JP4697007B2 - Electrostatic speaker - Google Patents

Description

  The present invention relates to an electrostatic speaker.

  Conventionally, a speaker called an electrostatic speaker (condenser speaker) is known (for example, Non-Patent Documents 1 and 2). The electrostatic speaker has two parallel flat electrodes facing each other with a gap as a basic structure. Two parallel flat electrodes have a structure in which one is fixed (referred to as a fixed electrode or a fixed plate) and the other is movable (referred to as a movable electrode, a vibration electrode, a vibration plate, or a vibration film). Many. When an input signal is superimposed on the bias voltage applied between the parallel plane electrodes, the attractive force between the parallel plane electrodes changes. The electrostatic speaker outputs sound by vibrating the diaphragm with this suction force.

  The electrostatic loudspeakers described in Non-Patent Documents 1 and 2 have a structure in which the outer peripheral portion of the diaphragm is fixed (supported) to the fixed electrode, that is, the diaphragm is supported by applying tension. Yes. In the electrostatic speaker having this structure, the amplitude of the diaphragm depends on the tension applied to the diaphragm and the intensity of the input signal. Since the amplitude of the diaphragm is smaller than that of a normal electrodynamic speaker, it is necessary to increase the area of the diaphragm in order to obtain a sound pressure equivalent to that of the electrodynamic speaker. In other words, there is a problem that the electrostatic speaker becomes large. Furthermore, since the outer periphery of the diaphragm is fixed, there is a problem that when the amplitude of the diaphragm is increased to increase the sound pressure, the central part of the diaphragm contacts the fixed electrode. Alternatively, when the tension of the vibrating membrane is weakened to increase the sound pressure, there is a problem that the vibrating membrane vibrates irregularly and distortion occurs.

  Here, as a technique for solving the problem of sound pressure in an electrostatic speaker, for example, there is a technique described in Non-Patent Document 3. Non-Patent Document 3 discloses an electrostatic speaker having a so-called edgeless structure in which the outer periphery of the movable electrode is not fixed (supported).

"Sound narrow path (27)", [online], [Search February 15, 2006], Internet <URL: http://www.dynamicaudio.co.jp/audio/5555/7f/oto/oto27. html> "Audio Quad ESL-63", [online], [Search February 15, 2006], Internet <URL: http://www.euronet.nl/users/temagm/audio/esl63.htm> Masanori Okazaki, 4 others, “Condenser speaker with diaphragm that vibrates piston in all bands and its application”, Acoustical Society of Japan 2004 Fall Meeting Presentation, Acoustical Society of Japan, September 2004, p. 563-564

Even in the technique described in Non-Patent Document 3, in order to produce a so-called three-way speaker, it was necessary to use separate, that is, three speaker units for each band. Further, according to Non-Patent Document 3, the frequency characteristics of each speaker unit cannot be designed to a desired one.
The present invention has been made in view of the above circumstances, and provides an electrostatic speaker adapted to a plurality of frequency bands.

In order to solve the above-described problem, the present invention has a vibration electrode that has a surface and vibrates in response to an input signal, a surface that faces the surface of the vibration electrode, and is fixedly spaced from the vibration electrode. A cushioning material disposed in contact with the vibration electrode between the electrode and the surface of the vibration electrode and the surface of the fixed electrode, and has a plurality of regions in a cross section parallel to the surface of the vibration electrode. And the electrostatic speaker which has a cushioning material from which the stiffness in at least 2 area | region among said several area | region differs is provided.
The frequency characteristic of the sound wave generated by the vibration of the vibrating electrode is influenced by the stiffness of the cushion material. Therefore, an electrostatic loudspeaker adapted to a plurality of frequency bands can be manufactured by using a cushion material having regions having different stiffnesses.

  In a preferred aspect, the electrostatic loudspeaker is a region in which the stiffness of a region close to the center of the vibration electrode is far from the center of the vibration electrode in two adjacent regions among the plurality of regions. It may be higher than the stiffness.

