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JPH09182190

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DESCRIPTION JPH09182190
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker device, and more particularly to a speaker device using an electrostatic speaker.
[0002]
2. Description of the Related Art For example, there is known an electrostatic type speaker in
which a speaker unit is constructed by arranging a pair of fixed electrodes opposite to each other
and arranging a vibrator between the fixed electrodes. For this electrostatic speaker unit, a drive
signal is applied between a pair of fixed electrodes, and a DC bias voltage is applied between the
electrode of the vibrator and the fixed electrode to meet the drive signal. Generate sound
pressure.
[0003]
FIG. 6 is an external view of an electrostatic speaker unit according to the structural technique
proposed by the applicant earlier, and FIG. 7 is a cross-sectional view thereof. The speaker unit 1
is formed by joining a frame 2 and a frame 3 by a screw N. Further, as can be seen from FIG. 7A,
fixed electrodes 4A and 4B are disposed in the facing state inward of the frame 2 and the frame
3. The fixed electrodes 4A and 4B are exposed to the outside from openings 2a and 3a formed at
the centers of the frames 2 and 3, respectively. Further, as can be seen from FIG. 6, the fixed
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electrode 4A (and 4B) is a rectangular flat plate, and a large number of openings H are formed.
[0004]
A vibrating film 9 is disposed in the gap between the fixed electrodes 4A and 4B. The peripheral
end of the vibrating membrane 9 is sandwiched by the metal frame 7 and the vibrating body
electrode 8 and mounted in the frames 2 and 3 via the elastic body 6. The vibrating film 9 is
formed, for example, by applying a conductive thin film to a polyester film.
[0005]
The vibrating membrane 9 located in the gap between the fixed electrodes 4A and 4B is provided
with an air gap of a predetermined length with respect to the fixed electrodes 4A and 4B. As
shown enlarged in FIG. 7B, the spacers 5A and 5B are disposed around the fixed electrodes 4A
and 4B, and the diaphragm 9 is sandwiched between the spacers 5A and 5B, that is, The length
of the air gap (the separation distance da between the fixed electrode 4A and the vibrating
membrane 9 and the separation distance db between the fixed electrode 4B and the vibrating
membrane 9) is set with high precision by the thickness of the spacers 5A and 5B. There is.
[0006]
For example, a drive signal and a bias voltage are applied to the speaker unit having such a
structure by a circuit as shown in FIG. That is, a commercial power supply is input to the primary
winding side of the step-up transformer 11, and the secondary winding side of the step-up
transformer 11 is a multistage multiple formed by the diodes 12 to 18 and the capacitors 19 to
26. Connected to the voltage rectifier circuit. The output of this multistage voltage doubler
rectifier circuit is connected to an intermediate tap on the secondary winding side of the
transformer 30.
[0007]
The secondary winding of the transformer 30 is connected to the fixed electrodes 4A and 4B
through the resistors 28 and 29, respectively, and one end of the secondary winding of the step-
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up transformer 11 is connected to the vibrator TC through the resistor 27 from the terminal TC.
Since it is connected to the electrode 8 (that is, the vibrating membrane 9), a DC bias voltage is
applied between the vibrating membrane 9 and the fixed electrode 4A, and between the vibrating
membrane 9 and the fixed electrode 4B. The DC bias voltage is set to a high voltage of, for
example, 2.5 KV.
[0008]
Further, from the power amplifier to which this speaker device is connected, an audio signal is
supplied between terminals connected to the primary winding side of the transformer 30. When
this audio signal flows to the primary winding side of the transformer 30 through the resistor 31,
it is boosted by the transformer 30 and appears as a drive signal on the secondary winding side,
and this drive signal is fixed from the terminals TF and TR The voltage is applied to the
electrodes 4A and 4B.
[0009]
In the case of such an electrostatic speaker, the driving force F is generally expressed by the
following equation based on Coulomb's law. Where q1 and q2 are charges of each electrode, r is
a distance between the electrodes, and K is a proportional constant. The electrostatic loudspeaker
is operated by the driving force F represented in this manner.
[0010]
By the way, in such a speaker device, the fixed electrodes 4A and 4B have a substantially
rectangular shape, and the entire surface of the electrode facing the vibrating film 9 is parallel to
the vibrating film 9. That is, the separation distance from the vibrating membrane 9 is da (db)
shown in FIG. 7 at any part on the electrode surface. Accordingly, the driving force applied to the
vibrating membrane 9 is uniform to the entire film surface of the vibrating membrane 9.
