JP2004357130A - Diaphragm for speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a miniaturized diaphragm for a speaker having improved acoustic performance at low cost by developing an improved material for the diaphragm based on a mixed material consisting of a woody material subjected to special surface processing and a synthetic resin with good mass-producibility. <P>SOLUTION: The diaphragm for the speaker comprises a mixed material containing a non-chlorine synthetic resin and cellulose powder whose grain size distribution is 5 μm to 500 μm. To give the affinity between the non-chlorine synthetic resin and the cellulose powder, the cellulose powder is subjected to surface treatment. The proportion of the cellulose powder in the mixed material is set in the range of 30 wt% to 70 wt%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a structure of a speaker diaphragm, which is a component having a function of emitting sound waves in a speaker.
[0002]
[Prior art]
Conventionally, a speaker is, as is well known, an electromechanical transducer that converts electrical signal energy into mechanical vibration energy as a main part, and vibrates when driven by mechanical vibration energy output from the electromechanical transducer, A diaphragm that emits acoustic energy. FIG. 1 schematically shows the structure of a diaphragm of such a general speaker together with peripheral members. When a voice coil 3 is attached to the center of the diaphragm 1, the outer periphery of the diaphragm 1 has a flexible edge. 2, and the center of the diaphragm is held by a damper 4 which is also flexible so that it can freely vibrate inside a frame (not shown). The voice coil 3 is inserted in a magnetic field of a magnetic circuit (also not shown). When a signal current is input to the voice coil 3, the center of the diaphragm 1 is driven and vibrates. Emits sound waves.
[0003]
[Problems to be solved by the invention]
At this time, if the outer peripheral portion and the central portion of the diaphragm 1 vibrate in the same phase at all frequencies, the sound pressure frequency characteristics of the reproduced sound are flattened in a normal audible frequency band, and good sound quality is obtained. However, in reality, the diaphragm itself is also flexible, so that when the driving frequency increases, the phase near the outer periphery is delayed with respect to the center, and the center and the outer periphery have opposite phases at a specific frequency. Vibration occurs, and the radiated sound waves cancel each other, resulting in a dip in the frequency characteristics.At a certain frequency, the vicinity of the outer periphery or the unique part of the diaphragm surface resonates strongly and a peak is generated. Sound quality was degraded. In particular, the phenomenon in which the diaphragm 1 splits and resonates in this way is generally an asymmetric bending vibration of the diaphragm material and often causes higher-order harmonic distortion. It is known that the shape of the plate and the physical properties of the material are involved, and in particular, typical physical properties such as density, Young's modulus and tan δ (that is, the mechanical internal loss of the material) greatly affect the frequency characteristics and the level of distortion. Although the direction in which these physical property values are directed is almost being clarified, it is necessary to achieve the technical requirements in actual materials and to improve the flatness of the frequency characteristics to improve the reproduction sound quality. In the design of the above, there was a problem to be solved in that much effort was required for the development of the diaphragm material.
[0004]
Therefore, in order to solve the above problems from the standpoint of diaphragm material, the present invention focuses on synthetic resins having good workability for imparting a shape and cellulosic materials such as wood having excellent physical properties. In addition, it is an object of the present invention to develop a mixed material suitable for a speaker diaphragm from a synthetic resin and a cellulosic powder material, and to provide a speaker diaphragm excellent in acoustic performance and excellent in productivity at low cost.
[0005]
[Means for Solving the Problems]
The speaker diaphragm of the present invention for achieving the above object is formed by molding a mixed material of a non-chlorine synthetic resin and a cellulose powder having a particle size distribution of 5 μm to 500 μm.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
The speaker diaphragm of the present invention for solving the above-mentioned problem (hereinafter, for convenience of explanation, the main body of the diaphragm is abbreviated as diaphragm 1) is made of a non-chlorine synthetic resin and a particle size distribution of 5 μm to 500 μm ( More preferably, the thickness is 10 μm to 400 μm). The non-chlorine-based synthetic resin may be either a thermosetting synthetic resin or a thermoplastic synthetic resin. As the non-chlorine-based synthetic resin, for example, polyolefin-based, polystyrene-based, and polyester-based synthetic resins are generally used. Among them, polypropylene resin is excellent in terms of mechanical properties, easiness of processing, prevention of environmental pollution after disposal, and the like. As the cellulosic powder, a powder of a fibrous material such as wood powder, paper flake, pulp powder, linter powder, bamboo powder, kenaf, jute, bagasse or the like is used. The cellulosic powder is subjected to a surface treatment as required, and its purpose is to increase the affinity by chemically bonding the surface of the cellulosic fibrous material to the synthetic resin. The mixing ratio of the cellulosic powder to the synthetic resin is preferably about 30% to 70% by weight of the mixed material, more preferably 40% to 60% by weight. . If the mixing ratio of the cellulosic powder is too large, fragility appears and becomes unsuitable for some applications.
