JPH04211598A - Diaphragm for speaker - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Description: FIELD OF INDUSTRIAL APPLICATION This invention relates to a diaphragm for a speaker that has excellent acoustic characteristics in the high frequency range. 2. Description of the Related Art Various types of acoustic speakers are used, among which dynamic speakers are most commonly used. This type works on the principle of converting electrical signals into sound using a diaphragm connected to a moving coil that moves in a magnetic flux. Speakers with different frequency ranges are used together, such as one for bass, one for medium, and one for treble. Each size is different, and the characteristics required of the diaphragm are also different. The most widely used material for diaphragms is paper. Although this is a suitable material as it is cheap and lightweight, its low stiffness makes accurate conversion difficult above a few hundred hertz. In order to improve this problem, various diaphragm materials have been studied. When the Young's modulus of the diaphragm material is E and the density is ρ, the material with a larger E/ρ has better conversion characteristics in the high frequency range. In other words, the higher the Young's modulus and the lower the density, the better the high-pitched sound characteristics. For example, Be has been proposed as an alternative to paper. E/ρ of this is 50×10
It is 10 dyn·cm/g, which is excellent. However, Be is highly toxic, and sufficient consideration must be taken to avoid toxicity during the manufacturing process. It also has poor workability. Ti has also been proposed as a diaphragm. However, since the density is large, E/ρ is small. [0004] Japanese Patent Publication No. 57-29919 describes silicon Si
is proposed as a diaphragm. E/ρ of this is 50×1
The internal loss is about 0.010 dyn cm/g and 0.01.
2 and large. In addition, by alloying silicon with boron B, Si
A diaphragm made of B alloy or a diaphragm made of silicon carbide alloy SiC, which is an alloy of silicon and carbon, has also been proposed. These E/ρ are said to reach approximately 140×10 10 dyn·cm/g. These utilize the fact that silicon has a small density ρ (ρ=2.3 g/cm 3 ). However, Si, SiB, and SiC diaphragms also have a still small E/ρ and cannot provide sufficient high-pitched sound characteristics.

