JPS5947520B2 - Diaphragm for electroacoustic equipment - Google Patents

Description

[Detailed description of the invention] The present invention relates to a diaphragm for a speaker.

Conventionally, speaker diaphragms (hereinafter referred to as diaphragms) are usually made of paper.

However, paper has a specific elastic modulus (E/ρ, E: elastic modulus, ρ
:density) is not so large, diaphragms using this material, especially cone-shaped or dome-shaped diaphragms, have the disadvantage that the sound pressure level at reproduction frequencies, especially in the high-frequency range, is low.

Therefore, a diaphragm with a higher elastic modulus and lower density is desired.

One of them is a diaphragm made by mixing short carbon fibers and pulp and making it into paper (hereinafter referred to as a mixed paper diaphragm).

This composite diaphragm attempts to solve the above-mentioned drawbacks of paper diaphragms by using carbon fiber with a high specific elastic modulus, and it is true that the specific elastic modulus is considerably improved compared to paper diaphragms. are doing.

However, since carbon fiber is rigid, it does not get entangled with paper fibers, and because short fibers are used, the sound speed, which is one of the indicators of high-frequency sound characteristics, is approximately 1,600 m/sec. and that of the paper diaphragm, about 1300
There is not much difference compared to the value of m/sec.

On the other hand, Japanese Utility Model Application Publication No. 51-98535 discloses a so-called unidirectional carbon fiber bundle (multifilament) made by impregnating a B-stage thermosetting resin into a sheet of carbon fiber bundles (multifilaments) arranged parallel to each other. The so-called yarn prepreg is obtained by tearing the yarn prepreg into flat strips along the fiber axis direction to form a fabric as warp and weft yarns, and this so-called textile prepreg is pressurized and heated to form it. A diaphragm made of FRP (hereinafter referred to as an FRP diaphragm) is described.

This FRP diaphragm does not use short fibers like the mixed paper diaphragm described above; in other words, the carbon fibers are continuous, so the sound speed is improved compared to the mixed paper diaphragm.

However, on the other hand, it has the following drawbacks.

That is, in the conventional FRP diaphragm described above, the dead threads constituting the fabric are obtained by tearing a unidirectional prepreg along its fiber axis direction.

However, it is almost impossible to always obtain yarns of constant fineness by tearing unidirectional prepreg, which is a sheet-like aggregate of single yarns with a diameter of several microns.

That is, the warp and weft of the fabric used in this diaphragm has significant unevenness in fineness and is not constant.

Furthermore, since the yarn is impregnated with a sticky B-stage thermosetting resin, normal weaving operations using a loom are extremely difficult.

Even if weaving were possible, it would be almost impossible to arrange the warp and weft yarns at equal density due to the above-mentioned tackiness.

That is, the above-mentioned woven fabric has significant unevenness in the density of the warp and weft yarns, that is, the weaving density.

However, if the fineness or weaving density of the yarn is uneven, the distribution of carbon fibers will not be uniform and the elastic modulus of the diaphragm will differ partially, resulting in asymmetrical split vibrations or The sound pressure level may decrease.

Furthermore, acoustic distortion represented by second-order distortion etc. also increases.

In addition, when a fabric prepreg is constructed by weaving so-called yarn prepreg, there is no resin between the threads, so the surface becomes more uneven. It may remain as a void inside.

If there are voids in the diaphragm, the speed of sound slows down in those areas and the sound becomes distorted.

Additionally, uneven distribution of carbon fibers can result in warping, which can make mounting to a frame or attaching a voice coil difficult.

The purpose of this invention is to solve the above-mentioned drawbacks of conventional diaphragms,
The object of the present invention is to provide a diaphragm with uniform distribution of carbon fibers, little unevenness in elastic modulus, almost no voids, excellent acoustic characteristics, and high productivity.

In order to achieve the above object, the present invention provides a cone-shaped or dome-like structure made by reinforcing resin with at least one woven fabric having an elastic modulus of 15,000 kg/mm2 or more and having carbon fibers of the same fineness as warp and weft yarns. A shaped diaphragm, characterized in that the fabric has warp and weft yarns of equal density, no joints, and four sets of symmetrical planes with respect to the plane containing the axis of the cone or dome. A diaphragm for a speaker is provided.

An embodiment of the diaphragm of the present invention will be described with reference to the drawings, together with a method for manufacturing the cone-shaped diaphragm.

First, carbon fibers (multifilaments) having an elastic modulus of 15,000 kg/mm 2 or more and the same fineness are used as warp and weft yarns, and are woven, for example, in a plain weave.

