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JP2008236224

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2008236224
The present invention provides an electrostatic speaker capable of adjusting the distance to an
electrode at each location of a diaphragm. An electrostatic loudspeaker (1) according to the
present invention comprises a first electrode (20U) and a second electrode (20L), which are
disposed opposite to each other, and the first electrode and the second electrode. A first elastic
member (40) provided between the first surface and a first surface (Pu) opposite to at least the
first electrode constituting the shape of the first elastic member, and a second surface (Pd)
opposite to the second electrode A second elastic film provided between the first surface and the
first electrode and between the second surface and the second electrode, and the diaphragm (10)
which is displaceable by electrostatic force and covers the And members (30U, 30L). [Selected
figure] Figure 1
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
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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 pushpull 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. Further, as an electrostatic loudspeaker, for example,
an electrostatic loudspeaker having a so-called edgeless structure in which the outer periphery of
the movable electrode is not fixed (supported) described in Non-Patent Document 1 is also
known. M. Okazaki, 4 others, "Condenser speaker with diaphragm that vibrates in all bands and
its application", Proceedings of the 2004 Acoustical Society of Japan Annual Conference on
Acoustics, The Japan Acoustics Society, September 2004, p. 563-564
[0003]
The magnitude of the electrostatic force acting on the vibrating membrane is inversely
proportional to the distance between the vibrating membrane and the electrode. It is preferable
to apply an electrostatic force to the entire vibrating film as uniformly as possible on the whole
vibrating film, considering that it is ideal that the entire vibrating film does not divide and vibrate
uniformly, but for this purpose, the vibrating film and electrodes should be high. It is necessary
to arrange in parallel with accuracy. However, even if the accuracy of the arrangement is
sufficiently high, the electrode itself is distorted and high parallelism can not be realized, so that
the surface accuracy of the electrode is also required to have a predetermined accuracy. Here, as
the electrode, typically, a punching metal (PM) having holes for securing sound wave
transmission to a metal plate is used, but a slight distortion is generated by the mechanical force
received at the time of processing there's a possibility that. Alternatively, the surface accuracy of
the metal plate itself as the electrode material may not be sufficiently secured. As described
above, it is not easy to parallelize the electrode and the vibrating film (in other words, to keep the
distance between the two) with high accuracy because it costs processing time and labor for the
electrode and is not easy.
[0004]
Further, in a flat type speaker including an electrostatic type speaker, the generated sound wave
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has a predetermined directivity characteristic because the radiation area of the sound wave
becomes large due to the structure of using a vibrating film which is a two-dimensional sounding
body in a flat type speaker . 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. Depending on the purpose of use
and the environment of the speaker, such directional characteristics are not preferable, and
methods of correcting and controlling the directional characteristics of the generated acoustic
wave have been tried. That is, by intentionally making the voltage between the vibrating
membrane and the electrode different at each place, the electrostatic force acting on the
vibrating membrane is made different at each place of the vibrating membrane. Specifically, it is
a method of using a metal plate subjected to bending as an electrode. According to this method, it
is possible to make the distance between the vibrating membrane and the electrode different
from place to place, but it is not easy to apply a desired bending process to the electrode with
high accuracy. A method is also conceivable in which the flat electrode is configured of a
plurality of sub-electrodes, and the distance to the vibrating film is made different for each subelectrode. In this method, in principle, the desired electrostatic force can be applied to any place,
but in order to improve this accuracy, it is necessary to increase the number of each subelectrode, and inevitably the electrodes themselves And the method of feeding each of the subelectrodes becomes complicated. The present invention has been made in view of the abovedescribed background, and it is an object of the present invention to provide an electrostatic
speaker capable of adjusting the distance to an electrode at each location of a vibrating
membrane.
