the fabric with the sealing layer is formed into the shape of a membrane.

[0018] Furthermore, a loudspeaker according to the present disclosure includes a magnetic circuit, one of the diaphragms described above, a coil former, and a voice coil. A magnetic gap is provided in the magnetic circuit. The coil former has a first end coupled to the diaphragm and a second end disposed in the magnetic gap. The voice coil is wound around the coil former and disposed in the magnetic gap.

[0019] In such a design, the short nanofibers in the sealing layer or coating permeate the fabric, which is a basic element. Accordingly, the short nanofibers can increase the stiffness and strength of the basic element, extend the upper limit frequency of the loudspeaker, and reduce distortion. Short description of the drawings Fig. 1 is a sectional view of a tweeter including a diaphragm according to a first exemplary embodiment of the present disclosure. Fig. 2A is an enlarged sectional view of the Fig. 1 shown membrane during a manufacturing process. Fig. Figure 2B is an enlarged sectional view of the membrane in a Fig. 2A following manufacturing process. Fig. 2C is an enlarged sectional view of the Fig. 1 shown membrane. Fig. Figure 3 shows a relationship between the percentage of nanofibers and the elastic modulus of the membrane. Fig. 4 shows measurement results of a practical example and a comparison example. Fig. 5 is a frequency response of the speaker membranes. Fig. 6A is an enlarged sectional view of a membrane according to a second exemplary embodiment of the present disclosure during a manufacturing process. Fig. Figure 6B is an enlarged sectional view of the membrane in a Fig. 6A following manufacturing process. Fig. 6C is an enlarged sectional view of the membrane according to the second exemplary embodiment of the present disclosure. Fig. 7A is an enlarged sectional view of a membrane according to a third exemplary embodiment of the present disclosure during a manufacturing process. Fig. 7B is an enlarged sectional view of the membrane according to the third exemplary embodiment of the present disclosure. Fig. 8 is a sectional view of a general double cone speaker. Description of embodiments

[0020] Hereinafter, each embodiment of the present disclosure will be described with reference to the drawings. (First exemplary embodiment)

[0021] Fig. 1 is a sectional view of a tweeter incorporating a diaphragm according to the present invention.

[0022] The loudspeaker includes a soft dome diaphragm 1A, a magnetic circuit 5, a frame 7, a voice coil 8, and a bobbin 9. The diaphragm 1A is manufactured by forming a fabric into the shape of a diaphragm. In the fabric, warp and weft threads intersect each other linearly at a predetermined angle. The magnetic circuit 5 includes a yoke 2, a magnet 3, and a plate 4. A magnetic gap 6 is arranged between the yoke 2 and the plate 4. The frame 7 is attached to the yoke 2 near the magnetic gap 6 and supports the outer periphery of the diaphragm 1A. The bobbin 9 has a first end 9a attached to the back surface of the diaphragm 1A and a second end 9b around which the voice coil 8 is wound. The second end 9b is arranged in the magnetic gap 6.

[0023] Fig. 2C is an enlarged sectional view of the membrane 1A. A sealing layer 13A is disposed on the first surface 10A of the fabric 10, where warp threads 11 and weft threads 12 intersect. The sealing layer 13A seals mesh openings 10a defined by the warp threads 11 and weft threads 12. The coating 17A extends through the fabric 10 from the second surface 10B of the fabric 10 to the sealing layer 13A. The coating 17A is formed from a first composite material 16A, which is a mixture of short nanofibers 14A and plastic 15A.

[0024] It should be noted that nanofibers are fibrous substances with a diameter of at least 1 nm and less than 1000 nm and a length at least 100 times their diameter. Accordingly, the length of each of the short nanofibers 14A is at least 0.1 µm and less than 100 µm. In contrast, the size of each mesh opening 10a is generally between 50 µm and 100 µm. Since nanofibers do not extend linearly, the short nanofibers 14A can sufficiently remain in the mesh openings 10a.

[0025] For example, an air layer 31 is disposed between the upper part of the warp thread 11 and the sealing layer 13A adjacent to the weft thread 12. There are cases where the air layer 31 is formed, and cases where the air layer 31 is not formed due to the interference with the sealing layer 13A and the first composite material 16A. In addition, the air layer 32 is disposed between the lower surface of the warp thread 11 and the first composite material 16A adjacent to the weft thread 12. Similarly, there are cases where an air layer 32 is formed, and cases where the air layer 32 is not formed due to the interference with the first composite material 16A.

