JP2013236216

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DESCRIPTION JP2013236216
Abstract: The present invention provides a technique for reproducing evanescent waves that are
sharply attenuated in the radiation direction using a plurality of speakers arranged on a
cylindrical surface, and determining a filter coefficient for forming a listening area in a cylindrical
shape. Do. A filter coefficient determination device determines filter coefficients of a local
reproduction device that reproduces an evanescent wave using a plurality of speakers. In the
filter coefficient determination device, the speaker is disposed on the cylindrical surface, the
direction satisfying the reproduction condition of the evanescent wave is the axial direction of
the cylindrical surface, and the wave number k in the axial direction is larger than the wave
number k of the sound source The wave number k in the axial direction is calculated, and the
filter coefficient is calculated using the wave number calculation unit in which the number n of
waves in the circumferential direction of the cylindrical surface is an arbitrary constant, the
speaker placement information, the wave number k, and the number n of waves. And a filter
coefficient calculation unit. [Selected figure] Figure 9
Filter coefficient determination device, local reproduction device, filter coefficient determination
method, and program
[0001]
The present invention relates to a local reproduction device capable of transmitting sound only
to a listener who is in a specific place (near the device), and a technique for determining the
coefficients of filters used in the local reproduction device.
[0002]
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1
When a speaker is used to emit sound, it is possible to listen to the reproduced sound from
almost all directions with respect to the speaker although there is an influence of the directivity
characteristic of the speaker.
Therefore, when aiming at construction of a local reproduction system which reproduces a sound
only to a specific place, it is necessary to devise a loud speaker such as a speaker and a
reproduction system. If it is possible to transmit sound only to listeners who are in a specific
place, the reproduced sound will not be a noise for people other than the listeners when
communication is performed by e.g. It is possible to protect privacy. As a means for realizing this
local reproduction method, a method of reproducing an evanescent wave having steep distance
attenuation characteristics is known as a prior art (see Non-Patent Document 1).
[0003]
Non-Patent Document 1 reproduces an evanescent wave by virtually reproducing a wave
propagating slower than the speed of sound in air using a plurality of speakers discretely
arranged on a plane. Further, Non-Patent Document 2 reproduces an evanescent wave using a
plurality of loudspeakers discretely arranged concentrically on the same straight line and NonPatent Document 3. A prior art local playback device 90 is shown in FIG. As the local playback
device 90 moves away in the z direction, the listening sound pressure decays exponentially, and
the listening area becomes 91 in the figure.
[0004]
Hiroaki Ito, Kenichi Furuya, Yoichi Haneda, "Studies on Area Reproduction Using Evanescent
Waves," Proceedings of the Acoustical Society of Japan (Autumn), 2010, pp. 689-690 Hiroaki Ito,
Kenichi Furuya, Yoichi Haneda, "Straight Evanescent wave reproduction method using a speaker
array, Proceedings of the Acoustical Society of Japan (Spring), 2011, pp. 947-948 Hiroaki Ito,
Kenichi Furuya, Yoichi Haneda, "On the Evanescent Wave Reproduction Method Using a Circular
Loudspeaker Array", Proceedings of the Acoustical Society Conference (Autumn), 2011, pp. 713714
[0005]
However, as shown in FIG. 1, in the case of the local reproduction device 90 using a flat speaker
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array, the listening area 91 is limited to the flat plate shape in front of the array.
In the case of a local reproduction device 80 using a linear speaker array as shown in FIG. 2, the
desired attenuation characteristics can be obtained only on a certain plane 81. Also in the case of
the local reproduction device 70 using a circular speaker array as shown in FIG. 3, the desired
attenuation characteristics can be obtained only in the same plane 71 (all directions) as the array.
Further, the sound field produced by using the local reproduction device 80 with a linear speaker
array or the local reproduction device 70 with a circular speaker array has a problem that the
filter design becomes nonuniform.
