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JP2007274361

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DESCRIPTION JP2007274361
An acoustic wave having desired directivity characteristics is generated by a simple method. An
electrostatic speaker 1 according to the present invention includes a diaphragm 10 and an
electrode 20, and a first to n-th (n is a positive integer) region (A to D) set on the electrode. The
k-th (k = 2 to n integer) region is set to surround the periphery of the (k-1) -th region, and a
plurality of through holes of the same shape are Ha to Hd) are provided at the same interval, and
at least one of the shape or the arrangement interval of the through holes is different for each of
the regions. [Selected figure] Figure 2
Speaker, speaker net and speaker net design device
[0001]
The present invention relates to a speaker and a speaker net.
[0002]
There are loudspeakers classified into so-called flat type loudspeakers due to their structural
features.
A typical example is an electrostatic speaker (capacitor speaker). Electrostatic speakers are
particularly noteworthy in that they can be designed to be lightweight and compact. An
electrostatic speaker is typically a pair of parallel flat electrodes facing each other across a gap,
and a conductive sheet-like member inserted between the electrodes and fixed at both ends
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1
(hereinafter referred to as a diaphragm). And the like. The sound generation mechanism in such a
so-called push-pull electrostatic speaker is typically as follows. When a predetermined voltage is
applied to the plane-parallel electrode and the diaphragm, a force that is drawn to one of the
electrodes due to the generated potential difference acts on the diaphragm. The diaphragm is
fixed at both ends but has a certain degree of elasticity, so that the central portion thereof is
displaced, and as a result, the diaphragm is bent. In this state, when the potential difference is
reversed, a force in the reverse direction acts on the diaphragm, and the vibrator bends in the
reverse direction. The diaphragm vibrates by repeating such reversal of the potential difference.
As described above, the vibration state (such as the frequency and the amplitude) of the
diaphragm can be changed by appropriately applying a voltage to the electrode. If the applied
voltage value is changed according to the input signal, the diaphragm vibrates accordingly, and
as a result, a sound corresponding to the input signal is generated from the diaphragm (see
Patent Documents 1 to 3 and the like) . The generated musical tone 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.
[0003]
However, in a so-called flat type speaker including an electrostatic type speaker, the radiation
area of the acoustic wave generated by the sounding body (for example, a vibrating film)
becomes large due to its structure, so usually the characteristics and vibration of the vibrating
film It is known that an acoustic wave having a directivity characteristic in which a plurality of
local maximum values (main lobe and side lobes) of the output level appear in a specific direction
is generated corresponding to the state.
[0004]
In a planar speaker, as a method for generating an acoustic wave in which the output level of a
side lobe is suppressed or an acoustic wave having a wide directivity, a plurality of planar
speakers are provided as a speaker unit, and an input signal supplied to each unit There is known
a speaker array technology in which the level, delay and the like of the speaker array are
controlled (see Non-Patent Document 1).
Patent No. 3353031 gazette Patent No. 3277498 gazette Japanese Patent Publication No. 70358758 gazette D. B. (Don) Keele Jr. "Implementation of Straight-Line and Flat-Panel
Beamwidth Transducer (CBT) Loudspeaker Arrays Using Signal Delays" Audio Engineering
Society, Convention Paper Presented at the 113th Convention, 2002 October 5/8 L. A.,
California, USA
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[0005]
However, for example, in the case of forming a speaker array using an electrostatic speaker, a
plurality of sets of electrodes and diaphragms are prepared, or one diaphragm is divided and the
vibration state is controlled independently for each area. You need to be able to do it.
Furthermore, an electrical circuit is also required to control the level of the signal supplied to
each speaker unit and the delay. This complicates the overall structure of the speaker and
increases the manufacturing cost. As described above, in the conventional flat type speaker, it
was not possible to realize the desired directional characteristics with a simple configuration. The
present invention has been made in view of the above-described background, and it is an object
of the present invention to provide a speaker capable of realizing desired directional
characteristics with a simple configuration and a device for changing the characteristics of
acoustic waves attachable to the speaker. To aim.
