JPS6128278B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electric speaker using a flat diaphragm, and an object of the present invention is to shift the resonance frequency of a resonance mode in which a diameter node occurs in the flat diaphragm to outside the reproduction band, thereby expanding the reproduction band. When a flat diaphragm is allowed to vibrate freely, it vibrates in many complex vibration modes. FIG. 1 shows the node pattern of a resonance mode and the resonance frequency at which the resonance mode occurs when a circular flat diaphragm is caused to freely vibrate. The resonant frequency in Figure 1 is nodal circle 1
The value is shown when the resonance frequency ₁₀ of the vibration mode in which the vibration occurs is set to 1.0. In Fig. 1, the broken lines indicate the nodes of the vibration mode, m is the number of nodal circles, and n
indicates the number of diameter nodes. FIG. 2 shows a conventional electric speaker using a flat diaphragm. In FIG. 2, 1 is a yoke, 2 is a magnet, 3 is a pole piece fixed to the upper surface of the magnet 2, and 4 is a plate having a hole, and there is a gap between the hole edge of the plate 4 and the pole piece 3. An annular magnetic gap is formed. Reference numeral 5 denotes a frame fixed to the upper surface of the plate 4, and a circular flat plate diaphragm 6 is attached to this frame 5.
is supported via an annular edge member 7.
A coil bobbin 8 is fixed to the center of the lower surface of the circular flat diaphragm 6, and a voice coil 9 is wound around the coil bobbin 8. This voice coil 9 is placed in the magnetic gap. 10 is a damper that supports the coil bobbin 8. As shown in FIG. 2, when the coil bobbin 8 is attached to the center of the circular flat plate diaphragm 6 and driven, a vibration mode in which diameter nodes occur does not occur, but only a mode in which nodal circles occur. In the electrodynamic speaker shown in FIG. 2, a coil bobbin 8 having the same diameter as that of the nodal circle is attached to the nodal part of the vibration mode in which one nodal circle is generated on the circular flat plate diaphragm. When driven, the vibration mode in which one nodal circle occurs is removed, and the reproduction band is expanded. However, an electrodynamic speaker using a large-diameter circular flat plate diaphragm requires a large-diameter coil bobbin, making it difficult to drive the speaker in a circular motion. For this reason, conventionally, as shown in FIGS. 3A, B, and C, a plurality of small diameter coil bobbins 8, 8',
A method has been considered in which the coil bobbins 8'' and 8 are fixed to the nodal part a and driven at multiple points.In this way, when a plurality of small diameter coil bobbins are fixed to the nodal part of the flat plate diaphragm 6 and driven. , it is possible to eliminate the mode in which one nodal circle occurs.However, such a multi-point driving method has the disadvantage that a split vibration mode in which the diameter node b occurs at low frequencies.For example, in FIG. , B, and C show the resonance mode of the diameter node that occurs at the lowest frequency when multi-point driving is performed using two, three, and four small coil bobbins 8, 8', 8'', and 8. However, these small coil bobbins are arranged at the position of the nodal circle of the resonance mode produced by one nodal circle, and the vibration mode produced by this one nodal circle is eliminated. When driven with two small coil bobbins 8, 8' as shown in FIG. 3A, a resonance mode appears in which two diameter nodes occur. In general, when driving with n small coil bobbins, n diameter nodes emerge from a resonant mode. As shown in FIG. 1, this resonance frequency occurs at a very low frequency, for example ₀₂ = 0.47. Table 1 shows the resonant frequency constant α _no of a homogeneous free disk
It shows. From this value, the resonance frequency of each vibration mode can be calculated using the following equation. a: Outer diameter of the diaphragm (m) t: Thickness of the diaphragm (m) ρ: Density (Kg/m ³ ) E: Young's modulus (N/m ² ) σ: Poisson's ratio

