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DESCRIPTION JP2009188592

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DESCRIPTION JP2009188592
An object of the present invention is to improve the sensitivity by reducing the stray capacity of a
portion where a support ring of a diaphragm and a fixed pole overlap via a spacer without
sacrificing other performance and cost aspects. SOLUTION: An unevenness 211 having a crosssectional waveform is formed in a sticking portion of a diaphragm 210 to a support ring 22, and
within this unevenness 211, after being cured, it exerts a strength that is not inferior to a
pressing force applied to a storage in a knit case. The support ring 22 and the fixed electrode 31
are formed by filling the high strength adhesive 23 a to be bonded and attaching the diaphragm
210 to the support ring 22 and bringing the support ring 22 into contact with the spacer 40 in a
multipoint manner. The area of the overlapping portion through the spacer 40 is substantially
reduced to reduce the stray capacity. [Selected figure] Figure 1
コンデンサマイクロホンユニット
[0001]
The present invention relates to a condenser microphone unit, and more particularly, to a
technology for reducing the stray capacitance of a portion where a support ring and a fixed pole
of a diaphragm overlap via a spacer.
[0002]
First, the general configuration of the condenser microphone unit will be described with
reference to the sectional view of FIG.
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The condenser microphone unit includes a bottomed cylindrical unit case 10 made of, for
example, an aluminum material. The front end plate 10a corresponds to the bottom, and a front
acoustic terminal hole 11 is drilled in the bottom, and the rear end side of the unit case 10 is
open.
[0003]
In the unit case 10, the diaphragm 21 tensioned to the support ring 22 and the fixed electrode
31 supported by the insulating seat 32 are disposed opposite to each other via the electrically
insulating spacer 40 shown in FIG. In the closed state, and thereby an acoustoelectric transducer
is configured.
[0004]
The support ring 22 is made of metal, and the diaphragm 21 is made of a thin synthetic resin
film on which a metal deposition film is formed.
As shown in FIG. 4, the diaphragm 21 is attached to the support ring 22 via an adhesive 23.
[0005]
The fixed electrode 31 is made of a metal plate having a large number of air holes 311, and in
the case of the electret type, the surface of the fixed electrode 31 is provided with an electret
dielectric film. The insulating seat 32 is made of a disc body of synthetic resin, and one surface of
the insulating seat 32 supports the fixed electrode 31.
[0006]
The circuit board 50 is disposed on the back side of the insulating seat 32 so as to close the
opening of the unit case 10. Since the condenser microphone unit is unidirectional, the circuit
board 50 is provided with the rear acoustic terminal hole 51.
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[0007]
In relation to this, a sound wave introducing hole 321 for making a sound wave from the rear
acoustic terminal hole 51 act on the back side of the diaphragm 21 through the air hole 311 of
the fixed pole 31 is bored in the insulating seat 32. Further, a back air chamber 322
communicating with the sound wave introduction hole 321 is formed on the back side of the
fixed electrode 31 in the insulating seat 32, and a predetermined acoustic resistance material
323 is accommodated in the back air chamber 322.
[0008]
An FET (field effect transistor) 52 as an impedance converter is mounted on the circuit board 50.
An electrode terminal 53 electrically connected to the fixed pole 31 via a coil spring 54 is
disposed at a central portion of the insulating seat 32, and the electrode terminal 53 is in contact
with the gate pole of the FET 52.
[0009]
Finally, the rear end edge 10b of the unit case 10 is crimped, whereby the contents in the unit
case 10 are pressed and fixed. A screw type lock ring screwed into the unit case 10 may be used
as a fixing means instead of the caulking.
[0010]
In the above-described configuration, as shown in FIG. 4, a portion (overlapping portion) A where
the support ring 22 and the fixed pole 31 overlap through the electrically insulating spacer 40 is
inevitably formed, and thereby stray capacitance (floating portion Capacity) occurs. In the
condenser microphone unit, the stray capacitance causes the sensitivity to decrease.
[0011]
As one of methods of increasing the sensitivity by reducing the stray capacity, for example, as
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shown in FIG. 5, there is a method of reducing the width (area) of the overlapping portion A by,
for example, reducing the outer diameter of the fixed pole 31. . However, this method has the
following problems.
[0012]
That is, in the general-purpose unit, the fixed pole 31 is manufactured by an inexpensive press
process with priority given to the cost. However, sags often occur in the outer peripheral portion
of the fixed pole 31.