According to another aspect of the present invention, there is provided a vibration electrode that has a surface and vibrates in response to an input signal, a fixed electrode that has a surface facing the surface of the vibration electrode and is spaced apart from the vibration electrode, and the vibration electrode A plurality of cushion materials disposed so as to be in contact with the vibration electrode, respectively, and at least two cushion materials of the plurality of cushion materials have different stiffnesses. An electrostatic speaker is provided.
The frequency characteristic of the sound wave generated by the vibration of the vibrating electrode is influenced by the stiffness of the cushion material. Therefore, by using a plurality of cushion materials having different stiffnesses, an electrostatic speaker adapted to a plurality of frequency bands can be manufactured.

In a preferred aspect, the electrostatic speaker is configured such that, in two adjacent cushion materials among the plurality of cushion materials, the stiffness of the cushion material that is close to the center of the vibration electrode is a distance from the center of the vibration electrode. May be higher than the stiffness of the distant cushion material.
In still another preferred aspect, the electrostatic speaker may include a plurality of vibration electrodes, and the plurality of cushion materials may be arranged so as to be in contact with different vibration electrodes.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a speaker unit 1 according to an embodiment of the present invention. The speaker unit 1 is a so-called push-pull type electrostatic speaker having two fixed electrodes, a fixed electrode 10 and a fixed electrode 50. The speaker unit 1 has a vibrating membrane 30 sandwiched between the fixed electrode 10 and the fixed electrode 50. The vibration film 30 functions as a vibration electrode in the electrostatic speaker. A cushion material 20 is provided between the fixed electrode 10 and the vibration film 30. Similarly, a cushion material 40 is provided between the fixed electrode 50 and the vibrating membrane 30. A spacer 60 is provided between the fixed electrode 10 and the fixed electrode 50.

  The fixed electrode 10 and the fixed electrode 50 are planar electrodes. The fixed electrode 10 and the fixed electrode 50 are formed of a conductive material having a structure that transmits sound waves, such as punching metal, for example. Alternatively, the fixed electrode 10 and the fixed electrode 50 may be formed of a nonwoven fabric obtained by depositing a conductive material such as metal by sputtering. Further alternatively, the fixed electrode 10 and the fixed electrode 50 may be formed of a nonwoven fabric coated with a conductive dye. In short, the fixed electrode 10 and the fixed electrode 50 may be formed using any material as long as the material has both conductivity and sound wave transmission.

  The vibration film 30 is an electrode having a planar shape. The vibration film 30 is a material obtained by depositing a conductive material such as a metal on a film (thin film or sheet) using a polymer material such as PET (polyethylene terephthalate), PP (polypropylene, polypropylene), or polyester. It is formed by. Alternatively, the vibration film 30 may be formed of a material obtained by applying a conductive dye to a film. The vibration film 30 is sandwiched between the cushion material 20 and the cushion material 40. The vibration film 30 is supported by the cushion material 20 and the cushion material 40. In the prior art, the outer peripheral portion of the diaphragm is fixed to the fixed electrode, that is, tension is applied to the diaphragm. However, in the present embodiment, the outer peripheral portion of the vibrating membrane 30 is not fixed to the fixed electrode 10 (fixed electrode 50). That is, no tension is applied to the vibrating membrane 30. In this embodiment, an example in which the film-like vibration film 30 is used as the vibration electrode of the electrostatic speaker will be described. However, the vibration electrode may be formed using a plate-like material such as a balsa plate. Good.

  A bias voltage is supplied to the fixed electrode 10 from a power source (not shown). Furthermore, the speaker unit 1 has an input unit for inputting an audio signal (input signal) from a signal source (not shown). The input signal is superimposed on the bias voltage and supplied to the fixed electrode 10. Thus, a voltage corresponding to the input signal is applied between the fixed electrode 10 and the vibrating membrane 30. When a potential difference is generated between the fixed electrode 10 and the vibrating membrane 30 due to the applied voltage, an electrostatic force acts on the vibrating membrane 30. That is, the vibration film 30 is displaced, that is, vibrates according to the input signal. Sound corresponding to the vibration state (frequency, amplitude, phase, etc.) is generated from the vibration film 30. In the present embodiment, since the speaker unit 1 is a push-pull type electrostatic speaker, an application voltage having an opposite phase is supplied to the fixed electrode 50. By supplying a signal having an antiphase, an electrostatic force having the same direction and magnitude as the electrostatic force acting between the fixed electrode 10 and the vibrating membrane 30 acts between the fixed electrode 50 and the vibrating membrane 30. That is, in the push-pull type electrostatic speaker, the electrostatic force acts twice on the vibration film 30 as compared with the single type.