In this case, the number of weaving yarns is controlled so that the warp yarn density is the same as the weft yarn density, although the weaving efficiency is somewhat lowered.

As a result, in the obtained fabric, the warp and weft yarns have the same fineness, and the warp yarns and the weft yarns have approximately the same density.

The above-mentioned woven fabric is preferably woven so that its bending resistance is 40 or less according to the method specified in JISL 1079, Section 5, 17 A, in order to improve misalignment during molding, which will be described later.

Next, the fabric is cut into a circular shape, and a hole slightly smaller than the inner diameter of the voice coil bobbin is bored in the center thereof.

Next, the perforated circular fabric described above is placed in a desired cone-shaped male mold so that the holes in the fabric align with the center axis of the mold, and the fabric is filled with thermosetting resin containing a curing agent. For example, unsaturated polyester resin or epoxy resin is applied to make the material into prepreg.

That is, a resin is applied to so-called raw fabric to obtain a fabric prepreg, and unlike the fabric prepreg used in the conventional diaphragm described above, a fabric prepreg is not obtained by weaving yarn prepreg.

As a result, the resin/resin has penetrated into the grains of the fabric, and the surface of the fabric prepreg is extremely smooth.

Therefore, there is almost no concern that the woven prepreg will entrap air.

Next, a female mold is placed on top of the woven prepreg,
Apply pressure and heat to harden the resin.

At this time, the warp and weft yarns of the fabric are smoothly displaced at their intersection points.

That is, a weave misalignment occurs, and this weave misalignment allows the fabric to better conform to the cone shape.

Next, the so-called molded product is taken out of the mold and subjected to finishing processing, as shown in Figure 1 (schematic perspective view) and Figure 2 (
As shown in the schematic plan view), a cone-shaped diaphragm is obtained in which the resin 1 is reinforced by an integral carbon fiber plain fabric 2 having no seams, and the warp and weft yarns are regularly arranged.

Thus, in such a diaphragm, the fabric has four sets of planes of symmetry with respect to the plane containing the axis of the cone.

That is, planes AA', BB', and c that include the axis of the cone
-c' and DD', respectively.

As will be described later, even when a plurality of fabrics are stacked one on top of the other, each fabric still has four sets of symmetry planes.

This plane of symmetry is created because the texture of the fabric is uniformly misaligned during forming, and the distribution of warp and weft yarns is uniform and unbiased.

Note that since the diaphragm shown in the drawing uses only one woven fabric, the direction of the fibers in the ridgeline direction is not strictly the same.

In other words, it is slightly anisotropic, but if this becomes a problem, a quasi-isotropic diaphragm can be created by overlapping multiple carbon fiber fabrics with their warp directions shifted by 30 degrees. be obtained.

In the above, instead of placing the raw fabric in the mold, a fabric prepreg formed by impregnating the raw fabric with a B-stage thermosetting resin may be placed.

Also in this case - as above, the surface of the textile prepreg is very smooth, with almost no irregularities.

The dome-shaped diaphragm can also be obtained in exactly the same manner as the cone-shaped diaphragm.

However, since the dome is hemispherical, a carbon fiber fabric cut to a slightly larger size than that used to form a cone-shaped diaphragm is used.

Further, in this case, there is no need to provide a hole in the center.

In this case as well, it goes without saying that the fabric has four sets of symmetry planes.

As explained above, the diaphragm of the present invention is made by reinforcing a resin with a carbon fiber fabric in which the warp and weft yarns have the same fineness and the warp yarns and weft yarns have the same density. The distribution of fibers is uniform and there is very little unevenness in elastic modulus.

Therefore, it is possible not only to prevent the sound pressure level from decreasing in the treble region where asymmetric divided vibrations occur, but also to reduce acoustic distortion.

Moreover, it is not only lightweight and highly efficient, but also has a high speed of sound because the carbon fiber is continuous and unbroken, and its volume content is high.

Furthermore, since the distribution of carbon fibers is uniform, there are few types of configurations, and there is no difficulty in mounting to a frame or attaching a voice coil.

In addition, the diaphragm of the present invention has a manufacturing method different from that of the conventional F
Unlike RP diaphragms, the product is not molded using a woven fabric prepreg made by weaving so-called yarn prepreg, but instead is molded by making a so-called raw fabric into a prepreg.
The surface of the woven prepreg is extremely smooth and has almost no irregularities.

Therefore, there are almost no voids caused by the fabric prepreg entrapping air.

Therefore, it is also possible to prevent the occurrence of acoustic distortion due to the slowing of the speed of sound in the void portion.