[0006]
The present invention relates to a speaker net in which a sound emitting surface of a speaker is
covered with a plate-like member, which is a first to n-th (n is a positive integer) region set on the
plate-like member, The region of (integer from 2 to n) is set to surround the periphery of the (k1) th region, and in each of the regions, a plurality of openings of the same shape are provided at
the same intervals, and A speaker net is provided, wherein at least one of the shape of the
openings and the arrangement interval is different in each of the regions. According to the
present invention, the speaker net is formed on the acoustic wave propagation surface by
forming the speaker net in which the holes having different sizes or arrangement intervals are
formed for each area in the plate member without using the electric filter circuit. It is possible to
change the spatial characteristics of the acoustic wave passing through the net.
[0007]
In a preferred aspect, at least one of the cross-sectional area and the arrangement interval of the
opening in the k-th region is larger than the cross-sectional area or the arrangement interval of
the opening in the (k-1) -th region.
[0008]
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In a preferred embodiment, the shapes of the plurality of regions are each square.
In another preferred embodiment, the shapes of the plurality of regions are each a circle.
[0009]
According to another aspect of the present invention, there is provided an electrostatic
loudspeaker having a diaphragm and a plate-like electrode, wherein the first to n-th regions (n is
a positive integer) are set on the electrodes. The k-th (k is an integer from 2 to n) region is set to
surround the (k-1) th region, and in each of the regions, a plurality of openings of the same shape
have the same distance. An electrostatic speaker is provided, wherein the shape and / or the
arrangement interval of the openings are different in each of the regions.
[0010]
According to still another aspect of the present invention, there is provided a device for designing
a speaker net in which a sound emitting surface of a speaker is covered with a plate-like member,
and directional characteristic specifying means for specifying directional characteristics of
acoustic waves; Region setting means for setting a plurality of two-dimensional regions in the
plate-like member based on the directivity characteristic specified in the above, and transmission
coefficients corresponding to a plurality of two-dimensional regions set by the region setting
means A speakernet design apparatus comprising: coefficient calculation means to be calculated;
and means for determining the shape and arrangement interval of openings formed in each twodimensional region based on the transmission coefficient calculated by the coefficient calculation
means. .
[0011]
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 loudspeaker 1 according to
the first embodiment of the present invention.
As shown in the figure, the electrostatic loudspeaker 1 is roughly constituted of a vibrating
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membrane 10 and two parallel flat electrodes 20 (hereinafter simply referred to as electrodes
20) opposed thereto.
[0012]
The vibrating film 10 is made of, for example, PET (polyethylene terephthalate, polyethylene
terephthalate), PP (polypropylene, polypropylene), or other film formed by depositing a metal
film or applying a conductive paint, for example, having a thickness of several microns to several
tens of microns. In a fixing means (not shown) made of an insulating material such as vinyl
chloride, acryl (methyl methacrylate), rubber, etc., for example, the four sides of the membrane
are static in a state where a predetermined tension acts on the vibrating membrane 10 It is fixed
to a housing (not shown) of the electronic speaker 1.
[0013]
The electrode 20 is a punching metal in which a plurality of through holes (indicated by H in the
same figure) are opened in a conductive plate-like member such as a metal plate having a
thickness t, and the housing of the electrostatic speaker 1 It is fixed to (not shown).
At this time, it is preferable that the distance j from the vibrating membrane 10 to both
electrodes 20 be arranged to be equal. In other words, the position just between the opposing
electrodes is the fixed position of the vibrating membrane 10 (precisely, the vibrating membrane
10 in the non-displaced state).