  The spacer 60 has a function of fixing the fixed electrode 10 and the fixed electrode 50 to each other and insulating them. The spacer 60 is formed of an insulating material such as vinyl chloride, acrylic (methyl methacrylate), or rubber. The spacer 60 is fixed to the fixed electrode 10 and the fixed electrode 50 using an adhesive or the like.

The cushion material 20 and the cushion material 40 are for making the frequency characteristics of the speaker unit 1 desired characteristics. The cushion material 20 and the cushion material 40 have a plurality of regions in an arbitrary cross section parallel to the surface of the vibration film 30. The elastic modulus is different in at least two of the plurality of regions. In the direction perpendicular to the surface of the vibration film 30, the elastic modulus of the cushion material 20 (cushion material 40) is constant. Each region is formed using an elastic body or elastic material having a predetermined elastic modulus (for example, it can be expressed by a linear elastic modulus (Young's modulus) in the thickness direction). The elastic modulus of the cushion material 20 and the cushion material 40 is determined as follows. For example, as described in Shinji Sakamoto, “Speaker and Speaker System”, Nikkan Kogyo Shimbun, 1967, the minimum resonance frequency f ₀ of the system is expressed by the following equation (1).

ここで、Ｃ_０は固定電極１０（固定電極５０）および振動膜３０により形成されるコンデンサの静電容量である。固定電極１０（固定電極５０）と振動膜３０との間に直流電界および入力信号が加えられない状態における固定電極１０（固定電極５０）と振動膜３０との距離をｄ、直流電界および入力信号が加えられたときの振動膜３０の変位をｘ_０とすると、Ｃ_０は次式（２）のように表される。

Here, C ₀ is the capacitance of the capacitor formed by the fixed electrode 10 (fixed electrode 50) and the vibration film 30. The distance between the fixed electrode 10 (fixed electrode 50) and the vibrating membrane 30 in a state where no DC electric field and input signal are applied between the fixed electrode 10 (fixed electrode 50) and the vibrating membrane 30 is d, the DC electric field and the input signal. when x ₀ the displacement of the vibrating film 30 at the time when the added, C ₀ is expressed by the following equation (2).

また、Ｅ_０は、固定電極１０（固定電極５０）に印加されるバイアス電圧、すなわち、共通接地から固定電極１０（固定電極５０）の電位である。εは、クッション材２０（クッション材４０）の誘電率である。Ｓは、振動膜３０の、固定電極１０（固定電極５０）と対向する面の面積である。Ｍ_ＭＤは、振動膜３０の質量である。Ｍ_ＭＡは、振動膜３０の片側の空気付加質量（放射質量）である。

E ₀ is a bias voltage applied to the fixed electrode 10 (fixed electrode 50), that is, a potential of the fixed electrode 10 (fixed electrode 50) from the common ground. ε is the dielectric constant of the cushion material 20 (cushion material 40). S is the area of the surface of the vibrating membrane 30 facing the fixed electrode 10 (fixed electrode 50). M _MD is the mass of the vibrating membrane 30. _MMA is the air additional mass (radiation mass) on one side of the vibrating membrane 30.

