JP4636726B2 - Condenser microphone diaphragm and method of manufacturing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a diaphragm for a condenser microphone and a method for manufacturing the same, and more particularly to a diaphragm suitable for a microphone unit having a small diameter that can extend the low-frequency reproduction limit.
[0002]
[Prior art]
In the condenser microphone, the vibration of the diaphragm due to sound or the like is captured as a change in capacitance by a back electrode plate provided on the back side thereof, and the change in capacitance is output as an electric signal.
[0003]
Generally, a thin film film made of a thermoplastic resin such as polyethylene terephthalate (PET) or polyphenylene sulfide (PPS) having a film thickness of 2 to 4 μm is used for the diaphragm, and the microphone unit is attached to a support ring. It arrange | positions so that a back electrode plate may be opposed. Usually, the interval is set to about 25 to 50 μm.
[0004]
In the electret type, since the polarization voltage exists on the back electrode plate, the diaphragm is attracted to the back electrode plate side by the attractive force of the electric field. Normally, the polarization voltage is applied uniformly to the back plate, so the diaphragm approaches the back plate side with a curve whose center is the apex, and in the worst case the center May come into contact with the back plate, leading to failure.
[0005]
Therefore, in the conventional general condenser microphone, tension is applied to the diaphragm so as to overcome the electrostatic attractive force from the back electrode plate side, and the diaphragm is stretched on the support ring.
[0006]
[Problems to be solved by the invention]
However, this increases the stiffness of the diaphragm, and at the same time sacrifices the low frequency reproduction limit. This is more conspicuous as the microphone unit has a smaller diameter, and has been a problem particularly with unidirectional condenser microphones.
[0007]
Accordingly, it is an object of the present invention to provide a diaphragm suitable for a microphone unit having a small diameter, which has a high adsorption stability with respect to the back electrode plate and can extend the low-frequency reproduction limit, and a method for manufacturing the diaphragm. . In addition, according to the present invention, a unidirectional microphone having a low-frequency reproduction limit similar to that of a large caliber while having a small caliber can be obtained.
[0008]
[Means for Solving the Problems]
To achieve the above object, the present onset Ming, while being attached to the support ring, the diaphragm of the condenser microphone comprising a thermoplastic resin film to face arranged with the back plate by a predetermined distance of the microphone unit The entire film is formed in a fine wavy shape, and a convex portion protruding toward the opposite side of the back electrode plate is formed on the peripheral edge portion along the inner periphery of the support ring of the film. The convex portion is provided with a slack that is visible to the film in a free state of the film and is eliminated by an electrostatic attraction acting from the back electrode plate side and becomes invisible. It is said.
[0009]
In this way, by providing the diaphragm with a displacement that is attracted when combined with the back electrode plate, the low-frequency reproduction limit can be extended. Moreover, since the sensitivity is improved as a whole, the S / N ratio is also improved.
[0011]
In the present invention, the convex portions may be formed in an annular shape along the inner circumference of the support ring, or a plurality of the convex portions may be scattered at predetermined intervals along the inner circumference of the support ring. You may let them.
[0012]
The manufacturing method according to the invention, by cooling after pressing the first mold having fine irregularities thermoplastic resin film as a diaphragm material under predetermined heating temperature, the fine wave throughout the film A first step of applying, a second step of applying a predetermined tension to the film obtained in the first step and attaching the film to the support ring, and a first step having a negative pressure suction hole in a portion along the inner periphery of the support ring. 2 A film attached to the support ring is placed on the mold, and a part of the film is placed in the negative pressure suction hole using the second mold as a negative pressure at a heating temperature lower than that in the first step. The film is cooled after being deformed, and a convex portion is formed on the peripheral edge along the inner periphery of the support ring of the film so that the film can be visually observed in a free state of the film. Electrostatic suction acting from the plate side It is characterized in that is eliminated and a third step of providing the slack to be impossible visually by.
[0013]
In addition, it is preferable to further implement the 4th process which cools after heating for a predetermined time by the heating temperature still lower than the said 3rd process by making the said film into a free state as a so-called aging process after the said 3rd process.