[Table] As is clear from the above table, even if you try to extend the band by about 4 times by arranging a large number of small coil bobbins on a nodal circle, this split vibration will appear at low frequencies. In order to increase the distributed vibration caused by this diameter node to ₂₀ or more, six or more coil bobbins must be provided. However, providing six or more coil bobbins means that six or more magnetic circuits are required, which is not practical. FIG. 4 shows an electrodynamic speaker in which a plurality of small coil bobbins are attached to the position of a nodal circle in a vibration mode where one nodal circle occurs on the diaphragm. The present invention moves the resonant frequency of the resonant mode in which the diameter node occurs when multiple coil bobbins are driven at multiple points to outside the reproduction band. This will be explained with figures. FIG. 5 shows an electrodynamic speaker according to this embodiment, which is different from the conventional example shown in FIG. 4 in the structure of the flat diaphragm 11. 6 and 7 show the circular flat diaphragm of this embodiment, in which an annular protrusion 12 is formed on the outer periphery of one side of the flat diaphragm 11. FIG. The effect of forming the annular protrusion 12 on the outer periphery of one side of the flat diaphragm 11 to increase the thickness of the outer periphery will be described with reference to Table 2.

[Table] In Table 2, a ₀ indicates the diameter of the diaphragm, and a ₁ indicates the inner diameter of the ring provided on the diaphragm. Table 2 shows the case where the thickness ratio t ₁ /t ₀ = 2.0 and the same material, a ₁ /a
The resonance frequency constants α ₀₃ , α ₀₄ and mass ratio when ₀ is changed are shown. The mass ratio is shown with a homogeneous disk without a ring set to 1. From Table 2, α ₀₃ does not change much depending on (a ₁ /a ₀ ), but the value is larger than α ₀₃ =3.30 for a homogeneous disk. Also, α ₀₄ changes depending on (a ₁ /a ₀ ), but when a ₁ /a ₀ = 0.95, α ₀₄ = 5.88, which is approximately
It can be seen that it can be increased to a value of α ₂₀ . Therefore, in this case, by driving with four small coil bobbins, the reproduction band can be expanded to approximately ₂₀ . FIGS. 8A and 8B show a flat diaphragm according to another embodiment of the present invention. In this embodiment, the flat diaphragm 13
A ring 14 made of a different material is fixed to the outer periphery of one side of the ring. FIG. 9 shows still another embodiment, in which a ring 15 having a triangular cross section is fixed to the outer periphery of one side of the flat diaphragm 13. Each of the above embodiments is an example of an electrodynamic speaker using a circular flat diaphragm, but as shown in FIG. It is a good thing. In FIG. 10, 8 is a coil bobbin, and this coil bobbin 8 is a rectangular flat plate diaphragm 1.
It is fixed at the nodal circle (broken line) that occurs at 6. The present invention has the above-described configuration, and according to the present invention, the resonance frequency of the resonance mode in which the diametral node occurs can be raised to outside the reproduction band of the speaker with a simple configuration, and the reproduction band can be expanded.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the node pattern of the resonant mode during free vibration of a circular flat plate diaphragm, Figure 2 is a cross-sectional view of a conventional electrodynamic speaker, and Figures A, B, and C are diagrams of conventional multi-layer speakers. A diagram showing nodes of a point-driven electrodynamic speaker, FIG. 4 is a sectional view of a co-dynamic speaker, and FIG. 5 is a sectional view of an electrodynamic speaker in an embodiment of the present invention.
FIG. 6 is a perspective view of a diaphragm of a co-dynamic speaker, FIG. 7 is a sectional view thereof, and FIGS. FIG. 9 is a sectional view of a flat diaphragm according to still another embodiment of the invention, and FIG. 10 is a bottom view of a flat diaphragm according to still another embodiment of the invention. 1...Yoke, 2...Magnet, 3...Pole piece, 4...Plate, 5...Frame, 7
... Edge member, 8 ... Coil bobbin, 9 ... Voice coil, 10 ... Damper, 11 ... Flat plate diaphragm, 12 ... Protrusion, 13 ... Flat plate diaphragm, 1
4,15...Ring.

Claims (1)

[Claims] 1. In an electrodynamic speaker in which a plurality of coil bobbins are fixed to the nodal portion of a flat diaphragm and are driven at multiple points,
An electrodynamic speaker including an annular protrusion or ring provided on the outer periphery of one side of the flat diaphragm. 2. The electrodynamic speaker according to claim 1, wherein the inner diameter of the protrusion or ring is 90% or more of the outer diameter of the flat diaphragm.