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JP2008259158

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DESCRIPTION JP2008259158
To provide an electrostatic speaker capable of correcting directivity characteristics with a simple
configuration. An electrostatic loudspeaker (1) according to the present invention includes a
vibrating membrane (10), and a porous electrode (see FIG. 1) spaced apart from the vibrating
membrane to apply a driving force to the vibrating membrane by electrostatic force. 20L, 20R),
and the effective area density of the porous electrode decreases as approaching the outer edge of
the electrode. The porous electrode is composed of a plurality of sub-electrodes (201 to 203)
each having a different effective area density. [Selected figure] Figure 2
Electrostatic speaker
[0001]
The present invention relates to the structure of an electrostatic speaker.
[0002]
A speaker called an electrostatic speaker (capacitor speaker) is known.
Electrostatic loudspeakers are attracting attention because they are relatively simple in structure,
so they can be designed to be lightweight and compact, and that they can be theoretically
handled easily. Electrostatic loudspeakers are typically two parallel flat electrodes facing each
other across an air gap, and a conductive sheet-like member inserted between the electrodes and
having its both ends supported by a housing etc. , A diaphragm or a diaphragm (so-called push-
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pull type). When a predetermined bias voltage is applied to the vibrating film and the voltage
applied to the electrodes is changed, the electrostatic force acting on the vibrating film changes,
and thereby the vibrating film is displaced. When the applied voltage is changed in accordance
with the input musical tone signal, the diaphragm repeats displacement (i.e., vibrates)
accordingly, and an acoustic wave corresponding to the input musical tone signal is generated.
The generated musical tone is emitted to the outside through, for example, a hole formed in a
metal plate electrode or other porous layer.
[0003]
In a flat type speaker including an electrostatic type speaker, the generated sound wave has a
predetermined directivity characteristic because the radiation area of the sound wave is large
due to the structure of using a vibrating film which is a two-dimensional sound generator.
Typically, the sound pressure is maximum (main maximum or sub maximum) in a certain
direction (for example, the front direction of the diaphragm), but the sound pressure is minimum
in another direction (for example, a diagonal direction) It is known that such sound pressure
distribution characteristics appear. Here, for example, if it is possible to perform a correction to
suppress only the sound wave (main lobe) propagating in the main maximum direction and
suppress the sound wave (side lobe) transmitted in the sub maximum direction, the sound wave
having sharp directivity is To realize. As a method of correcting and controlling directivity, there
is known a speaker array technology in which a plurality of speaker units are provided and the
level and delay of input signals supplied to each unit are controlled (see Non-Patent Document 1).
D. B. (Don) Keele Jr. By the "Implementation of Straight-line and Flat-Panel Beamwidth
Transducers (CBT) Loudspeaker Arrays Using Signal Delays" Audio Engineering Society,
Convention Paper Presented at the 113th Convention, 2002 October 5/8 L. A., California, USA
[0004]
However, in the case of forming a speaker array using an electrostatic speaker, it is possible to
prepare a plurality of sets of electrodes and diaphragms, or to divide a diaphragm and control the
oscillation state independently for each area. You need to do so. Furthermore, an electrical circuit
for controlling the signal supplied to each speaker unit is also required. This complicates the
overall structure of the speaker and increases the manufacturing cost. As described above, in the
conventional electrostatic speaker, the directivity characteristic can not be corrected with a
simple configuration. The present invention has been made in view of the above-described
background, and it is an object of the present invention to provide an electrostatic speaker
capable of correcting a desired directional characteristic with a simple configuration.
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[0005]
In order to solve the above problems, the present invention, in one aspect, includes: a vibrating
membrane; and a porous electrode spaced apart from the vibrating membrane to apply a driving
force to the vibrating membrane by an electrostatic force, Provided is an electrostatic
loudspeaker characterized in that the areal density of the electrode decreases as it approaches
the outer edge of the porous electrode.
[0006]
In a preferred embodiment, the porous electrode is comprised of a plurality of sub-electrodes
each having a different effective area density.
[0007]
In another preferred embodiment, the distribution of the effective area density has a shape in
which the isosurface density lines are concentric.
[0008]
In yet another preferred embodiment, the distribution of the effective area density is uniform in
one direction, and has a shape that increases from the center toward the outer edge in the
direction perpendicular to the one direction.
[0009]
In still another preferred embodiment, the porous electrode has a reticulated structure.
[0010]
In still another preferred embodiment, the porous electrode is a conductive non-woven fabric.
[0011]
According to the electrostatic loudspeaker according to the present invention, the directivity
characteristic can be corrected with a simple configuration.
[0012]
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Embodiment FIG. 1 is a perspective view of the general structure of an electrostatic speaker 1
according to an embodiment of the present invention.