[0014]
In addition, the electrostatic speaker 1 is provided with a power supply (not shown) so that
voltages of opposite polarities are applied to the respective electrodes 20 and a bias voltage can
be applied to the vibrating film 10. In addition, the electrostatic speaker 1 includes an input unit
for inputting an audio signal from the outside, and causes the diaphragm 10 to vibrate according
to the audio signal by changing the inversion timing of the applied voltage according to the audio
signal. It can be done. An acoustic wave generated by the vibration of the vibrating membrane 10
passes through the electrode 20 and is emitted to the outside of the speaker.
[0015]
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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 film 10, only one electrode 20 may be used.
The point is that an electric field that changes with time according to the time change of the
input sound signal is formed using the electrode 20, and the charged vibrating membrane 10
may be in a state capable of being displaced by electrostatic force from this electric field. That is,
in the present invention, the material constants of the vibrating membrane 10 such as the
electrical conductivity and the elastic modulus, the fixing method of the vibrating membrane 10
and the magnitude of the tension applied to the vibrating membrane 10 are not limited.
Moreover, in the same figure, although the example in which the hole is similarly opened in both
the electrodes 20 is shown, it does not restrict to this, a hole is formed in one electrode 20
(electrode on the acoustic wave emission side) On the other hand, the opposite side (back side)
electrode 20 may be a metal plate with no holes. That is, it is sufficient that the acoustic wave
generated in the vibrating membrane 10 be emitted to the outside through one of the electrodes.
However, it is preferable that both electrodes 20 have the same structure (that is, a metal plate in
which holes are formed at the same position) in order to apply a uniform electrostatic force as
much as possible to the vibrating film 10 in which holes are formed on the metal plate. .
[0016]
The present invention is characterized by the structure of the hole formed in the electrode 20,
which will be described in detail below. FIG. 2 is a view of the electrode 20 as viewed from above
(from below). As shown in the figure, in the electrode 20, in order from the outer side, in other
words, an outer area is formed around the inner area (so that the outer area surrounds the inner
area). Areas A, B, C, and D having a square outer periphery are defined. Then, in each region, a
plurality of holes Ha, Hb, Hc, and Hd of the same size (diameter of cross section) 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 spacing of the holes, and the arrangement pattern
thereof differ depending on the region on the electrode 20 (that is, nonuniformly distributed). ) Is
characterized. The term “pattern” as used herein refers to, for example, the shape of an array
of parallel type (grid-like), square staggered (45 ° staggered), zigzag (60 ° staggered), or the
like. FIG. 2 shows an example in which holes are formed in a pattern of parallel removal in all
areas. In the figure, in the region A, an example is shown in which the diameter is d and the
closest distance (pitch) is a. As described above, 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. It is characterized in that the electrode
has a function as a filter capable of changing the directivity characteristic and the frequency
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characteristic of the
[0017]
The degree of change in the acoustic wave directivity characteristic and the frequency
characteristic before and after entering the electrode 20 differs depending on the pattern of the
holes provided in the electrode 20 (the shape and arrangement position of the holes).
Hereinafter, the method of determining the number of regions and the size (area) of the regions
described above and the method of determining the arrangement method of holes (the shape and
arrangement pattern of holes) will be described in detail.
[0018]
Prior to this, the relationship between the frequency of the acoustic wave, the effective area of
the diaphragm where the acoustic wave is generated, the directivity characteristics in each
frequency band, and the shape and number of the holes of the electrodes and the transmission
coefficient of the acoustic wave is shown. . In addition, 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. Further, in the present invention, the depth of the through hole can
also be changed depending on the place, but in this case, naturally, the thickness t of the
electrode 20 in that part changes depending on the place.
[0019]
(1) Relationship between directivity degree, frequency, and effective area The directivity factor
(index indicating the sharpness of directivity of acoustic wave) Q has a frequency of f, and the
effective area of the diaphragm where the acoustic wave is generated (in FIG. 2) Assuming that
the area of each area which is a square shape is S, it can generally be expressed as follows.
[0020]
[0021]
As an example, when considering a circular piston vibration of radius a having an infinite baffle
as a vibrating film, it is known that the directivity factor on the central axis can be expressed as
follows.