[0013]
As a result, it becomes difficult to ensure the distance between the fixed electrode 31 and the
diaphragm 21 accurately due to the sag, and variations in performance such as sensitivity are
likely to occur.
Therefore, in the case of adopting the above-mentioned method, the introduction of a highprecision pressing process is required, and the cost is sacrificed.
[0014]
As another method, Patent Document 1 proposes reducing the stray capacity by using a film
material having a low relative dielectric constant as a spacer. According to this, it is not
particularly necessary to reduce the outer diameter of the fixed pole 31, but because of the
speciality of the film, it is difficult and expensive to obtain a thickness suitable for the design of
the unit. There is a problem of
[0015]
Japanese Utility Model Application Publication 6-34399
[0016]
Therefore, the object of the present invention is to reduce the stray capacitance of the portion
where the support ring of the diaphragm and the fixed pole overlap through the spacer without
sacrificing other performance and cost in the condenser microphone unit. , To improve the
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sensitivity.
[0017]
In order to solve the above-mentioned problems, according to the present invention, a
diaphragm, which is attached to a support ring via an adhesive, and a fixed electrode supported
by an insulating seat are disposed opposite to each other via a spacer. Comprising the
acoustoelectric transducer, the acoustoelectric transducer being housed in a cylindrical unit case
with a bottom, and applying a predetermined pressing force from the opening side of the unit
case by a fixing means In the condenser microphone unit, irregularities having a cross-sectional
waveform are formed in the sticking portion of the diaphragm to the support ring, and the
adhesive is filled in the irregularities and exhibits strength not to lose the pressing force after
curing. It is characterized in that a strong adhesive is used.
[0018]
According to a preferred aspect of the present invention, the unevenness of the cross-sectional
waveform is formed over the entire surface of the diaphragm.
[0019]
According to the present invention, a concavo-convex having a cross-sectional waveform is
formed in the sticking portion of the diaphragm to the support ring, and within this concavoconvex, a strength that exerts a strength not losing the pressing force applied to the storage in
the knit case after curing Since the support ring is in multipoint contact with the spacer by filling
the diaphragm with the strength adhesive and attaching the diaphragm to the support ring, the
support ring and the fixed electrode are interposed by the spacer The area of the overlapping
portion can be substantially reduced, and the stray capacity can be reduced.
[0020]
In this case, the unevenness of the cross-sectional waveform with respect to the diaphragm can
be easily formed by the existing heating mold, and the high-strength adhesive can be a
commercially available product, so that no particular burden is imposed on the cost.
[0021]
Further, by forming the concavities and convexities of the cross-sectional waveform over the
entire surface of the diaphragm, the diaphragm can be easily manufactured as compared with the
case where the concavities and convexities are formed only in the sticking portion to the support
ring, and the tension is low with respect to the support ring. Even if it is stretched, it is not
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absorbed in a plane by electrostatic attraction from the fixed electrode side, and it becomes
possible to set the stiffness lower than that of a flat diaphragm with the same diameter. .
[0022]
Next, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic enlarged cross-sectional view showing the overlapping portion of the
support ring of the diaphragm and the fixed pole through the spacer, which is an essential part of
the present invention, and FIGS. 2 (a) and 2 (b) are support rings for the diaphragm. It is a typical
expanded sectional view similar to FIG. 1 which shows an example of the procedure of sticking
to.
For the entire configuration of the condenser microphone unit, refer to FIG. 3 described above.
[0023]
According to the present invention, in order to reduce the stray capacity, irregularities of the
cross-sectional waveform are formed in the adhered portion of the diaphragm to the support
ring, but in the condenser microphone unit according to this embodiment, as shown in FIG. The
diaphragm 210 in which the unevenness | corrugation 211 of cross-sectional waveform is
formed over is used.
The unevenness 211 of the cross-sectional waveform can be formed, for example, by the molding
technology disclosed in Japanese Patent No. 2681207 according to the proposal of the present
applicant.
[0024]
That is, a fine mesh material of about # 300, for example, of synthetic resin such as nylon or
metal such as stainless steel wire is disposed in a heating mold (not shown), and a diaphragm
material is placed thereon. A thermoplastic film such as polyethylene terephthalate or
polyphenylene sulfide may be placed and heat-formed, and the mesh of the mesh material may
be transferred to the thermoplastic film.
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[0025]
The diaphragm 210 is attached to the support ring 22 with the adhesive 23a at a peripheral edge
thereof under a predetermined tension (at least a tension not causing slack), but in this case, the
adhesive 23a High strength adhesives are used.