[0007]
As a surface treatment to be applied to the cellulose powder as needed, for example, it is effective to esterify the cellulose powder substance with a polybasic acid anhydride such as maleic anhydride. By mixing the esterified cellulose-based powder substance with a synthetic resin and a trace amount of an organic peroxide such as benzoyl peroxide, the affinity between the cellulose-based powder and the synthetic resin is increased, and the mixing ratio of the cellulose-based powder can be increased. Not only that, when mixing both materials, even if a large amount of cellulosic powder is mixed, it does not lower the fluidity, so that its production is easy and the moldability is good. ing. Also, when the affinity between the cellulose powder and the synthetic resin increases, not only can the mixing ratio be increased, but even if the synthetic resin to be mixed is a polyolefin-based synthetic resin, it paints products and adheres parts. In this case, painting and bonding can be directly performed only by surface treatment by simple mechanical polishing. As a matter of course, it is needless to say that the adhesion and the stability of the coating film are further improved by performing a plasma irradiation treatment or a primer treatment such as a primer coating as in the normal case.
[0008]
The chlorine-free synthetic resin mixed with the cellulose powder may be a thermoplastic synthetic resin or a thermosetting synthetic resin. However, a polyolefin-based synthetic resin, particularly a polypropylene resin, is suitable from the viewpoints of ease of molding, basic physical properties of the material, material reuse, waste material treatment, material price and the like. The molding is performed by injection molding, but may be of course extrusion molding. In these molding means, a molding machine for general-purpose resin can be used. The molding temperature of the mixed material is suitably in the range of about 160 ° C to 200 ° C. Also, for example, wood flour of cypress is used as the cellulosic powder to be mixed, and the scent of wood can be maintained in the product by controlling the molding temperature within the above range. In this case, it goes without saying that the cellulosic powder to be used may be emphasized or mixed with a synthetic fragrance.
[0009]
In the speaker diaphragm of the present invention described above, the affinity for the synthetic resin molecules is increased by the surface treatment of the cellulosic powder to be mixed. can do. In addition, when the ratio of the cellulosic powder is large, the rigidity of the diaphragm 1 is high. Further, when the diaphragm 1 is bent and deformed as in the case where the diaphragm 1 divides and vibrates, the tan δ ( (Mechanical internal loss) and tan δ of the mixed synthetic resin act effectively to show a large value of tan δ as a whole. The increase in the Young's modulus and the increase in tan δ of the diaphragm 1 described above are not only caused by the fact that the resonance of the diaphragm 1 is unlikely to occur when the speaker is operated and the frequency characteristics are improved, but also the diaphragm due to the division resonance. (1) The level of the non-linear distortion or excessive distortion caused by the bending deformation is reduced, and this has an effect of preventing deterioration of the reproduced sound quality.
[0010]
Also, the fluidity of the mixed material is extremely good due to the increase in the affinity between the cellulose powder and the molecules of the synthetic resin, and a diaphragm having a thickness of about 0.1 mm to 0.5 mm can be molded. In the case of injection molding as a molding means, an ordinary molding machine for general-purpose resin can be used, so that no extra cost is required for capital investment, and there is no difficulty in production because molding conditions are the same as usual. Also, since the fluidity is maintained even if the mixing ratio is large, the production efficiency does not decrease, and the cylinder and screw of the mold and the molding machine are further compared with the case where other inorganic fillers are used. Since the wear is small, the maintenance cost of the equipment can be kept low.
[0011]
With respect to the diaphragm 1 of the present invention, the mixed material constituting the diaphragm main body can be reused, and because it uses a non-chlorine-based synthetic resin, it can be incinerated even when discarded. And little residual ash is generated, so the burden on environmental pollution is small.