[0014]
Further, the scope of the present invention includes a unidirectional condenser microphone provided with a diaphragm having the above-mentioned convex portions.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described. First, a basic configuration of a microphone unit 10 used for a unidirectional condenser microphone will be described with reference to FIG.
[0016]
The microphone unit 10 includes a diaphragm 11 and a back electrode plate 21. The diaphragm 11 is disposed opposite to the back electrode plate 21 via the spacer 13 while being attached to the support ring 12.
[0017]
The back electrode plate 21 is housed in a cylindrical housing 22 made of an electrical insulating material. E. A dielectric 23 such as P is pressure-bonded. A conductive connector plate 24 is disposed on the back side of the back electrode plate 21 so as to be in close contact therewith. The back electrode plate 21 and the connector plate 24 are provided with through holes 25 and 26 as sound paths, respectively.
[0018]
An impedance converter 28 made of FET or the like is accommodated in a recess 27 of the housing 22 formed at the lower part of the connector plate 24, and one lead terminal thereof is soldered to the connector plate 24. A through-hole as a sound passage having an acoustic resistance material 29 is also formed at the bottom of the housing 22.
[0019]
FIG. 2A shows a schematic plan view of the diaphragm 11 used in the microphone unit 10, and FIG. 2B shows a cross-sectional view thereof. According to this, the diaphragm 11 as a whole is formed in a wave shape composed of fine irregularities. A chain line in FIG. 2A exaggerates and enlarges a fine wave portion 111 attached by a mesh-shaped mold described later.
[0020]
In addition, a plurality of convex portions 112 are formed at equal intervals in the peripheral portion along the inner periphery of the support ring 12 of the diaphragm 11. The protruding direction of the convex portion 112 is on the opposite side of the back electrode plate 21. By this convex portion 112, the diaphragm 11 is slackened.
[0021]
This slack is preferably visible when the diaphragm 11 is in a free state. FIG. 2A shows the slack portion 113 by a solid line, and FIG. 2B shows the slack portion 113 by a large wave. As shown. That is, the diaphragm 11 includes a fine wave portion 111 and a slack portion 113 made of a large wave.
[0022]
FIG. 3A shows a schematic plan view of the diaphragm 11 when facing (combining) with the back electrode plate 21 to which the polarization voltage is applied, and FIG. 3B shows a cross-sectional view thereof. . From this figure, the slack 113 attached to the diaphragm 11 disappears.
[0023]
That is, the slack 113 attached to the diaphragm 11 is a slack that is eliminated when the diaphragm 11 is attracted to the back electrode plate 21 side by the electrostatic attraction force acting from the back electrode plate 21 and is not visible. It is preferable.
[0024]
FIG. 4 shows an example of a molding apparatus for obtaining the diaphragm 11 with a wave composed of fine irregularities. The molding apparatus 40 includes a cooling unit 411 provided on a lower base 41, and a molding die 43 is supported on the cooling unit 411 by a spring 42 so as to be moved up and down. A heating means 431 is attached to the back surface of the mold 43.
[0025]
On the side of the upper base 44 facing the lower base 41, a pressure pot 45 that moves up and down with respect to the mold 43 by the air cylinder 441 is provided. The pressurizing pot 45 has an open lower surface, and an O-ring 451 is attached to the lower end thereof.
[0026]
Next, an example of a method for manufacturing a diaphragm according to the present invention will be described. First, the unevenness forming member 46 having a fine mesh count is disposed on the mold 43 of the first molding apparatus 40, and the diaphragm material 11a is disposed thereon. In this example, NBC Kogyo Co., Ltd. # 508 nylon mesh is used for the concave / convex forming member 46, and the diaphragm material 11a is a PPS film having a thickness of 2 μm and vacuum-deposited gold on one side. Placed on top.
[0027]
Next, when the molding die 43 is heated by the heating means 431 and reaches a predetermined temperature, the pressure pot 45 is lowered to supply pressurized air to the molding die 43. In the case of a PPS film, the heating temperature is preferably about 220 ° C. and the heating time is about 60 minutes.