Furthermore, the diaphragm of this invention has an elastic modulus of 15,000 kg.
/ mm2 or more, so-called high-elasticity carbon fiber is used, and the carbon fiber is continuous because it is a woven fabric, and the woven fabric has no seams. It has a high elastic modulus, and not only does the sound pressure level decrease less in the high-pitched range, but the sound velocity is also high.

Further, since the diaphragm of the present invention uses a woven fabric, the internal loss is large and the reproduction frequency characteristic is relatively flat.

In other words, a diaphragm is generally deformed by the bending force caused by piston movement, but since woven fabrics have bends (crimps) due to the interlacing of warp and weft yarns, it is difficult to use resin with such woven fabrics. In the reinforced diaphragm of the present invention, bending stress is concentrated at the bent portions of the warp and weft yarns, and a large amount of energy is consumed in those portions.

In other words, a large internal loss occurs due to the shape of the fiber, and this internal loss suppresses resonance and reduces the peaks and valleys in the reproduced frequency characteristics.

Furthermore, the diaphragm of the present invention can be manufactured by applying a resin to a carbon fiber raw fabric placed in a mold, or by making the raw fabric into a prepreg and then pressurizing and heating it with a mold, Since it does not require difficult operations such as weaving yarn prepreg, it not only has good workability but also can be manufactured in large quantities with a constant quality.

Example Carbon fiber "Trading Card" T 300 (number of filaments: 3000) manufactured by Toshi Co., Ltd. is vertically arranged in the horizontal direction at a density of 5 filaments/cm, making carbon fiber plain woven fabric #6343 Then, a woven prepreg was obtained by impregnating it with epoxy resin #2500 for Punri leg, also manufactured by the same company, to a weight of about 42%.

Next, the above woven prepreg was cut into a size of 15 cm square, placed in a mold having a cone-shaped cavity and preheated to about 120°C, and after further preheating for about 4 minutes, it was cut to about 10 kg/cm2. The resin was cured by applying pressure and heating for about 60 minutes under a pressure of 100.degree. C., and the resin was removed from the mold to obtain a cone-shaped diaphragm of the present invention.

This diaphragm has an outer diameter of approximately 86 mm and a voice coil hole diameter of approximately 3
4 mm, and the top angle was about 86°.

When the diaphragm was visually inspected, no morphological defects such as distortions or tears were visible.

It was also observed that the warp and weft yarns were uniformly misaligned, creating four sets of symmetrical planes.

Furthermore, when the cross section was observed using an optical microscope, it was found that the resin had well penetrated between the warp and weft yarns and between the single yarns that constitute them, and there were hardly any voids or areas where there was an excessive amount of resin.

Furthermore, the resin layer on the surface was so thin that it was difficult to see, and the thickness of the diaphragm was almost equal to the thickness of the fabric.

These observation results show that the diaphragm of the present invention not only has a uniform distribution of carbon fibers, but also has few voids, and therefore has little unevenness in elastic modulus, and does not produce asymmetrical split vibrations.
It can prevent the sound pressure level from decreasing in the high frequency range, has low acoustic distortion and morphological distortion, is thin, lightweight, and has high efficiency, has a high volume content of carbon fiber, and has a high specific modulus. This shows that the drop in sound pressure level in the high frequency range is small and the speed of sound is high.

These facts are also supported by the following facts.

That is, when the weight of the diaphragm was measured, it was approximately 2.
It was very light at 5g.

The thickness was approximately 0.23 mm, but considering the thickness of the fabric used (approximately 0.27 mm), this means that the warp and weft yarns were well spread in the resin during molding.

Furthermore, the volume content of carbon fibers is approximately 47%, and the proportion occupied by carbon fibers is very high.

Furthermore, the longitudinal wave propagation velocity, which is an index of sound velocity, was measured on a test piece cut from the above-mentioned diaphragm, and was approximately 3700 m.
/sec, which is actually about 2.3 times the value of about 1600 m/sec for a conventional mixed paper diaphragm.

[Brief explanation of drawings]

1 and 2 are schematic diagrams showing one embodiment of the diaphragm of the present invention, with FIG. 1 being a perspective view and FIG. 2 being a plan view. 1: Thermosetting resin, 2: Carbon fiber plain woven fabric.

Claims (1)

[Claims] 1. A cone-shaped or dome-shaped diaphragm made by reinforcing a resin with at least one fabric whose warp and weft are carbon fibers having an elastic modulus of 15,000 kg/mm or more and having the same fineness, the fabric having a warp and weft. A diaphragm for a speaker, characterized in that the densities of weft threads are equal to each other, there is no joint, and there are four sets of symmetrical planes with respect to a plane containing the axis of a cone or dome.