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JPH07336797

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH07336797
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker device, and is particularly suitable for a speaker device using an electrostatic speaker.
[0002]
2. Description of the Related Art There is known an electrostatic type speaker in which a speaker
unit is configured such that a pair of fixed electrodes are opposed to each other and a vibrating
body is disposed 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. 5 is an external view of an electrostatic speaker unit according to the structural technique
proposed by the applicant previously, and FIG. 6 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. As can be seen from FIG. 6 (a),
fixed electrodes 4A and 4B are disposed in the opposite state inward of the frame 2 and the
frame 3, respectively. 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. 5, the fixed electrode 4A (and 4B) is a rectangular flat plate, and a large number of openings
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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 C having a predetermined length with respect to the fixed electrodes 4A and 4B.
As shown enlarged in FIG. 6B, 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. The length of the air
gap C (gap size) is set with high precision by the thickness of the spacers 5A and 5B.
[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 stepup 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
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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.
[0010]
The electrostatic speaker is operated by the driving force F expressed in this manner. Therefore,
considering the charge by the DC bias as q1 and the charge by the AC drive signal as q2, the
drive power is the DC bias and the AC drive signal. It is understood that it depends on the
product of Therefore, in order to increase the driving force and improve the sensitivity, it is
generally performed to raise the DC bias voltage to the upper limit.
[0011]
By the way, the upper limit value is the withstand voltage of the air gap C. The withstand voltage
of the air gap C is usually said to be 1 kV / mm. However, in practice, considering that the AC
drive signal is superimposed on the DC bias voltage, or that the withstand voltage of the air gap C
is reduced due to moisture in the air, adhesion of dust to the fixed electrode, etc. The bias voltage
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can not be increased. If the withstand voltage of the air gap C is exceeded, corona discharge or
arc discharge occurs, causing a large noise or breaking of the vibrating film 9. Therefore, it has
been difficult to sufficiently increase the sensitivity of the speaker device.
[0012]
In order to avoid the said discharge and destruction and to improve a sensitivity, it is possible to
perform the insulation process by powder coating etc. on the surface of a fixed electrode. That is,
as schematically shown in FIG. 8A, the insulating film 32 is formed on the surfaces of the fixed
electrodes 4A and 4B.
[0013]
An equivalent circuit of the speaker unit portion of FIG. 8A is as shown in FIG. 8B. In this
equivalent circuit, CI1 and CI2 are capacitances of the insulating film 32, CA1 and CA2
capacitances of the air gap C, RI1 and RI2 are resistances of the insulating film 32, RS1 and RS2
are components of the air gap C (spacer 5A, 5B) surface resistance.
[0014]
Considering the operation in this case, the bias voltage VBa generated in the air gap C is obtained
by resistance division. However, VBo is a bias power supply voltage.
[0015]
Further, when the AC drive signal VDa is viewed between the fixed electrodes 4A and 4B,
However, VDo is a supply drive voltage.
[0016]
Considering the sensitivity improvement based on this (Equation 2) (Equation 3), the following
condition is required.
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[0017]
By satisfying (Equation 4), a sufficient bias voltage can be obtained, and by satisfying (Equation
5), a sufficient sensitivity as a drive signal can be obtained.
And in order to satisfy (Equation 4), it is conceivable to use a high insulating material such as
vinyl chloride or acrylic for the spacers 5A and 5B which are gap components, and as for
(Equation 5), it is usually used as an insulating material Since the dielectric constant of epoxy and
the like used is sufficiently higher than that of air, the equation (5) will be easily satisfied.
[0018]
Furthermore, in the case where the insulating film 32 is provided in this way, by setting the
resistances RI1 and RI2 of the insulating film 32 high, audible high voltage noise is generated
even if a leak occurs. It is also possible to obtain the feature of being able to prevent the
occurrence of breakage of parts.
[0019]
However, when the insulating film 32 is provided on the fixed electrodes 4A and 4B, it is very
difficult to obtain uniform insulation performance on the electrodes, and the manufacturing cost
is also increased.
In addition, the flatness of the electrode surface is deteriorated, making it difficult to obtain a
uniform air gap, and variations in output sound pressure occur. Furthermore, the fixed electrodes
4A and 4B are formed of, for example, a panning metal or a wire mesh, and a large number of
openings H are provided as shown in FIG. And the output sound pressure is reduced.
[0020]
SUMMARY OF THE INVENTION In view of such problems, the present invention is very simple to
realize a speaker device having the same or higher performance than the case where the abovedescribed electrode is provided with an insulating film. To aim.
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[0021]
For this purpose, a drive signal is applied between a pair of fixed electrodes held so as to face
each other, and a bias voltage is applied between an electrode of the vibrator held between the
fixed electrodes and the fixed electrode. In a speaker device that generates sound pressure
according to a drive signal, capacitor elements are arranged in series between each fixed
electrode and a drive signal supply source.
[0022]
[Operation] By arranging a capacitor element in series between the fixed electrode and the drive
signal supply source, for example, a transformer, the resistances of the capacitances CI1 and CI2
of the insulating film and the insulating film 32 described in FIG. RI1 and RI2 can be obtained by
the capacitor element.
[0023]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the
speaker apparatus of the present invention will be described below with reference to FIGS.
In these embodiments, the bias voltage and drive signal supply circuit system and the structure
of the speaker unit are the same as those of the prior art described with reference to FIGS.