[0028]
After the heating, the pressure pot 45 is further lowered, the mold 43 is brought into contact with the cooling means 411 and cooled for a predetermined time, the pressure pot 45 is raised, and the diaphragm material 11a is taken out. Thereby, the diaphragm raw material 11a to which the wave which consists of fine unevenness was attached is obtained.
[0029]
Then, as shown in FIG. 5, the diaphragm material 11 a is bonded to the support ring 12 with a predetermined tension. In this example, the support ring 12 has an outer diameter of 7.6 mm and an inner diameter of 5.6 mm. The adhesive was a two-component epoxy adhesive.
[0030]
Next, the convex portion 112 is formed on the diaphragm material 11 a that is bonded and fixed to the support ring 12. For this purpose, a mold 60 shown in FIG. 6 is used. FIG. 6A is a schematic plan view of the mold 60, and FIG. 6B is a cross-sectional view taken along line AA. Moreover, FIG. 7 shows a cross-sectional view at the time of forming the convex portion.
[0031]
With reference to these drawings, the mold 60 includes a diaphragm mounting surface 61 and a support ring mounting surface 62. The outer diameter of the diaphragm mounting surface 61 is substantially the same as the inner diameter of the support ring 12, and a plurality of negative pressure suction holes connected to a negative pressure source such as a vacuum pump (not shown) at the periphery of the diaphragm mounting surface 61. 611 is formed at equal intervals.
[0032]
The support ring mounting surface 62 is formed concentrically with respect to the diaphragm mounting surface 61 at a position lower than the diaphragm mounting surface 61 by the thickness of the support ring 12 outside the diaphragm mounting surface 61. Has been.
[0033]
Although not shown, the molding die 60 is provided with a diaphragm heating means and cooling means as in the molding apparatus 40. The heating means and cooling means may be incorporated in the mold 60 or may be externally attached.
[0034]
In forming, as shown in FIG. 7, the support ring 12 is placed on the support ring placement surface 62 with the diaphragm material 11 a facing upward. And after heating the diaphragm raw material 11a to predetermined temperature with a heating means, the inside of the negative pressure suction hole 611 is made into a negative pressure with a negative pressure source.
[0035]
Thereby, a part of the diaphragm material 11a corresponding to the negative pressure suction hole 611 is drawn into the negative pressure suction hole 611, and the convex portion shown in FIG. 2 is formed on the periphery along the inner diameter of the support ring 12 of the diaphragm material 11a. 112 is formed.
[0036]
Then, by switching from heating to cooling thereafter, the shape of the convex portion 112 is made permanent, and the diaphragm 11 having the fine wave portion 111 and the slack portion 113 made of a large wave shown in FIG. 2 is obtained.
[0037]
The heating temperature in the molding die 60 is set to be lower than the heating temperature in the molding apparatus 40 so as not to break the wave portion 111 composed of fine irregularities formed in the molding apparatus 40. The heating temperature was about 120 ° C. and the heating time was 2 hours.
[0038]
In this example, after the diaphragm 11 is removed from the mold 60, the diaphragm 11 is in a free state, that is, before being incorporated into the capacitor unit 10, and is further lower than the heating temperature (about 120 ° C.) in the mold 60. After heating at a temperature of 70 ° C. for about 2 hours, it was cooled and an aging treatment was performed.
[0039]
In this embodiment, the plurality of convex portions 112 are arranged at equal intervals along the inner circumference of the support ring 12. However, the convex portions 112 are arranged in a ring shape along the inner circumference of the support ring 12. It may be formed.
[0040]
FIG. 8 shows a frequency response characteristic graph of a unidirectional condenser microphone having a diameter of 8.4 mm provided with a diaphragm according to the present invention, and FIG. 9 shows a conventional single unit having the same diameter provided with a flat diaphragm as a comparative example. The frequency response characteristic graph of a directional condenser microphone is shown. In both cases, a is at 0 ° with respect to the sound source, and b is at 180 ° with respect to the sound source.
[0041]
As can be seen from these graphs, the low frequency reproduction limit remains in the vicinity of about 100 Hz in the conventional example, whereas in the example of the present invention, the low frequency reproduction characteristic is almost flat up to about 50 Hz. . This is almost equivalent to the low-frequency reproduction limit of the conventional unidirectional microphone unit having a diameter of 12 mm.