[0005] Japanese Patent Publication No. 55-33237 proposes a diaphragm made of a diamond-shaped carbon molded film obtained by ion beam evaporation of carbon ions. This uses diamond-like carbon to increase E/ρ. Using Al, Ti, and plastic as a base, set it to a negative potential of -40V and apply a voltage of 10-5 to 1
In a high vacuum of 0-6 Torr, carbon ions C+ generated by hitting a carbon electrode with argon are ion beam
The carbon film is deposited on the substrate by applying it to the substrate as a film. However, this can only produce a porous carbon film that is electrically conductive, and is considered to be an amorphous carbon film whose main component is graphite rather than diamond. Diamond has a high E/ρ of 300×1
It reaches 010 dyn·cm/g. If a speaker diaphragm could be made from diamond, it would have excellent high-frequency characteristics. However, the speaker diaphragm is 2
It must be a thin plate, such as 0 μm or 50 μm. Moreover, it requires a considerable space with a diameter of 20 to 30 mmφ. Of course, it is impossible to make such a wide and thin plate using naturally occurring diamond grains as raw material. [Means for Solving the Problems] The speaker diaphragm of the present invention is characterized in that it is made only of diamond produced by chemical vapor phase synthesis and is processed into the shape of a speaker diaphragm. shall be. [Operation] To give an overview of the manufacturing method, a substrate made of Si processed into the shape of a diaphragm for a speaker, or a substrate made of metal processed into the shape of a diaphragm for a speaker and coated with Si, Placed in a vacuum chamber, the substrate is heated and a diamond film is grown on the substrate by chemical vapor phase synthesis while flowing a raw material gas containing hydrocarbons.The substrate and diamond film are cooled and taken out of the vacuum chamber. The substrate is dissolved and removed to obtain a diaphragm-shaped diamond film. [0009] Since the diaphragm has a hemispherical shell (dome shape),
Using such a dome-shaped substrate, a diamond film must be grown on it. The base body is made entirely of silicon Si, or it is made of metal processed into a dome shape and the surface thereof is coated with Si. Of course, the best option is one made entirely of Si. FIG. 1 shows an example of the shape of the base body. This is entirely made of Si polycrystal, and has an outer diameter of 25.5 mm and a height of 7 mm, for example. Generally, the outer diameter of the dome base is 20 to 30 mm, and the height is about 5 to 10 mm. [0010] Such a substrate is subjected to a chemical vapor phase synthesis apparatus (C
VD) and coated with a diamond film. FIG. 2 shows a process diagram. First, prepare the base. This may be made entirely of Si as shown in FIG. 1, or may be made of metal with Si attached as shown in FIG. 6. Next, this is heated in a CVD apparatus, a raw material gas containing carbon and hydrogen is introduced, and the gas is excited by some method to coat the heated substrate with a diamond film. This must have a considerable thickness, 20 μm.
A film thickness of about 100 μm is required. If it is too thin, it will not have enough rigidity and will not be able to maintain its own shape. If it is too thick, the treble characteristics will deteriorate and the cost will increase. Diamond growth is stopped when a predetermined thickness is reached. In other words, the supply of raw material gas is stopped and the heating temperature of the substrate is gradually lowered. After the temperature reaches room temperature, the CVD apparatus is opened and the substrate is taken out. Then, the substrate Si or the metal and Si are dissolved and removed using a suitable chemical. This leaves a dome-shaped diamond film. This is a single diamond diaphragm. The reason why the substrate is made of Si is as follows. If a metal other than Si is used as the substrate, the defect density will be extremely high because of the large difference in thermal expansion coefficient from the diamond film. Furthermore, when the substrate is dissolved and removed, the diamond film may break down into pieces. This is of no use. Diamond growth is 850 ~
Although it is carried out at a high temperature of 1000° C., it must be cooled down to room temperature after film formation. Many metals have large coefficients of thermal expansion. Strong compressive stress is generated in the diamond during the cooling process. Due to this stress, when the temperature is lowered, many cracks and fissures occur in the diamond film in all directions, and in severe cases, the diamond decomposes. The coefficient of linear expansion of diamond is extremely small, 1×10-6 K-1 at room temperature (20°C) and 5.
8 x 10-6 K-1 and increases with temperature. The coefficient of linear expansion of Si is also sufficiently small, 2.5×10-6 at room temperature.
K-1, about 4 x 10-6 K-1 at 530°C. For example, when cooling from 1000° C. to 20° C., the difference in linear expansion coefficient between Si and diamond during this process is much smaller than in other combinations. Therefore, if the entire substrate is made of Si or the surface of the substrate is made of Si, the compressive stress generated on the diamond surface during the slow cooling process will be reduced, and the probability of cracks, fractures, and defects will also be reduced. [0014] As the chemical vapor phase synthesis method (CVD),
Filament CVD method ■Microwave plasma CVD method ■Thermal plasma CVD method can be used. Filament CVD method uses W, Ta
Generate thermoelectrons by passing current through a filament such as
This excites the source gas. The microwave plasma CVD method is a method in which a 2.45 GHz microwave is introduced into a vacuum chamber through a dielectric window, and electrons are vibrated at the microwave frequency to strike neutral atoms and molecules with the electrons to turn them into plasma. Thermal plasma CVD
The method is to use the nozzle as an electrode and apply positive and negative voltages.
By flowing a raw material gas through a nozzle, an arc discharge is caused and this is converted into plasma. [Example] [Example 1] Polycrystalline silicon was processed into the shape of a speaker diaphragm by cutting. A diamond film with a thickness of 25 μm was formed on this surface by a known microwave plasma CVD method. Thereafter, the silicon substrate was dissolved in a mixed solution of hydrofluoric acid and nitric acid at room temperature. In this way, a diamond diaphragm with a thickness of 25 μm was obtained. The treble resonance frequency of this diaphragm is 65,000Hz
Met. The treble resonance frequency of a Be diaphragm of the same shape is 28,000 Hz, and the treble resonance frequency of Al2O3 is 35,000 Hz. It can be seen that the treble characteristics of the diamond diaphragm of the present invention are extremely excellent. [Example 2] Mo was cut into the shape of a diaphragm for a speaker. Si, Ti, and W were each deposited on the surface to a thickness of 1 μm to form three types of substrates. A diamond film was coated to a thickness of 10 μm using a known microwave plasma CVD method on four types of samples, including a sample containing only Mo without a deposited layer and a sample of these three types of substrates. This was cooled and the defect density was measured in that state. Thereafter, the Mo substrate was removed using a mixed solution of hydrochloric acid, hydrofluoric acid, and nitric acid. The thin films of Mo, Si, Ti, and W were dissolved, leaving only the diamond. Some were able to maintain their dome-like shape, while others disintegrated into pieces. The results are shown in Table 1. [Table 1] [0018] From these results, it can be seen that the diamond film formed by vapor depositing Si on the substrate has few defects, and the condition after dissolving and removing the substrate is also sound, and it is suitable for use as a diaphragm for speakers. It can be seen that it is excellent as Example 3 Diamond was grown on a dome-shaped substrate using a known filament CVD apparatus. FIG. 3 shows a schematic configuration of a filament CVD apparatus. A cooling support 2 is provided within the vacuum chamber 1 . Cooling water 3 is passed through this. A base body 4 is placed on the cooling support base 2. A filament 5 is stretched horizontally on the base 4, and both ends are supported by electrodes 6, 6. A current is applied from an external power source 7 to the filament 5 via the electrodes 6, 6. Gas inlet 8 where raw material gas is above
