JP2007274361A - Speaker, speaker net, and design device thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate acoustic waves having desired directional characteristics by a simple method. <P>SOLUTION: An electrostatic speaker 1 has a vibrating membrane 10 and an electrode 20. First to n-th (n: a positive integer) regions A-D are set onto the electrode. A k-th (k: an integer of 2-n) region is set while surrounding (k-1)-th region. In each region, a plurality of through holes Ha-Hd having the same shape are provided at the same interval. At least one of the shape and the arrangement interval of the through-hole should differ for each region. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a speaker and a speaker net.

  Some speakers are classified into a so-called planar speaker because of their structural features. A typical example is an electrostatic speaker (condenser speaker). Electrostatic speakers are particularly attracting attention because they can be designed to be lightweight and compact. An electrostatic speaker is typically two parallel flat electrodes facing each other across a gap, and a conductive sheet-like member inserted between the electrodes and fixed at both ends (hereinafter referred to as a vibrating membrane). It is comprised from. The sound generation mechanism in such a so-called push-pull type electrostatic speaker is typically 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.). . The generated musical sound passes through an electrode having good acoustic wave permeability (for example, a through-hole formed in a metal plate electrode) and is emitted to the outside.

  However, in a so-called planar speaker including an electrostatic speaker, the radiation area of an acoustic wave generated by a sounding body (for example, a vibrating membrane) increases due to its structure. It is known that an acoustic wave having a directivity characteristic such that a plurality of maximum values (main lobes and side lobes) of output levels appear in a specific direction corresponding to the state is generated.

As a method for generating acoustic waves with suppressed side lobe output level or wide directivity in a planar speaker, a plurality of planar speakers are provided as speaker units, and input signals are supplied to each unit. A loudspeaker array technique is known that controls the level and delay of the signal (see Non-Patent Document 1).
Japanese Patent No. 3353531 Japanese Patent No. 3277498 Japanese Patent Publication No. 7-038758 DB (Don) KeeleJr., “Implementation of Straight-Line and Flat-Panel BeamwidthTransducer (CBT) Loudspeaker Arrays Using Signal Delays” Audio Engineering Society, Convention Paper Presented at the 113th Convention, 2002 October 5/8 LA, California, USA

However, when constructing a speaker array using, for example, electrostatic speakers, prepare multiple sets of electrodes and diaphragms, or divide one diaphragm and control the vibration state independently for each area It needs to be possible. Furthermore, an electric circuit for controlling the level and delay of a signal supplied to each speaker unit is also required. This complicates the structure of the entire speaker and increases the manufacturing cost. As described above, the conventional planar speaker cannot realize desired directivity characteristics with a simple configuration.
The present invention has been made in view of the above-described background, and provides a speaker capable of realizing desired directivity with a simple configuration and an apparatus for changing the characteristics of acoustic waves that can be attached to the speaker. Objective.

  The present invention relates to a first to nth (n is a positive integer) region set on the plate-shaped member in a speaker net that covers a sound emitting surface of the speaker with a plate-shaped member, and kth (k = Integer of 2 to n) is set so as to surround the (k-1) th region, and a plurality of openings of the same shape are provided at the same interval in each region, and A speaker net is provided in which at least one of the shape and the arrangement interval of the openings is different for each region. According to the present invention, without using an electrical filter circuit, a speaker net in which holes having different sizes or different arrangement intervals are formed in a plate-like member for each region is arranged on the acoustic wave propagation surface, thereby providing a speaker. The spatial characteristics of the acoustic wave passing through the net can be changed.

  In a preferred aspect, at least one of the cross-sectional area or the arrangement interval of the openings in the k-th region is larger than the cross-sectional area or the arrangement interval of the openings in the (k−1) -th region.

  In a preferred aspect, each of the plurality of regions has a square shape. In another preferred embodiment, each of the plurality of regions has a circle shape.