[0006]
In the present invention, an evanescent wave that attenuates sharply in a direction away from the
cylindrical surface (hereinafter, also referred to as a radial direction because it is a direction
extending from the center of the circle of the cylindrical surface) using a plurality of speakers
arranged on the cylindrical surface. It is an object of the present invention to provide a local
reproduction device that reproduces a sound and to form a listening area in a cylindrical shape,
and a technique for determining a coefficient of a filter used in the device.
[0007]
In order to solve the above problems, according to a first aspect of the present invention, a filter
coefficient determination device determines filter coefficients of a local reproduction device that
reproduces an evanescent wave using a plurality of speakers.
In the filter coefficient determination device, the speaker is disposed on the cylindrical surface,
the direction satisfying the reproduction condition of the evanescent wave is the axial direction
of the cylindrical surface, and the wave number kz in the axial direction is larger than the wave
number k of the sound source The wave number kz in the axial direction is calculated, and the
filter number is calculated using the wave number calculation unit in which the number n of
waves in the circumferential direction of the cylindrical surface is an arbitrary constant, the
speaker placement information, the wave number kz, and the number n of waves And a filter
coefficient calculation unit.
[0008]
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In order to solve the above problems, according to a second aspect of the present invention, a
filter coefficient determination device determines filter coefficients of a local reproduction device
that reproduces an evanescent wave using a plurality of speakers. In the filter coefficient
determination device, the speaker is disposed on the cylindrical surface, the direction satisfying
the reproduction condition of the evanescent wave is the circumferential direction of the
cylindrical surface, and the wave number in the axial direction of the cylindrical surface is equal
to or less than the wave number k of the sound source. kz is determined, and the wave number kr
in the radial direction of the cylindrical surface is calculated as kr = √ (k <2> -kr <2>), and the
circumferential direction is more than the product of the wave number kr and the radius r of the
cylindrical coordinate system A wave number calculation unit that calculates the number n of
waves in the circumferential direction so that the number n of waves increases, and a filter
coefficient calculation unit that calculates filter coefficients using speaker placement information,
the wave number kz, and the number n of waves ,including.
[0009]
In order to solve the above problems, according to a third aspect of the present invention, a filter
coefficient determination device determines filter coefficients of a local reproduction device that
reproduces an evanescent wave using a plurality of speakers. In the filter coefficient
determination device, the speaker is disposed on the cylindrical surface, the direction satisfying
the reproduction condition of the evanescent wave is the axial direction and the circumferential
direction of the cylindrical surface, and the wavenumber kz in the axial direction is larger than
the wavenumber k of the sound source Wave number kz in the axial direction is calculated so
that the number n of waves in the circumferential direction of the cylindrical surface is an
arbitrary constant, and a filter using the speaker placement information, the wave number kz,
and the number n of waves A filter coefficient calculation unit for calculating the coefficients,
kmax being the maximum value of the wave number k, α1, β1 and ka each being arbitrary
constants larger than 1, and the wave number calculation unit sets the wave number kz to (1) kz
= It is calculated as any one of α 1 k max, (2) k z (k) = β 1 k, (3) k z (k) = ± √ (ka <2> + k <2>).
[0010]
In order to solve the above problems, according to a fourth aspect of the present invention, a
filter coefficient determination method determines filter coefficients of a local reproduction
method for reproducing an evanescent wave using a plurality of speakers. In the filter coefficient
determination method, the speaker is disposed on the cylindrical surface, the direction satisfying
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the reproduction condition of the evanescent wave is the axial direction of the cylindrical surface,
and the wave number kz in the axial direction is larger than the wave number k of the sound
source Calculate wave number kz in axial direction, calculate wave number using wave number
calculation step with wave number n in circumferential direction of cylindrical surface as
arbitrary constant, and speaker placement information, wave number kz and wave number n
Calculating the filter coefficient.
