JP2007274362A - Electrostatic speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for controlling directional characteristics, or the like in an electrostatic speaker. <P>SOLUTION: The electrostatic speaker has an electrode 20, and a sheet-like conductive oscillator 10 that is arranged separately opposite to the electrode and is displaced according to a potential difference to the electrode. The space between the oscillator in a non-displaced state and the electrode should differ at least at two positions. The electrostatic speaker allows electrostatic force operating on the oscillator to differ depending on the places of the oscillator by changing the space between the oscillator and the electrode corresponding to the places, thus controlling various kinds of characteristics, such as the directional characteristics and output characteristics of sound generated by the oscillation of the oscillator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal structure of an electrostatic speaker.

  A speaker called an electrostatic speaker (condenser speaker) is known. Electrostatic speakers are particularly attracting attention because they can be designed to be lightweight and compact. An electrostatic speaker typically has two parallel flat electrodes facing each other across a gap, and a conductive sheet-like member (hereinafter referred to as a diaphragm or diaphragm) inserted between the electrodes and fixed at both ends. ). The sound generation mechanism is roughly as follows. When a predetermined voltage is applied to the parallel flat electrode and the diaphragm, a force attracted to one electrode side by the generated potential difference acts on the diaphragm. The diaphragm is fixed at both ends, but has a certain degree of elasticity, so that its central portion is displaced, and as a result, the diaphragm is bent. When the potential difference is reversed in this state, a reverse force acts on the diaphragm, and the vibrating body bends in the reverse direction. If such reversal of the potential difference is repeated, the diaphragm vibrates. As described above, by appropriately applying a voltage to the electrode, the vibration state (frequency, amplitude, etc.) of the diaphragm can be changed. When the applied voltage value is changed according to the input signal, the diaphragm vibrates accordingly, and as a result, sound corresponding to the input signal is generated from the diaphragm (see Patent Documents 1 to 3, etc.). .

  However, it is known that a flat speaker generally has a strong directivity of acoustic characteristics. The directivity has frequency characteristics. That is, it is known that the directivity is stronger in the high frequency band than in the low frequency band. As described above, there is a problem that the sound that can be heard depending on the location is not uniform because the directivity differs depending on the frequency band. Moreover, since the area of the diaphragm is relatively large, side lobes may appear.

Here, as a typical method for realizing desired directivity, a speaker array technique is known in which a plurality of speaker units are provided and the level and delay of an input signal supplied to each unit are controlled. Yes. However, when a speaker array is configured using an electrostatic speaker, it is possible to prepare a plurality of pairs of electrodes and diaphragms, or to divide one diaphragm and control the vibration state independently for each region. It is necessary to have a proper configuration. Furthermore, an electric circuit for controlling a signal supplied to each speaker unit is required. This complicates the structure of the entire speaker and increases the manufacturing cost. As described above, in the conventional electrostatic speaker, it is difficult to control the characteristics of the generated sound.
Japanese Patent No. 3353531 Japanese Patent No. 3277498 Japanese Patent Publication No. 7-038758

  The present invention has been made in view of the above-described background, and an object thereof is to provide a technique capable of controlling the characteristics of sound generated in an electrostatic speaker.

The electrostatic speaker according to the present invention includes an electrode and a sheet-like vibrating body that is spaced apart from the electrode and is displaced according to a potential difference from the electrode, and the vibrating body in a non-displaced state The distance between the electrode and the electrode is different at two or more positions.
According to the present invention, the electrostatic force acting on the vibrating body can be varied depending on the location of the vibrating body by varying the distance between the vibrating body and the electrode depending on the location. Thereby, various characteristics such as directivity characteristics and output characteristics of sound generated by vibration of the vibrating body can be controlled.

  In a preferred aspect, the apparatus further includes an elastic body interposed between the vibrating body and the planar electrode.

  The interval may be determined based on a directivity characteristic of sound generated by vibration of the vibrating body. The directivity may be determined based on a weighting characteristic for suppressing side lobes.

  In another preferable aspect, the electrode includes a plurality of regions having a plane parallel to the vibrating body in the non-displacement state.