The embodiment is characterized in the configuration from the terminals TF, TC, TR to the fixed
electrodes 4A, 4B and the vibrating membrane 9, and only this portion will be described.
[0024]
FIG. 1 (a) is a schematic view showing a first embodiment, and FIG. 1 (b) is an equivalent circuit
diagram thereof.
As can be seen from FIG. 1 (a), in the case of this embodiment, the insulating capacitor 40A is
connected in series between the fixed electrode 4A and the terminal TF, and the insulating
capacitor is also connected between the fixed electrode 4B and the terminal TR. 40B are
connected in series.
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[0025]
If this is shown as an equivalent circuit, it will become like FIG.1 (b). Here, CC1 and CC2 are
capacitances of the insulating capacitors 40A and 40B, CA1 and CA2 are capacitances of the air
gap C, RC1 and RC2 are resistances of the insulating capacitors 40A and 40B, RS1 and RS2 are
components of the air gap C This is the surface resistance of (the spacers 5A, 5B).
[0026]
That is, by arranging the insulating capacitors 40A and 40B so that this equivalent circuit can be
understood as compared with the equivalent circuit of FIG. 8B described above, the fixed
electrodes 4A and 4B are electrically coated with insulation. The same thing as the case can be
realized.
[0027]
Therefore, by selecting the insulating capacitors 40A and 40B so that the above-mentioned
(Equation 4) and (Equation 5) are satisfied, a sufficient bias voltage can be obtained, and
sufficient sensitivity as a drive signal is obtained. It will be taken.
[0028]
That is, capacitors having a certain degree of capacity may be selected and used as the insulating
capacitors 40A and 40B such that the capacitance CC (CC1, CC2) thereof is sufficiently larger
than the capacitance CA (CA1, CA2) of the air gap C.
[0029]
In this embodiment, by arranging the insulating capacitors 40A and 40B in this manner, it is not
necessary to apply the insulating coating to the fixed electrodes 4A and 4B, thereby reducing the
manufacturing cost and achieving an output air pressure by realizing a uniform air gap. The
problems of uniformizing the output sound pressure and preventing the reduction of the output
sound pressure due to the reduction of the opening area are very easily solved.
And the insulation performance equivalent to or more than the case where the insulation coating
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is applied very easily is obtained, and in terms of speaker sensitivity, high performance can be
realized.
[0030]
From the above (Equation 7), the larger the capacitance CC of the insulating capacitors 40A and
40B, the better. However, the larger the capacitance CC of the insulating capacitors 40A and 40B,
the larger the resistance RC (RC1, RC2) of the insulating capacitors 40A and 40B. .
For this reason, if the capacitance Cc is set too large, in some cases the above (Equation 6), which
is a condition relating to the bias voltage, may not be satisfied.
[0031]
Therefore, as shown in FIG. 2A as the second embodiment, adjustment resistors 41A and 41B are
disposed in parallel to the insulating capacitors 40A and 40B.
An equivalent circuit in this case is as shown in FIG. 2B, and the resistance values of the
adjustment resistors 41A and 41B are RP1 and RP2.
[0032]
In this case, the resistance value RC in the above (Equation 6) is a parallel combination of the
resistance component RC (RC1, RC2) of the insulating capacitors 40A, 40B and the resistance
value RP (RP1, RP2) of the adjustment resistors 41A, 41B. It becomes resistance, that is, the
resistance value RC can be lowered. Therefore, in this embodiment, even if the capacitance CC of
the insulating capacitors 40A and 40B is set to be quite large, the condition of the above
(Equation 6) can be simultaneously satisfied, and a speaker device with higher performance can
be realized.
[0033]
FIGS. 3 and 4 show the third and fourth embodiments, respectively, which have the configuration
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of the first and second embodiments and the fixed electrode on which the insulating film 32 as
described in FIG. 8 is formed. It is a combination of the structures 4A and 4B.
[0034]
As described above, the provision of the insulating film 32 causes various problems. However,
when these do not particularly cause a major obstacle, for example, when the manufacturing cost
may increase, the fixed electrode may be formed. An insulating capacitor 40A is connected
between 4A and the terminal TF, and an insulating capacitor 40B is connected between the fixed
electrode 4B and the terminal TR as shown in FIG. 3, or in parallel with the insulating capacitors
40A and 40. By disposing the resistors 1A and 41B at the same time, a high-performance speaker
device with higher sensitivity can be realized.
[0035]
Although the embodiments have 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
[0036]
As described above, according to the speaker device of the present invention, the capacitor
element is arranged in series between the fixed electrode and the drive signal supply source, for
example, the transformer, so that the fixed electrode is insulated with a very simple structure.
The insulation performance equivalent to or higher than that of the case where the paint is
applied is obtained, and there is an effect that the improvement of the speaker sensitivity can be
realized.
Furthermore, by obtaining insulation with the capacitor element, the insulation resistance value
and the withstand voltage characteristic can be easily and uniquely determined, which is very
preferable in design.
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[0037]
In addition, even in the speaker device that requires low manufacturing cost by not insulatingcoating the fixed electrode, the sound quality is stabilized, the variation in the output sound
pressure due to the improvement in the mechanical accuracy of the speaker unit is reduced, and
the aperture area is not reduced. There is an advantage that it is possible to eliminate the
reduction in the output sound pressure and to obtain the freedom of the appearance finish.
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