JPS5838716Y2 - electrodynamic speaker - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electrodynamic speaker that can reduce the temperature rise of the voice coil.

FIG. 1 shows a conventional electrodynamic speaker of this type.

In FIG. 1, 1 is a yoke formed integrally with the center pole 2, 3 is an annular magnet fixed to the yoke 1,
Reference numeral 4 denotes an annular yoke fixed to the magnet 3, and an annular magnetic gap is formed between the inner circumferential surface of the yoke 4 and the outer circumferential surface of the center pole 2.

Reference numeral 5 denotes a frame fixed to the yoke 4, and a flat diaphragm 6 is supported in a hole of the frame 5 by an annular edge member 7.

The flat diaphragm 6 has an aluminum honeycomb core material, and surface materials are bonded to both sides of the core material.

A coil bobbin 8 is fixed to one side of the flat diaphragm 6, and a ventilation hole 9 is formed in the coil bobbin 8.

Reference numeral 10 denotes a voice coil wound around the coil bobbin 8, and this voice coil 10 is located in the magnetic gap section.

11 is a magnetic fluid filled in the magnetic gap.

In FIG. 1, when an audio signal is applied to the voice coil 10, the coil bobbin 8 and the flat diaphragm 6 vibrate together,
radiate sound.

When a large input is applied to the voice coil 10, the voice coil 10 generates heat, but the heat of the voice coil 10 is transmitted to the yoke 4 or the center pole 2 via the magnetic fluid 11 that comes into contact with the voice coil 10, and is dissipated. be done.

Therefore, the temperature rise in the voice coil 10 is reduced, the input resistance of the speaker is improved, and the maximum output sound pressure is improved.

The magnetic fluid 11 is made of Fe3O4 in a nonvolatile solvent.
The surface of ferromagnetic fine particles having a diameter of 300 A or less is coated with a surfactant and is dispersed in a colloidal form.

The ferromagnetic fine particles are attracted and held in the gap by the magnetic field in the magnetic gap while attracting the surrounding dispersion solvent.

Various materials are generally used as dispersion solvents for magnetic fluids, such as hydrocarbons, water, kerosene, liquid paraffin, fluorocarbons, ester oils, and mineral oils. A solvent with low mechanical resistance is required, and a solvent with low vapor pressure and low viscosity is preferred, and of course, the higher the thermal conductivity, the better.

Practically speaking, lower vapor pressure is given top priority in terms of reliability, so higher fatty acid esters such as diesters are used.

Esters are obtained by esterifying acids and alcohols, and esters with various characteristics can be synthesized by combining acids and alcohols, so there is a large degree of freedom in selection.

For example, dioctyl sebacate C8H1700C(CH2)8COOC8H1□ (melting point = 55°C, vapor pressure 4mmHg temperature 248°C, viscosity 1
9.9 centipoise) and diisooctyl azelaate H
17C800C(CH2)7COOC8H17 (melting point -
40℃, vapor pressure 5mmHg temperature 237℃, viscosity 20 centipoise) and diisooctyl adipate (freezing point -7
Temperature 215°C, viscosity 17.7 at 0°C, vapor pressure 4mmHg
centipoise) and have low vapor pressure even at high temperatures and are highly reliable.

The above viscosity is the viscosity at 20°C. Expressing the above three examples in molecular formula, dioctyl sebacate C26H5oO
4. Diisooctyl azelaate C2,H4804 and diisooctyl adipate C22H4204, which are the reaction of a fatty acid with a large number of carbon atoms and a higher alcohol.Both have boiling points between 300 and 400℃, which is higher than silicate esters and have a higher vapor pressure. low.

Furthermore, it has a melting point of -40 to -70°C, so it can be used even in cold regions.

When Fe3O4 is milled with a ball mill for a long time in the presence of a surfactant such as oleic acid or sodium oleate in such an ester, Fe finely divided by the milling is produced.
Since the carboxyl group of the surfactant is immediately adsorbed onto the surface of 3O4 and coated with fatty chains directed outward, re-agglomeration of fine particles does not occur, and as the grinding progresses, Fe3O4 begins to disperse in a colloidal form in the ester.

After a certain degree of pulverization, Fe3O4 particles having a large diameter, for example, 300A or more, are removed using a centrifuge to obtain a magnetic fluid for use in speakers that does not aggregate even in a strong magnetic field and does not settle under gravity.

The vapor pressure and freezing point of this magnetic fluid are determined mostly by the dispersion solvent, ester.

Further, the viscosity is determined by the coating thickness of the surfactant in the magnetic fluid and the initial viscosity of the dispersion solvent, and the viscosity is higher than that of the dispersion solvent, and a low viscosity of 75 to 1000 centipoise, particularly 75 to 200 centipoise, is often used.

In the conventional example shown in FIG. 1 as well, the magnetic fluid 11 for the speaker is made by colloidally dispersing ferromagnetic powder with a diameter of 300 A or less in an ester with a high boiling point and low vapor pressure such as diester as described above. It is used a lot.