[0042]
Further, in the case of the present invention example, since the diaphragm has high adsorption stability, performance similar to that of a conventional unidirectional microphone unit having an S / N ratio of 12 mm can be obtained. Thus, the present invention is particularly suitable for a small-diameter unidirectional microphone unit.
[0043]
【The invention's effect】
As described above, according to the present invention, a convex portion that forms a fine wave on the entire diaphragm and protrudes toward the opposite side of the back plate on the peripheral edge along the inner periphery of the support ring. By making the diaphragm have slack in advance, the adsorption stability with respect to the back plate is high, and the low-frequency regeneration limit can be extended accordingly. The present invention is particularly suitable for a small-diameter unidirectional microphone unit.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the internal structure of a unidirectional microphone including a diaphragm according to the present invention.
FIGS. 2A and 2B are a plan view and a cross-sectional view of the diaphragm according to the embodiment of the present invention in a free state. FIGS.
FIG. 3 is a plan view and a cross-sectional view when a diaphragm according to an embodiment of the present invention is combined with a back electrode plate.
FIG. 4 is a front view showing the molding apparatus for applying a minute wave to the diaphragm of the present invention with a part cut away.
FIG. 5 is a plan view showing a state in which a diaphragm obtained by the molding apparatus is attached to a support ring.
FIGS. 6A and 6B are a plan view and a cross-sectional view of a molding die in which convex portions are provided on the diaphragm of the present invention.
FIG. 7 is a cross-sectional view showing a state where a convex portion is molded by the molding die.
FIG. 8 is a frequency response characteristic graph of a unidirectional condenser microphone according to the present invention.
FIG. 9 is a frequency response characteristic graph of a conventional unidirectional condenser microphone.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Unidirectional condenser microphone 11 Diaphragm 11a Diaphragm material 111 Fine wave 112 Protrusion 113 Looseness 12 Support ring 21 Back electrode plate 22 Housing 24 Connector plate 28 Impedance 40 Molding device 43 Molding die 45 Pressure pot 46 Concavity and convexity formation Member 60 Mold 61 Diaphragm placement surface 611 Negative pressure suction hole 62 Support ring placement surface

Claims (6)

In the state of being attached to the support ring, in the diaphragm of the condenser microphone made of a thermoplastic resin film arranged to face the back electrode plate of the microphone unit at a predetermined interval,
The entire film is formed in a fine wavy shape, and a convex portion protruding toward the opposite side of the back electrode plate is formed on the peripheral portion along the inner periphery of the support ring of the film. The protrusion is provided with a slack that is visible to the film in a free state of the film and is eliminated by an electrostatic attraction acting from the back electrode plate side and becomes invisible. Condenser microphone diaphragm. The diaphragm of the condenser microphone according to claim 1, wherein the convex portion is formed in an annular shape along the inner periphery of the support ring. The diaphragm of the condenser microphone according to claim 1, wherein a plurality of the convex portions are scattered at predetermined intervals along the inner periphery of the support ring. A unidirectional condenser microphone comprising the diaphragm according to any one of claims 1 to 3 . Cooled after pressing the first mold having fine irregularities thermoplastic resin film as a diaphragm material under a predetermined heating temperature, a first step of applying a fine waves throughout the film, said first A second step of applying a predetermined tension to the film obtained in one step and attaching the film to the support ring; and the support ring on a second mold having a negative pressure suction hole in a portion along the inner periphery of the support ring. The film attached to the substrate is placed, and the second mold is brought to a negative pressure at a heating temperature lower than that in the first step, and a part of the film is drawn into the negative pressure suction hole to be deformed, and then cooled. An electrostatic attraction force acting on the film in the free state of the film and forming a convex portion on the peripheral edge along the inner periphery of the support ring of the film and acting from the back plate side Disappears and becomes invisible Manufacturing method of the diaphragm of the condenser microphone, characterized in that it comprises a third step of providing the body. The diaphragm for a condenser microphone according to claim 5 , further comprising a fourth step of cooling the film after being heated in a free state at a heating temperature lower than that of the third step for a predetermined time after the third step. Production method.

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