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DESCRIPTION JPS62213400

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DESCRIPTION JPS62213400
[0001]
FIELD OF THE INVENTION The present invention relates to condenser (including electret or bank
electret) microphones. [Summary of the invention] In a microphone in which a diaphragm
constituting a capacitor and a fixed back electrode face each other via a spacer, the spacer is
constituted by an outer peripheral spacer portion and an inner divided spacer portion, and the
diaphragm is substantially The separation between the poles is reduced by preventing division
vibration and raising the upper limit of the response, and preventing the diaphragm and the back
electrode from coming in contact with each other by the division spacer part. , The sensitivity is
increased. [Prior Art] In order to enhance the sensitivity of a capacitor type microphone
(including electret type or back electret type), it is necessary to increase the bias DC voltage
between the diaphragm and the back electrode forming the capacitor, or to increase the
sensitivity. It is necessary to reduce the facing distance between the electrode plates or to
increase the area of the diaphragm. Problems to be Solved by the Invention Increasing the bias
voltage is limited by the problem of insulation and the problem of built-in power supply (battery).
Further, if the distance between the electrodes is reduced, the area of the diaphragm is increased,
or the bias voltage is increased as described above, the electrostatic attraction between the
diaphragm (film) and the back electrode is increased. Therefore, it is necessary to increase the
tension in the surface direction of the diaphragm or the diaphragm so that the diaphragm does
not contact the back electrode, which makes it difficult to manufacture the microphone with a
limited external shape. Further, if the diaphragm area is increased or the tension is increased, the
sensitivity of the high frequency band is lowered and the band becomes narrow. SUMMARY OF
THE INVENTION In view of these problems, the present invention aims to obtain a capacitor type
microphone having high sensitivity and wide band frequency characteristics with a simple
configuration. [Means for Solving the Problems] As shown in FIG. 1A, FIG. 2 or FIG. 3, the
condenser microphone of the present invention comprises a diaphragm 1 forming a condenser
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1
and a fixed back pole 4 as a spacer 2. In the configuration facing each other, the spacer is divided
so that the diaphragm 1 causes divided vibration, an outer peripheral spacer portion 2a
surrounding the outer periphery of the vibration surface, and a division disposed inside the outer
peripheral spacer portion And the spacer portion 2b. [Operation] By generating the divided
vibration, the high frequency limit of the response-frequency characteristic is increased. Further,
since the inter-electrode discharge is prevented by the interposition of the dividing spacer
portion, it is possible to make the spacer thickness thinner and to improve the sensitivity.
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A is a cross-sectional view showing the
basic configuration of a condenser type microphone, and FIG. 1B is a plan view of a spacer
between electrode plates.
As is well known, in this type of microphone, a metal foil or a metallized film is used for the
diaphragm 1, and the spacer 2 is surrounded to be opposed to the back electrode 4 (fixed side)
having a large number of pores 3. A bias DC voltage E is applied between the diaphragm 1 and
the back pole 4, and the potential change of the back pole 4 accompanying the vibration of the
diaphragm 1 is taken out as a microphone output. The spacer 2 is provided with an outer
peripheral spacer portion 2a as shown in FIG. 1B, and the thickness thereof holds the space
between the diaphragm 1 and the back electrode 4 at a constant interval. A dividing spacer
portion 2b is further provided inside the area surrounded by the outer peripheral spacer portion
2a. In the example of FIG. 1B, the spacer portion 2b is continued to the outer peripheral spacer
portion 2a, and is formed at a position which divides the vibration area of the diaphragm
approximately into two. Such a spacer 2 can be made by punching or etching a sheet of
insulating film such as polyester, polyimide or polystyrene. Since the dividing spacer portion 2b
is provided, inter-electrode discharge does not occur even if the thickness of the spacer 2 is made
thinner than in the prior art. As a result, the interelectrode capacitance substantially increases
and the sensitivity increases. In addition, the S / N improves as the sensitivity increases. The
spacer 2 is drawn in by electrostatic attraction between the diaphragm 1 and the back electrode
4, and the outer peripheral spacer portion 2 a and the dividing spacer portion 2 b are in close
contact with the diaphragm 1. Therefore, the vibration area of the diaphragm 1 is divided into
two parts by the dividing spacer part 2b, and the diaphragm 1 divides and vibrates in each
divided part. That is, the stiffness of the diaphragm 1 increases at a high place, and as a result,
the high frequency limit of the output frequency characteristic of the microphone is extended,
and the frequency band becomes wider. Incidentally, since the capacitor type microphone has a
good low frequency characteristic in principle, even if the low frequency characteristic is
somewhat deteriorated due to the divided vibration of the diaphragm 1, it can be electrically
compensated in the amplification system. Since the spacer 2 is crimped between the diaphragm 1
and the back electrode 4 by electrostatic attraction, there is no need to fix the spacer 2 on the
surface side of the back electrode 4 with an adhesive. It may be adhesively fixed if necessary. The
dividing spacer portion 2 b may be formed at a position avoiding the pores 3 of the back
electrode 4. The present invention is also applicable to the electleft type of FIG. 2 or FIG. 3
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known as a condenser microphone. In FIG. 2, an electret film in which charges are permanently
fixed is used as the diaphragm 1, and it has a structure in which the back electrode 4 is faced via
the spacer 2 as in FIG. 1A.