  In another aspect, the present invention is an electrostatic speaker having a vibrating membrane and a plate-like electrode, and is a first to nth (n is a positive integer) region set on the electrode. , The k-th (k = 2 to n) region is set so as to surround the (k−1) -th region, and a plurality of openings having the same shape are arranged at the same interval in each region. An electrostatic speaker is provided, wherein at least one of a shape and an arrangement interval of the openings is different for each region.

  In still another aspect, the present invention is an apparatus for designing a speaker net that covers a sound emitting surface of a speaker with a plate-like member, the directivity specifying means for specifying the directivity of acoustic waves, and the directivity specifying means Based on the directivity characteristic specified in step 1, the region setting means for setting a plurality of two-dimensional regions on the plate member, and the transmission coefficient corresponding to the plurality of two-dimensional regions set by the region setting unit, respectively Provided is a speaker network design device comprising: a coefficient calculating means for calculating; and a means for determining the shape and arrangement interval of openings formed in each two-dimensional region based on the transmission coefficient calculated by the coefficient calculating means. .

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view of the basic structure of the electrostatic speaker 1 according to the first embodiment of the present invention. As shown in the figure, the electrostatic loudspeaker 1 is generally composed of a vibrating membrane 10 and two parallel flat electrodes 20 (hereinafter simply referred to as electrodes 20) facing the vibrating membrane 10.

  The vibrating membrane 10 is, for example, a conductive film having a thickness of several microns to several tens of microns, for example, 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 (not shown) made of an insulating material such as vinyl chloride, acrylic (methyl methacrylate), rubber or the like, with a predetermined tension acting on the vibration membrane 10, for example, four sides thereof are static. The electric speaker 1 is fixed to a housing (not shown).

  The electrode 20 is a punching metal in which a plurality of through holes (indicated by H in the figure) are formed in a conductive plate member such as a metal plate having a thickness t, and the case of the electrostatic speaker 1 (Not shown). At this time, it is preferable that the distance j from the vibrating membrane 10 to both the electrodes 20 is equal. In other words, the position just between the opposing electrodes is the fixed position of the vibration film 10 (more precisely, the vibration film 10 in the non-displaced state).

  The electrostatic speaker 1 includes a power source (not shown), and can apply voltages of opposite polarities to the electrodes 20 and a bias voltage to the vibrating membrane 10. The electrostatic speaker 1 includes an input unit for inputting a sound signal from the outside, and changes the inversion timing of the applied voltage according to the sound signal, thereby causing the vibration film 10 to vibrate according to the sound signal. Be able to. The acoustic wave generated by the vibration of the vibrating membrane 10 passes through the electrode 20 and is emitted outside the speaker.

  Although FIG. 1 shows a case where two electrodes 20 are used to simultaneously apply an attractive force and a repulsive force to the vibrating membrane 10 on the vibrating membrane 10, only one electrode 20 may be used. In short, it is only necessary that an electric field that changes with time according to a change in time of the input audio signal is formed using the electrode 20 and that the charged vibrating membrane 10 can be displaced by receiving an electrostatic force from this electric field. That is, in the present invention, there are no limitations on factors such as the material constant of the vibrating membrane 10 such as electrical conductivity and elastic modulus, the fixing method of the vibrating membrane 10 and the magnitude of the tension exerted on the vibrating membrane 10. In addition, in the same figure, an example in which holes are similarly formed in both electrodes 20 is shown, but the present invention is not limited to this, and a hole is formed in one electrode 20 (electrode on the acoustic wave emission side). On the other hand, the electrode 20 on the opposite side (rear surface) may be a metal plate with no holes. That is, it is only necessary that the acoustic wave generated in the vibrating membrane 10 is emitted to the outside through one of the electrodes. However, it is preferable that both the electrodes 20 have the same structure (that is, a metal plate in which holes are formed at the same position) in order to cause a uniform electrostatic force to act on the vibration film 10 in which holes are formed on the metal plate. .

