JPS6134720B2 - - Google Patents

Description

Detailed Description of the Invention The present invention seals a cooling fluid in the magnetic circuit, transfers the heat generated in the voice coil to the magnetic circuit via the cooling fluid, and reduces the temperature rise of the voice coil. An object of the present invention is to provide an electrodynamic speaker in which the enclosed coolant does not splash out due to impact.

FIG. 1 shows a conventional electrodynamic speaker of this type. In Figure 1, 1 is the center pole 2
is a yoke that is integrally formed, and a through hole 3 is formed in the center of the center pole 2 and yoke 1. 4 is an annular magnet bonded to the yoke 1; 5 is an annular yoke bonded to the upper surface of the magnet 4; an annular magnetic field is formed between the inner peripheral surface of the yoke 5 and the outer peripheral surface of the center pole 2; A void is formed. 6 and 6' are the center poles 2 above, respectively.
This is an annular groove formed on the outer peripheral surface of the yoke 5 and the inner peripheral surface of the yoke 5, and the magnetic gap is divided into two by the annular grooves 6 and 6'. 7 is an annular frame fixed to the upper surface of the yoke 5;
A diaphragm 8 is supported on. A coil bobbin 9 is fixed to the diaphragm 8, and a voice coil 10 is wound around the coil bobbin 9. Reference numeral 11 denotes a magnetic fluid filled in the outer magnetic gap of the two divided magnetic gaps. This magnetic fluid 11
is a colloidal dispersion of magnetic ultrafine particles such as iron oxide in a nonvolatile solvent. Reference numeral 12 denotes a cooling liquid stored in the magnetic circuit, and the cooling liquid has excellent heat transfer properties such as ethylene glycol, propylene glycol, higher alcohol, glycerin aqueous solution and is incompatible with the magnetic fluid 11, such as higher alcohol, glycol, glycerin, water, or the like. Mixtures thereof etc. are used. This coolant 12 is a magnetic fluid 1
1 and enclosed within a magnetic circuit.
13 is a hole formed in the yoke 1;
3 is fitted with a pipe 14. This pipe 1
4 is for releasing thermal expansion of the cooling liquid 12.

In FIG. 1, when an audio signal is applied to the voice coil 10, the coil bobbin 9 and the diaphragm 8 vibrate together to produce sound.

The heat generated in the voice coil 10 is transmitted to the magnetic circuit having a large heat capacity via the coolant 12, thereby preventing the temperature of the voice coil 10 from rising.

However, the above-mentioned conventional electrodynamic speaker has a drawback that the cooling liquid 12 is thrown out of the magnetic circuit due to impact. When the electrodynamic speaker shown in FIG. 1 is dropped from a height of, for example, 15 cm with its diaphragm 8 facing down, the force Mα, the product of the acceleration α of the impact and the mass M of the coolant 12, is applied to the magnetic fluid 11. , the sealing force of the magnetic fluid 11 is broken, and the coolant 12 jumps out and adheres to the inside of the diaphragm 8 . If the amount of the coolant 12 that has flown out is large, the mass of the vibration system becomes large and the sound pressure level decreases. Furthermore, if the falling distance is large, the magnetic fluid 11 will also fly out together with the coolant 12, and the sealing function of the coolant 12 will be lost, causing the coolant 12 to leak. The sealing force of the magnetic fluid 11 is proportional to the product of the saturation magnetic flux density of the magnetic fluid 11 and the magnetic flux density of the magnetic gap.
1 saturation magnetic flux density from current 100 Gauss to 325 Gauss
Although it is possible to make it larger, increasing the saturation magnetic flux density of the magnetic fluid 11 increases the viscosity and increases the mechanical resistance, which is not practical. It is also possible to improve the sealing force by increasing the magnetic flux density of the magnetic gap, but the magnetic saturation of the iron forming the yoke is 15 to 20 KGauss, so the magnetic flux density of the magnetic gap should be increased to 15 to 20 KGauss or more. It cannot be done. It is also possible to reduce the mass M of the coolant 12 in order to reduce the impact force, but if the amount of the coolant 12 is small, it may be caused by slight evaporation of the coolant 12 or by variations in the amount of the coolant 12 filled. , the voice coil 10 will not enter the coolant 12, and the temperature of the voice coil 10 will increase significantly.

On the other hand, if even an instantaneous large inertial force caused by an impact can be prevented, the cooling liquid 12 can be prevented from flying out by the sealing force of the magnetic fluid, that is, the holding force in the magnetic gap. For example, with viscoelastic materials, there is a time delay in the transmission of force, so the instantaneous peak value due to impact is reduced. The reason why the sealing force against impact force increases as the viscosity of the magnetic fluid increases is as described above.

However, in order to reduce the mechanical resistance to vibration of the coil bobbin 9 and voice coil 10, it is not possible to increase the viscosity of the magnetic fluid.
The viscosity must be less than 1000 centipoise,
The viscosity of the coolant 12 in contact with the voice coil 10 is preferably 200 centipoise or less so that the sound pressure decreases within -1 dB.

As described above, the splashing of the coolant can be prevented by increasing the viscosity of the coolant or magnetic fluid, but in order to reduce the drop in sound pressure, the viscosity cannot be increased too much.