In the present invention, the high strength adhesive is an adhesive having the following strength.
[0026]
As described above with reference to FIG. 3, after the acoustoelectric converter including the
diaphragm 21 and the fixed electrode 31 (stored in the unit case) is accommodated in the unit
case 10, for example, the rear end edge of the unit case 10 By pressing 10b, the contents in the
unit case are fixed by the pressing force, but with a high-strength adhesive, the strength after
curing is not inferior to the pressing force by the above-described caulking, that is, it is not
crushed ( A commercially available product is, for example, an epoxy-based adhesive 1565
(product number) manufactured by Cemedine Co., Ltd., as a commercially available adhesive.
[0027]
In bonding the diaphragm 210 to the support ring 22, as shown in FIG. 2 (a), after the adhesive
23a is applied to the support ring 22 with a predetermined thickness, as shown in FIG. 2 (b) The
support ring 22 is pressed against the diaphragm 210.
[0028]
At this time, the adhesive 23 a is filled in the concave portion of the unevenness 211 so as to
cure the adhesive 23 a, taking care not to crush the unevenness 211 of the adhered portion.
Thereafter, the surplus portion of the diaphragm protruding from the outer diameter of the
support ring 22 is cut off with a cutter or the like.
[0029]
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According to this, since the concavo-convex shape of the sticking part of the diaphragm 210 with
respect to the support ring 22 is maintained and the adhesive 23a is hardened with high
strength, as shown in FIG. And the spacer ring 40. Even if the rear end 10b of the unit case 10 is
crimped as described above, the support ring 22 contacts the spacer 40 in a multipoint manner
via the unevenness 211. It will be done.
[0030]
Therefore, the area of the portion where the support ring 22 and the fixed pole 31 overlap via
the spacer 40 is substantially reduced, and the stray capacity can be reduced.
[0031]
Incidentally, in the case of the conventional example shown in FIG. 3 in the unidirectional electret
condenser microphone having a diameter of 10 mm, the stray capacitance at the portion A where
the support ring 22 and the fixed pole 31 overlap via the spacer 40 is 8.6 pF. there were.
[0032]
On the other hand, according to the present invention, as the first embodiment of the present
invention, irregularities 211 having a cross-sectional waveform are formed on the diaphragm
210 and attached to the support ring 22 with the high strength adhesive 23a. The capacitance
was 6.3 pF.
Since the effective capacitance is about 10 pF, according to the inventive example, the sensitivity
is improved by about 1.1 dB.
[0033]
In the first embodiment, the unevenness of the cross-sectional waveform formed on the
diaphragm 210 is an unevenness equivalent to mesh degree # 508 (508 pieces / 1 inch), and the
area of the overlapping portion A is 1.29 × 10. It was <-5> (m <2>).
[0034]
In the above-described embodiment, the rear end 10b of the unit case 10 is crimped to press and
fix a storage (such as an acousto-electrical converter) of the unit case, but it is not shown in the
rear end opening of the unit case 10. The lock ring may be screwed to press and fix the storage
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of the unit case.
[0035]
Therefore, the strength after curing of the adhesive 23a is relatively determined in relation to the
pressing force by caulking or tightening of the lock ring.
Further, in the above-described embodiment, the unevenness 211 of the cross-sectional
waveform is formed on the entire surface of the diaphragm 210, but the unevenness 211 of the
cross-sectional waveform may be formed at least in the adhered portion to the support ring 22.
[0036]
FIG. 5 is a schematic enlarged cross-sectional view showing an overlapping portion of the
support ring of the diaphragm and the fixed electrode via a spacer, which is the main part of the
present invention.
The typical expanded sectional view similar to FIG. 1 which shows an example of the procedure
of sticking a diaphragm to a support ring.
Sectional drawing which shows the conventional common capacitor microphone unit.
FIG. 10 is a schematic enlarged cross-sectional view showing an overlapping portion of a support
ring of a diaphragm and a fixed pole via a spacer in a conventional example.
FIG. 5 is a schematic enlarged cross-sectional view similar to FIG. 4 for explaining a conventional
method for reducing the stray capacity in the overlapping portion.
Explanation of sign
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[0037]
DESCRIPTION OF SYMBOLS 10 Unit case 21,210 Vibrator 211 Irregularities 23a High-strength
adhesive 22 Support ring 31 Fixing pole 32 Insulating seat 40 Spacer 50 Circuit board
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