[0011]
Here, it is assumed that F = F0 sin (.omega.t) is generated as the uniform driving force F over the
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entire surface of the vibrating film 9 by the applied voltage. The frequency characteristic of the
displacement distribution z of the vibrating membrane 9 at this time is as shown in Formula 3.
Here, m and n indicate the order of the natural vibration mode of the vibrating membrane 9, and
Ξ indicates the displacement distribution of the natural vibration with a standard function.
Further, V is a volume, M is the total mass of the vibrating membrane 9, and ωm, n and ω are
mn order resonant angular frequencies and angular frequencies.
[0012]
As an example, the case where the side length of the substantially rectangular diaphragm 9 is a
in the x-axis direction and b in the y-axis direction will be described. Regarding the x and y axes,
as shown in FIG. 6, the longitudinal direction is the x-axis direction and the short direction is the
y-axis direction as viewed in the plane direction of the vibrating membrane 9. In this case, the
displacement distribution of the natural vibration mode is expressed by (Equation 4).
[0013]
By substituting the equation 4 into the equation 2, the displacement distribution z of the
vibrating membrane 9 can be expressed as follows:
[0014]
FIGS. 5 (a) to 5 (d) illustrate four types of resonance modes as a part of the vibration mode
represented by the equation (5).
FIG. 5 (a) shows a resonance mode in the case of (m, n) = (1, 1) in the above equation (5), that is,
all film surfaces of the vibrating film 9 vibrate in the same direction at a certain frequency. It is in
the state of Further, when (m, n) = (3, 1) at a frequency higher than this, as shown in FIG. 5B, a
mode in which vibrations of peaks / valleys / peaks appear in the longitudinal direction (x-axis
direction).
[0015]
FIG. 5 (c) is a mode when (m, n) = (1, 3), and vibrations of peaks / valleys / peaks appear in the
short direction (y-axis direction), and further (m, n). As a mode when it becomes =) (3, 3), it
becomes an oscillating state where peaks and valleys appear complexly in the longitudinal
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direction and the short direction as shown in FIG. 5 (d).
[0016]
As described above, a large number of resonance modes are generated in the vibrating film 9,
whereby the frequency characteristic becomes as shown in FIG.
In FIG. 9, the influence site due to the resonance of the mode in which the value of (m, n) is (1, 1)
(3, 1) (5, 1) (7, 1) is shown.
[0017]
As described above, the occurrence of a large number of resonance modes causes the following
problems in the speaker device in which the entire surface of the fixed electrodes 4A and 4B
facing the vibrating film 9 is parallel to the vibrating film 9: It was First, as can be seen from FIG.
9, a peak dip occurs in the frequency characteristic of the amplitude of the film center of the
vibrating film 9, and a smooth characteristic can not be obtained. Then, since many resonances
occur in the use band, peak dips occur in the frequency characteristics of the sound pressure to
be output. In particular, the sound pressure becomes low in the frequency band corresponding to
the resonance mode vibrating in the opposite phase as illustrated in FIGS. 5 (b), (c) and (d).
[0018]
That is, there is a problem that good frequency characteristics can not be obtained for the sound
pressure and the vibration amplitude.
[0019]
SUMMARY OF THE INVENTION In view of these problems, the present invention arranges a fixed
electrode and a vibrating body in an opposing state, applies a drive signal to the fixed electrode,
and provides an electrode of the vibrating body and the fixed electrode. To apply a driving
voltage according to the driving signal to the vibrating body so that a good frequency
characteristic of sound pressure and vibration amplitude can be obtained in the speaker device
generating the sound pressure. The purpose is
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[0020]
For this reason, the surface of the fixed electrode is such that the separation distance to the
vibrator surface for each part on the fixed electrode surface is in a state in which the driving
force applied to the vibrator is proportional to the displacement distribution in the surface
direction of the natural vibration mode of the vibrator. Set the shape.
That is, the surface shape of the fixed electrode is, for example, curved, and the distance from
each part on the fixed electrode surface to the vibrator surface is made different depending on
each position, and the driving force applied to the vibrator is the surface of the natural vibration
mode of the vibrator By making it proportional to the displacement distribution in the direction,
an electrostatic loudspeaker that generates only a single resonance mode is realized.