The present invention eliminates the above-mentioned drawbacks of the conventional art, and one embodiment of the present invention will be described below with reference to FIG. 2.

In FIG. 2, reference numeral 15 is an annular porous body made of a non-magnetic material, and this porous body 15 is located in a space within the magnetic circuit surrounded by the center pole 2, magnet 4, and yokes 1 and 5. It is stored. Note that one inner peripheral edge of the annular porous body 15 is cut out to prevent vibration of the coil bobbin 9 from being prevented by the porous body 15. The porous body 15 is a sintered metal made by sintering powder of aluminum, copper, etc.
Made of foam metal or ceramic material such as aluminum oxide.

After filling the magnetic gap with the magnetic fluid 11, when the coolant 12 is filled through the pipe 14, the porous body 15
A cooling liquid 12 is filled in the air holes and the space around the voice coil 10 .

For example, the porosity of the porous body 15 formed by molding aluminum powder and sintering it at a temperature slightly lower than its melting point is
It is 30 to 50%, and a large amount of the cooling liquid 12 can be absorbed. In addition, foamed metal such as foamed copper can have a porosity of 90% or more, which further increases the amount of coolant absorbed.

In this way, the porous body 15 is housed and the cooling liquid 1
In the case where most of Because of the viscous resistance and because the mass of the coolant 12 directly applied to the magnetic fluid 11 becomes smaller, the coolant 12 due to the impact
This prevents the material from jumping out to the outside. Note that the diameter of the pores in the sintered metal is 0.1 mm or less, which is smaller than the diameter of 0.1 to 0.3 mm in the pores in the foamed metal, and is more effective in preventing the coolant 12 from splashing out.

FIG. 3 shows a second embodiment of the invention.
In this embodiment, the shape of the porous body 15 is annular with an L-shaped cross section, and the amount of material for the porous body 15 can be reduced.

FIG. 4 shows a third embodiment of the invention.
This embodiment is a modification of the embodiment shown in FIG. 2 in which a heat transfer rod 16 made of copper or aluminum is passed through the yoke 1 and bonded to the porous body 15, and a heat sink 17 is attached to the heat transfer rod 16. According to this embodiment, the heat dissipation efficiency of the cooling liquid 12 is increased.

Note that it is also possible to use a heat pipe as the heat transfer rod 16 in the embodiment shown in FIG. A heat pipe is a pipe made of aluminum, copper, etc., in which easily vaporized fluorocarbons, water, or the like is sealed under reduced pressure, and has excellent thermal conductivity.

FIG. 5 shows a modification of the embodiment shown in FIG. 4, in which a horn 18 made of cast aluminum is attached to the yoke 1, one end of a heat transfer rod or heat pipe 16 is connected to the horn 18, and the horn 18 is also used as a heat sink. This is what I did. In FIG. 5, 19 is an equalizer, 2
0 is a container.

FIG. 6 shows a fifth embodiment of the invention.
In FIG. 6, reference numeral 21 denotes a cylindrical porous body placed on the center pole 2 side of the space within the magnetic circuit, and this porous body 21 is made of a non-magnetic porous solid such as ceramic. The side end face is 0.1
It is corrugated to a height of ~1 mm to allow cooling fluid to flow through it. Reference numeral 22 denotes a porous sponge (porous body) made of a polymer or the like, which is housed in a space on the outer periphery of the porous body 21, and the cooling liquid 12 is absorbed into the porous body 21 and the sponge 22. ing.

FIG. 7 shows a sixth embodiment of the present invention, in which the space in the magnetic circuit is partitioned by a punching metal 23, and a sponge 22 is housed on the yoke 1 side, and this sponge 22 also absorbs the cooling liquid 12. This is what has been done.

In each of the above embodiments, the pipe 14 is provided, but this pipe 14 may be omitted.

The present invention has the above-mentioned configuration, and according to the present invention, most of the coolant sealed in the magnetic circuit is absorbed by the porous body housed in the magnetic circuit, so that no impact is applied. This has the advantage that the coolant will not spill out even if the

[Brief explanation of the drawing]

Figure 1 is a sectional view of a conventional electrodynamic speaker, Figure 2 is a cross-sectional view of a conventional electrodynamic speaker.
7 to 7 are cross-sectional views of electrodynamic speakers according to embodiments of the present invention. 1... Yoke, 2... Center pole, 3...
Through hole, 4... Magnet, 5... Yoke, 6, 6'...
...Annular groove, 7...Frame, 8...Diaphragm, 9...
...Coil bobbin, 10...Voice coil, 11...
...Magnetic fluid, 12... Coolant, 13... Hole, 14
... Pipe, 15 ... Porous body, 16 ... Heat transfer rod, 17 ... Heat sink, 18 ... Horn, 19 ...
Equalizer, 20... Container, 21... Porous body,
22...Sponge (porous material), 23...Punching metal.

Claims (1)

[Claims] 1. A magnetic circuit having an annular magnetic gap and an internal space that communicates with the magnetic gap, a magnetic fluid that fills the magnetic gap and seals the coolant stored in the internal space, and a non-magnetic porous body that is housed in and absorbs the coolant, and a voice coil that is disposed in the magnetic gap, and is configured to prevent the coolant from flying out of the magnetic gap due to impact. An electrodynamic speaker made up of