[0005]
MEANS FOR SOLVING THE PROBLEMS In order to solve the above-mentioned problems,
according to one aspect of the present invention, a first elastic member is provided between a
first electrode and a second electrode which are disposed facing each other, and between the first
electrode and the second electrode. A vibrating membrane displaceable by electrostatic force
covering at least a first surface facing the first electrode and a second surface facing the second
electrode in the first elastic member, and the first surface And a second elastic member provided
between the first electrode and the second surface, and a second elastic member provided
between the second surface and the second electrode.
[0006]
In a preferred embodiment, the distance from the first surface to the first electrode and the
distance from the second surface to the second electrode are the same.
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[0007]
In another preferred embodiment, the vibrating membrane has a U-shaped cross-sectional shape.
[0008]
In still another preferred embodiment, the vibrating membrane is composed of a first vibrating
membrane provided on the first surface and a second vibrating membrane provided on the
second surface.
[0009]
According to the electrostatic loudspeaker according to the present invention, the distance to the
electrode can be adjusted for each location of the diaphragm.
[0010]
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 speaker 1 includes a vibrating membrane 10, two
parallel flat electrodes (hereinafter simply referred to as electrodes) 20U and 20L facing the
vibrating membrane 10, and a portion between the vibrating membrane and the electrodes 20U
and 20L. Each of the cushioning members 30U and 30L is generally configured.
In the figure, the electrode surfaces of the electrodes 20U and 20L are fixed in the X direction
and the Y direction, and an example of an arrangement in which the vibrating membrane 10 can
vibrate in the Z direction perpendicular to the electrode surfaces is shown.
In the following, since the structures of the electrodes 20U and 20L are the same, "L" and "U" are
omitted unless it is particularly necessary to distinguish between the two.
About omission of description of "L" and "U", suppose that it is the same about other components.
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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.
[0011]
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. As a known
technique can be adopted as a method of feeding the electrode 20, components related to
feeding are not shown. Furthermore, the electrostatic speaker 1 has an input unit for inputting an
audio signal from the 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. Further, in
order to prevent the drawings from being complicated, illustration is also omitted for
components that generate and supply audio signals.
[0012]
The cushion material 30 is a rectangular solid of thickness d2 having a square flat surface having
a length of W vertically and horizontally. The cushioning material 30 is made of an insulating
material and functions as a shock absorbing material. For example, sponge, sheet-like cotton, or
insulating non-woven fabric is used. By providing the cushioning material 30 between the
electrode 20 and the vibrating membrane 10, it is possible to support the vibrating membrane
10 with respect to the housing and 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. The material and thickness of the cushioning members 30U and 30L are equal, and
therefore their mechanical properties (elastic modulus etc.) are also equal.
[0013]
The electrode 20 is a plate-like member having an electrode surface having a size of W in each of
the vertical and horizontal directions. For example, it is a punching metal (PM) by which the
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through-hole for securing a sound transmission to a metal plate was opened. Electrodes 20U and
20L are separated by distance D (precisely, the distance between the lower surface of electrode
20U and the upper surface of electrode 20L is D). It is fixed to (not shown). Alternatively, instead
of PM, a porous conductive material such as a wire mesh or a conductive non-woven fabric may
be used as the electrode 20.
[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 formed using a plate-like (film-like) material 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. Further, in the vibrating
membrane 10, a predetermined tension is applied to the vibrating membrane 10 in a fixing
means (not shown) formed of an insulating material such as Teflon (registered trademark),
acrylic (methyl methacrylate), rubber, etc. In the state, for example, one side of the edge may be
supported by the housing (not shown) of the electrostatic speaker 1.