For example, if the distance from each part on the fixed electrode surface to the vibrator surface
is made proportional to the displacement distribution of the (m, n) = (1, 1) mode, a static circuit
having only a resonant mode as shown in FIG. Electric speakers can be realized.
[0021]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the
speaker apparatus of the present invention will be described below with reference to FIGS. FIG. 2
shows a cross-sectional view of the speaker device of this example, and FIG. 3 shows a circuit
system to which a drive signal and a bias voltage are applied to the speaker unit. However, in the
speaker device of this embodiment, the shape of the fixed electrode and the portion
accompanying it are different from those of the prior art shown in FIGS. 6 to 8, and the same
functions as in FIGS. 7 and 8 in FIGS. The same reference numerals are given to parts, and the
description is omitted.
[0022]
As the cross-sectional shapes of the fixed electrodes 30A and 30B are shown in FIGS. 2 and 3, the
fixed electrodes 30A and 30B are formed in a state where the surface facing the vibrating
membrane 9 is curved. Then, as shown in FIG. 2, the edge portions of the fixed electrodes 30A
and 30B having a curved sectional shape are fixed in a state in which the vibrating membrane 9
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is sandwiched between the frame 2 and the frame 3 via the spacers 31A and 31B and the spacers
5A and 5B. Be done.
[0023]
Although not shown, the fixed electrodes 30A and 30B also have openings 2a and 3a formed at
the centers of the frame 2 and the frame 3 in the same manner as the fixed electrode 4A (4B) in
the example shown in FIG. Are exposed to the outside, and a large number of openings are
formed to guide the sound pressure generated by the vibrating membrane 9 to the outside.
[0024]
It is FIG. 1 which showed the arrangement | positioning state and shape about fixed electrode
30A, 30B and the vibrating membrane 9. In FIG.
In FIG. 1, in order to make the shapes of the fixed electrodes 30A and 30B easy to understand,
equally spaced lines corresponding to x, y plane coordinates are entered. As can be seen from
FIG. 1, each of the fixed electrodes 30A and 30B has a shape in which the surface facing the
vibrating film 9 bulges in a convex shape. Therefore, when viewed in the x and y coordinate
planes, the fixed electrodes 30A and 30B are formed. The distance from each coordinate position
of to the vibrating membrane 9 is not uniform.
[0025]
That is, in this example, the distance from each coordinate position of the fixed electrodes 30A
and 30B to the vibrating film 9 is such that the driving force applied to the vibrating film 9 is
proportional to the displacement distribution in the surface direction of the natural vibration
mode of the vibrating film 9 As described above, the surface shape of the fixed electrode is set,
and this will be described below.
[0026]
The distribution of the fixed electrodes 30A and 30B in the surface direction with respect to the
distance to the vibrating membrane 9 means that the driving force to be applied to the vibrating
membrane 9 is distributed.
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The driving force distribution is assumed to be proportional to the (m, n) = (1, 1) mode as the
natural vibration mode of the vibrating membrane 9. That is, it is assumed that the driving force
F0. This equation is substituted into (Equation 3) described above. From the orthogonality of the
standard function, except for m = 1 and n = 1, for the numerator part of (Equation 3), that is, for
the term “∫ (F 0 Ξm, n 2) dV”,
[0027]
Using this, the above equation (5) can be replaced by the equation (8) expressed only by the term
m = 1 and n = 1. That is, it is understood from this (Equation 8) that only the resonance of the (m,
n) = (1, 1) mode as shown in FIG. 5A appears. That is, by making the distribution of the driving
force F0 on the vibrating membrane 9 proportional to the natural vibration mode of the vibrating
membrane 9, only a single resonance mode can be generated.
[0028]
Based on such a principle, a method for actually obtaining a single resonance will be described.
The coulomb force acting on the vibrating membrane 9 is Here, .di-elect cons.0 is the dielectric
constant of air, S is the area of the vibrating film 9, Vdc is a DC bias voltage, Vsg is a signal
voltage, and d0 is the distance between the vibrating film 9 and the fixed electrodes (30A, 30B).
[0029]
From equation (9), it can be seen that the driving force F0 is inversely proportional to the square
of the distance between the vibrating membrane 9 and the fixed electrodes (30A, 30B).