[0026] Next, manufacturing processes of the membrane 1A are described with reference to Fig. 2A to Fig. 2C described. Fig. 2A and Fig. 2B are enlarged sectional views of the membrane 1A in respective manufacturing processes.

[0027] Fig. Figure 2A shows an enlarged sectional view of the fabric 10. The warp threads 11 and weft threads 12 of the fabric 10 are, for example, polyester fibers. The thickness of the fabric 10 is, for example, 0.17 mm. It should be noted that the fabric 10 to be used here to manufacture the membrane 1A has a long belt shape before being formed into the shape of a dome membrane.

[0028] In the first step, as in Fig. 2B, a waterproofing agent 18 is applied or sprayed onto the first surface 10A of the fabric 10 so that the waterproofing agent 18 penetrates the mesh openings 10a. The waterproofing agent 18 is, for example, a mixture of phenolic resin and urethane resin. The fabric 10 is thermoformed in this state into the shape of a dome membrane at 190°C to form the waterproofing layer 13A. It is possible to form the waterproofing layer 13A with an appropriate thickness by adjusting the viscosity and supply amount of the waterproofing agent 18, as well as the relative moving speed of the fabric 10 during uniform application of the waterproofing agent 18 by a roller, brush, or spraying.

[0029] In the second step, the first composite material 16A is applied to the second surface 10B of the membrane-shaped Fig. 2B. The first composite material 16A is, for example, a mixture of urethane resin as plastic 15A and short nanofibers 14A. The short nanofibers 14A are produced by milling, for example, bamboo pulp and have an average diameter of less than 1 µm.

[0030] The fabric 10 in this state is heat-dried at 120°C to form the first coating 17A derived from the first composite material 16A. The thickness of the coating 17A is, for example, approximately 10 µm.

[0031] It should be noted that the urethane resin contained in the first composite material 16A is an emulsion containing a solid content of approximately 30% and a hydrophilic solvent (dispersant), such as mainly water or ethanol. The short nanofibers 14A used to prepare the first composite material 16A are in a paste state, and the paste contains a solid content of 8% to 10% and water as a dispersant. The weight ratio of the urethane resin (plastic 15A) to the short nanofibers 14A in the coating layer 17A formed on the fabric 10, from which the solvent has been evaporated, is approximately, for example, urethane resin / short nanofibers = 8 / 2.

[0032] With this configuration, the sealing layer 13A prevents the short nanofibers 14A from being flushed out through the first surface 10A of the fabric 10, even when the average diameter of the short nanofibers 14A of the applied or sprayed composite material 16A is less than 1 µm. Accordingly, it is possible to retain the short nanofibers 14A in the fabric 10.

[0033] In this way, membrane 1A can be sufficiently reinforced by the elasticity of the short nanofibers. Fig. Figure 3 shows experimental results of changes in the elastic modulus of membrane 1A versus the weight percentage of short nanofibers in coating 17A. In the range indicated by the dashed lines, where the percentage of short nanofibers is 21% to 23%, proper elasticity is maintained. Although the elastic modulus of membrane 1A increases with the percentage of short nanofibers, the viscosity of the first composite material 16A increases, resulting in poor processability.

[0034] Fig. 4 shows a frequency response of sound pressure and distortion of a tweeter as a practical example of the present embodiment, which includes a diaphragm 1A with the coating 17A, and a tweeter of a comparative example. Fig. 5 shows the comparison results of the sound pressure frequency response. The tweeter of the comparative example uses a soft dome diaphragm, which is the same as the diaphragm 1A, except that the sealing layer 13A and the coating 17A are missing.

[0035] Due to the coating 17A, the stiffness and strength of the membrane 1A of the practical example are greater than those of the fabric 10, which is a basic element. Therefore, as can be seen from Fig. As can be seen from Figure 4, the tweeter of the practical example exhibits an extended upper limit frequency of the loudspeaker, less distortion of the sound, while maintaining the sound pressure characteristic and thus the higher sound quality, compared to the tweeter of the comparison example. In addition, as shown in Fig. 5, in the practical example the sound pressure is higher and the distortion is lower in the high frequency range of 25 kHz or higher than in the comparison example.

[0036] In the above embodiment, a mixture of phenol resin and urethane resin is used to form the sealing layer 13A; however, any of thermosetting resin and thermoplastic resin may be used as the resin.