  The present invention is characterized by the structure of the holes formed in the electrode 20, and this will be described in detail below. FIG. 2 is a view of the electrode 20 as viewed from above (downward). As shown in the figure, in the electrode 20, in order from the outside, in other words, the outer region is formed around the inner region (so that the outer region surrounds the inner region) Regions A, B, C, and D having a square outer periphery are defined. In each region, a plurality of holes Ha, Hb, Hc, Hd having the same size (cross-sectional diameter) are formed in a predetermined pattern. Thus, in the electrode 20 of the present application, the same holes are not uniformly distributed, but the size and interval of the holes and the arrangement pattern thereof vary depending on the region on the electrode 20 (that is, non-uniformly distributed). It is characterized by that). In addition, the pattern here means the shape of arrangement | sequences, such as a parallel type | mold (grid pattern shape), a square staggered type (45 degree zigzag), a zigzag type (60 degree zigzag). FIG. 2 shows an example in which holes are formed in a parallel cut pattern in all regions. In the same figure, in the area A, an example is shown in which the diameter is d and the closest interval (pitch) is a. Thus, in the present invention, the acoustic wave passing through this electrode is set by setting the distribution pattern of the holes provided in the electrode 20 provided on the acoustic wave passage surface according to the directivity characteristic or frequency characteristic to be realized. The electrode is provided with a function as a filter that can change the directivity characteristics and frequency characteristics of the electrode.

  The degree of change in acoustic directivity characteristics and frequency characteristics before and after entering the electrode 20 varies depending on the hole pattern (hole shape and arrangement position) provided in the electrode 20. Hereinafter, a method for determining the number of regions and the size (area) of the regions and a method for determining the hole arrangement method (hole shape and arrangement pattern) will be described in detail.

  Prior to this, the relationship between the acoustic wave frequency, the effective area of the vibrating membrane where the acoustic wave is generated, the directivity characteristics in each frequency band, the shape and number of electrode holes, and the acoustic wave transmission coefficient will be shown. . Unless otherwise specified, the shape of the hole is a concept including the shape of the cross section of the hole, the cross-sectional area, the diameter, and the depth. In the present invention, the depth of the through hole can also be changed depending on the location. In this case, however, the thickness t of the electrode 20 at that portion naturally changes depending on the location.

(1) Relation between degree of directivity, frequency and effective area Directivity coefficient (an index indicating the sharpness of directivity of acoustic wave) Q is frequency f, and the effective area of the diaphragm where the acoustic wave is generated (in FIG. 2) If the area of each region having a square shape is S, it can be generally expressed as follows.

  As an example, when considering a circular piston vibration of radius a having an infinite baffle as a vibration film, it is known that the directivity coefficient on the central axis can be expressed as follows.

In the above equation, c represents the speed of sound, a represents the diaphragm radius, and J ₁ represents a primary Bessel function. In the above formula, g (x) is a monotonically increasing function of x, there is x to take the second derivative value maximum value (this is referred to as characteristic point x ₀ a). In other words, the function g (x) is the slope abruptly changes in x = _{x 0.} The schematic shape of this function is shown in FIG.
In summary, the directivity coefficient Q is a function of f * S ^ (− 1/2), and the higher the frequency f and the smaller the effective area S, the sharper the directivity of the acoustic wave. That is. Therefore, if the effective area S is constant, the directivity sharply becomes sharper at a certain frequency or higher. For example, when S = 1 m ² , the directivity coefficient Q is substantially constant in a band where the frequency f is smaller than 100 to ²⁰⁰ Hz, but the directivity coefficient Q increases rapidly in a frequency band higher than that.

(2) Relationship between the transmission coefficient (TI) and the shape and arrangement of the holes When a plate (electrode 20) having a predetermined hole formed on the passage surface of the acoustic wave generated by the vibrating membrane is placed, The index TI indicating the output level of the transmitted acoustic wave (in other words, the difficulty of attenuation of the acoustic wave), n the number of holes formed per unit area, d the hole diameter, and the electrode thickness The following introduction is performed under the condition that the interval between the nearest holes is a, the aperture ratio (the ratio of the area occupied by holes in the plate) is P, and the frequency is constant.

  Although the closest distance a varies depending on the arrangement pattern, it is expressed by the following equation using the aperture ratio.