  In another preferable aspect, the apparatus further includes an elastic body configured by a plurality of elastic members inserted in a space region corresponding to each of the plurality of regions, and the elastic modulus of each elastic member is determined by the plurality of elastic members. The forces exerted on the corresponding areas of the vibrator are determined to be equal.

  In another preferred embodiment, the spacing varies continuously with respect to position.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing a cross section of a main structure of an electrostatic speaker 1 according to one aspect of the present invention. As shown in the figure, the electrostatic loudspeaker 1 includes a vibrating body 10 and two counter electrodes that are opposed to the vibrating body 10 and spaced apart so that at least the vibrating body 10 does not contact even if it is bent due to its elasticity. 20. The vibrating body 10 is a conductive film (or plate) obtained by depositing a metal film on a film such as PET (polyethylene terephthalate) or PP (polypropylene), or applying a conductive paint. In a fixing means T formed of an insulating material such as methyl methacrylate) or rubber, for example, the four corners are fixed to a casing (not shown) in a state where a predetermined tension is applied to the vibrating body 10. Note that the method for fixing the vibrating body 10 is not limited to this, and it is only necessary that the vibrating body 10 is supported between the opposing electrodes 20 so as to be able to vibrate around a predetermined position. However, as shown in FIG. 1, it is preferable that the vibrating body 10 is fixed at a position where the distance from both the counter electrodes 20 is equal (that is, just the center between the electrode plates).

  The counter electrode 20 is made of a metal plate, a punched metal having a hole in the metal plate, a sputtered nonwoven fabric, a nonwoven fabric coated with a conductive paint, and the like, and is made of a material having high sound wave transmission properties. The electric speaker 1 is fixed to a housing (not shown). In addition, the electrostatic speaker 1 includes a power source (not shown) and an input unit that inputs an audio signal from the outside, so that a voltage corresponding to the input audio signal can be applied to the counter electrode 20 and the vibrating body 10, respectively. It has become. When a predetermined potential difference is generated between the counter electrode 20 and the applied voltage, an electrostatic force that is attracted to one of the electrodes 20 acts on the vibrating body 10. That is, the vibrating body 10 is displaced (bends) in the vertical direction of the paper in the figure according to the input signal, and the vibration is generated by sequentially changing the displacement direction, and the sound corresponding to the vibration state (frequency, amplitude, phase) Is generated from the vibrating body 10. In the following, a case where the counter electrodes 20 are provided in pairs (so-called push-pull method) will be described, but a configuration in which only one counter electrode 20 is provided is also possible. In short, any configuration in which an electrostatic force according to an input signal acts on the vibrating body 10 may be used.

  As shown in the figure, in the present invention, the distance d between the counter electrode 20 and the vibrating body 10 in a non-displaced state varies depending on the location. As an example, an example is shown in which the interval is d3 in the region I and the region V, the interval is d2 in the region II and the region IV, and the interval is d1 in the region III.

  FIG. 2 shows a view of the electrostatic speaker 1 as viewed from above (or below). From this figure, it can be seen that there are three regions in which the distance to the vibrating body 10 (and hence the distance to the other counter electrode 20) is different in both counter electrodes 20.

  The interval d can be arbitrarily determined based on the directivity characteristics of sound generated by the vibrating body 10. This is because if the distance between the vibrating body 10 and the counter electrode 20 is different, the electrostatic force acting on the corresponding region in the vibrating body 10 is different. Specifically, since the sound pressure of the acoustic wave generated in the vibrating body 10 is inversely proportional to the square of the interval d, for example, if the sound pressure value is to be quadrupled, the interval d may be halved. Thus, by changing the distance d, the sound pressure of the acoustic wave generated from the vibrating body 10 can be controlled.

