JPS6231877B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a diaphragm used in electroacoustic transducers such as speakers and microphones. In general, the material of the diaphragm used for speakers etc. is lightweight, has a large specific modulus of elasticity E/ρ, and bending rigidity E/I (where E is Young's modulus, ρ is the density, I
(second moment of area) and internal loss tanδ. In other words, the larger the specific elastic modulus E/ρ, the higher the resonance frequency and the larger the piston motion range, which widens the frequency band of the speaker.The larger the bending stiffness E/I, the lower the distortion and the internal loss tanδ. The larger the value, the lower the Q value of the divided resonance of the diaphragm, which makes it possible to flatten the characteristics (no coloration in the reproduced sound). Therefore, the selection of materials is a major issue, but conventionally, in addition to paper, light metals with high Young's modulus, such as aluminum (Al) and boron, have been used.
Foil films made of ceramics such as (B), beryllium (Be), magnesium (Mg), titanium (Ti), or alumina (Al ₂ O ₃ ) have been used. However, the paper has a major drawback in that the specific elastic modulus E/ρ is small. On the other hand, although light metals have a relatively large E/ρ, their internal loss tan δ is very small, less than 0.01. Therefore, the internal loss of the entire diaphragm is small, resulting in a peak and dip in the frequency response, which is good. It is not possible to obtain suitable frequency characteristics,
Moreover, it had the disadvantage of causing coloration in the sound quality. On the other hand, although ceramics have the major characteristics of having a large E/ρ and being inexpensive,
Because it is brittle, there are problems with workability and handling. Thus, no matter which material is used, there are advantages and disadvantages, and it has not yet been possible to obtain a satisfactory diaphragm. This invention was made in view of the above circumstances,
The present invention provides a diaphragm for an electroacoustic transducer that improves the specific elastic modulus and internal loss of the entire diaphragm and makes it possible to obtain good frequency characteristics without coloring the reproduced sound. The core material and the skin material attached to at least one surface of the core material are formed of a composite material composed of reinforcing fibers and a closed foam resin matrix having mutually independent and discontinuous cells. It is in. Hereinafter, the present invention will be explained in detail based on embodiments shown in the drawings. FIG. 1 is a longitudinal section showing an embodiment of a speaker equipped with a diaphragm according to the present invention. In the figure, a speaker 1 includes a magnetic circuit assembly consisting of a pole piece 2, a magnet 3, and a top yoke 4, a vibration system assembly consisting of a diaphragm 6, a voice coil bobbin 7, a voice coil 8, etc., and a frame 5.
It is made up of. The pole piece 2 is provided with an annular bottom yoke 9 integrally provided on the outer periphery of one end, and the magnet 3 and top yoke 4 are sequentially stacked coaxially on the bottom yoke 9, and are bonded with adhesive. are integrally connected. The diaphragm 6 has a honeycomb structure made of a material to be described later, and its peripheral portion is fixed to the upper opening edge of the frame 5 via an edge 10.
Note that 11 is a gasket. On the other hand, the voice coil bobbin 7 has one end glued to the back surface of the diaphragm 6, the other end inserted into the magnetic gap 12 formed between the pole piece 2 and the top yoke 4, and the voice coil bobbin 7 on the outer peripheral surface of the other end. 8 is wound. Therefore, when a signal current is applied to the voice coil 8, the voice coil bobbin 7 is driven to vibrate the diaphragm 6. In the above embodiment, the diaphragm 6 includes a honeycomb core (core material) 13 made of aluminum foil in which honeycomb-shaped chambers, that is, many small hexagonal chambers (cells) are formed, and a honeycomb core (core material) 13 made of aluminum foil, and Adhesives not shown (adhesive film, etc.)
A honeycomb structure is formed by bonding the skin material 14 through the reinforcing fibers 16, as shown in FIG.
A composite material made of fiber reinforced plastic (FRP) to which a closed foam resin 15 having mutually independent and discontinuous cells is provided as a matrix is used. Note that the matrix here refers to a base material that bonds reinforcing fibers. Foamed resins include thermosetting resins such as epoxy resins, unsaturated polyester resins, phenolic resins, and polyimide resins, as well as polyamide resins, polyester resins, polypropylene resins, polystyrene resins,
Thermoplastic resins such as polyvinyl chloride resin, acrylonitrile, butadiene/styrene resin are used. Then, when molding the skin material 14, these resins are foamed using a foaming agent to form a closed foam resin 15 having mutually independent and discontinuous cells.
For example, azodicarbonamide and dinitrolibentamethylenetetramine are suitable as blowing agents for epoxy resins. On the other hand, the reinforcing fibers 16 of the closed foam resin 15 include carbon fiber, glass fiber, silicon carbide fiber,
High strength materials such as boron fibers, graphite fibers, organic high modulus fibers (e.g. aromatic polyamide fibers),
High modulus fibers are used, and carbon fibers are particularly preferred. These fibers usually have a diameter of several microns to more than ten microns, but are not necessarily limited to woven fabrics and may be non-woven fabrics. Next, the physical properties of the skin material according to the present invention and the conventional skin material are shown in a table.