Therefore, if the separation distance between the vibrating membrane 9 and the fixed electrodes
(30A, 30B) is distributed in the surface direction of the vibrating membrane 9, the driving force
can be distributed to the vibrating membrane 9.
[0030]
For this reason, the surface shapes of the fixed electrodes 30A and 30B are as shown in FIG. 1,
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and the separation distance with respect to the vibrating membrane 9 is made proportional to 1/2 power of Ξ1, 1 (m, n A speaker device can be formed in which only the resonance of the (1)
1 mode appears. The power of Ξ 1,1 is expressed by (Equation 10). Here, a is the length of the
vibrating membrane 9 in the x coordinate direction, and b is the length of the vibrating
membrane 9 in the y coordinate direction.
[0031]
Therefore, when the separation distance between the vibrating membrane 9 and the fixed
electrodes (30A, 30B) at each xy coordinate point is dxy when considered on the xy coordinate
plane, the separation distance may be set by dxy. However, k is an arbitrary coefficient and is a
value to be determined at design time. The shape of the fixed electrodes 30A and 30B which can
obtain the distribution of the separation distance in the surface direction of the vibrating
membrane 9 based on this (Equation 11) is shown in FIG.
[0032]
In the speaker device of the present example as described above, only the resonance of the (m, n)
= (1, 1) mode appears, and the frequency characteristic is as shown in FIG. That is, it is possible
to obtain good characteristics in which no peak dip occurs in frequency characteristics of sound
pressure and vibration amplitude.
[0033]
Although an example of the embodiment has been described above, the present invention can be
variously modified within the scope of the invention. For example, the present invention can be
applied to a speaker device or the like in which a large number of fixed electrodes and
diaphragms are used and they are disposed in a laminated manner, nested in an inner and outer
circumferential direction, or arranged in a planar direction. Applicable In the above-mentioned
example, although the case where a rectangular diaphragm was adopted was explained, the
shape of the diaphragm may be any shape. In any case, the natural vibration mode may be
measured or analyzed to have a distribution of driving force proportional thereto (that is, the
distribution of the distance from the fixed electrode).
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[0034]
In the above example, only the resonance of the (m, n) = (1, 1) mode appears, but other
resonances such as the (m, n) = (3, 1) mode appear. The same principle is also possible.
[0035]
Furthermore, in the above example, the electrostatic speaker device having a shape in which the
diaphragm is sandwiched by two fixed electrodes has been described, but the present invention is
similarly applied to an electrostatic speaker device in which the diaphragm is driven from one
side by one fixed electrode. Needless to say, it can be adopted.
[0036]
As described above, according to the speaker device of the present invention, the driving force
that is applied to the vibrating body for the separation distance to the vibrating body surface for
each part on the fixed electrode surface is in the plane direction of the natural vibration mode of
the vibrating body. By setting the surface shape of the fixed electrode so as to be in a state
proportional to the displacement distribution, an electrostatic speaker that generates only a
single resonance mode is realized, and the frequency of the sound pressure and vibration
amplitude by the vibrating body There is an effect that the characteristic can be made a good
characteristic without occurrence of peak dip.
[0037]
Brief description of the drawings
[0038]
1 is an explanatory view of the shape of the fixed electrode of the embodiment of the present
invention.
[0039]
2 is a cross-sectional view of the fixed electrode speaker unit of the embodiment.
[0040]
3 is a circuit diagram of a drive circuit system of the speaker unit of the embodiment.
[0041]
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4 is an explanatory view of the frequency characteristics of the speaker device of the
embodiment.
[0042]
5 is an explanatory view of various resonance modes.
[0043]
6 is an explanatory view of the appearance of the electrostatic speaker unit.
[0044]
7 is a cross-sectional view of the electrostatic speaker unit.
[0045]
8 is a circuit diagram of a drive circuit system of the electrostatic speaker unit.
[0046]
9 is an explanatory view of the frequency characteristic of the speaker device in the prior art.
[0047]
Explanation of sign
[0048]
DESCRIPTION OF SYMBOLS 1 Speaker unit 2, 3 frame 5A, 5B, 31A, 31B Spacer 7 Metal frame 8
Vibrator electrode 9 Vibrating film 30A, 30B Fixed electrode
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