Application of a bias voltage is unnecessary. FIG. 3 is referred to as a back electret type, in which
the electret film 5 is fixed to the surface of the back electrode 4 and the metallized diaphragm 1
is faced with the spacer 2 interposed therebetween. The same effects as described above can be
obtained by using the spacer as shown in FIG. 1B also in the electleft microphone shown in FIG. 2
or 3. In the electleft type or back electret type, when the interelectrode capacitance increases, the
voltage division ratio with the input capacitance of the FET input amplifier changes, and as a
result, the sensitivity increases. FIG. 4 shows various modifications of the spacer 2. A is an
example in which the dividing spacer portion 2b is protruded from one side of the outer
peripheral spacer portion 2a to almost the center of the vibration region, and B is made to
project a pair of dividing spacer portions 2b from two opposing sides of the outer peripheral
spacer portion 2a Example. In either case, the vibration region surrounded by the outer
peripheral spacer portion 2a is substantially divided into two parts, and divided vibration occurs
in each part. In FIG. 4C, the dividing spacer portion 2b is a square surrounding a smaller area
than the outer peripheral spacer portion 2a, and the spacer portion 2a and the outer peripheral
portion 2a are joined by a connecting portion 2C. The vibration plane is divided into three: two
peripheral parts and a central part. D is an example in which the vibration area is divided into
two uneven parts by one dividing spacer part 2b. E is an example in which an oblique dividing
spacer portion 2b is provided so that a part of the triangular corner is divided. FIG. 4F is an
example in which a dividing spacer portion 2b surrounding a small rectangular area is provided
inside the outer peripheral spacer portion 2a. In this example, since the outer peripheral spacer
portion 2a and the dividing spacer portion 2b are not continuous, the dividing spacer portion 2b
is adhesively fixed to the surface of the back electrode 4 at the time of assembly. The plane of
oscillation is divided into two parts, the inner and outer regions. FIG. 4G is an example in which a
point-like dividing spacer portion 2b is provided, and although the vibrating surface is not
divided into two parts in area, the diaphragm 1 causes divided vibration with the spacer portion
2b as a node, Vibrational surface division, and similar effects can be obtained. The outer shape of
the diaphragm 1 may be round or polygonal in addition to quadrilateral, and the divided shape of
the spacer 2 can be variously considered according to the outer shape of the diaphragm 1. FIG. 5
shows the frequency characteristics of the microphone when the spacer of FIG. 4F is used, and as
shown in the figure, the high frequency limit becomes higher and the sensitivity is improved as
compared with the case without the dividing spacer portion (dotted line). . In the case of using
the spacers 2 of FIGS. 1B and 4A to 4E and 4G, substantially similar frequency characteristics can
be obtained.
As described above, according to the present invention, since the interpolar spacer 2 of the
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condenser microphone is constituted by the outer peripheral spacer portion 2a surrounding the
vibration surface and the dividing spacer portion 2b inside thereof, the stiffness of the diaphragm
1 is increased. Increases locally, and the upper limit of the response rises to obtain a wider band
characteristic. Further, since it is prevented by the dividing spacer portion 2b that the diaphragm
1 is in contact with the back electrode 4 and discharged by the electrostatic attraction between
the electrodes, the spacer thickness is further reduced to reduce the distance between the
electrodes, As a result, the inter-electrode capacity can be increased to obtain high sensitivity and
high output, and the S / N can be relatively improved.
[0002]
Brief description of the drawings
[0003]
FIG. 1A is a cross-sectional view of an essential part of a condenser microphone according to an
embodiment of the present invention, FIG. 1B is a plan view of a spacer, and FIG. 2 and FIG. 4A to
4G are plan views showing modifications of the spacer, and FIG. 5 is a frequency characteristic
diagram.
In the reference numerals used in the drawings, reference numeral 1-1-----------Vibration plate 2---------------------------- ---------------------------------------------------------------------- --- Pores 4----------------------------Eletorestofilm.
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