[0011]
In order to solve the above problems, according to a fifth aspect of the present invention, a filter
coefficient determination method determines filter coefficients of a local reproduction method
for reproducing an evanescent wave using a plurality of speakers. In the filter coefficient
determination method, the speaker is disposed on the cylindrical surface, the direction satisfying
the reproduction condition of the evanescent wave is the circumferential direction of the
cylindrical surface, and the wave number in the axial direction of the cylindrical surface is k or
less Determine kz and calculate the wave number kr in the radial direction as kr = kr (k <2> -kr
<2>), and the number of waves in the circumferential direction from the product of this wave
number kr and the radius r of the cylindrical coordinate system includes a wave number
calculating step of calculating the number n of waves in the circumferential direction so as to
increase n, and a filter coefficient calculating step of calculating filter coefficients using the
speaker layout information, the wave number kz and the number n of waves. .
[0012]
In order to solve the above problems, according to a sixth aspect of the present invention, a filter
coefficient determination method determines filter coefficients of a local reproduction method
for reproducing an evanescent wave using a plurality of speakers. In the filter coefficient
determination method, the speaker is disposed on the cylindrical surface, the direction satisfying
the reproduction condition of the evanescent wave is the axial direction and the circumferential
direction of the cylindrical surface, and the wavenumber kz in the axial direction is larger than
the wavenumber k of the sound source Calculating the wave number kz in the axial direction so
that the number n of waves in the circumferential direction of the cylindrical surface is an
arbitrary constant, and using the speaker placement information, the wave number kz, and the
number n of waves Filter coefficient calculating step of calculating the coefficient, kmax is the
maximum value of wavenumber k, α1, β1 and ka are arbitrary constants each larger than 1,
and wavenumber kz is (1) kz = in the wavenumber calculating step It is calculated as any one of
α 1 k max, (2) k z (k) = β 1 k, (3) k z (k) = ± √ (ka <2> + k <2>).
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[0013]
With the local reproduction device according to the present invention and a technique for
determining the coefficients of the filter used for the device, it is possible to form a cylindrical
listening area different from the conventional one. Moreover, a uniform sound field can be
formed in all directions.
[0014]
The figure for demonstrating the conventional local reproduction ¦ regeneration apparatus 90.
FIG. The figure for demonstrating the local reproduction ¦ regeneration apparatus by the
conventional linear array. The figure for demonstrating the local reproduction ¦ regeneration
apparatus by the conventional circular array. The figure for demonstrating the wave equation in
a cylindrical coordinate system. The figure which shows the state in which an interface includes
all the wave sources. The figure for demonstrating the case where the direction which satisfy ¦
fills the reproduction ¦ regeneration conditions of an evanescent wave is an axial direction. The
figure for demonstrating the case where the direction which satisfy ¦ fills the reproduction ¦
regeneration conditions of an evanescent wave is a circumferential direction. FIG. 2 is an external
view of a local reproduction device 100. FIG. 2 is a conceptual view of the local playback device
100 viewed from the side. The concept which looked at the local reproduction apparatus 100
from the top. FIG. 6 is a diagram showing a process flow of the local reproduction device 100.
The figure which shows the processing flow of a wave number calculation part. FIG. 2 is an
external view of a local reproduction device 100 in which speakers are arranged in a helical
shape in advance.
[0015]
Hereinafter, embodiments of the present invention will be described. In the drawings used in the
following description, the same reference numerals are given to constituent parts having the
same functions and steps for performing the same processing, and redundant description will be
omitted.
[0016]
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<Theory of Evanescent Wave> The theory of the evanescent wave used in the present
embodiment will be described below.
[0017]
(1) General solution of wave equation in cylindrical coordinate system A sound wave propagates
according to a certain rule, and an equation representing the order of propagation of the sound
wave is called a wave equation and is expressed by equation (1).
[0018]
[0019]
x represents a position in the traveling direction of the sound wave, ∂ represents a partial
differential, t represents a time, c represents a speed of sound, and p represents a sound
pressure.