  Here, k is an amount determined by the arrangement pattern, k = 9.5 for the staggered arrangement, and k = 8.9 for the parallel arrangement.

  As is clear from (Equation 2), if the thickness t of the electrode 20 is uniform, the larger the number of holes, the larger the area (diameter) of the holes, and the narrower the interval, the more the acoustic wave transmission coefficient. Can be said to be large (ie, less likely to be attenuated). Further, it is known that if the index TI is the same value, the attenuation is larger as the frequency is higher, and the attenuation in the higher sound range is larger as the index TI is smaller.

As described above, if holes having the same shape and diameter are arranged on the electrode 20 at regular intervals, the directivity characteristics differ depending on the frequency. Specifically, as described in (Equation 1), an acoustic wave in a low frequency band has a gentle directivity and propagates in a wide direction, whereas an acoustic wave in a high frequency band has a strong directivity and has a predetermined direction. Will propagate in the direction.
In the following, for the purpose of generating an acoustic wave having a directivity in each frequency band with a constant directivity and no side lobe appearing in the high frequency band using the electrostatic speaker 1 of the present invention, The case where the shape and arrangement | positioning of the hole formed in the electrode 20 are determined using FIG. 4 and FIG.

  FIG. 4 is a block diagram showing a functional configuration of the hole pattern design apparatus 100 according to the present invention. As shown in the figure, the hole pattern design apparatus 100 includes a control unit 110, an input / output I / F 120, and a storage unit 130. The input / output I / F 120 is configured by a keyboard, a display, and the like, and receives instructions regarding directivity characteristics from the user. The storage unit 130 is a storage device such as a RAM, a ROM, and a hard disk, and stores various types of information that are referred to when the control unit 110 calculates the arrangement of holes and the shape of each hole. The control unit 110 includes a CPU and the like, and includes a region determination unit 111, a transmission coefficient determination unit 112, and a hole pattern determination unit 113 as functional modules.

  FIG. 5 shows an operation example of the hole pattern design apparatus 100. First, the user inputs information on the desired directivity described above with the electrostatic speaker 1 (step S10). For example, information such as the directivity in each frequency band and the frequency at which the sound pressure value of the side lobe is equal to or lower than a predetermined value.

  Subsequently, the region determination unit 111 sets a region (step S20). Specifically, the number of regions to be provided on the electrode 20 and the diameter of each region are determined. First, the number and value of frequency bands to be divided are determined by a predetermined method. These values may be designated by the user in step S10, or may be set as fixed values. The number of frequency bands is determined as the number of regions. FIG. 2 shows an example in which the number of bands to be divided is determined to be 4. For example, it is assumed that 0 to 500 Hz (band f1), 500 Hz to 2000 Hz (band f2), 2000 Hz to 8000 Hz (band f3), and 8000 Hz or more (band f4) are determined as frequency bands.

  Next, a region to be transmitted through the acoustic wave of each frequency is determined based on (Equation 1). In this example, in accordance with the purpose of making the directivity coefficient of each frequency band as equal as possible, a region having a smaller area S on the inner side is assigned to a higher frequency band. That is, since the area with the smallest area is the innermost area D, the area D is assigned to the frequency band with the highest directivity. As a result, region D is assigned to band f4, regions C to D are assigned to band f3, regions B to D are assigned to band f2, and regions A to D are assigned to band f1. In this way, the frequency band and the region are associated with each other on a one-to-one basis.

Next, the area S of each region is calculated using (Equation 1). Specifically, an area S corresponding to a region where the directivity coefficient Q is substantially constant in each frequency band is calculated based on (Equation 2). Specifically, it may be determined to S corresponding to the feature point x ₀ when the frequency f is given, respectively. For example, for f = 500 Hz or less, it can be found that it corresponds to S = 1 m ² which is the entire area. The value of S is the area of region A corresponding to 0 to 500 Hz (band f1). In this way, the areas of the regions A, B, and C are obtained. For example, to correspond to f = 500 Hz is to correspond to ^S = ^0.151m 2, f = 2000Hz to correspond to ^S = ^0.009m 2, f = 8000Hz is calculated as S = 0.0006m ^2, All areas S of each region are determined. When the size of the electrode (the area of the outermost region A) is designated in advance, the obtained area of each region may be multiplied by a predetermined normalization constant. In short, it is preferable to set the ratio of the areas of the regions so that the directivity coefficients in the frequency band are as equal as possible.

