JPH0648872B2 - Vibration plate for electro-acoustic transducer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a diaphragm used for a speaker, a microphone, and other electroacoustic transducers.

[Prior Art] A diaphragm used in an electroacoustic transducer is required to have an increased piston region, a high limit frequency (fH), and an increased input resistance. Therefore, it is lightweight and has a high Young's modulus. A material that has, for example, a lightweight metal such as titanium or aluminum is used. However, it is extremely difficult to satisfy all the above characteristics and the like with only a single material.

Therefore, a diaphragm in which boron is thermally diffused in a titanium substrate (Japanese Patent Publication No. 55-15913) or a diaphragm in which a BN solution is applied on a titanium substrate and a BN layer is formed by heat treatment at about 900 ° C. (Japanese Patent Publication No. 55-7757) and the like have been proposed.

However, those that form the compound layer by these heat treatments are manufactured by heat treatment at a heating temperature of about 550 to 700 ° C., which is the temperature at which titanium of the diaphragm base easily deforms, or from the body-centered cubic structure to the face-centered cubic structure. Since the heat treatment is performed at a temperature of 885 ° C or higher, which is a transformation temperature that easily causes deformation, the residual stress generated when forming into a vibration plate is released, and crystal precipitation occurs. In some cases, the plate-shaped base material is thermally deformed and becomes abnormal in dimension at the joint between the voice coil bobbin and the free edge, which adversely affects the electroacoustic conversion characteristics.

For this reason, there are restrictions in design such as using a shape and material that are not easily deformed by heat.

Further, when the thermal diffusion layer is formed, there is a problem in that the nonuniformity of the metal structure of the vibration plate substrate causes nonuniformity of the physical properties of the entire vibration plate, resulting in unstable quality.

[Problems to be Solved by the Invention] Further, by using the chemical vapor deposition method or electron beam method, boron carbide (B
_A diaphragm for a speaker in which a 4C) layer is formed has also been proposed (Japanese Patent Publication No. 53-45136).

However, the applicant himself later pointed out that this diaphragm had a problem that the adhesion between the titanium foil and the boron carbide layer was poor and the boron carbide layer was easily peeled off, resulting in poor durability. (See Japanese Patent Publication No. 56-33919).

The present invention has been made in view of the above points, and an object of the present invention is to provide a diaphragm for electroacoustic transducers with stable quality, light weight, high Young's modulus, and high rigidity.

[Means for Solving the Problems] The present invention provides an amorphous boron nitride having a high Young's modulus at a low temperature such that the substrate is not thermally deformed by the low pressure CVD method on a vibration plate substrate which is formed in a desired shape in advance. It is characterized in that a film is formed.

In the present invention, titanium, aluminum, or other lightweight metal is used as the diaphragm substrate. In some cases, an alloy containing these lightweight metals as a main component, or a compound such as a nitride, a carbide, or a carbonitride of these lightweight metals may be used.

Further, in the present invention, when forming the amorphous boron nitride film on the surface of the diaphragm substrate, it is desirable to form the amorphous boron nitride film at a temperature at which residual stress does not remain. That is, the present invention investigates the cause of the poor adhesion of the film when the above-mentioned B ₄ C hard film is formed, and finds that the presence of residual stress generated during the formation of the hard film has an effect. As a result of various studies on a method of forming a hard film without generating the above, it was found that a preferable result can be obtained by forming an amorphous boron nitride film by a low pressure CVD method. FIG. 1 is a diagram showing an example of the results of actual measurement of the relationship between the deposition rate of an amorphous boron nitride film and the residual stress. As is clear from this figure, when the amorphous boron nitride film is formed, if the film forming conditions are appropriately selected, the residual stress can be almost eliminated, and a film having good adhesion can be obtained.

Further, the hardness of the amorphous boron nitride film in the present invention is too low to obtain a proper Young's modulus, while if too hard, the residual stress during film formation becomes large and peeling easily occurs, so Vickers hardness ( It is desirable that the hardness is about 1000 to 3500 in Hv).

Further, the thickness of the amorphous boron nitride film may be set to an appropriate thickness as necessary, but if the thickness of the film is less than 0.1 μm, the improvement effect of high-pitched sound does not improve so much. The thickness of the film is preferably 0.1 μm or more. On the other hand, even if the thickness of the film is increased to several tens of μm or more, there is no particular problem in terms of electroacoustic conversion action, so that the film may be designed to have an arbitrary thickness. However, if the film thickness exceeds 5 μm, peeling is likely to occur, so the film thickness is preferably 5 μm or less.

〔Example〕

 Hereinafter, the present invention will be described in more detail based on examples.

(Example 1) Using a titanium foil having a thickness of 20 μm, a dome-shaped molded product having a dome height of 6.5 mm and a diameter of 25 mm was formed by a conventional method, and then ion-formed to a depth of about 2 μm on both sides. A dome-shaped diaphragm substrate that was subjected to a nitriding treatment was manufactured. This substrate was placed in a low pressure CVD apparatus, the reaction temperature was 450 ° C., the reaction pressure was 0.5 Torr, and the reaction gas was 5% B ₂ H ₆ (H ₂ dilution).
And NH ₃ and H ₂ as a carrier gas, respectively.
Film formation was carried out under the condition of H ₃ / B ₂ H ₆ = 5 for 1.5 hours to obtain a vibration plate having an amorphous boron nitride film of 3 μ thickness formed on the front and back surfaces of the substrate. Next, the flange portion was cut off, and the Young's modulus (E) was measured by the vibration lead method, and it was 1.16 × 10 ¹² dyn / cm ² . The specific gravity (ρ) measured by the water displacement method was 3.8 g / cm ³ . The result of measuring the hardness (Hv) with a Vickers hardness meter was 3,500.