  For example, to generate a sound with a sharp directional characteristic by suppressing side lobes that appear in the directional characteristic of a generated sound characteristic of a flat speaker, or to generate a sound with a wide directivity by suppressing a main lobe In addition, an optimal sound pressure weighting characteristic is determined in order to realize a desired directivity characteristic by, for example, performing a simulation on the relationship between the force applied to each place of the vibrating body and the change in the vibration state caused by the simulation. . Then, the distance d and the region (the number of regions and the “shape” of each electrode region) are set so as to correspond to this weighting characteristic. As this weighting characteristic, a known weighting characteristic such as a binomial distribution function, a normal distribution function, or a Dorfchebyshev characteristic can be used according to the directivity (suppression) characteristic to be realized. Then, by applying a predetermined discretization process to this weighting characteristic, the distance d between the regions and each region (in other words, the cross-sectional structure of the counter electrode 20) can be determined.

  In FIG. 2, the formation direction of the region is one-dimensional. However, the present invention is not limited to this. For example, as shown in FIG. 3, two-dimensional regions (regions A, B, and C in FIG. 2) are formed. May be.

  FIG. 4 is a cross-sectional view of the main structure of the electrostatic speaker 1 according to another preferred embodiment of the present invention. In this aspect, the elastic body 30 is inserted into the space between the vibrating body 10 and the counter electrode 20. The elastic body 30 can be deformed by an external force such as a non-woven fabric, cotton, sponge, or the like having a predetermined elastic modulus (for example, a linear elastic modulus (Young's modulus) in the thickness direction). For example, an adhesive layer is applied to the surface of the material, and the material is fixed to the counter electrode 20 via the adhesive layer. Or the structure which wrapped the some spring with the clothing material may be sufficient. In this aspect, when the vibrating body 10 is displaced (vibrated), the elastic body 30 is deformed according to the elastic modulus, and a force (restoring force) in the opposite direction to the displacement acts on the vibrating body 10.

This elastic modulus can be determined based on, for example, a desired frequency characteristic. In the electrostatic loudspeaker, the minimum resonance frequency f ₀ and the equivalent stiffness S _{M of the} system (the proportional constant between the applied load and the displacement, the unit is MKS system [N / m]; specifically vibration between the stiffness) due to the tension S _M given to the body 10, in general, it is known that the following relationship is established.

Here, C ₀ is the capacitance of the capacitor formed by the two facing electrodes 20 and the vibrating body 10. The distance between the counter electrode 20 and the vibrating body 10 in a state where no DC electric field and input signal are applied between the counter electrode 20 and the vibrating body 10 (that is, no displacement state) is d, and the DC electric field and input signal are applied. when the displacement amount x ₀ of the vibrator 10 when, following equation holds.

E ₀ is the bias voltage applied to the counter electrode 20, that is, the potential of the counter electrode 20 from the common ground. ε is the dielectric constant of the elastic body 30. S is the area of the surface of the vibrating body 10 facing the counter electrode 20. M _MD is the mass of the vibrating body 10. _MMA is an air additional mass (radiation mass) on one side of the vibrating body 10.

Solving the number 2 for the S _M, expressed by the following equation.

Here, S _ME is S _ME = εSE ₀ ² / (d + x ₀ ) ³ and represents the negative stiffness of the capacitor. As described above, the S _M is the equivalent stiffness of the system, in the present embodiment, this is the force that pulls the vibrator 10 from the fixed unit T (the tension), the elastic member by the displacement of the vibrating body 10 (stress) When mechanical distortion occurs in 30, this is caused by a force (restoring force) for pushing the vibrating body 10 back in the direction opposite to the displacement. Therefore, the equivalent stiffness S _M of the system in this embodiment is obtained by combining the stiffness S _M ^EB caused by the tension acting on the vibrating body 10 and the stiffness S _M ^T caused by the restoring force of the elastic body 30 as shown in the following equation. You can think of it as an addition.

Here, it is assumed that the tension is known and the value does not change according to the vibration state or the like. From (Equation 3) and (Equation 4), the following equation is obtained.

As is apparent from the above equation, if the desired minimum resonance frequency f ₀ is specified, the corresponding stiffness is determined. If the stiffness is determined, the elastic modulus of the elastic body 30 to be inserted can be determined by considering the shape and thickness of the elastic body. As the elastic modulus of the elastic body 30, for example, a 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. In short, it is only necessary to determine the stress-strain characteristics of the elastic body 30 such that the stiffness of the entire system satisfies the above equation when the elastic body 30 is inserted.