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[0022]
[0023]
In the above equation, c represents the speed of sound, a represents the diaphragm radius, and
J1 represents the first-order Bessel function.
In the above equation, g (x) is a monotonically increasing function of x, and there exists x (this
point will be referred to as a feature point x0) for which the twice-differentiated value takes a
maximum value.
In other words, the slope of the function g (x) changes rapidly at x = x0.
The schematic shape of this function is shown in FIG.
Summarizing the above, the directivity factor Q is a function of f * S ^ (-1/2), and the directivity
of the acoustic wave becomes sharper as the frequency f is higher and the effective area S is
smaller. It is. Therefore, if the effective area S is constant, the directivity sharply sharpens when
the frequency exceeds a certain frequency. For example, in the case of S = 1m <2>, the directivity
factor Q is substantially constant in a band where the frequency f is smaller than 100 to 200 Hz,
but the directivity factor Q rapidly increases in a frequency band higher than that.
[0024]
(2) Relationship between transmission coefficient (TI) and shape and arrangement of holes, etc.
When a plate (electrode 20) having a predetermined hole formed on the passage surface of the
acoustic wave generated by the vibrating membrane is used An index TI representing the output
level of the transmitted acoustic wave (in other words, the difficulty of attenuation of the acoustic
wave), the number of holes formed per unit area n, the diameter of the hole d, and the thickness
of the electrode Let t be the distance between the closest holes a and the aperture ratio P (the
ratio of the area occupied by the holes in the plate) be P, and the following conditions are
introduced under the condition that the frequency is constant.
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[0025]
[0026]
Although the closest interval a differs depending on the arrangement pattern, it is expressed by
the following equation using the aperture ratio.
[0027]
[0028]
Here, k is an amount determined by the arrangement pattern, k = 9.5 in the case of the staggered
arrangement, and k = 8.9 in the case of the parallel arrangement.
[0029]
As apparent from (Equation 2), assuming that 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
distance, the transmission coefficient of the acoustic wave Is larger (that is, less likely to be
attenuated).
In addition, it is known that if the index TI has the same value, the higher the frequency, the
larger the attenuation, and the smaller the index TI, the larger the attenuation in the high range.
[0030]
As described above, assuming that holes of the same shape and diameter are arranged at regular
intervals on the electrode 20, the directivity characteristics differ depending on the frequency.
Specifically, as described in (Equation 1), the acoustic wave in the low frequency band
propagates in a wide direction since its directivity is gentle, while the acoustic wave in the high
frequency band has strong directivity, and It will propagate in the direction.
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In the following, for the purpose of generating an acoustic wave having directivity such that
directivity is constant in each frequency band and side lobes do not appear in a high frequency
band using the electrostatic speaker 1 of the present invention, The case of determining the
shape and the arrangement of the holes formed in the electrode 20 will be described with
reference to FIGS. 4 and 5.
[0031]
FIG. 4 is a block diagram showing a functional configuration of the hole pattern designing device
100 according to the present invention.
As shown in the figure, the hole pattern design device 100 is configured of a control unit 110, an
input / output I / F 120, and a storage unit 130.
The input / output I / F 120 is configured of a keyboard, a display, and the like, and receives an
instruction on the directional characteristic from the user. The storage unit 130 is a storage
device such as a RAM, a ROM, a hard disk, etc., and stores various information to be referred to
when calculating the arrangement of holes and the shape of each hole in the control unit 110.
The control unit 110 includes a CPU or the like, and includes an area determination unit 111, a
transmission coefficient determination unit 112, and a hole pattern determination unit 113 as
functional modules.
[0032]
An operation example of the hole pattern designing device 100 is shown in FIG. First, the user
inputs information on the above-described desired directivity characteristics through the
electrostatic speaker 1 (step S10). For example, it is information such as the directivity degree in
each frequency band, and the frequency at which the sound pressure value of the side lobe is
equal to or less than a predetermined value.