[0012]
【Example】
FIG. 1 is a perspective view showing the appearance of the speaker diaphragm of the first embodiment. The diaphragm 1 of the first embodiment is a cone-shaped diaphragm whose outer shape is substantially conical and whose generatrix is curved. The outer periphery is held inside a frame (not shown) by an edge 2 (usually called a free edge) of another member. The voice coil 3 is mounted at the center, and the mounting portion to the voice coil is similarly held inside the frame by the damper 4.
[0013]
The configuration of the speaker diaphragm 1 of the first embodiment is as follows: 1) a polypropylene resin is used as a non-chlorine-based synthetic resin; and 2) 100 parts by weight of wood powder having an average particle size of 200 μm is a maleic anhydride. 3) using benzoyl peroxide as an organic peroxide, 49.5% by weight of the polypropylene resin, 50% by weight of the treated wood powder, and benzoyl veroxide. 0.5% by weight is mixed to form a mixed material for molding, and then 4) the mixed material is molded at a set resin temperature of 190 ° C., and the speaker diaphragm 1 of the first embodiment shown in FIG. Got. In the dimensions of the first embodiment, the diameter D is 100 mm, the thickness near the outer peripheral edge is 200 μm, the thickness near the center is 200 μm, and the diameter d of the voice coil mounting hole at the center is 20 mm. The density of the diaphragm 1 is 1.10 gr / c. c.
[0014]
An edge 2 made of a thin urethane foam resin sheet is attached to the outer peripheral portion of the diaphragm 1 of the first embodiment to produce a prototype speaker (diameter: 12 cm), and the output sound pressure level, the second harmonic level, and the third harmonic The frequency characteristics of the harmonic level were measured. FIG. 2 shows the results. In the figure, the characteristic (a) is the fundamental wave level, the characteristic (b) is the second harmonic level, and the characteristic (c) is the third harmonic level. For comparison, the output sound pressure level, the second harmonic level, and the third harmonic level of a prototype speaker using a comparative example diaphragm having substantially the same shape and dimensions as shown in FIG. The frequency characteristics of the second harmonic level are shown. In the figure, the characteristic (a) is the fundamental wave level, the characteristic (b) is the second harmonic level, and the characteristic (c) is the third harmonic level.
[0015]
FIG. 4 shows the temperature characteristics of the Young's modulus of the diaphragm material, and FIG. 5 shows the temperature characteristics of tan δ. 4 and FIG. 5, the characteristic (a) is a temperature characteristic diagram of the diaphragm material of the first embodiment, and the characteristic (b) is a mixed material of the diaphragm of the present invention having a mixing ratio close to the lower limit of the claims. Temperature characteristic diagram of reference example diaphragm material obtained by mixing 65% by weight of polypropylene resin and 35% by weight of treated wood flour as a model. Characteristic (c) is a comparative example diaphragm made of polypropylene resin mixed with 35% of mica. It is a temperature characteristic diagram of a material. The measurement range of each temperature characteristic is in a range of 0 ° C. to 50 ° C. in consideration of a practical use reference example.
[0016]
According to the result of comparing the various characteristics shown in FIGS. 2 and 3, within the frequency band of 50 Hz to 5 KHz, which is said to have the greatest effect on the audibility, there is no large difference in the sound pressure frequency characteristics of each speaker. The second harmonic level is about 7 dB lower at the peak frequency (about 60 Hz) in the first example diaphragm than in the comparative example diaphragm. Similarly, the third harmonic level is about 3 dB lower at the peak frequency (40 Hz). Such a low level of the higher harmonic means that there is little turbidity when listening to the reproduced sound, and clear and good music reproduction can be obtained. According to the results of a listening test conducted by 30 listeners on the first example diaphragm and the comparative example diaphragm, 23 out of 30 persons evaluated that the first example diaphragm was excellent, and the comparative example diaphragm Were evaluated as excellent, and 5 were judged to be equivalent. The reason why the higher harmonic level of the diaphragm of the first embodiment is lower than that of the comparative diaphragm is because the level of the bending vibration of the diaphragm itself is low due to the difference in the physical property values of the diaphragm material. It seems that there is not. Also, from the temperature characteristic diagrams of the Young's modulus and tan δ shown in FIGS. 4 and 5, the speaker diaphragm of the first embodiment has a small change in its physical property value even when the temperature changes, so that the rigidity of the diaphragm is small. In addition, there is a feature that the fluctuation is small even if the outside air temperature becomes high or low in the resonance suppressing action, and therefore, the reproduced sound quality does not change much depending on the season.
