JPS623987Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an improvement of a dust cap for a speaker.

As shown in FIG. 1, the speaker dust cap 31 is attached to the base of the diaphragm 32 of the speaker or the upper end of the coil bobbin 33, and usually has a dome shape.

The dust cap 31 originally serves to prevent dust from entering the magnetic gap 34 in the air, but other functions include reinforcing the rigidity of the base of the diaphragm 32 to prevent bell vibration and vibration. It also has the function of vibrating together with the plate 32 and emitting sound waves.

Therefore, the dust cap 31 not only prevents the intrusion of dust, but also has a strong rigidity because it has a reinforcing function.Like the diaphragm 2, the dust cap 31 is lightweight and has high rigidity because it acts as an acoustic radiation surface. A large loss is required.

From this point of view, attempts have been made to achieve the above requirements by using various materials such as pulp fibers, synthetic fibers, metals, etc., and by combining these materials to form composite structures.

However, since weight reduction, stiffness, and internal loss are fundamentally contradictory requirements, the reality is that these three requirements cannot be fully satisfied.

For example, an example of a dust cap using pulp fibers has a Young's modulus of 2×10 ^{10 dyn} /cm ² .
The tan δ is about 0.03, and the diaphragm using carbon fiber has a Young's modulus of 4.3 × 10 ^{10 dyn} / cm ² and the tan δ is about 0.03.
It is about 0.047.

Also, carbon fiber has a relatively large Young's modulus, but
On the other hand, as a result of the high density, the weight of the vibration system increases, and as a result, the second moment of area (Eh3/
12 However, the values of E: Young's modulus and h: thickness of the diaphragm become extremely small.

Furthermore, some metal materials are relatively lightweight and have high rigidity, but have the disadvantage of extremely low internal loss.

Therefore, this idea uses a non-woven fabric made of fibers such as polyester, polypropylene, acrylic, etc. as a base, and has an adhesive layer on both sides of the fabric made of EVA (ethylene vinyl alcohol), polyethylene, etc., which has a high internal loss and has heat-fusible properties. By bonding a fiber layer made of carbon fiber or carbon/pulp mixed fiber bound with phenolic resin,
This is a dust cap that is lighter in weight, has higher rigidity, and has greater internal loss than the conventional dust cap.Examples will be described in more detail below.

In Figure 1, 1 is a nonwoven fabric made of polyester fibers bound with phenolic resin, with a density of 0.045 g/cm ³ ,
The thickness is 5 mm.

Reference numeral 2 is an EVA film with a thickness of 200 μm, and reference numeral 3 is a fiber layer made by mixing 8 parts of carbon fiber with 2 parts of pulp fiber and binding with phenol resin, which has a denser fiber density than the nonwoven.

Then, centering on nonwoven fabric 1, on both sides
The EVA film 2 and the fiber layer 3 are respectively arranged and heated and pressed in a dome-shaped mold as shown in FIG.

At this time, the nonwoven fabric and the fiber layer are formed into a dome shape, and the EVA film is bonded to the heat-adhesive property, resulting in an integrated dust cap as shown in FIG.

As a result of measuring the physical properties of the dust cap, the density ζ = 0.25 g/cm ³ , Young's modulus E = 3.79 ×
A value of 10 ^{9 dyn} /cm ² and tan δ = 0.126 (based on the vibration reed method) was obtained.

This can reduce the density to about 1/2 to 1/4 and increase tan δ by about 3 times compared to the conventional dust cap.

In addition, the value of the second moment of area (Eh3/12), which is a guideline for the stiffness mentioned above, is 1.2 to 3.3 × for pulp fibers.
In contrast to the value of 1 to 4.8×10 ⁵ for 10 ⁶ carbon fiber, the dust cap of this invention was able to obtain a value of 9.4×10 ⁷ .

This is because this idea uses a nonwoven fabric made of synthetic resin fibers with extremely low density and large internal loss as an intermediate layer, and a highly rigid fiber layer with heat-fusible resin film layers with large internal loss on both sides. By forming this, a large internal loss can be imparted due to the internal loss of the nonwoven fabric and the internal loss of the adhesive layer, and high rigidity can be imparted by the fiber layer and the specificity of the laminated structure together with the material itself. It becomes possible to increase the moment of inertia of area by reducing the overall apparent density.

Therefore, a speaker equipped with a dust cap based on this invention can reduce the weight increase of the vibration system, improve conversion efficiency, and minimize deterioration, and due to its high rigidity, it can vibrate in the same phase as the speaker's diaphragm. The effect of suppressing high-frequency resonance due to internal loss suppresses mutual interference in the high-frequency resonance frequency band, making it possible to obtain even sound pressure frequency characteristics as the reproduction frequency band expands. In addition to being extremely useful, it also has the advantage of being extremely simple to manufacture since adhesion and shaping are performed in one press step.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the manufacturing process of the dust cap of this invention, FIG. 2 is a sectional view of the dust cap of this invention, and FIG. 3 is a sectional view of the speaker.

Claims (1)

[Scope of utility model registration request] It is characterized by having a nonwoven fabric made of synthetic fibers as a base, and a fiber layer made of carbon fibers or carbon and pulp mixed fibers bound with phenol resin bonded to both sides of the base via a thermoplastic resin adhesive. Dust cap for speakers.