A configuration in which no tension acts on the diaphragm 10 (that is, no tension) may be employed. Specifically, the fixing means T is omitted, and the vibrating body 10 is pressed from both sides by the elastic body 30 and with a predetermined pressure, so that the displacement (vibration) at the center portion is fixed while fixing the end of the vibrating body 10. An acceptable configuration may be used. In this case, S _M ^T = S _M ^EB . In other words, the elastic body 30 may be used as a medium for applying a certain stress between the opposing electrodes as well as providing a restoring force when the vibrating body 10 is displaced.

  Furthermore, you may vary the elasticity modulus of the elastic body 30 for every area | region. As described above, if the elastic modulus is different, the restoring force related to the vibrating body 10 in the region is different. Therefore, the vibration state of the vibrating body 10 can be changed for each place by changing the elastic modulus for each place. . As an example, as shown in FIG. 5, this can be realized by inserting elastic members 31, 32 and 33 having different elastic moduli for each region. In the figure, an example is shown in which an elastic member 31 is inserted into regions I and V, an elastic member 32 is inserted into regions II and IV, and an elastic member 33 is inserted into region III.

In this case, the elastic modulus of the elastic member corresponding to each region can be determined based on, for example, frequency characteristics to be realized by the electrostatic speaker 1. As an example, the distance d and the elastic modulus can be determined so that all f ₀ in each region are equal. Or you may determine the elasticity modulus (and space | interval d which concerns on each area | region) in consideration of the characteristic of the acoustic wave output.

  Hereinafter, a method for designing the structure of an electrostatic speaker when the elastic body 30 is used (specifically, a method for determining the elastic modulus of the elastic body to be inserted and the distance d between the vibrating membrane 10 and the electrode 20). This will be described with reference to FIG. This method can be implemented in a general computer apparatus in software or hardware. Here, an example in which the design method according to the present invention is executed using a general computer device configured by an input / output device, a storage device, and various processors that receive an instruction from the user and output a calculation result is shown. I will explain to you.

First, a virtual region is set on the vibrating body 10 (step S10). The shape, size, and number of regions are arbitrary, but may be specified by the user, for example. If you want to achieve acoustic characteristics such as directivity with high accuracy, you can set a large number of areas.If you want to prioritize electrode manufacturing and processing costs, reduce the number of areas and reduce the number of processing steps. It is good to reduce it. Next, for each region, the stiffness S _M ^EB due to the tension acting on the vibrating body 10 and the stiffness S _M ^T due to the restoring force of the elastic body 30 are determined (step S20). Here, the stiffnesses S _M ^EB and S _M ^T may be specified by the user or may be predetermined values. Next, the electrostatic force to be applied to the vibrating body 10 corresponding to each region on the electrode 20, that is, the dielectric constant of each region is determined (step S30). Specifically, for example, it is determined by the following method. The sound pressure level of the acoustic wave generated in the vibrating body 10 depends on the dielectric constant of the system. In view of this, the value of the sound pressure level and the value of the dielectric constant necessary for generating an acoustic wave of the sound pressure are calculated in advance by a predetermined method and stored in the storage device in association with each other. When the user inputs a desired sound pressure level value, the processor determines a dielectric constant value corresponding to the sound pressure level value. Subsequently, an elastic member is determined in consideration of the calculated elastic modulus and dielectric constant (step S40). Specifically, a database that stores the elastic modulus (elastic characteristics) and dielectric constant (dielectric characteristics) of a plurality of elastic members is constructed, and the processor searches the database and finds the most suitable elastic modulus and dielectric constant. An elastic member having suitable physical properties can be determined using a predetermined matching algorithm. Finally, the distance d between the vibrating body 10 and the electrode 20 is determined (step S50). Specifically, the user inputs a desired directional characteristic (for example, inequality information of the sound pressure of the main lobe and the side lobe of the acoustic wave), and the processor calculates the weighting characteristic based on the directional characteristic information. The distance d (in other words, the arrangement position of the electrode 20 and the cross-sectional shape thereof) is determined so as to correspond to this weighting characteristic.