[0017]
Although the embodiments that are considered to be representative of the present invention have been described above, the present invention is not necessarily limited to only the structures of the embodiments, and a method of changing and using a material equivalent to a material and a method of heating a mold are described. It has the above-mentioned constitutional requirements according to the present invention, such as modification of molding means, and can achieve the object of the present invention, and can be appropriately modified and implemented within a range having the following effects. .
[0018]
【The invention's effect】
Since the speaker diaphragm of the present invention described above has an increased affinity for synthetic resin molecules due to the action of the esterification surface treatment of the cellulose-based powder, the cellulose-based powder should be mixed at a relatively large ratio. And exhibits a density, a Young's modulus and a large tan δ suitable for a diaphragm material. The above-mentioned various physical property values are desirable values for the diaphragm because, when the speaker diaphragm is used as a speaker and operated, the unevenness of the peak dip of the divided resonance band of the diaphragm which greatly affects the reproduced sound quality. Is relatively small, the frequency characteristics are nearly flat and the distortion is low, which is evident from the results of the comparative listening test. Further, since the temperature characteristics of the Young's modulus and tan δ of the diaphragm material are good, the timbre is stable with respect to changes in the environmental temperature, and the reproduced sound quality does not fluctuate throughout the season.
[0019]
In the field of manufacturing, the flowability of the mixed material is extremely good due to the increase in the affinity between the cellulose powder and the molecules of the synthetic resin, and a molding machine for general-purpose resins is used for both injection molding and extrusion molding. Since it can be done, not only is there no extra cost for capital investment, but also the molding conditions are the same as usual, so there is no difficulty in production. Even if the mixing ratio is large, the fluidity is maintained, so that the production efficiency does not decrease. In addition, since the wear of the cylinders and screws of the mold and the molding machine can be reduced, the maintenance cost of the equipment can be reduced as compared with the case where other inorganic fillers are used.
[0020]
Further, with respect to the product of the present invention, the mixed material constituting the diaphragm can be reused, and since it is made of a non-chlorine synthetic resin, it can be incinerated even when discarded. Since the generation of ash is small, it has a useful effect that the load on the environment is small.
[Brief description of the drawings]
FIG. 1 is a perspective view of a speaker diaphragm according to a first embodiment.
FIG. 2 is a sound pressure level frequency characteristic diagram and a high-order harmonic level frequency characteristic diagram of a prototype speaker using the diaphragm of the first embodiment.
FIG. 3 is a sound pressure level frequency characteristic diagram and a higher harmonic level frequency characteristic diagram of a prototype speaker using a comparative example diaphragm in which a diaphragm material is changed.
FIG. 4 is a temperature characteristic diagram showing the temperature change of the Young's modulus of the diaphragm material of each of the first embodiment, the comparative example diaphragm, and the reference example diaphragm.
FIG. 5 is a temperature characteristic diagram showing a temperature change of tan δ of each diaphragm material of the first embodiment, the comparative example diaphragm, and the reference example diaphragm.
[Explanation of symbols]
1 diaphragm 2 edge 3 voice coil 4 damper

Claims (8)

A speaker diaphragm made of a mixed material of a chlorine-free synthetic resin and a cellulose powder having a particle size distribution of 5 μm to 500 μm. The speaker diaphragm according to claim 1, wherein a mixing ratio of the cellulosic powder in the mixed material is 30% by weight to 70% by weight. The speaker diaphragm according to claim 1, wherein the non-chlorine-based synthetic resin in the mixed material is a polyolefin-based synthetic resin, a polyester-based synthetic resin, or a polystyrene-based synthetic resin. The speaker diaphragm according to claim 1 or 2, wherein the cellulosic powder is a cellulosic powder that has been subjected to a surface treatment for imparting an affinity to a non-chlorine-based synthetic resin. The speaker diaphragm according to any one of claims 1 to 3, wherein the mixed material is colored by a coloring material. The speaker diaphragm according to any one of claims 1, 2 and 4, wherein the cellulosic powder is a substance having an inherent fragrance, and is molded at a temperature range of 160 ° C to 200 ° C during molding. The speaker diaphragm according to any one of claims 1 to 6, wherein the surface treatment for imparting affinity to the non-chlorine-based synthetic resin to the cellulose-based powder is an esterification treatment with a polybasic acid anhydride. The speaker diaphragm according to claim 7, comprising a mixed material of a chlorine-free synthetic resin, the cellulose powder, and an organic peroxide.

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