[0037] In the above embodiment, water-soluble urethane resin is used to prepare the coating 17A; however, any liquid medium in which short nanofibers are dispersed can be used. Since the short nanofibers are hydrophilic, the plastic contained in the first composite material is also preferably a synthetic resin or elastomer that can be dispersed in water. Specific examples of the plastic contained in the first composite material include polyester resin, olefin resin, acrylic resin, polyamide resin, and latex.

[0038] Although it is described that the ground bamboo pulp is used as short nanofibers 14A, chitin nanofibers from crab shells or the like and synthetic nanofibers can also be used.

[0039] In the above embodiment, the sealing layer 13A is formed before the fabric 10 is formed into a membrane shape; however, the sealing layer 13A may be formed after the fabric 10 is formed into a membrane shape.

[0040] In the above embodiment, the coating layer 17A is formed on the fabric 10 having the sealing layer 13A and formed into a membrane shape; however, the fabric 10 may be formed into a membrane shape after the sealing layer 13A and the coating layer 17A are formed on the fabric 10.

[0041] It is described that the weight ratio of the urethane resin to the short nanofibers in the coating layer 17A is approximately urethane resin / short nanofibers = 8 / 2, for example. However, the weight ratio of the resin to the short nanofibers is not limited to such an example. For example, the sound quality can be improved when the relationship 6 / 4 ≤ urethane resin / short nanofibers ≤ 9 / 1 is satisfied. In particular, when the relationship 7 / 3 ≤ urethane resin / short nanofibers is satisfied, the sound quality can be significantly improved. (Second exemplary embodiment)

[0042] In the first exemplary embodiment, only the coating 17A disposed on the second surface 10B of the fabric 10 contains short nanofibers 14A. In contrast, in the second exemplary embodiment, both the sealing layer and the coating contain short nanofibers.

[0043] Fig. 6C illustrates an enlarged sectional view of a membrane 1B according to the present embodiment. A sealing layer 13B is disposed on the first surface 10A of the fabric 10, in which warp threads 11 and weft threads 12 intersect each other. The sealing layer 13B seals mesh openings 10a defined by the warp threads 11 and weft threads 12. The sealing layer 13B is formed from a second composite material 16B, which is a mixture of short nanofibers 14B and plastic 15B. Furthermore, the coating 17A penetrates the fabric 10 from the second surface 10B of the fabric 10 to the sealing layer 13B. The configuration of the coating 17A is the same as that in the first exemplary embodiment.

[0044] Next, manufacturing processes of the membrane 1B are described with reference to Fig. 6A to Fig. 6C. Fig. 6A and Fig. 6B are enlarged sectional views of the membrane 1B in respective manufacturing processes.

[0045] Fig. 6A is an enlarged sectional view of the fabric 10. The warp threads 11 and weft threads 12 of the fabric 10 are, for example, polyester fibers. The thickness of the fabric 10 is, for example, 0.17 mm. Note that the fabric 10 to be used in manufacturing the membrane 1B here has a long belt shape before being formed into a dome-shaped membrane. In other words, the fabric 10 is the same as that of the first exemplary embodiment.

[0046] In the first step, as in Fig. 6B, the second composite material 16B is applied or sprayed onto the first surface 10A of the fabric 10 such that the second composite material 16B penetrates the mesh openings 10a. In this state, the fabric 10 is thermoformed into a dome shape at 190°C to form the sealing layer 13B.

[0047] The second composite material 16B is a mixture of short nanofibers 14B, phenolic resin, and urethane resin. The second composite material 16B contains a solid content of approximately 30% and a hydrophilic solvent (dispersant), such as primarily water or ethanol.

[0048] The short nanofibers 14B are produced, for example, by grinding bamboo pith and have an average diameter of less than 1 μm. The state of the short nanofibers 14B used to prepare the second composite material 16B is a paste, and the paste contains a solid content of 8% to 10% and water as a dispersant. The weight ratio of the plastic 15B, which is a mixture of phenolic resin and urethane resin, to the short nanofibers 14B in the sealing layer 13B formed on the fabric 10 and from which the solvent was evaporated, is approximately plastic / short nanofibers = 8 / 2, for example. However, similar to the coating layer 17A, the weight ratio of the plastic 15B to the short nanofibers 14B in the sealing layer 13B is not limited to such an example. For example, the sound quality can be improved when the relationship 6 / 4 ≤ plastic / short nanofibers ≤ 9 / 1 is satisfied.

[0049] It should be noted that a part of the short nanofibers 14B may be flushed out through the mesh openings 10a which are in the process of sealing, but by adjusting the viscosity of the resin 15B, a part or all of the short nanofibers 14B remain.