[0020]
The general solution (frequency domain) of the wave equation in the cylindrical coordinate
system (r, φ, z) in FIG. 4 (where r represents the radius, φ represents the angle, and z represents
the height) is Given.
[0021]
[0022]
Here, j is an imaginary unit, ω is the angular frequency of the sound source, kr and kz are each
in the r direction and the z direction (in addition, the r direction is the aforementioned radiation
direction.
Hereinafter, the z-direction is also referred to as axial direction ) wave number, H <(1)> n
(krr) is an n-th first kind Hankel function, H <(2)> n (krr) is an n-th Two types of Hankel
functions, An (kz, ω) and Bn (kz, ω) represent arbitrary constants.
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[0023]
In order to determine the above-mentioned arbitrary constants An (kz, ω) and Bn (kz, ω), it is
necessary to define boundary conditions at a certain boundary surface r = a.
Assuming that the boundary surface 94 (r = a) includes all the wave sources 93 as shown in FIG.
5 (however, in the figure, 95 indicates a sound pressure analysis region), the general solution of
equation (2) is It can be rewritten as equation (3).
[0024]
[0025]
At this time, the sound pressure can be represented regardless of the value of the constant Bn
(kz, ω).
Since the measured sound pressure on the boundary surface 94 (r = a) satisfies the equation (3),
it can be expressed as follows.
[0026]
[0027]
The relationship between the space spectrum Pn (r, kz) and the measured sound pressure P (r, φ,
z, ω) in the cylindrical coordinate system can be expressed as follows.
[0028]
[0029]
[0030]
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Therefore, when the boundary condition (condition that r = a includes all wave sources) is
satisfied, from the right side when r = a is substituted into the right side of formula (4) and
formula (B), It can be expressed as
[0031]
[0032]
Substituting this into equation (3) gives:
[0033]
[0034]
(2) Evanescent wave generation conditions in the axial direction Wavelength λz (λz = 2π / kz)
along the axial direction z is the wavelength λ of the sound emitted from the sound source (λ =
2π / k, where k is the sound emitted from the sound source If the wave number is shorter than
the wave number), an evanescent wave is generated in the radiation direction (see FIG. 6, where
96 indicates a listening area).
このときｋｚ＞ｋである。
Further, the relationship of k <2> r = k <2> -k <2> z (7) holds between the wave number k of the
sound source and the wave number kr in the radial direction and the wave number kz in the axial
direction.
Under the condition of kz> k,
[0035]
[0036]
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9
となる。
When kr is a purely imaginary number, the Hankel function H <(1)> n in the equation (6) is
rewritten to a modified Bessel function Kn (k'rr).
The relational expression between the Hankel function and the modified Bessel function is
expressed by the following equation.
[0037]
[0038]
Here, assuming that the variable k 'rr of the modified Bessel function is large, the following
approximation holds.
[0039]
[0040]
Therefore, the ratio of the Hankel function in equation (6) is rewritten as follows.
[0041]
[0042]
From the above, the equation of the evanescent wave in the case of satisfying the generation
condition in the axial direction is given by the equation (12), and it holds for kz> k.
[0043]
[0044]
(3) Evanescent Wave Generation Condition in the Circumferential Direction Here, it is assumed
that kz ≦ k, and the case where the evanescent wave generation condition in the axial direction
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is not satisfied will be considered.
[0045]
Even when the wavelength λφ (λφ = 2πa / n) along the circumferential direction φ is shorter
than the wavelength λ (λ = 2π / k) of the sound source, an evanescent wave is generated in
the direction away from the cylindrical surface (that is, the radiation direction) (FIG. 7) See also,
in the figure, 98 indicates a listening area).
Here, 2πa is the circumferential length of the circle formed by the boundary surface r = a, and n
is the number of waves in the circumferential direction.
At this time, since 2πa / n <λ, consider the case where n is sufficiently large.