In each aspect described above, the distance d between the vibrating body and the counter electrode is discretely changed, but the distance d is continuously changed so that there is no gap between the adjacent areas. May be. FIG. 7 shows an electrostatic speaker 1A configured as described above. In this case, the method of determining the distance d (in other words, the cross-sectional shape of the counter electrode 20) can be determined based on at least one of directivity and output characteristics as described above.
For example, with regard to directivity control, if the existing array speaker technology is used, it is possible to control directivity even when a planar speaker is used as the speaker unit. In practice, it is difficult to control the directivity with high accuracy because the number of speaker units having a size is practically limited. On the other hand, if the distance d is continuously changed as in the present application, the force acting on an arbitrary position of the diaphragm can be controlled. Therefore, high-precision directivity control that is difficult with existing array technology is possible. Can be performed by one speaker unit (ie, one vibrating body and electrode).

  Further, like the electrostatic speaker 1B shown in FIG. 8, the shape of the elastic body 30 is processed so as to match the curved surface shape of the counter electrode, and this is formed between the counter electrode 20 and the vibrating body 10 as described above. It may be inserted. In this case, for example, the elastic modulus of the elastic body 30 may be changed discretely or continuously depending on the location. In order to change it continuously, for example, a predetermined continuous distribution may be given to the temperature inside the elastic body 30 using a heater or the like. This is because the elastic modulus is generally a function of temperature.

  Or you may fix the vibrating body 10 in the state which applied the bending stress instead of the state which applied tension like the electrostatic speaker 1C shown in FIG. That is, the bent state is a non-displaced state, and the vibrating body 10 is vibrated based on this state. At this time, the point that the interval d is continuously changed is the same as the embodiment shown in FIG. In this case, it is possible to realize sharper directivity characteristics by making the vibrating body 10 constantly concave with respect to the sound wave transmission direction.

It is sectional drawing of the structure of the electrostatic speaker which concerns on 1 aspect of this invention. It is the figure which looked at the same electrostatic speaker from the upper part. It is the figure seen from the upper direction or the downward direction of the structure of the electrostatic speaker which concerns on the other aspect of this invention. It is sectional drawing of the structure of the electrostatic speaker which concerns on the other aspect of this invention. It is sectional drawing of the structure of the electrostatic speaker which concerns on the further another aspect of this invention. It is a figure for demonstrating the method of designing the structure of the same electrostatic speaker. It is sectional drawing of the structure of the electrostatic speaker which concerns on the further another aspect of this invention. It is sectional drawing of the structure of the electrostatic speaker which concerns on the further another aspect of this invention. It is sectional drawing of the structure of the electrostatic speaker which concerns on the further another aspect of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1A, 1B, 1C ... Electrostatic speaker, 10 ... Vibrating body, 20 ... Electrode, 30, 31, 32, 33 ... Elastic body, T ... Fixing means.

Claims (7)

Electrodes,
A sheet-like vibrating body that is spaced apart from the electrode and is displaced according to a potential difference with the electrode;
The electrostatic loudspeaker characterized in that an interval between the vibrating body and the electrode in a non-displaced state is different at two or more positions. The electrostatic speaker according to claim 1, further comprising an elastic body interposed between the vibrating body and the electrode. The electrostatic speaker according to claim 1, wherein the interval is determined based on a directivity characteristic of sound generated by vibration of the vibrating body. The electrostatic loudspeaker according to claim 3, wherein the directivity is determined based on a weighting characteristic for suppressing side lobes. The electrostatic speaker according to claim 1, wherein the electrode includes a plurality of regions having surfaces parallel to the vibrating body in the non-displacement state. An elastic body composed of a plurality of elastic members inserted in a space region corresponding to each of the plurality of regions;
The electrostatic speaker according to claim 5, wherein the elastic modulus of each elastic member is determined so that the forces exerted by the plurality of elastic members on the corresponding regions of the vibrating body are equal to each other. The electrostatic speaker according to claim 1, wherein the interval continuously changes with respect to a position.

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