As shown in the figure, the electrostatic loudspeaker 1 comprises a vibrating membrane 10, two
parallel flat electrodes (hereinafter simply referred to as electrodes) 20L and 20R facing the
vibrating membrane 10, and between the vibrating membrane 10 and the electrodes 20L and
20R. And cushion members 30L and 30R respectively provided on the
In the figure, the electrode surfaces of the electrodes 20L and 20R are fixed in the X direction
and the Y direction, and an example of the arrangement in which the vibrating membrane 10 can
vibrate in the Z direction perpendicular to the electrode surfaces is shown.
Hereinafter, since the structures of the electrodes 20L and 20R are the same, “L” and “R”
will be omitted unless there is a need to distinguish between the two.
About omission of description of "L" and "R", suppose that it is the same about other components.
The ratio of the thickness of each component such as the vibrating film, the cushioning material,
and the electrode shown in the following drawings is set for convenience of the description and
does not necessarily reflect the actual size.
[0013]
Further, in the electrostatic speaker 1, a desired voltage is applied to each of the electrodes 20
from a power supply (not shown), and a bias voltage is applied to the diaphragm 10.
Since a conventional technique can be adopted as a method of supplying power to the electrode
20, components related to power supply are not shown.
Furthermore, the electrostatic speaker 1 has an input unit for inputting an audio signal from the
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outside, and by changing the value of the applied voltage according to the audio signal, the
vibrating membrane 10 can be made to vibrate according to the audio signal. It can be done. The
sound wave generated by the vibration of the vibrating membrane 10 passes through at least one
of the electrodes 20 and is emitted to the outside of the speaker. In order to prevent the
drawings from being complicated, illustration of components for generating and supplying audio
signals is also omitted.
[0014]
The vibrating film 10 is, for example, a film made of PET (polyethylene terephthalate,
polyethylene terephthalate), PP (polypropylene, polypropylene) or the like by vapor-depositing a
metal film or applying a conductive paint, and has a thickness of several microns to several tens
of microns. It is a plate-like (film-like) member having a conductivity on the order of microns.
Alternatively, it may be one obtained by laminating a metal thin film, or one obtained by applying
a high voltage to the insulating film and polarizing it. The vibrating membrane 10 is a fixing
means (not shown) formed of an insulating material such as vinyl chloride, acrylic (methyl
methacrylate), rubber, etc., in a state where a predetermined tension is acting on the vibrating
membrane 10, For example, one side of the edge may be supported by the housing (not shown)
of the electrostatic speaker 1, or may be supported by the elastic force of the cushions 30L and
30R without providing such a support. It may be of any configuration.
[0015]
The cushion material 30 functions as a buffer material made of an insulating material, and is, for
example, a sponge, a sheet of cotton, or an insulating non-woven fabric. By inserting the cushion
material 30, it is possible to support the vibrating membrane 10 with respect to the housing or to
apply appropriate elastic stress to the vibrating membrane 10. The mechanical properties and
the like are not particularly limited, but it has air permeability greater than that of the electrode
20, and for example, an air permeability of 95% or more is employed.
[0016]
The electrode 20 has a square shape on its electrode surface, and is fixed to a housing (not
shown) of the electrostatic speaker 1. At this time, the distance d (for example, about 0.1 to 10
mm) from the vibrating membrane 10 to both the electrodes 20L and 20R is arranged to be
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equal. In other words, the exactly middle position of the opposing electrodes is the fixed position
of the vibrating membrane 10 (precisely, the vibrating membrane 10 in the non-displaced state,
which is a state when no signal is input). The shape of the electrode surface is not limited to a
square, and may be, for example, a rectangle.
[0017]
FIG. 2 is a view of an example of the electrode 20 as viewed from the Z direction. As shown in the
figure, the electrode 20 is composed of a frame 200, a plurality of twenty sub-electrodes 201,
twelve sub-electrodes 202, and four sub-electrodes 203. The frame 200 is made of a conductive
material (for example, a metal plate) for providing the sub-electrodes 201, 202, 203, to which an
electrode for applying a voltage is attached. Thereby, the same voltage is applied to a total of 36
sub electrodes. Although the method of fixing each sub electrode 201-203 to the flame | frame
200 is arbitrary, for example, the part which provides each sub electrode from one metal plate is
cut off, and the flame | frame 200 is formed. The method of fixing each sub electrode 201 to 203
to the frame 200 is optional as long as the conductivity is ensured, but may be adhered by
welding, for example, or the frame 200 is provided with a predetermined groove or the like. A
method may be used in which each sub electrode is fitted and fixed.
[0018]
Each of the sub electrodes 201 to 203 is disposed in each of the regions Rc, Ri, and Ro, which are
virtually set in order from the inside on the electrode 20, and is a porous electrode configured
using a porous material. is there. In addition, all of the sub electrodes 201 to 203 are configured
using a conductive material. By applying a voltage, the sub electrodes 201 to 203 exert an
electrostatic force on the vibrating membrane 10.