[0050] It is possible to form a sealing layer 13B having an appropriate thickness by adjusting the viscosity and supply amount of the second composite material 16B and the relative moving speed of the fabric 10 when uniformly applying the second composite material 16B by a roller, a brush, or by spraying.

[0051] In the second step, the first composite material 16A is applied to the second surface 10B of the Fig. 6B, which has been formed into a membrane, is applied or sprayed on. In a similar manner to the first exemplary embodiment, the fabric 10 shown in Fig. The first composite material 16A shown in Figure 6C is a mixture of, for example, urethane resin as the plastic 15A and short nanofibers 14A. The short nanofibers 14A are produced, for example, by milling bamboo pulp and have an average diameter of less than 1 µm. The coating 17A is then formed in a manner similar to the first exemplary embodiment.

[0052] With this configuration, the sealing layer 13B also prevents the short nanofibers 14A from being flushed out through the first surface 10A of the fabric 10, even if the average diameter of the short nanofibers 14A in the applied or sprayed first composite material 16A is less than 1 µm. Accordingly, it is possible to retain the short nanofibers 14A in the fabric 10.

[0053] In the tweeter including the diaphragm 1B, due to the sealing layer 13B and the coating 17A, the rigidity and strength of the diaphragm 1B are greater than those of the fabric 10, which is a basic element. Accordingly, the tweeter including the diaphragm 1B exhibits an extended upper limit frequency of the speaker, less distortion while maintaining the sound pressure level, and higher sound quality compared to the tweeter including a diaphragm without the sealing layer 13B and the coating 17A.

[0054] In addition, the adhesion strength of the coating 17A to the fabric 10 is expected to increase by coupling a portion of the short nanofibers 14B in the sealing layer 13B with a portion of the short nanofibers 14A in the coating 17A.

[0055] In the present embodiment, a mixture of phenolic resin and urethane resin is used to form the sealing layer 13B; however, any of thermosetting resin and thermoplastic resin may be used as the resin. However, when selecting the resin to be blended, it is desirable to consider the elastic modulus, dimensional stability, formability, and wettability to the short nanofibers 14B and the fabric 10 after curing.

[0056] Furthermore, the percentage of plastic in the sealing layer 13B is not particularly limited. Furthermore, instead of a mixed plastic, a single type of plastic may be used as the plastic 15B. This also applies to the sealing layer 13A according to the first exemplary embodiment and also to the sealing layer 13B according to a third exemplary embodiment described below.

[0057] Although it is described that the ground bamboo pulp is used as short nanofibers 14A and 14B, chitin nanofibers from crab shells or the like and synthetic nanofibers can also be used.

[0058] Although it is described that the material of the short nanofibers 14A is the same as the material of the short nanofibers 14B, the materials may be different. Specifically, for example, one of the materials may be bamboo nanofibers and the other may be chitin nanofibers. Furthermore, the length and average diameter of the short nanofibers 14A may be the same as or different from the length and average diameter of the short nanofibers 14B.

[0059] It is described that the sealing layer 13B is formed before the fabric 10 is formed into a membrane shape; however, the sealing layer 13B may be formed after the fabric 10 is formed into a membrane shape.

[0060] In the above embodiment, the coating layer 17A is formed on the fabric 10 having the sealing layer 13B and formed into a membrane shape. However, the fabric 10 may be formed into a membrane shape after the sealing layer 13B and the coating layer 17A have been formed on the fabric 10.

[0061] As described above, the membrane 1B according to the present embodiment includes a woven fabric 10 as a base member, a sealing layer 13B, and a coating layer 17A. The coating layer 17A is formed from a first composite material 16A that is a mixture of short nanofibers 14A as a plurality of first short nanofibers and plastic 15A as the first plastic. The sealing layer 13B is formed from a second composite material 16B that is a mixture of short nanofibers 14B as a plurality of second short nanofibers and plastic 15B as the second plastic. The sealing layer 13B is arranged on the first surface 10A of the woven fabric 10 so as to seal the mesh openings 10a. The coating layer 17A penetrates the woven fabric 10 from the second surface 10B of the woven fabric 10 to the sealing layer 13B. (Third exemplary embodiment)

[0062] In the first exemplary embodiment, the sealing layer 13A is disposed on the first surface 10A of the fabric 10, the coating 17A is disposed on the second surface 10B of the fabric 10, and the coating 17A contains short nanofibers 14A. In contrast, in the present embodiment, a sealing layer contains short nanofibers, and no coating 17A is included.