  Next, an arrangement pattern including the shape and arrangement interval of holes provided in each region is determined. First, the transmission coefficient determination unit 112 determines the value of the transmission coefficient TI for each region based on the corresponding frequency value (step S30). As described above, TI is an index representing the difficulty of attenuation of acoustic waves passing through the region. However, the acoustic wave attenuation level AT depends not only on the TI but also on the frequency. That is, the attenuation level AT is a function of the frequency f and TI. In this aspect, the attenuation level AT to be set in each frequency band is first determined based on information such as the sidelobe suppression degree related to the designated directivity, and from here the frequency corresponding to each region (in the above example, TI corresponding to 500 Hz, 2000 Hz, and 8000 Hz) is determined. More specifically, the frequency dependence and TI dependence of the AT are calculated in advance by simulation or experiment, and the attenuation level, the TI, and the frequency as shown in FIG. The table T is stored, and the TI is determined with reference to the table T. As a result, for example, the TI is determined to be 15, 65, 3009, and 10840 for the regions A, B, C, and D, respectively.

  As can be seen from this example, in this aspect, small TIs are set in order from the outer region according to each frequency. As a result, the electrode 20 has a frequency filter function in which the acoustic wave in the low frequency band passes through without being attenuated while the high frequency is cut in the outer region. And the frequency band of the acoustic wave which passes without being attenuated as it goes to the inner region becomes wider. In the example of FIG. 2, only the acoustic wave of 0 to 500 Hz or less which is the lowest frequency band passes in the outermost region A, and almost the entire frequency band (ideally 10,000 Hz or more) in the innermost region D. ) Is configured to pass acoustic waves.

  Next, the hole pattern determination unit 113 calculates the hole diameter d and the interval a based on the determined TI values using (Equation 2) and (Equation 3) (step S40). As can be seen from (Equation 3), there are an infinite number of combinations for determining d, a, etc., for a given TI value. An example of the combination is shown in FIG. FIG. 7A shows an example in which the thickness t of the electrode 20 and the diameter d of the holes are made constant while the hole interval a is varied. In this case, holes of the same size are formed in each region, but the interval (that is, the probability density of holes) varies from region to region. Thus, when forming the hole of the same shape, there exists a merit that processing cost may be cheap. On the other hand, FIG. 7B shows an example in which d and a are determined so that the aperture ratio is as equal as possible in each region. In this case, both the size and interval of the holes are different for each region. If the aperture ratio is made uniform in this way, there is a merit that sound quality is improved because the electrostatic force acting on the vibrating membrane 10 is stabilized.

  As described above, in the present invention, the directivity can be made uniform by setting a frequency band and assigning a region having a different sound wave radiation area for each frequency band. Further, by forming holes having different arrangement distributions and sizes in each region, the electrode 20 is given a function as an assembly of a plurality of low-pass filters. It is possible to attenuate the directivity of the entire acoustic wave by attenuating the level of the high frequency band.

  In the above-described example, the shape of the region and the shape of the electrode are square, but may be a circle as shown in FIG. However, it is the same in that the region that produces the effect of transmitting only the low frequency is sequentially provided at the outer edge portion and the region that transmits the high frequency region is surrounded by the inside. Also, the hole formation pattern may be different for each region. For example, as shown in FIG. 8, the holes may be arranged in a staggered pattern in the region A, while the holes may be arranged concentrically in the regions B, C, and D. Further, in the above-described example, the regions are sequentially formed on the outer side so as to include the inner region. However, the method of forming the region is not limited to this, for example, as shown in FIG. You may form so that it may surround. In addition, as described above, the concept of “region” is not introduced to discretize the electrode region, but the hole size and the distribution of arrangement may be continuously changed according to desired desired characteristics. Moreover, the shape of the hole does not need to be cylindrical (that is, the cross section is a circle).