[0019]
The porous electrode is, for example, a metal plate provided with a through hole. Now, if it is
assumed that a capacitor is formed using each set of sub-electrodes, the capacitance value is
smaller than in the case where a capacitor is similarly formed using electrodes of the same area.
This is because, although the capacitance is proportional to the electrode area, the apparent area
as the electrode is reduced by the portion where the hole is opened. Hereinafter, the capacitance
with respect to the capacitance in the case where it is assumed that there is no porous structure
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(for example, “a hole”) is referred to as an effective capacitance, and the area of the region
excluding the hole portion from the electrode surface is effective. It is called an area. For
example, when a punching metal (PM) having an aperture ratio of 40% is used as the electrode
20, the effective area is 0.6.
[0020]
Also, although the details will be described later, the concept of porous or porous structure of the
present invention does not mean that the structure obtained by forming "pores" in a single plate
such as punching metal is not limited. For example, it may be obtained by forming micro through
holes by chemical treatment or the like, or may be obtained by bundling or fixing fibrous
materials by a predetermined method. Good. In short, the electrode according to the present
embodiment has a structure having air permeability by having a space therein, and the apparent
surface area for applying a driving force to the vibrating membrane 10 due to this structure is
Any material that is decreasing may be used. In the present embodiment, the case where a
punching metal is used as the electrode 20 will be described as an example.
[0021]
FIGS. 3A to 3C show the structures of the sub electrodes 201 to 203. FIG. As shown in the figure,
each sub-electrode is a punching metal composed of the holes H and the non-perforated area F,
but the aperture ratio, that is, the effective area is different for each sub-electrode. Specifically,
the sub-electrode 201 disposed at the outermost side of the electrode 20 has the largest aperture
ratio (small effective area), and the sub-electrode 203 disposed at the innermost side of the
electrode 20 has the smallest aperture ratio (effective The area is getting bigger. As described
above, in the present embodiment, the size of the effective area per unit area (hereinafter
referred to as effective area density) in the electrode 20 as a whole is larger at the center and
smaller toward the outer edge. Configured to be In other words, the number of holes is smaller at
the central portion and the effective area is dense, and the number of holes is smaller at the outer
edge and the effective area is rough.
[0022]
According to the configuration of the electrode of the present embodiment, the electrostatic force
that acts on the vibrating film 10 from the electrode 20 can be made different depending on the
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location. More specifically, in the vibrating membrane 10, the electrostatic force applied
decreases from the center to the outer edge. As a result, compared to the conventional
electrostatic speaker, the sub maximum (side lobe) component is suppressed in the directivity
characteristic of the sound wave generated in the vibrating film 10.
[0023]
Other Embodiments Regarding the size and shape of the holes in each of the sub electrodes 201
to 203, the value (absolute value) of the aperture ratio, and the arrangement method of the holes,
the effective area density is large in the central portion of the electrode 20 as a whole. It is
optional as long as the effective area density is relatively reduced toward the outer edge.
Preferably, a hole having a diameter of about 2 to 20 and an opening ratio of about 20 to 40% is
used.
[0024]
Further, with respect to the shape, number, size, and ratio of virtual regions provided on the
electrodes 20 (in other words, a method of dividing the regions of the electrodes 20), the central
region is larger in effective region and closer to the outer edge. It is optional as long as it is
configured to be relatively small. The number of regions is preferably 2 to 6. The shape of the
region may be, for example, concentric. The arrangement of the shapes of the sub-electrodes is
also arbitrary as long as the effective area density is large at the central portion of the electrode
20 as a whole and the effective area density is relatively smaller toward the outer edge. . For
example, when each region is set concentrically, each sub electrode may be fan-shaped. The
distance between the sub electrodes can be set appropriately. Also, the shape of the electrode 20
does not have to be square. For example, as shown in FIG. 4, a rectangular electrode 21 may be
used. Specifically, the execution area density decreases from the center to the outer edge in the
one direction (long side direction), but the effective area density is equal in the direction (short
side direction) perpendicular thereto. The sub electrodes 213, 212 and 211 are disposed.
[0025]
Also, as the porous sub electrode, a net-like conductive member as shown in FIGS. 5A to 5C may
be used instead of the punching metal. For example, it is a wire mesh into which a bar-like metal
material is woven. Then, by arranging the sub-electrodes 223, 222 and 221 from the central
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portion of the electrode 20 toward the outer edge portion, the effective region density of the
central portion is large as the electrode 20 as a whole, and the effective region density is relative
to the outer edge Configured to be as small as possible. In addition, as a metal mesh, if it is a
fixed space ratio (for example, 20 to 50%) which does not substantially deteriorate the sound
transmission performance, use arbitrary ones for the weave, the wire diameter, the mesh and the
material. Can. For example, a woven wire mesh of JIS G3555, 3556 or the like, which has a mesh
size of about 20 to 500, can be used. Here, the mesh means the number of eyes between 25.4
mm on one side.