[0015]
A cushioning material 40 is provided inside the vibrating membrane 10 folded in a U-shape at
the end R. The vibrating membrane 10 is disposed so as to cover both surfaces and one side
surface of the cushioning material 40. As a result, in the vibrating membrane 10, the cushioning
film 40 and the cushion are in a state where the vibrating membrane area Pu faces the electrode
20U, the vibrating membrane area Pd faces the electrode 20L, and the end R is folded in a Ushape. It is supported by the pressure received from the members 30U and 30L. The cushioning
material 40 is a substantially rectangular solid having a thickness d1 and vertical and horizontal
lengths W, but has a curved surface on one side surface (R). As a result, both the electrode 20
and the vibrating membrane are kept parallel. The cushioning material 40 is disposed at a
position (C) just halfway between the electrodes 20U and 20L. By this arrangement, the distance
(d2) from the upper surface of the vibrating membrane 10 to the electrode 20U and the distance
(d2) from the lower surface of the vibrating membrane 10 to the electrode 20L become equal. In
addition, in the same figure, in order to prevent that a drawing becomes complicated, the state
which the diaphragm does not vibrate (displacement) is shown. Also in the following figures, it is
assumed that the vibrating membrane is not displaced. The material of the cushioning material
40 is the same as that of the cushioning material 30.
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[0016]
In this arrangement, for example, W is 0.1 to 1 m and D is approximately 0.1 mm to 5 mm, so d1
is sufficiently smaller than W. The area where the vibrating membrane 10 vibrates can be
regarded as substantially only the vibrating membrane areas Pu and Pd. Here, since the
cushioning material 40 is disposed at the above-described position, the electrostatic force
received by the vibrating membrane area Pu from the electrode 20U and the electrostatic force
received by the vibrating membrane area Pd from the electrode 20L are always equal in
magnitude. Here, the material and thickness of the cushion members 30U and 30L are the same,
and the distance between the vibrating film region Pu and the electrode 20U is equal to the
distance between the vibrating film region Pd and the electrode 20L. Is kept equipotential.
Accordingly, the electrostatic loudspeaker 1 is equivalent to a system in which two conventional
electrostatic loudspeakers formed of a pair of parallel flat electrodes spaced apart from a single
diaphragm by a distance d2 are vertically stacked. Therefore, it is not necessary to use a special
power supply method for generating musical tones, and the same one as in the prior art can be
used.
[0017]
Next, with reference to FIG. 2, a preferred embodiment in the case of using the electrode 21 with
poor surface accuracy (that is, distorted) will be described. FIG. 2 shows a cross-sectional
structure of an electrostatic speaker according to the related art and the present invention using
the electrodes 21U and 21L which are both bent inward (the vibrating film side). When such an
electrode 21 is used, the conventional electrostatic speaker 900 including the vibrating film 901,
the cushion material 30, and the electrode 21 has a structure as shown in FIG. 2A. As shown in
FIG. 2A, the distance s from the vibrating membrane 901 to the electrode 21 in the central
portion Pc and the distance s from the vibrating membrane 901 to the electrode 21 in the
peripheral portion Pe due to the bending of the electrode 21 Are not equal. This means that the
electrostatic force acting varies depending on the location of the vibrating membrane 901. When
the vibrating membrane 901 is in such a state, the motion of the vibrating membrane 901 may
not be uniform, and the directivity characteristics of the generated acoustic wave may be
disturbed.
[0018]
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On the other hand, FIG. 2B shows an example of the cross-sectional structure of the electrostatic
speaker 2 when the present invention is applied. As shown in FIG. 2B, in the electrostatic speaker
2 provided with the U-shaped electrode 21 and the cushion material 41 provided therein, the
vibration film areas Pd and Pu are provided at all places. It can be seen that the distances s to the
electrodes 21 are equal. That is, in the vibrating film regions Pd and Pu, equal electrostatic force
works at all places, and ideal vibration can be generated. This is due to the effect of the
cushioning material 41, and the shape of the cushioning material 41 will be described with
reference to FIG.
[0019]
Fig.3 (a) is sectional drawing of the cushion material 41, FIG.3 (b) is an external appearance
perspective view of the cushion material 41 which has the end surface T represented to Fig.3 (a).