The Young's modulus (E) of the diaphragm base is 0.89 × 10 ¹² dy
It was n / cm ² . The specific gravity (ρ) was 4.51. The hardness (Hv) was 1,100.

In producing the above-mentioned diaphragm, the temperature of the surface of the diaphragm during the low pressure CVD treatment was measured with an infrared thermometer, and it was maintained at about 450 ° C., which may cause thermal deformation of the diaphragm substrate. The temperature was maintained below the temperature (about 550 ° C.), and the obtained diaphragm had good dimensional accuracy.

The same edge of polyester fiber cloth coated with acrylic resin was attached to this diaphragm, the voice coil was adhered, and incorporated in the magnetic circuit of a conventional moving coil type dome speaker to form a dome type speaker unit. Then, the sound pressure frequency characteristic was measured. The result is the second
Shown in the figure.

The speaker using the diaphragm having the amorphous boron nitride film of the present invention has a low resonance frequency (f ₀ ) of about 1100 Hz,
The high frequency limit frequency (fH) is about 31,200Hz. Further, it has an unusually low distortion rate as a hard dome, and has an excellent characteristic of -50 dB with respect to the basic sound pressure in the vicinity of fH.

On the other hand, for comparison, a diaphragm base for which an amorphous boron nitride film was not formed was used to form a speaker unit for dome-type sound in the same manner as above, and the sound pressure frequency characteristics were measured. The results are shown in FIG. In the speaker using the diaphragm of the comparative example in which the amorphous boron nitride film is not formed, f ₀ is about 1,260 Hz and fH is about 28,500 Hz.
Is the frequency characteristic of.

As is clear from a comparison of FIGS. 2 and 3, the one using the diaphragm having the amorphous boron nitride film of the present invention, compared with the one of the comparative example, despite the weight increase due to the BN film. The high frequency range has been extended to about 2,700 Hz. Also, f ₀
The increase in weight also contributes to the reduction of about 160 Hz, which indicates that the expansion of the reproduction frequency range is extremely large.

(Example 2) Under the same conditions as in Example 1 except that the film formation time was 5 minutes,
A diaphragm having an amorphous boron nitride film with a thickness of 1 μm was manufactured. As a result of measuring physical properties in the same manner as in Example 1, E = 0.95 × 10 ¹² dyn / cm ² , ρ = 4.50 g / c
m ³ and Hv = 3500.

When the temperature of the surface of the diaphragm during the low pressure CVD treatment was measured, it remained at about 450 ° C. as in Example 1, and the obtained diaphragm had good dimensional accuracy.

Using this diaphragm, a dome-type acoustic speaker unit was formed in the same manner as in Example 1, and sound pressure frequency characteristics were measured. As a result, f ₀ was about 1260 Hz and fH was about 28,700 Hz.

(Example 3) By adjusting the treatment method of the low pressure CVD method, the reaction temperature was 550 ° C, the reaction pressure was 0.5 Torr, 5% B ₂ H ₆ (H ₂ dilution) and NH ₃ were used as the reaction gas, and H ₂ was used as the carrier gas. , NH ₃ /
Film formation was carried out for 1 hour under the condition of B ₂ H ₆ = 10 to produce a vibration plate having an amorphous boron nitride film with a thickness of 3 μm formed on the surface of the substrate. When the physical properties were measured by the same method as in Example 1,
E = 1.15 × 10 ¹² dyn / cm ² , ρ = 3.75 g / cm ³ , Hv = 1
It was 000. The temperature of the diaphragm surface was maintained at about 550 ° C during the reduced pressure CVD treatment, but the diaphragm base material did not undergo thermal deformation, and the resulting diaphragm had good dimensional accuracy with no practical problems. Met.

Next, using this diaphragm, a dome-type speaker unit for acoustics was formed in the same manner as in Example 1, and the sound pressure frequency characteristics thereof were measured.

The measurement results were f ₀ of about 1,100 Hz and fH of about 32,100 Hz.

〔The invention's effect〕

As described in detail above, the diaphragm of the present invention in which the amorphous boron nitride layer is formed has a desired film thickness and hardness of the amorphous boron nitride film by the low temperature treatment which does not cause the substrate to be thermally deformed on the diaphragm substrate by the low pressure CVD method. The electroacoustic sound has excellent characteristics because the quality is stable, the treble limit frequency (fH) is high, the treble range is wide, and the sound pressure reproduction range is wide. There is an advantage that a converter can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a film forming temperature and a residual stress when forming an amorphous boron nitride film of the present invention, and FIG. 2 is a result of measuring a sound pressure frequency characteristic of an electroacoustic transducer using a diaphragm according to the present invention. FIG. 3 and FIG. 3 are diagrams showing the results of measuring the sound pressure frequency characteristics of the electroacoustic transformer using the comparative diaphragm without coating.

Claims (4)

[Claims] 1. A diaphragm for an electroacoustic transducer, comprising an amorphous boron nitride film formed on a diaphragm base. 2. The electroacoustic apparatus according to claim 1, wherein the diaphragm substrate is made of titanium, aluminum, other lightweight metals, alloys of these lightweight metals, or compounds of these lightweight metals. Vibration plate for converter. 3. The diaphragm for an acoustic transducer according to claim 1 or 2, wherein the amorphous boron nitride film has a Vickers hardness of 1000 to 3500. 4. The thickness of the amorphous boron nitride film is 0.
The diaphragm for an electroacoustic transducer according to any one of claims 1 to 3 of the patent contract, which is 1 μm or more.