The asymptotic expansion of the Hankel function for n → ∞ is
[0046]
[0047]
となる。
Here, ζ = krr = kr (assuming kz = 0).
When (部 / n) <1, the real part of the equation can be ignored, and at this time the Hankel
function decreases in proportion to kr <−n>.
Therefore, the ratio of the Hankel function in equation (6) is rewritten as follows.
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[0048]
[0049]
From the above, the equation of the evanescent wave in the case of satisfying the generation
condition in the circumferential direction is given by the equation (15), and holds for kr <n.
It can be said that the relation holds for krr <n from kr = krr.
[0050]
[0051]
In the general solution of the wave equation in the cylindrical coordinate system, we focused on
the evanescent wave equation that sharply attenuates in the radial direction, and configured the
device to reproduce the evanescent wave by a plurality of speakers (speaker array) arranged on
the cylindrical surface.
There are two types of evanescent wave generation conditions described above, and a method of
determining filter coefficients in which the respective conditions are integrated will be described
in the following embodiment.
[0052]
<Local Reproduction Device 100 According to First Embodiment> FIGS. 8, 9, and 10 show the
configuration of the local reproduction device 100. FIG.
FIG. 8 is an external view of the local playback apparatus 100, FIG. 9 is a conceptual view of the
local playback apparatus 100 as viewed from the side, and FIG. 10 is a conceptual view of the
local playback apparatus 100 as viewed from above.
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In the local reproduction device 100, it is assumed that M × L speakers 110 lm (where m = 1,...,
M, l are roman letters L and l = 1,..., L).
M is the total number of speakers in the circumferential direction, and L is the total number of
speakers in the axial direction.
, M × L A / D converters 160 lm, M × L filter multipliers 120 lm, M × L D / A converters 150
lm, M × L amplifiers 140 lm, and a filter A coefficient calculation unit 170 and a wave number
calculation unit 180 are included (see FIG. 9).
The filter multiplication unit 120 lm is configured by a digital filter.
[0053]
The speakers 110 lm are discretely disposed in the circumferential direction and the axial
direction of the cylindrical surface (see FIG. 8).
The spacing between the speakers may not be constant, but is preferably constant in each
direction.
The position of the speaker 110 lm in FIG. 8 is (a, φm, zl).
a represents the radius (in other words, the distance from the axis of the cylindrical surface), φ
m represents the angle, z l represents the height, a is common to all the speakers 110 lm, and φ
m and z l have different values depending on each speaker. Become.
It is assumed that the position (hereinafter also referred to as arrangement information ) (a,
φm, zl) of these speakers 110lm is stored in advance in a storage unit (not shown) by the
manufacturer or the user.
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[0054]
The local reproduction device 100 receives the analog input signal S (k) through the signal input
terminal 30 (see FIG. 11, (s1), where k represents the number of waves of the sound source).
Note that the wave number k of the sound source of the input signal is f assuming the frequency
of the input signal and c the speed of sound
[0055]
[0056]
It can be expressed as.
The A / D converter 160lm receives the analog input signal S (k), converts it into a digital input
signal S (k), and outputs the digital input signal S (k) to the filter multiplier 120lm.
[0057]
On the other hand, the wave number calculation unit 180 determines the wave number (the
number n of waves in the circumferential direction and the wave number in the axial direction
according to the direction and wave number determination pattern of evanescent wave
reproduction conditions set in advance by the manufacturer or user prior to reproduction). Both
numbers of kz) are calculated (s2) and output to the filter coefficient calculation unit 170.
The filter coefficient calculation unit 170 calculates the filter coefficient H (a, φm, zl, k) using the
position (a, φm, zl) of the speaker 110lm, the wave number kz and the number n of waves (s3),
The filter multiplication unit 120 lm is set.
[0058]
The filter multiplication unit 120 lm multiplies the digital input signal S (k) by the filter
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coefficient H (a, φm, zl, k) to generate a drive signal D (a, φm, zl, k) (s4), / A converter 150 lm to
output.