As shown in the figure, the cushioning material 41 used in the electrostatic speaker 2 is different
in shape from the cushioning material 40 used in the electrostatic speaker 1. Specifically, the
cushion material 41 is formed to have the same shape as the bending condition (the shape of the
curved surface) of the electrode 21. When the cushion material 41 is used, as shown in FIG. 2,
the shapes of the vibrating film regions Pu and Pd become the same as the shapes of the cross
sections of the electrodes 21U and 21L, respectively. In other words, the vibrating membrane 10
is held in a bent state so as to have the same degree of bending as the electrode 21.
[0020]
As described above, in the present embodiment, the shape of the vibrating membrane 10 can be
changed in accordance with the shape of the cushioning materials 40 and 41 provided inside the
electrodes 20 and 21. Therefore, for example, by making the shape of the vibrating film different
according to the shape (for example, the degree of distortion) of the electrodes 20 and 21, the
distance s to the electrode is kept constant at substantially any place on the vibrating film. Can.
Alternatively, regardless of the shape of the electrodes 20 and 21, it is also possible to change
the shape of the vibrating membrane 10 in order to achieve the desired directivity.
[0021]
<Other Embodiments> As described above, the shape of the cushioning material 40 for defining
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the shape of the vibrating membrane 10 can be freely designed according to the purpose. For
example, in the case where the degree of deflection of the electrode is convex upward, according
to the degree of deflection, a cushion material formed as shown in (a) of FIG. 4 (cross-sectional
view) and FIG. 42 may be used.
[0022]
However, the element that defines the shape of the vibrating membrane 10 does not have to be
the shape of the cushioning material 40 alone. As described above, the vibrating membrane 10 is
in contact with the cushioning material 30 and the cushioning material 40, and the factors
determining the shape of the vibrating membrane include at least the pressure received from the
cushioning materials 30 and 40. Here, if the elastic properties of the cushion members 30 and
40 are different, the pressure acting on the vibrating film 10 is also different. Therefore, there is
a possibility that depending on the difference in elastic properties of the cushioning materials 30
and 40, which of the forces acting on the vibrating film 10 by the cushioning materials 30 and
40 becomes dominant, the shape of the cushioning material 40 is necessarily the purpose It does
not necessarily exactly match the shape of the vibrating membrane 10. That is, the shape of the
vibrating membrane 10 is defined by at least one of the shape of the cushioning material 30 and
the shape of the cushioning material 40, and as a result, the shape of the vibrating membrane 10
is in a desired state. Just do it.
[0023]
Also, the cushioning members 30 and 40 are not limited to those having square (or substantially
square) two surfaces (upper surface and lower surface) and four side surfaces, and the upper
surface and lower surface may be rectangular or circular. Moreover, the shape of the plane of the
electrode 20 is not necessarily the same.
[0024]
The method of processing and forming the cushioning material 40 is arbitrary. For example,
when it is desired to realize an upwardly convex shape as in the cushion material 42, as shown in
FIG. 5A, by laminating rectangular materials 430 to 439 of a predetermined thickness by a
predetermined method, The cushioning material 43 may be formed. According to this method, a
cushion having a substantially desired curved surface shape even if it is a material that is
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processed (cut or cut out, etc.) into a smooth curved surface or whose shape is difficult to
maintain after processing The material can be produced.
[0025]
Alternatively, as shown in FIG. 5B, another material 441 may be formed on the core material 440
with a predetermined thickness by a predetermined method. For example, a foam urethane
processed into a desired shape is used as a central material, and cotton is fixed with a certain
thickness around it. In general, when a cotton material is used as the cushioning material 40, it is
difficult to arrange cotton at a certain place while maintaining a desired shape. However,
according to this method, since processing can be easily performed by the processing of hard
wire, etc., after processing foamed urethane into a desired shape according to the distortion of
the electrode and other purposes, cotton with a certain thickness around this is produced. By
fixing the above, it is possible to easily form the cushion material 44 having a desired shape as a
whole.