【table】

[Table] However, foamed carbon fiber (foamed CFRP) is made by impregnating reinforcing carbon fiber with the above-mentioned foamed resin, and foaming and molding this using a foaming agent. Figure 3 shows the fiber volume content Vf, matrix resin volume ratio Vm, and bending Young's modulus E of foamed CFRP.
The symbol ● in the figure indicates E≧6(×
The distribution of 10 ¹³ dyn/cm ² ) is 5 (×10 ¹³ dyn/cm 2 ).
cm ² )≦E<6 (×10 ¹³ dyn/cm ² ), and the ○× marks indicate the distribution state of E<5 (×10 ¹³ dyn/cm ² ). In addition, Figure 4 shows the fiber volume content of foamed CFRP.
This figure shows the relationship between Vf and Young's modulus of bending E. As is clear from the above table, when the skin material 14 is made of a composite material such as foamed carbon fiber (foamed CFRP), although the density ρ and Young's modulus E are somewhat lower than that of aluminum (Al), the specific elasticity Since the ratio E/ρ is about 2.5 times larger, a good reproduction frequency band can be obtained as a diaphragm. Further, since this composite material has a large internal loss tan δ, the Q value of the divided vibration of the diaphragm 6 is reduced, and a frequency characteristic with a small peak and dip can be obtained. Therefore, the frequency characteristics are flattened, and the reproduced sound is no longer colored. Moreover, the structure is simple and can be manufactured at low cost, the materials can be selected for the core material and the skin material, and the design has a large degree of bending, making it suitable as a diaphragm. Also,
The diaphragm 6 made of a honeycomb structure is light and has strong bending rigidity, and has the great advantage that it does not deform itself during vibration. FIG. 5 is a longitudinal sectional view showing another embodiment of the invention. In this embodiment, a core material 13' is formed of a foamed resin such as styrene foam, and skin materials 14 made of the above-mentioned material are adhered to the display surface of this core material 13', so that the diaphragm 6' has a sandwich structure. This embodiment is different from the above-mentioned embodiment, and all other components are the same, so the same reference numerals are used to indicate the same constituent members and the explanation thereof will be omitted. As explained above, according to the diaphragm for an electroacoustic transducer according to the present invention, the skin material attached to at least one surface of the core material made of a honeycomb core or a foamed resin is combined with reinforcing fibers in a discontinuous manner independent of each other. Since the diaphragm is made of a composite material composed of a closed foam resin matrix having cells of 1 to 1, the specific modulus of elasticity and internal loss of the diaphragm itself can be improved. As a result, the frequency band is expanded, and the reproduced sound has good frequency characteristics with no coloration.The effect is very large.In addition, the structure is simple and can be manufactured at low cost, and the material can be freely selected. It has various effects such as high power.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of a speaker using a diaphragm for an electroacoustic transducer according to the present invention;
Figure 2 is an enlarged perspective view of the main parts of the skin material, Figure 3 is a diagram showing the relationship between the fiber volume content Vf of foamed CFRP, the matrix resin volume ratio Vm, and the bending Young's modulus E, and Figure 4 is the fiber of foamed CFRP. FIG. 5, which is a diagram showing the relationship between the volume content Vf and the bending Young's modulus E, is a longitudinal sectional view of a speaker showing another embodiment of the present invention. 6, 6'... Vibration plate, 13... Honeycomb core (core material), 13'... Core material (foamed resin), 14...
...Skin material, 15...Closed foam resin, 16...Reinforcing fiber.

Claims (1)

[Scope of Claims] 1. A diaphragm for an electroacoustic transducer comprising a core material and a skin material coated on at least one surface of the core material, wherein the skin material comprises reinforcing fibers,
A diaphragm for an electroacoustic transducer, characterized in that it is a composite material composed of a closed foam resin matrix having mutually independent and discontinuous cells. 2 The reinforcing fiber is carbon fiber, glass fiber,
The diaphragm for an electroacoustic transducer according to claim 1, wherein the diaphragm is made of any one of graphite fiber, silicon carbide fiber, boron fiber, and organic high modulus fiber. 3. The diaphragm for an electroacoustic transducer according to claim 1, wherein the core material is a honeycomb core. 4. The diaphragm for an electroacoustic transducer according to claim 1, wherein the core material is a foamed resin having mutually independent discontinuous cells or continuous cells.