[0059]
The D / A converter 150lm converts the digital drive signal D (a, φm, zl, k) into an analog drive
signal D (a, φm, zl, k) and outputs the analog drive signal D (a, φm, zl, k) to the amplifier 140lm.
The amplifier 140 lm amplifies the analog drive signal D (a, φm, zl, k) and supplies it to the
speaker 110 lm. The M × L speakers 110 lm reproduce the analog drive signal D (a, φm, zl, k)
according to the input signal S (k) (s 5), and output an acoustic signal. The details of the filter
multiplication unit 120 lm, the filter coefficient calculation unit 170, and the wave number
calculation unit 180 will be described below. <Filter Multiplication Unit 120lm> In filter
multiplication unit 120lm, filter coefficient H (a, φm, zl, k) output from filter coefficient
calculation unit 170 and digital input signal S (k) converted by AD converter 160lm. , And
generates and outputs a drive signal D (a, φm, zl, k) which is a signal for driving the speaker 110
lm.
[0060]
A filter coefficient H (a, φm, zl, k) calculated by the filter coefficient calculation unit 170
described later prior to reproduction is set in the filter multiplication unit 120 lm. When the
digital input signal S (k) is input to the filter multiplication unit 120lm, the filter multiplication
unit 120lm convolves the input digital input signal S (k) with the filter coefficient H (a, φm, zl, k).
A digital drive signal D (a, φm, zl, k) for generating an evanescent wave is generated, and this
drive signal D (a, φm, zl, k) is output to a corresponding D / A converter 150lm. The drive signal
D (a, φm, zl, k) is expressed by the following equation.
[0061]
[0062]
The method of calculating the filter coefficient will be described in the filter coefficient
calculation unit 170.
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[0063]
<Filter Coefficient Calculation Unit 170> The filter coefficient calculation unit 170 combines the
arrangement information (a, φm, zl) of the speaker 110lm, the wave number kz for reproducing
the evanescent wave, and the number n of waves (hereinafter, kz and n). The filter coefficient H
(a, φm, zl, k) given to the filter multiplication unit 120 lm is calculated and output to the filter
multiplication unit 120 lm.
[0064]
The filter coefficient calculation unit 170 uses the wave number kz in the axial direction, the
number n of waves in the circumferential direction, and the speaker position (a, φm, zl),
[0065]
[0066]
The filter coefficient H (a, φm, zl, k) is calculated by
Equation (17) is the filter coefficient H (a, φm, zl, k) in the frequency domain.
[0067]
Assuming that the sampling frequency of the input signal in the A / D converter 160 lm is fs, the
number of frequency band divisions is Q, and q = 0, 1,..., Q−1, each frequency band is
[0068]
[0069]
It represents.
From equation (C), k has different values depending on each frequency band f (q)
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[0070]
[0071]
となる。
The wave number information kz and n used in the equation (17) are calculated by the wave
number calculation unit 180 described later using the wave number k (and the direction
satisfying the reproduction condition of the evanescent wave, the wave number determination
pattern). Can calculate the filter coefficient in each frequency band f (q).
The filter coefficient calculation unit 170 sets the inverse Fourier transform of the filter
coefficient in the frequency band f (q) as the filter coefficient in the filter multiplication unit 120
lm.
That is, the filter coefficients in the Q frequency domains are calculated, converted into filter
coefficients in the time domain by inverse Fourier transform, and set in the filter multiplication
unit 120 lm.
If the value of the frequency band division number Q is increased, the accuracy as a filter is
increased but the calculation cost is increased.
Q can be set arbitrarily, and has, for example, several hundred values.
In addition, the operation can be speeded up by setting it to the power of two.