The thermal conductivity of such magnetic fluid is 0.1-0.15J
7m, sec,' is relatively small for a liquid.1 Thermal conductivity of water is 0.6 J 7m, sec,'K cr)
-g-7.

However, even in the conventional electrodynamic speaker shown in FIG. 1, the heat dissipation effect is not sufficient.

Therefore, the present inventor has already proposed a speaker having the structure shown in FIGS. 2 to 4.

This electrodynamic speaker uses a heat dissipating fluid that has a higher thermal conductivity than the magnetic fluid in addition to the magnetic fluid.

In FIG. 2, reference numerals 12 and 13 are annular grooves formed on the outer circumferential surface of the center pole 2 and the inner circumferential surface of the yoke 4, respectively, and the magnetic poles forming the magnetic gap are the grooves 12.13.
13, and magnetic fluid 1 is placed on the diaphragm side of the magnetic gap.
1 is filled.

14 is yoke 1, center pole 2, magnet 3, yoke 4
, is a heat dissipation fluid filled in a space in a magnetic circuit surrounded by magnetic fluid 11, and this heat dissipation fluid 14 is
The speaker shown in FIG. 2 has a better heat dissipation effect than the speaker shown in FIG. 1 because it has better thermal conductivity than the speaker shown in FIG.

Figure 3 shows a further improvement of the spill force in Figure 2.
15 is a cylindrical heat transfer copper ring disposed on the inner peripheral surface of the magnet 3; 16 is a heat pipe whose one end is inserted and fixed into the L heat transfer copper ring 15; and 17 is provided at the other end of the heat pipe 15. This is a heat sink.

In FIG. 3, the heat generated in the voice coil 10 is also radiated from the heat radiating plate 17 via the heat radiating fluid 14, the heat transfer copper ring 15, and the heat pipe 16.

FIG. 4 shows yet another example, in which 18 is a heat transfer copper ring placed in the space within the magnetic circuit, and the heat dissipating fluid 14 is refluxed by a pump 20 coupled via a pipe 19, 19'. Heat is radiated from a heat sink 21 attached to the pipe 19'.

The characteristics required for the magnetic fluid and the heat dissipation fluid in the electrodynamic speaker having the above structure are as follows.

(A) The two fluids do not react and are not compatible, and the sealing function of the heat dissipation fluid by the magnetic fluid does not deteriorate.

(B) It is a low viscosity fluid and does not interfere with the vibration of the voice coil and coil bobbin.

(C) In particular, the vapor pressure of the magnetic fluid is low, and the viscosity does not increase due to evaporation of the magnetic fluid.

(D)? u Has a low solidification point and does not solidify even at low temperatures.

(E) High thermal conductivity, effectively transmitting heat from the voice coil.

(F) Use a magnetic fluid with high saturation magnetic flux density.

As mentioned above, magnetic fluids using ester oils such as diesters having long chain structures as dispersion solvents are currently most suitable for use in speakers.

When this magnetic fluid is mixed with hydrocarbons or organic solvents, benzene ring compounds such as benzene and dolenine, carbon tetrachloride,
It dissolves uniformly in most solvents such as halogen compounds such as methylene chloride, hydrocarbons such as n-hexane, higher alcohols such as 2-octatool, petroleum ether, liquid paraffin, and esters.

This is because the higher fatty acid ester, which is the dispersion solvent for the magnetic fluid, is compatible with the above solvent, and the long chain structure of the surfactant such as oleic acid, which colloids Fe3O4, has an affinity with the above solvent. be.

Fe mixing a solvent such as acetone, methyl alcohol, ethyl alcohol, methyl ethyl ketone with the above magnetic fluid
Aggregation of 3O4 and cloudiness were observed.

This is considered to be a phenomenon that occurs because the higher fatty acid ester is compatible with the above-mentioned solvents such as acetone, but the surfactant has no affinity with the above-mentioned solvents.

When a magnetic fluid containing higher fatty acid ester as a dispersion medium is mixed with various liquids, water, glycol, I discovered glyceryl silicone oil.

Glycol is a dihydric alcohol with a molecular structure having two hydroxyl groups, and glyceryl is a trihydric alcohol with a molecular structure having three hydroxyl groups.

Water has a boiling point of 100°C and a high freezing point of 0°C, so it evaporates easily and freezes easily in cold regions, making it impractical.

In contrast, glycols, such as ethylene glycol (boiling point 198°C, freezing point -13°C, viscosity 21 centipoise)
, diethylene glycol (boiling point 245℃, freezing point 8℃,
viscosity 36 centipoise), triethylene glycol (boiling point 287°C, freezing point -7°C, viscosity 48 centipoise),
Propylene glycol (boiling point 187℃, solidification point -60℃)
℃, viscosity 56 centipoise), and the vapor pressure is low at 0℃.
So let's not fix 4.

Further, the viscosity is lower than that of magnetic fluid, which is 75 to 1000 centipoise.