[0026]
Parameters such as the material and thickness of the vibrating film 10, the material and shape of
the electrode 20, the shape, the thickness, the shapes of the cushion members 30 and 40 to 44,
and the material and thickness are the distance from the vibrating film area Pu to the electrode
20U and the vibrating film area Pd As long as the condition that the distance from the electrode
20L to the electrode 20L is equal is satisfied. For example, the materials of the cushioning
material 30 provided between the vibrating membrane and the electrodes and the cushioning
materials 40 to 44 provided inside the vibrating membrane may be different. However, when
emphasis is placed on achieving the same characteristics as a conventional electrostatic speaker
using a single diaphragm, the mass of the film is sufficiently smaller than the load mass of air,
and the cushion material 30 and the cushion are cushioned. Preferably, the elastic properties of
the members 40-44 are substantially identical.
[0027]
The shape of the vibrating membrane 10 (in other words, the method of covering the cushioning
material 40) does not have to be U-shaped as shown in FIG. For example, the vibration film may
cover the entire cushioning material 40 (for example, in the case where the cushioning material
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is a rectangular parallelepiped, two opposing surfaces to the electrode and four side surfaces).
Further, the cushioning material 40 does not have to have a shape (for example, a rectangular
parallelepiped) that allows the side surface to be defined or conceived with the electrode film
regions Pu and Pd facing the electrodes 20U and 20L, for example, all having a curved surface.
May be In short, in a preferred embodiment, the electrode (upper side) -cushioning materialvibrating membrane (upper side; preferably, a portion of the vibrating membrane that can be
regarded as substantially facing the electrode 1) -cushioning material- vibrating membrane
(lower side; suitably In the vibrating membrane, each element is disposed in the order of: a
portion which can be regarded as substantially facing the electrode 2) -cushion materialelectrode (lower side).
[0028]
For example, as shown in (a) and (b) of FIG. 6, instead of one U-shaped vibrating membrane 10,
electrostatic loudspeakers 3 and 4 are formed using two vibrating membranes 10U and 10L. It
may be configured. The electrostatic loudspeakers 3 and 4 shown in the same figure differ in the
shape of the cushioning materials 45 and 46 used (and the presence or absence of distortion of
the electrode 20). Also in this case, the distance from the vibrating membrane 10U to the
electrode 20U and the distance from the vibrating membrane 10L to the electrode 20L are the
same. The vibrating membranes 10U and 10L are independently supported. In this case, each of
the vibrating membranes 10U and 10L may be supported only by the cushioning materials 40
and 30, or may be supported by a not-shown housing in a predetermined method. Also, the
vibrating membranes 10U and 10L are maintained at the same potential. According to this
configuration, an electrostatic speaker substantially equivalent to the case where one U-shaped
diaphragm shown in FIGS. 1 and 2 is used is realized.
[0029]
In the above embodiment, although the distance from the vibrating membrane 10U to the
electrode 20U is the same as the distance from the vibrating membrane 10L to the electrode
20L, the elastic characteristics of the cushioning materials 30U and 30L are made different or
the vibration is By providing a mechanism for supporting the membrane 10 and the cushioning
material 40, the two distances described above may be made different as long as the positions of
the vibrating membrane 10 and the cushioning material 40 are held within a certain range.
[0030]
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FIG. 2 is a cross-sectional view of the electrostatic speaker 1;
It is the figure which compared the conventional electrostatic speaker 900 and the electrostatic
speaker 2 which concerns on this invention. It is a figure showing an appearance structure of a
cushion material 41. It is a figure showing the appearance structure of cushioning material. It is a
figure showing the appearance structure of cushion materials 43 and 44. FIG. 2 is a crosssectional view of electrostatic speakers 3 and 4;
Explanation of sign
[0031]
1 to 4, 900: electrostatic speaker, 10, 901: diaphragm, 10 U: first diaphragm, 10 L: second
diaphragm, 20 U, 20 L, 21 U, 21 L,. Electrode, 30 U, 30 L, 40 to 46 ... cushioning material, 430 to
439, 440, 441 ... material.
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