[0033]
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Subsequently, the area determination unit 111 sets an area (step S20). Specifically, the number
of areas to be provided on the electrode 20 and the diameter of each area 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.
Then, 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 four. 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.
[0034]
Next, the region to be transmitted to the acoustic wave of each frequency is determined based on
(Equation 1). In this example, in accordance with the purpose of equalizing the directivity factor
of each frequency band as much as possible, a higher frequency band is assigned a smaller area
of the area S inside. That is, since the area having the smallest area is the innermost area D, the
area D is allocated to the frequency band having the highest directivity. Thus, as a result, the
region D is allocated to the band f4, the regions C to D to the band f3, the regions B to D to the
band f2, and the regions A to D to the band f1. In this way, frequency bands and regions are
associated one to one.
[0035]
Next, the area S of each region is calculated using (Equation 1). Specifically, the area S
corresponding to the region in which the directivity factor Q is substantially constant in each
frequency band is calculated based on (Equation 2). Specifically, when the frequency f is given, S
corresponding to the feature point x0 may be obtained. For example, for f = 500 Hz or less, it is
found that it corresponds to the entire area S = 1m <2>. The value of this S is the area of the
region A corresponding to 0 to 500 Hz (band f1). Thus, the areas of the regions A, B and C are
obtained. For example, f = 500 Hz corresponds to S = 0.151 m <2>, f = 2000 Hz corresponds to S
= 0.009 m <2>, f = 8000 Hz corresponds to S = 0.0006 m < 2> is calculated, and the area S of
each region is determined. When the size of the electrode (the area of the outermost area A) is
designated in advance, the area of each area obtained may be multiplied by a predetermined
normalization constant. The point is that it is preferable to set the ratio of the area of each region
so that the directivity coefficients in the frequency band become as equal as possible.
[0036]
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Next, an arrangement pattern including the shape and arrangement interval of the holes
provided in each region is determined. First, the transmission coefficient determination unit 112
determines, for each region, the value of the transmission coefficient TI based on the value of the
corresponding frequency (step S30). As described above, TI is an index that represents the
attenuation of the acoustic wave passing through the area. However, the attenuation level AT of
the acoustic wave depends not only on TI but also on frequency. That is, the attenuation level AT
is a function of the frequency f and TI. In the present embodiment, the attenuation level AT to be
set in each frequency band is first determined based on the information such as the side lobe
suppression degree according to the designated directivity characteristic, and from this, the
frequency corresponding to each area (in the above example Each TI corresponding to 500 Hz,
2000 Hz, 8000 Hz) is determined. More specifically, the frequency dependence and the TI
dependence of AT are calculated in advance by simulation or experiment, and the attenuation
level as shown in FIG. The stored table T is stored and TI is determined with reference to this
table T. As a result, for example, the TIs of the regions A, B, C, and D are determined to be 15, 65,
3009, and 10840, respectively.
[0037]
As can be seen from this example, in this aspect, small TIs are set in order from the outer area
according to each frequency. As a result, in the outer region, the electrode 20 has a frequency
filter function that allows low frequency band acoustic waves to pass without attenuation while
high frequencies are cut. And as it goes to the inner area, the frequency band of the acoustic
wave which passes without attenuation becomes wider. In the example of FIG. 2, only the
acoustic wave of 0 to 500 Hz or lower which is the lowest frequency band passes in the
outermost area A, and almost the entire frequency band (ideally 10000 Hz or higher) in the
innermost area D An example is shown in which the acoustic wave of) is passed.
[0038]
Next, the hole pattern determination unit 113 calculates the hole diameter d and the interval a
using (Equation 2) and (Equation 3) based on the determined value of TI (step S40). As can be
seen from (Equation 3), there are innumerable combinations of determination methods such as d
and a for a given value of TI. An example of the combination is shown in FIG. FIG. 7A shows an
example in which while the thickness t of the electrode 20 and the diameter d of the holes are
made constant, the spacing a of the holes is made different. In this case, although the holes of the
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same size are formed in each area, the intervals (that is, the probability density of the holes) will
be different for each area. In the case of forming holes of the same shape as described above,
there is an advantage that the processing cost can be reduced. On the other hand, FIG. 7 (b) is 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 spacing of the holes will be different for each region. When
the aperture ratio is made uniform as described above, the electrostatic force acting on the
vibrating film 10 is stabilized, which is advantageous in that the sound quality is improved.