[0063] Fig. 7B is an enlarged sectional view of a soft dome membrane 1C according to the present embodiment. A sealing layer 13B is disposed on the first surface 10A of the fabric 10, in which warp threads 11 and weft threads 12 intersect each other. The sealing layer 13B seals mesh openings 10a defined by the warp threads 11 and weft threads 12. The sealing layer 13B is formed from a second composite material 16B, which is a mixture of short nanofibers 14B and plastic 15B. The second composite material 16B is the same as that of the second exemplary embodiment. In other words, the mixing ratio of short nanofibers 14B to plastic 15B is the same as that of the second exemplary embodiment.

[0064] Membrane 1C can be manufactured according to the following procedures. Fig. 7A is an enlarged sectional view of the fabric 10. The fabric 10 is the same as those in the first and second exemplary embodiments.

[0065] In the first step, as in Fig. 7B, the second composite material 16B is applied or sprayed onto the first surface 10A of the fabric 10 so that the second composite material 16B penetrates the mesh openings 10a, and then the sealing layer 13B seals the mesh openings 10a.

[0066] It should be noted that a part of the short nanofibers 14B of the second composite material 16B may be flushed out through the mesh openings 10a which are in the process of sealing, but by adjusting the viscosity of the resin 15B of the second composite material 16B, a part or all of the short nanofibers 14B remain.

[0067] By changing at least some of the constituent or processing conditions of the second composite material 16B, it is possible to cause the sealing layer 13B to penetrate the fabric 10 more deeply than in the second exemplary embodiment. For example, reducing the viscosity of the second composite material 16B allows the second composite material 16B to penetrate the fabric 10 more deeply.

[0068] In the second step, the fabric 10, which has undergone the sealing process, is thermally formed into a dome at 190 °C.

[0069] The stiffness and strength of the diaphragm 1C are increased by the short nanofibers 14B of the sealing layer 13B, compared to the fabric 10. Accordingly, the tweeter including the diaphragm 1C has an extended upper limit frequency of the loudspeaker, less distortion while maintaining the sound pressure level, and higher sound quality, compared to the tweeter including a soft dome diaphragm without the sealing layer 13B.

[0070] In the above embodiment, the sealing layer 13B is formed before the fabric 10 is formed into a membrane shape. However, the sealing layer 13B may be formed after the fabric 10 is formed into a membrane shape.

[0071] In each of the above embodiments, polyester fibers are used for the fabric 10. Examples of other fibers that can be used for the fabric 10 include chemical fibers other than polyester fibers (such as aramid or liquid crystal polymer), ceramic fibers, carbon fibers, metal fibers, natural fibers (such as cotton or silk), and fiber blends thereof.

[0072] By making the average diameter of the short nanofibers 14A and 14B in each of the above embodiments preferably greater than 0 nm and less than 100 nm, this makes it possible to further increase the rigidity and strength of the diaphragms, further push the upper limit frequency of the loudspeaker, and further reduce distortion. Even better, by making the average diameter of the short nanofibers 14A and 14B in each of the above embodiments preferably greater than 0 nm and less than 20 nm, this makes it possible to significantly increase the rigidity and strength of the diaphragms, further push the upper limit frequency of the loudspeaker, and further reduce distortion. Reducing the average diameter of the short nanofibers can even more significantly improve the performance of the loudspeaker.However, because of the time and multiple steps required for manufacturing, the price of the speaker diaphragm tends to increase. Accordingly, it is important to determine the average diameter of the short nanofibers with a good balance between performance and price requirements for a speaker being developed.

[0073] Although the shape of the diaphragm in each of the above embodiments is a dome shape in the tweeter, it may be the cone shape of a cone speaker. In particular, a diaphragm according to any of the embodiments of the present disclosure may be used as a sub-cone 22 positioned in the center region of a Fig. 8 is arranged. In this case, when the fabric 10 is formed into the shape of a membrane, the fabric 10 is formed into the shape of a cone. Industrial applicability

[0074] The present disclosure contributes to increasing rigidity to improve high frequency characteristics and reduce distortion in a loudspeaker. Reference symbols in the drawing 1A, 1B, 1C membrane 2 yokes 3 Magnet 4 plate 5 Magnetic circuit 6 Magnetic gap 7 frames 8 voice coil 9 coil carriers 9a first end 9b second end 10 fabrics 10a mesh opening 10A first area 10B second area 11 warp threads 12 weft threads 13A, 13B waterproofing layer 14A, 14B short nanofiber 15A, 15B plastic 16A first composite material 16B second composite material 17A coating 18 waterproofing agents 22 Lower cone