  In the above-described example, an example in which the hole design method according to the present invention is applied to an electrode of an electrostatic speaker is shown, but the present invention is not limited thereto. For example, if a hole is formed in a plate-like member (material does not ask | require) by the method of this invention, this board will function as a directivity characteristic change filter and a frequency filter as mentioned above. Therefore, if this plate is attached to the front surface (sound emitting surface) of the speaker as a speaker net, the directivity characteristics and frequency characteristics of the sound emitted from the speaker can be changed. Here, it is possible to prepare a plurality of speaker nets having different hole patterns in advance, and select and attach a speaker net suitable for directivity characteristics or frequency characteristics required according to the acoustic environment. Needless to say. Moreover, when manufacturing such a speaker net, it is not limited to a method in which a plate-like member is first prepared and through holes are formed one by one. In short, it is only necessary to determine the arrangement of the region (opening) through which the sound wave is transmitted according to the above-described method and not to transmit the sound wave in the other region. For example, a process such as braiding a metal wire member is performed. Such an opening and a non-opening may be formed.

1 is a perspective view of a schematic structure of an electrostatic speaker 1 according to the present invention. 3 is a diagram for explaining an example of a pattern of holes formed in an electrode 20. FIG. It is a graph showing a directivity coefficient. It is a block diagram for demonstrating the function structure of the hole pattern design apparatus 100 which concerns on this invention. 6 is a block diagram illustrating an operation example of the hole pattern design apparatus 100. FIG. It is a figure which shows the memory content of the table T stored in the memory | storage part 130. FIG. It is a figure which shows the data of the hole pattern in each area | region. It is a figure which shows the data of the hole pattern in each area | region. 6 is a diagram for explaining a pattern example of another hole formed in the electrode 20. FIG. 6 is a diagram for explaining a pattern example of another hole formed in the electrode 20. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrostatic speaker, 10 ... Vibration film, 20 ... Electrode, 100 ... Hole pattern design apparatus, 110 ... Control part, 111 ... Area | region determination part, 112 ... Transmission coefficient determination unit, 113 ... hole pattern determination unit, 120 ... input / output I / F, 130 ... storage unit.

Claims (6)

In the speaker net that covers the sound emitting surface of the speaker with a plate-like member,
The first to nth (n is a positive integer) region set on the plate-shaped member, and the kth (k = 2 to n) region is the (k-1) th region. A plurality of openings having the same shape are provided at the same interval in each region, and at least one of the shape or the arrangement interval of the openings is different for each region. A speaker net characterized by The cross-sectional area or the arrangement interval of the openings in the k-th region is larger than the cross-sectional area or the arrangement interval of the openings in the (k-1) region. The speaker net according to 1. The speaker net according to claim 1, wherein each of the plurality of regions has a square shape. The speaker network according to claim 1, wherein each of the plurality of regions has a circular shape. An electrostatic speaker having a vibrating membrane and a plate-like electrode,
The first to nth (n is a positive integer) region set on the electrode, and the kth (k = 2 to n) region is the circumference of the (k−1) th region. A plurality of openings having the same shape are provided at the same interval in each region, and at least one of the shape or the arrangement interval of the openings is different for each region. An electrostatic speaker. An apparatus for designing a speaker net that covers a sound emitting surface of a speaker with a plate-like member,
Directivity characteristic specifying means for specifying the directivity characteristics of acoustic waves;
Based on the directivity characteristic specified by the directivity characteristic specifying means, an area setting means for setting a plurality of two-dimensional areas on the plate member;
Coefficient calculation means for calculating transmission coefficients corresponding to a plurality of two-dimensional areas set by the area setting means;
A speaker network design apparatus comprising: means for determining a shape and an arrangement interval of openings formed in each two-dimensional region based on the transmission coefficient calculated by the coefficient calculation means.

Images