[0072]
<Wave Number Calculation Unit 180> The wave number calculation unit 180 receives the
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direction (axial or circumferential direction) satisfying the evanescent wave reproduction
condition and the wave number determination pattern (the type of wave number determination
pattern will be described later) as input. The number n is calculated and output to the filter
coefficient calculation unit 170. The processing flow of the wave number calculation unit 180 is
shown in FIG. The wave number calculation unit 180 first determines whether the axial
direction or the axial direction and circumferential direction is input or the
circumferential direction is input as the direction satisfying the reproduction condition of the
evanescent wave (s21). Below, the wave number calculation method in each input condition is
demonstrated. The calculated wavenumber kz in the axial direction and the number n of waves in
the circumferential direction are output to the filter coefficient calculation unit 170 (s27).
[0073]
(1) When Wave Number kz in Axial Direction Meets Regeneration Condition of Evanescent Wave
Here, a wave number calculation method is shown in the case where the direction satisfying the
regeneration condition of the evanescent wave is input as the axial direction (see FIG. 12).
[0074]
First, the wave number kz in the axial direction is determined so as to satisfy kz> k, which is the
condition under which the evanescent wave is generated in the axial direction (s22).
Next, the number n of waves in the circumferential direction is determined. n can be determined
as an arbitrary constant (s23). For example, a can be determined as n = ka, where a is the radius
of the cylindrical surface.
[0075]
By using the determined wave number kz and the number n of waves, the evanescent wave
represented by equation (12) is reproduced.
[0076]
[0077]
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This has a characteristic that sound pressure attenuates exponentially in the radial direction.
Therefore, although it has a feature that attenuates more sharply than a single speaker, there is a
disadvantage that the audible range becomes too narrow depending on the setting of the wave
number.
[0078]
Below, the determination method (wave number determination pattern) of three types of wave
numbers kz is shown.
(I) A method of determining the wavenumber kz using the maximum value kmax of the
wavenumber k of the sound source Assuming that the maximum value of the wavenumber k of
the sound source is kmax, kz = α1kmax is calculated. However, α 1 is an arbitrary constant
greater than 1. The kz determined in this way does not depend on the wavenumber k of the
sound source. In other words, it does not depend on wavenumbers k (0), k (1), ..., k (Q-2) other
than the maximum value kmax = k (Q-1) shown in the equation (C '). The value of α here is about
1 to several tens of degrees, and changing the value tends to change the position of the
unattenuated frequency, so that attenuation characteristics can be controlled according to the
frequency characteristics of the input signal. . From the equation (C ') and the equation (18),
kmax = 2.pi.fmax / cfmax = f (Q-1).
[0079]
(Ii) A method of determining the wave number kz as a constant multiple of the wave number k of
the sound source With β1 being an arbitrary constant larger than 1, it is calculated as kz (k) =
β1k. The value of β1 here is about 1 to several tens. In addition, since k is a value which
changes according to each frequency band f (q) from a formula (C '), kz also becomes a value
which changes according to each frequency band f (q) and k.
[0080]
(Iii) A method of determining the wave number kz from the attenuation control term In the
evanescent wave equation (12), the exponential attenuation term in the r direction of P (r, φ, z)
is e <-kar> (provided that the subscript ka is If it represents ka),
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[0081]
[0082]
It is expressed as
Equation (20) indicates that the wavenumber kz in the axial direction can be determined from an
arbitrary attenuation amount and the wavenumber k of the sound source.
Therefore, the wave number calculation unit 180 calculates the wave number kz by equation
(20). As to the value of ka to be specified, if it is too large, it will be attenuated immediately in the
vicinity of the device, so it is a standard to design with ka = 1 to several tens. As described above,
since k is a value that changes according to each frequency band f (q) according to equation (C
′), as in the case of (ii), kz is also added to each frequency band f (q) and k The value changes
accordingly.
[0083]
[0084]
(2) When the Number n of Waves in the Circumferential Direction Meets the Regeneration
Condition of the Evanescent Wave Here, a wave number calculation method is shown when the
direction satisfying the regeneration condition of the evanescent wave is input as the
circumferential direction (see FIG. 12).