and flows into the vacuum chamber 1 from there. The filament 5 is heated to generate thermoelectrons, which turn the source gas into plasma. The base body is heated by the radiant heat of the filament 5 and its temperature increases. Exhaust gas is removed from the vacuum exhaust port 9. The process is as shown in FIG. A Si polycrystalline substrate processed into a dome shape was used as the substrate. This is shown in Figure 1, and it has a shape similar to a hemisphere, like a sphere cut out by a small circle (a circle that does not pass through the center). The diameter is 25.5 mm, and the height from the bottom to the top is 7 mm. The surface of this dome-shaped Si substrate was scratched with #600 diamond powder. This dome-shaped Si substrate 4 was placed on a sufficiently cooled support base 2. The inside of the vacuum chamber 1 is evacuated to a sufficiently high vacuum. After this, hydrogen gas is introduced into the vacuum chamber 1 from the raw material gas inlet 8 at a rate of 100 sccm,
Methane gas is sent at 20 sccm and the pressure is 50 Torr.
It was maintained at r. The filament 5 was made of tungsten W, and was energized to reach a temperature of 2,100°C. The Si substrate is heated by the radiant heat of the filament to a temperature suitable for vapor phase growth. Thermionic electrons are emitted from the filament, which excites the methane gas, resulting in plasma consisting of positive ions, neutral radicals (active species), and electrons. This undergoes a gas phase reaction on the Si substrate and diamond polycrystals grow. [0022] When a diamond film of a predetermined thickness is formed, the supply of raw material gas is stopped and the temperature of the substrate is gradually lowered. After the temperature reached room temperature, the Si substrate was taken out and immersed in a solution containing a mixture of hydrofluoric acid and nitric acid at a ratio of 1:1 to dissolve and remove only the Si substrate. Diamonds don't melt, so a dome-shaped diamond remained. This dome-shaped diamond weighs 60mg
There was a weight of [0023] This was used as a diaphragm for a speaker and its acoustic characteristics were measured. Figure 4 shows the frequency sound pressure characteristics. For comparison, the acoustic characteristics of a Ti speaker diaphragm having the same shape and thickness were measured under the same conditions, and the results are shown in FIG. In both cases, the horizontal axis is frequency (Hz) and the vertical axis is sound pressure level (dB).
It is. The diamond diaphragm according to the present invention is 20,
It can be seen that there is a sufficient sound pressure level even above 000 Hz, and the high-pitched resonance frequency is 70,000 Hz. 70,0
It can play up to 00Hz (70kHz). However, the resonant frequency of the Ti diaphragm is 17,000H.
z, and it can be seen that high frequencies of 25,000 Hz or higher cannot be reproduced with sufficient intensity. [Example 4] A diamond film was produced under the same conditions as in Example 3 using a Si-coated Mo substrate. A filament CVD apparatus was used. The base has an outer diameter of 3
Mo processed into a hemispherical shape of 0.5mm and height 7.5mm
5,000 Å (
0.5 μm) coated. A cross-sectional view is shown in FIG. Then, the surface of the dome-shaped substrate was scratched using #600 diamond powder. This was installed in the apparatus shown in FIG. 3, and a diamond film was grown under the same conditions as in Example 3. After cooling, it was taken out to the outside and the substrate was melted. First, Mo is dissolved in aqua regia (hydrochloric acid:nitric acid=3:1). Thereafter, Si is dissolved and removed using 1:1 fluoronitric acid. In this way, a single diamond diaphragm weighing 60 mg was obtained. The acoustic characteristics of this diaphragm were measured. As with Example 3, it was found that the reproduction ability in the high frequency range was significantly improved. [Example 5] A diamond film was grown while changing the synthesis conditions and the material of the substrate. This study mainly investigates how the material of the substrate affects the diamond film. Here, a filament CVD method and a microwave plasma CVD method were used. FIG. 7 shows a schematic diagram of a microwave plasma CVD apparatus. Non-metallic (
A substrate 13 is mounted on a support 12 in a vacuum chamber 11 (for example, quartz). Raw material gas is introduced through the gas inlet 14 and exhausted through the vacuum exhaust port 15 . A heater (not shown) is provided in the support base 12 to heat the base 13 to an appropriate temperature. A magnetron 16 is located on the side of the vacuum chamber 11 . A 2.45 GHz microwave is generated from here and propagated in the waveguide 17. On the opposite side is a plunger 18 that holds the conductor plate so that it can move forward and backward. The effective length of the waveguide 17 is determined by the plunger 18, and a standing wave of the lowest mode (or a mode close to it) is created within the waveguide 17. Electrons in the source gas are vibrated by the microwaves, which excites the gas and turns it into plasma 19. [0026] The sample is NO. 1 to NO. There are up to 7. The base is NO. 1 is Si only, NO. 2 is Si/Mo (Mo
coated with Si), NO. 3 is Si/W, NO. 4
is Si only, NO. 5 is Mo only, NO. 6 is Mo only, NO. 7 is W only. The raw material gases are hydrogen and methane. Maintain pressure between 40-80 Torr. The presence or absence of cracking when the substrate was dissolved and removed was examined. Furthermore, NO. Regarding the sample No. 3, the Raman spectra were examined and the spectra are shown in FIG. NO. 2.NO
．． The thickness of the Si coating layer in No. 3 is 5000 Å (0.5
μm). Table 2 shows the results of this experiment. [Table 2] Sample No. 2 according to the method of the present invention. 1~NO.
In No. 4, a good dome-shaped diamond diaphragm was manufactured. All of these have a substrate made of Si or a substrate surface made of Si. In contrast, No. 1, which was used as a comparative example. 5~NO. No. 7 uses a substrate other than Si. In some of these, cracks occurred during the diamond coating, or cracks occurred in the diamond film after coating was completed. And when the base is melted, NO. 5~NO. All samples No. 7 were broken and could not be used as diaphragms. For this reason, the entire substrate is made of Si or the surface is made of Si.
It is clear that it must be covered by FIG. 8 shows sample No. This is the Raman spectra of No. 3. The horizontal axis is the wave number (cm-1), and the vertical axis is the intensity. There is a sharp peak at 1333 cm-1, which is a signal from crystalline diamond, and it can be seen that there are many crystalline diamonds. Signals from amorphous carbon are widely distributed in this wavenumber range, so if there is a large amount of amorphous carbon, the peak at 1333 cm-1 will be low, and the other parts will be a spectrum that is broadly raised. Since this is almost absent, it is clear that the sample is composed of crystalline diamond with almost no amorphous carbon. [0030] According to the present invention, it is possible to provide a speaker diaphragm made only of high quality diamond. E/ρ of diamond is Be, Ti, Al2O
It is possible to create a diaphragm that is much larger and has excellent high-pitched sound characteristics than those of 3, etc., and can reproduce high-pitched sounds of 80 kHz (80,000 Hz) without distortion. This is an excellent invention.