In addition, _{S M} is the equivalent stiffness of the system. As in the prior art, the electrostatic speaker of structure for fixing (supporting) the outer peripheral portion with respect to the fixed electrode of the vibrating film by applying a tension (tension) on the vibration film (diaphragm) is, S _M vibration Represents the tension applied to the membrane. However, in the structure not to apply tension to the vibrating film as in the present embodiment, it is not possible to use tension as S _M. Therefore, in the present embodiment, (a proportionality constant between an applied load and displacement, has dimensions of N / m) stiffness of the cushion material 20 (the cushion material 40) is used as the S _M. If the stiffness is determined, the elastic modulus of the cushion material 20 (cushion material 40) can be determined by considering the shape and thickness of the cushion material 20 (cushion material 40). As the elastic modulus, for example, Young's modulus can be used in a range where the stress-strain characteristic is linear, and a secant coefficient can be used in a range where the stress-strain characteristic is non-linear.

ここで、Ｓ_ＭＥ＝２εＳＥ_０ ^２／（ｄ＋ｘ_０）^３であり、コンデンサの負スティフネスを表す。このように、クッション材のスティフネスＳ_Ｍは、系の最低共振周波数ｆ_０の関数となる。式（３）に所望の最低共振周波数、すなわち最低共振周波数の設計値を代入すると、クッション材２０（クッション材４０）のスティフネスが得られる。こうして算出されたスティフネスを有するクッション材を用いることにより、所望の最低共振周波数を有する静電型スピーカを作製することができる。クッション材２０（クッション材４０）のスティフネスＳは、式（３）で算出されるスティフネスＳ_Ｍに対しあらかじめ決められた誤差範囲内に収まっていればよい。例えば、スピーカユニット１は、０．８≦（Ｓ／Ｓ_Ｍ）≦１．２を満たすスティフネスＳを有するクッション材を用いて作製されてもよい。 Solving equation (1) _{S M,} the following equation (3).

Here, S _ME = 2εSE ₀ ² / (d + x ₀ ) ³ , which represents the negative stiffness of the capacitor. Thus, the stiffness S _M of the cushion material is a function of the lowest resonance frequency f ₀ of the system. When the desired minimum resonance frequency, that is, the design value of the minimum resonance frequency, is substituted into Equation (3), the stiffness of the cushion material 20 (cushion material 40) can be obtained. By using the cushion material having the stiffness calculated in this way, an electrostatic speaker having a desired minimum resonance frequency can be manufactured. Stiffness S of the cushion material 20 (the cushion material 40) has only to fall within the error range determined in advance with respect to the stiffness S _M calculated by Equation (3). For example, the speaker unit 1 may be manufactured using a cushion material having a stiffness S that satisfies 0.8 ≦ (S / S _M ) ≦ 1.2.

FIG. 2 is a diagram illustrating a first embodiment of a configuration of a plurality of regions in the cushion material. In FIG. 2, only the fixed electrode 10 and the cushion material 20 are shown in order to avoid the drawing from becoming complicated. In the example of FIG. 2, the cushion material 20 has three regions, regions 20-1 to 20-3. If the stiffness in the area 20-1 to 20-3 each represents an _S M1 _{to S M3,} stiffness _S M1 _{to S M3 satisfies S M1 <S M2 <S M3} . In other words, the stiffness of each region in the state of being fixed to the fixed electrode 10 becomes lower from the central portion to the peripheral portion of the fixed electrode 10. This relationship is the same for the vibration film 30. That is, the stiffness of each region becomes lower as it goes from the central part to the peripheral part of the vibration film 30. As can be seen from Equation (1), the lower the resonance frequency, the higher the stiffness. That is, regions having three levels of stiffness, low, medium, and high correspond to a low sound range, a mid sound range, and a high sound range, respectively. For example, the low stiffness region functions as a woofer, the middle stiffness region functions as a squawker, and the high stiffness region functions as a tweeter. In this way, a speaker unit having a plurality of frequency characteristics can be manufactured by using a plurality of cushion materials having different stiffnesses.

  As shown in FIG. 2, the vibration film 30 is easily held at the center in the thickness direction by arranging a cushion material having a higher stiffness, that is, a harder material at the center. Thereby, workability and reliability are improved. Further, there is an effect of improving the characteristics of the speaker unit 1 such as reduction of distortion of output sound and reduction of risk of discharge. The position where the cushion material having high stiffness is arranged is not limited to the center portion of the vibration film 30. By using a cushion material having high stiffness in a region corresponding to a high region that does not require a low region, the positional accuracy of the entire diaphragm 30 can be further increased.