[0039]
As described above, in the present invention, it is possible to equalize the directional
characteristics by setting the frequency band and assigning the area having the different sound
emission area to each frequency band. Furthermore, by forming holes having different
arrangement distributions and sizes in each region, the electrode 20 is provided with a function
as if it is a collection of a plurality of low pass filters, and provided on the propagation surface of
acoustic waves. The level of the high frequency band can be attenuated to make the directivity as
the whole acoustic wave blunt.
[0040]
In the above-described example, the shape of the region and the shape of the electrode are
square, but may be, for example, a circle as shown in FIG. However, it is the same in that an area
which produces an effect of transmitting only the low frequency is sequentially provided at the
outer edge portion and an area which transmits the high frequency area is sequentially enclosed.
Further, the formation pattern of the holes may be different for each region. For example, as
shown in FIG. 8, in the area A, the holes are arranged in a zigzag shape, while in the areas B, C,
and D, the holes may be arranged concentrically. Further, in the above-described example, the
regions are sequentially formed on the outer side so as to include the inner region, but the
method of forming the regions is not limited thereto. For example, as shown in FIG. It may be
formed to be surrounded by Also, instead of discretizing the electrode region by introducing the
concept of "region" as described above, the distribution of the size and arrangement of the holes
may be continuously changed according to desired desired characteristics. Also, the shape of the
holes need not be cylindrical (i.e. circular in cross section).
[0041]
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In the example mentioned above, although the example which applied the design method of a
hole concerning the present invention to an electrode of an electrostatic type speaker was shown,
it does not restrict to this. For example, if a hole is formed in a plate-like member (regardless of
the material) by the method of the present invention, this plate functions as a directivity
characteristic change filter and a frequency filter as described above. Therefore, if this plate is
attached to the front (sound emitting surface) of the speaker as a speaker net, it is possible to
change the directivity characteristic and the frequency characteristic of the sound emitted from
the speaker. Here, it is possible to prepare a plurality of speaker nets in which different hole
patterns are formed in advance, and to select and attach a speaker net adapted to the directivity
characteristic or the frequency characteristic required according to the acoustic environment etc.
It goes without saying. Moreover, when manufacturing such a speaker net, it is not restricted to
the method of preparing a plate-shaped member first and forming a through-hole in this one at a
time. In short, the arrangement of the region (opening) through which the sound wave passes
may be determined according to the above-described method, and the sound wave may not be
transmitted in the other regions. Such openings and non-openings may thereby be formed.
[0042]
FIG. 1 is a perspective view of the general structure of an electrostatic speaker 1 according to the
present invention. FIG. 6 is a view for explaining an example of a pattern of holes formed in an
electrode 20; It is a graph showing a directivity factor. It is a block diagram for demonstrating
the function structure of the hole pattern design apparatus 100 which concerns on this
invention. FIG. 7 is a block diagram showing an operation example of the hole pattern designing
device 100. It is a figure which shows the memory content of 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. FIG. 7 is a
view for explaining another pattern example of holes formed in the electrode 20; FIG. 7 is a view
for explaining another pattern example of holes formed in the electrode 20;
Explanation of sign
[0043]
DESCRIPTION OF SYMBOLS 1 ... Electrostatic type speaker, 10 ... Vibrating film, 20 ... Electrode,
100 ... Hole pattern design apparatus, 110 ... Control part, 111 ... Area determination part, 112 ...
Permeability coefficient determination unit, 113 ... hole pattern determination unit, 120 ... input /
output I / F, 130 ... storage unit.
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