A typical example of gutceryl is glycerin (boiling point: 290°C, freezing point: 18°C, viscosity: 945 centipoise), but it can be dissolved in water and glycol in any ratio to create a liquid mixture with a viscosity of 50 centipoise or less and a coagulation point of 0°C or less. is possible.

Note that glycol and water are also soluble in any proportion.

The thermal conductivity of glycol and glyceryl is lower than that of water, but the thermal conductivity of magnetic fluid using higher fatty acid ester as a dispersion medium is 0.1 to 0.15 m, sec,', so both are large, and the heat dissipation effect of the voice coil is also high. Improved.

The thermal conductivity at 50°C is 0.0 for ethylene glycol.
26 J 7m, sec, °K, diethylene glycol is 0.21 J 7m, sec, °K, triethylene glycol is 0.20 J 7m, sec, ', propylene glycol is 0.20 J 7m, sec, 'K ,
Glycerin is 0.29 J/m, sec, °.

Also, a mixed solution of 80% ethylene glycol and 20% water has a thermal conductivity of 0.31 J 7m, sec,', and as the proportion of water increases, the thermal conductivity increases, but on the other hand, the boiling point decreases and the freezing point increases, reaching 0°C. come closer to

That is, it exhibits intermediate properties between water and ethylene glycol.

Silicone oil has almost the same thermal conductivity as the above-mentioned magnetic fluid.

FIGS. 5 and 6 are graphs of voice coil temperature rise versus effective human power W for a 20 second sine wave for a tweeter with a voice coil diameter of 25φ.

A is the data of the conventional example shown in Fig. 1, B, C, D
are the characteristics when B (20 centipoise silicone oil) and C (water) are used as the heat dissipation fluid 14 in the structure of the example shown in FIG. 4, in addition to D (ethylene glycol) of the example, and FIG. B, C, and D in FIG. 6 are the characteristics when the pump 20 is stopped, and B, C, and D in FIG. 6 are the characteristics when the pobbin 20 is operated and the flow is refluxed at a flow rate of 4 to 5 cc/sec.

The characteristics shown in FIGS. 5B, C, and D, in which the heat dissipating fluid 14 is kept stationary, are almost the same as the measurement results in the embodiment shown in FIG.

C (water) has low reliability but high thermal conductivity, and B (silicon oil) has high reliability but low thermal conductivity.

When refluxed, ethylene glycol shows almost the same rise in voice coil temperature as water, and it can be seen that the thermal conductivity at the interface between the voice coil and flowing ethylene glycol is as high as that of water.

This is thought to be because the intermolecular force between the voice coil and coil bobbin and ethylene glycol is relatively large, so that the thermal motion of the molecules is easily transmitted.

As described above, higher fatty acid esters with low vapor pressure and high boiling points are used as sealing magnetic fluids, and glycol, glyceryl, and mixed solutions of these and water are used as heat dissipation fluids with relatively high boiling points and freezing points of 0°C or less. If it is sealed and brought into contact with the voice coil or coil bobbin, it has a large heat dissipation effect and has a low viscosity, so the rise in voice coil temperature can be reduced to that of the conventional example shown in Fig. 1, and there is less mechanical resistance to voice coil vibration. It also has the advantage of little drop in sound pressure.

In the embodiments shown in FIGS. 2 and 3, it is also possible to use a magnetic fluid in which glycol, glyceryl, a mixture of these polyhydric alcohols and water, etc., is used as a dispersion solvent as the heat dissipation fluid.

The electrodynamic speaker of the present invention has the above-described configuration, and the present invention has the advantage that the temperature rise of the voice coil can be reduced and a highly reliable electrodynamic speaker can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional conductive speaker, Figures 2 to 4
Each figure is a sectional view of an electrodynamic speaker according to an embodiment of the present invention, and FIGS. 5 and 6 are diagrams showing temperature rises in the voice coils of the conventional electrodynamic speaker and the electrodynamic speaker of the present invention. 1...Yoke, 2...Center pole, 3...Magnet, 4...Yoke, 5...
...Frame, 6...Diaphragm, 7...
...Edge member, 8...Coil bobbin, 9...
...Vent hole, 0...Voice coil, 11.
...Magnetic fluid, 12゜13 ...Groove, 14
... Heat radiation fluid, 15 ... Heat transfer copper ring, 6 ... Heat pipe, 17 ... Heat sink plate, 18 ... Heat transfer Hot copper ring, 19.19'・
...Pipe, 20...Pump, 21...
...heat sink.

Claims (1)

[Scope of utility model registration request] A space inside a magnetic circuit composed of a center pole, a yoke, and a magnet is filled with a heat dissipation fluid, and a magnetic gap of the magnetic circuit is filled with a magnetic fluid to seal the heat dissipation fluid. The heat dissipation fluid is a polyhydric alcohol such as glycol or glyceryl, or a mixed solution of these polyhydric alcohols and water; An electrodynamic speaker characterized by using magnetic fluid with powder dispersed in it.