  FIG. 3 is a cross-sectional view showing a cross section of the fixed electrode 10 and the cushion material 20 taken along A-A ′ of FIG. 2. For convenience of explanation, the vibrating membrane 30 is also shown in FIG. As described above, the cushion material 20 is disposed such that a plurality of regions (regions 20-1 to 20-3) are in contact with the single vibrating membrane 30. As described above, the cushion material 20 has a plurality of regions on the surface in contact with the vibration film 30. The same applies to the cushion material 40.

  FIG. 4 is a diagram illustrating an example of a method for manufacturing the speaker unit 1. The cushion material 20 is fixed to the fixed electrode 10 using, for example, an adhesive. First, of the plurality of regions, the region 20-3 that is the region having the largest stiffness (that is, the hardest) is fixed on the fixed electrode 10 (FIG. 4A). Next, the area 20-2, which is the area with the second largest stiffness, is fixed around the area (FIG. 4B). Finally, the region 20-1 that is the region having the smallest stiffness is fixed to the outermost peripheral portion (FIG. 4C). In this way, it is easy to handle and convenient if cushion materials are arranged in order from a hard region. Note that the speaker unit 1 may be manufactured by fixing the cushion material 20 to the diaphragm 30 instead of fixing the cushion material 20 to the fixed electrode 10. Also in that case, it is the same that cushion materials are arranged in order from a hard region.

FIG. 5 is a diagram showing a second embodiment of a configuration of a plurality of regions in the cushion material. As shown in FIG. 5, the plurality of regions may be arranged in a line in the vertical or horizontal direction.
FIG. 6 is a diagram illustrating a third embodiment of a configuration of a plurality of regions in the cushion material. The plurality of regions are not necessarily arranged radially, and may be arranged so that the high stiffness region and the low stiffness region are in contact with each other.
The arrangements shown in FIGS. 2, 5, and 6 are merely examples, and the structure of the speaker unit 1 is not limited to this. Any cushioning material may be used as long as it has a plurality of regions having different stiffnesses.

  FIG. 7 is a schematic diagram illustrating a configuration of a speaker unit according to another embodiment. This speaker unit has a plurality of subunits corresponding to different frequency bands. In the example shown in FIG. 7, the speaker unit has three subunits. Each subunit corresponds to a low range, a mid range, and a high range, respectively. Each subunit has at least one set of fixed electrode 10 and vibrating membrane 30. A cushion material 20 is provided between the fixed electrode 10 and the vibrating membrane 30. In order to distinguish each unit, in FIG. 7, it distinguishes using subscripts 1-3. As described above, the plurality of regions of the cushion material 20 may be disposed so as to be in contact with different fixed electrodes 10 and vibrating membranes 30.

FIG. 8 is a diagram illustrating the frequency characteristics of the speaker unit 1. In the example of FIG. 8, the vibrating film 30 is a PET film having a thickness of 3 μm (micrometers) deposited with Al having a thickness of 400 Å (angstroms). Further, as the fixed electrode 10 and the fixed electrode 50, punching metal having a hole area ratio of 41.9% is used. A voltage of 5.25 kV is used as the bias voltage, and a sine wave of 4000 Vpp is used as the input signal. In FIG. 8, the solid line indicates the actual measurement value of the frequency characteristics when a high stiffness (specifically 133329 N / m) material is used as the cushioning material, and the dotted line indicates the low stiffness (specifically 28920 N / m) as the cushioning material. The measured value of the frequency characteristic when using this material is shown. By using a cushion material with low stiffness, the minimum resonance frequency f ₀ of the speaker unit 1 can be lowered.

FIG. 9 is a diagram comparing the calculated value of the frequency characteristic of the speaker unit 1 with the actual measurement value. FIG. 9A shows a calculated value by simulation, and FIG. 9B shows an actually measured value by experiment. In particular, in the frequency region of 2 kHz or less, the calculated value and the actually measured value are in good agreement. Thus, according to the present embodiment, an electrostatic speaker having a desired minimum resonance frequency f ₀ can be manufactured.