Claims

[1] Loudspeaker membrane (1A, 1B), comprising: a fabric (10) formed into a shape of a membrane, the fabric (10) having a first surface (10A) and a second surface (10B) on a back side of the fabric (10) to the first surface (10A); a sealing layer (13A, 13B) arranged on the first surface (10A) of the fabric (10), the sealing layer (13A, 13B) sealing a mesh opening (10a) defined by warp threads (11) and weft threads (12) of the fabric (10); and a coating (17A) formed from a first composite material (16A) which is a mixture of a plurality of first short nanofibers (14A) and a first plastic (15A), wherein the coating (17A) penetrates the fabric (10) from the second surface (10B) of the fabric (10) to the sealing layer (13A, 13B). [2] The loudspeaker diaphragm (1B) according to claim 1, wherein the sealing layer (13B) is formed of a second composite material (16B) which is a mixture of a plurality of second short nanofibers (14B) and a second plastic (15B). [3] The speaker diaphragm (1B) according to claim 2, wherein in the sealing layer (13B), a weight ratio of the second resin (15B) to the plurality of second short nanofibers (14B) is at least 1.5 and at most 9. [4] The loudspeaker diaphragm (1A, 1B) according to any one of claims 1 to 3, wherein in the coating, a weight ratio of the first plastic (15A) to the plurality of first short nanofibers (14A) is at least 1.5 and at most 9. [5] The speaker diaphragm (1B) according to any one of claims 2 to 4, wherein an average diameter of the plurality of first short nanofibers (14A) and the plurality of second short nanofibers (14B) is more than 0 nm and less than 1 µm. [6] The speaker diaphragm (1B) according to any one of claims 2 to 4, wherein an average diameter of the plurality of first short nanofibers (14A) and the plurality of second short nanofibers (14B) is more than 0 nm and less than 100 nm. [7] The speaker diaphragm (1B) according to any one of claims 2 to 4, wherein an average diameter of the plurality of first short nanofibers (14A) and the plurality of second short nanofibers (14B) is more than 0 nm and less than 20 nm. [8] A method for manufacturing a loudspeaker diaphragm (1A, 1B), the method comprising: Forming a sealing layer (13A, 13B) on a first surface (10A) of a fabric (10), the forming taking place before or after the fabric (10) has been formed into a shape of a membrane, the sealing layer sealing a mesh opening (10a) which is delimited by warp threads (11) and weft threads (12) of the fabric (10); when the sealing layer (13A, 13B) is formed before the fabric (10) is formed into the shape of the membrane, (i) applying or spraying a first composite material (16A) onto a second surface (10B) of the fabric (10) such that the first composite material (16A) penetrates to the sealing layer (13A); subsequently forming the fabric (10) into the shape of the membrane and drying the fabric (10), wherein the first composite material (16A) is a mixture of a plurality of first short nanofibers (14A) and a first plastic (15A), and the second surface (10B) lies on a back side of the fabric (10) to the first surface (10A), or (ii) after forming the fabric (10) with the sealing layer (13A, 13B) into the shape of the membrane, applying or spraying a first composite material (16A) onto the second surface (10B) of the fabric (10) such that the first composite material (16A) penetrates to the sealing layer, and drying the fabric (10); and when the fabric (10) has been formed into the shape of the membrane, applying or spraying the first composite material (16A) onto the second surface (10B) of the fabric (10) so that the first composite material (16A) penetrates to the sealing layer (13A, 13B), and drying the fabric (10). [9] A method for manufacturing the loudspeaker diaphragm (1B) according to claim 8, wherein the sealing layer (13B) is formed by applying or spraying a second composite material (16B) onto the first surface (10A) of the fabric (10), the second composite material (16B) being a mixture of a plurality of second short nanofibers (14B) and a second plastic (15B). [10] Loudspeaker, comprising: a magnetic circuit (5) in which a magnetic gap (6) is provided; the loudspeaker diaphragm (1A, 1B) according to any one of claims 1 to 9; a coil carrier (9) having a first end (9a) coupled to the loudspeaker membrane (1A, 1B) and a second end (9b) arranged in the magnetic gap (6); and a voice coil (8) wound around the coil carrier (9).

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