[Brief explanation of the drawing]

FIG. 1 is a front view of a Si substrate used to manufacture the diamond diaphragm of the present invention.

FIG. 2 is a process diagram for manufacturing the diamond diaphragm of the present invention.

FIG. 3 is a schematic diagram of a filament CVD apparatus used to manufacture the diamond diaphragm of the present invention.

FIG. 4 is a frequency sound pressure characteristic diagram of a diamond diaphragm manufactured by the method of the present invention.

FIG. 5 is a frequency sound pressure characteristic diagram of a known titanium diaphragm.

FIG. 6 is a cross-sectional view of a base formed by coating a metal base with Si.

FIG. 7 is a schematic configuration diagram of a microwave plasma CVD apparatus used in the present invention.

FIG. 8 is a Raman spectrum diagram of a diamond diaphragm manufactured by the method of the present invention.

[Explanation of symbols]

1 Vacuum chamber 2 Cooling support stand 3 Cooling water 4 Base 5 Filament 6 Electrode 7 Power supply 8 Gas inlet 9 Vacuum exhaust port 10 Pressure gauge 11 Vacuum chamber 12 Support stand 13 Base 14 Gas inlet 15 Vacuum exhaust port 16 Magnetron 17 Waveguide 18 Plunger 19 Plasma

Claims (1)

[Claims] 1. A diaphragm for a speaker, characterized in that it is made by chemical vapor synthesis, is made of only diamond, and has the shape of a diaphragm for a speaker.