[0026]
Alternatively, a conductive non-woven fabric may be used as the porous sub electrode. A
conductive layer is formed over the entire surface of the nonwoven fabric. For example, a metal
such as aluminum is sputtered onto the non-woven fabric. Alternatively, metal printing may be
performed on the non-woven fabric. Alternatively, the conductive paint may be applied to the
non-woven fabric. Here, the non-woven fabric is a fiber having porous (porous) structural fibers
and is, for example, a sheet-like shape. For example, they are made by combining in a fixed
direction or at random and chemically bonding with an adhesive resin, mechanical entanglement,
entanglement with a pressure-applied water stream, or bonding with a fused fiber. For example,
as the innermost sub electrode, one having a basis weight of 40 g / m 2, a thickness of 0.1 mm,
and a fiber diameter of 2 denier is used. In this case, changing the basis weight will change the
effective area of the sub electrode. That is, each sub-electrode composed of conductive nonwoven fabrics of different weight may be arranged such that the effective area density is large at
the central part as the whole electrode and the effective area density becomes relatively smaller
toward the outer edge .
[0027]
In the embodiment described above, an example in which the electrode 200 is configured by
providing the plurality of sub electrodes 201 to 203 in the frame 200 has been described.
However, the present invention is not limited thereto. The effective area density may be
configured to be relatively smaller as it proceeds. For example, a punching metal or a conductive
non-woven fabric may be used as the frame 200, and sputtering may be performed on the
corresponding electrode having different effective regions on the frame. In this case, the effective
area density can be substantially continuously changed. Alternatively, without providing the
frame 200, the entire electrode is made of a metal mesh, and by setting the area weight for each
area, the effective area density is large at the central portion, and the effective area density
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becomes relatively smaller toward the outer edge. You may configure it.
[0028]
The materials of the respective sub-electrodes may be used in combination of different types
instead of using the same type. For example, it can be different for each area. For example, in one
region, a punching metal sub electrode is disposed, and in another region, a non-woven sub
electrode is disposed. The point is that the electrode may have an electrostatic property that the
electrostatic force applied to the vibrating membrane 10 is the strongest near the center and
becomes weaker toward the outer edge.
[0029]
Further, as shown in FIG. 6, the electrostatic speaker 2 may be configured by providing
supporting members 40L and 40R on the outside of both the electrodes 20L and 20R. Even when
a non-woven fabric is used for the entire electrode or the sub electrode, the deflection of the
electrode or the sub electrode can be prevented to keep the shape constant. The support member
40 is preferably in the form of a grid so as not to substantially impair the sound transmission.
This shape can be obtained, for example, by winding a so-called flexible tube which is formed by
winding a wire in the shape of a triangle around a helical spring, holds a bent shape and is also
excellent in bending durability. .
[0030]
Although the cushioning material 30 is provided between the electrode 20 and the vibrating film
10 in the above embodiment, the cushioning material 30 may be omitted. In this case, in order to
prevent contact between the vibrating membrane 10 and the electrode, for example, it is
preferable to provide spacers at the four corners of the vibrating membrane.
[0031]
Alternatively, the cushioning material 30 may be formed of the insulating non-woven fabric
having the above-described structure used for the electrode 20, and a conductive layer may be
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provided on the outer surface (that is, the electrode side) of the cushioning material 30. In this
case, the cushioning material 30 also functions as the electrode 20, and there is no need to
separately provide the electrode 20.
[0032]
Further, although the example of the push-pull type electrostatic speaker using the pair of
opposing electrodes 20L and 20R has been shown in the embodiment described above, the
present invention is not limited thereto, and only one electrode according to the present
invention is used. It is also possible to configure a push-type electrostatic speaker.
[0033]
FIG. 1 is an external perspective view of an electrostatic speaker 1;
It is a figure for demonstrating the structure of the electrode 20. FIG. It is a figure which shows
the structure of the sub electrodes 201-203. It is a figure for demonstrating the structure of the
electrode 21. FIG. It is a figure which shows the structure of the sub electrodes 211-213. FIG. 2 is
a cross-sectional view of an electrostatic speaker 2;
Explanation of sign
[0034]
1, 2 ... electrostatic type speaker, 10 ... diaphragm, 20L, 20R, 21L, 22R ... electrode, 30L, 30R ...
cushioning material, 40L, 40R ... support member, 200, 210 ... frame, 201, 202, 203, 211, 212,
213, 221, 222, 223 ... sub electrode.
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