In the above-described embodiment, the aspect in which the speaker unit 1 is a push-pull type electrostatic speaker has been described. However, the speaker unit 1 may be a so-called single-type electrostatic speaker having only one fixed electrode. In the case of a single-type electrostatic speaker, the coefficient of the second term of the numerator inside the square root of the equation (1) is not “2” but “1”. That is, when the number of fixed electrodes is n, the negative stiffness of the capacitor can be expressed as S _ME = nεSE ₀ ² / (d + x ₀ ) ³ . In the case of a push-pull type electrostatic speaker, S _ME = 2εSE ₀ ² / (d + x ₀ ) ³ , and in the case of a single type electrostatic speaker, S _ME = εSE ₀ ² / (d + x ₀ ) ³ .

  Moreover, although the cushion material 20 demonstrated the aspect which has three area | regions in the above-mentioned embodiment, the number of the area | regions which the cushion material 20 has is not limited to three. The cushion material 20 may have two or four or more regions each having a different elastic modulus.

  Moreover, in the above-mentioned embodiment, the single cushioning material 20 demonstrated the aspect which has a some area | region. The speaker unit 1 may include a plurality of cushion materials having a single region, that is, a cushion material having a uniform elastic modulus. In this case, the elastic modulus of at least two cushion materials among the plurality of cushion materials is different. The plurality of cushion materials may be arranged so as to be in contact with each other, that is, densely, between the fixed electrode 10 (fixed electrode 50) and the vibration film 30, or may be arranged with a gap therebetween, ie, roughly. Also good.

It is a figure which shows the structure of the speaker unit 1 which concerns on one Embodiment of this invention. It is a figure which shows 1st Embodiment of the structure of the some area | region in a cushion material. It is sectional drawing which shows the cross section of a cushion material. FIG. 3 is a diagram illustrating an example of a method for manufacturing the speaker unit 1. It is a figure which shows 2nd Embodiment of a structure of the some area | region in a cushion material. It is a figure which shows 3rd Embodiment of a structure of the some area | region in a cushion material. It is a schematic diagram which shows the structure of the speaker unit which concerns on another embodiment. It is a figure which illustrates the frequency characteristic of the speaker unit. It is a figure which compares the calculated value and the measured value of the frequency characteristic of the speaker unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Speaker unit, 10 ... Fixed electrode, 20 ... Cushion material, 30 ... Vibration film, 40 ... Cushion material, 50 ... Fixed electrode, 60 ... Spacer

Claims (5)

A vibrating electrode having a surface and vibrating in response to an input signal;
A fixed electrode having a surface facing the surface of the vibration electrode and spaced from the vibration electrode;
A cushioning material disposed between the surface of the vibration electrode and the surface of the fixed electrode so as to be in contact with the vibration electrode, and having a plurality of regions in a cross section parallel to the surface of the vibration electrode, An electrostatic loudspeaker comprising: a cushion material having different stiffnesses in at least two of the plurality of regions.   The stiffness of a region close to the center of the vibration electrode in two adjacent regions among the plurality of regions is higher than the stiffness of a region far from the center of the vibration electrode. Item 4. The electrostatic speaker according to Item 1. A vibrating electrode having a surface and vibrating in response to an input signal;
A fixed electrode having a surface facing the surface of the vibration electrode and spaced from the vibration electrode;
A plurality of cushioning members disposed between the surface of the vibration electrode and the surface of the fixed electrode so as to be in contact with the vibration electrode, respectively;
The electrostatic loudspeaker characterized in that the stiffness of at least two of the plurality of cushion materials is different.   In two adjacent cushion materials among the plurality of cushion materials, the stiffness of the cushion material that is close to the center of the vibration electrode is higher than the stiffness of the cushion material that is far from the center of the vibration electrode. The electrostatic speaker according to claim 3.   The electrostatic speaker according to claim 3, wherein the number of the vibration electrodes is plural, and the plurality of cushion materials are arranged so as to be in contact with different vibration electrodes, respectively.

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