[0085]
First, the wave number kz which satisfies kz ≦ k is determined (s24).
Next, the wave number kr in the circumferential direction is determined from the wave number k
of the sound source and the wave number kz in the axial direction using the relationship of
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equation (7) (s25).
Finally, the number n of waves that satisfies n> krr is determined (s26).
[0086]
By using the determined wave number kz and the number n of waves, the evanescent wave
represented by equation (15) is reproduced.
[0087]
[0088]
This has a characteristic that the sound pressure is attenuated according to the power function
with respect to the radiation direction.
Therefore, although the attenuation characteristics are gentler compared to the case of
reproducing in the axial direction, it is possible to control the attenuation characteristics by
adjusting the number of waves, and it can be said that it is easy to control the audible range. .
[0089]
Below, the determination method (wave number determination pattern) of the number n of two
types of waves is shown.
(I) A method of determining the number n of waves using the maximum value of the wave
number k of the sound source Assuming that the maximum value of the wave number k of the
sound source is kmax, it is calculated as n = α2 kmaxa. However, α2 is an arbitrary constant
greater than one. The n determined in this way does not depend on the wavenumber k of the
sound source (in other words, it does not depend on the wavenumber k other than the maximum
value kmax). The value of α2 here is a guideline of 1 to several tens, and changing the value
tends to change the position of the unattenuated frequency, so it is possible to control the
attenuation characteristic according to the frequency characteristic of the input signal . Note that
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kmax is the same as the value described in (1) (i).
[0090]
(Ii) A method of determining the number n of waves as a constant multiple of the wave number k
of the sound source Calculate β (2) as an arbitrary constant larger than 1 as n (k) = β2 ka. The
value of β2 here is about 1 to several tens. The value of k is the same as the value described in
(1) (ii).
[0091]
(3) When both the wave number in the axial direction and the number of waves in the
circumferential direction satisfy the reproduction conditions of the evanescent wave Here, when
both the axial direction and the circumferential direction are input as the direction satisfying the
reproduction condition of the evanescent wave The wave number calculation method is shown
(refer FIG. 12). When both the axial direction and the circumferential direction are input, since
the restriction of the generation condition in the axial direction is stronger, the calculation
method is the same as in the case where the axial direction is input.
[0092]
That is, first, the wave number kz in the axial direction is determined so as to satisfy kz> k, which
is the condition for generating the evanescent wave in the axial direction (s22). Next, the number
n of waves in the circumferential direction is determined (s23). Note that, if kz> k, n can be
determined to be an arbitrary constant, since the condition for generating an evanescent wave in
the circumferential direction is satisfied no matter what n is selected. For example, a can be
determined as n = ka, where a is the radius of the cylindrical surface.
[0093]
By using the determined wave number kz and the number n of waves, the evanescent wave
represented by equation (12) is reproduced.
[0094]
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[0095]
This has a characteristic that sound pressure attenuates exponentially in the radial direction.
Therefore, although it has a feature that attenuates more sharply than a single speaker, there is a
disadvantage that the audible range becomes too narrow depending on the setting of the wave
number.
[0096]
Below, the determination method (wave number determination pattern) of three types of wave
numbers kz is shown.
(I) A method of determining the wavenumber kz using the maximum value kmax of the
wavenumber k of the sound source Assuming that the maximum value of the wavenumber k of
the sound source is kmax, kz = α1kmax is calculated. However, α 1 is an arbitrary constant
greater than 1. The kz determined in this way does not depend on the wavenumber k of the
sound source. In other words, it does not depend on the wavenumbers k (0), k (1),. The value of
α here is about 1 to several tens of degrees, and changing the value tends to change the position
of the unattenuated frequency, so that attenuation characteristics can be controlled according to
the frequency characteristics of the input signal. . From the equation (C ') and the equation (18),
kmax = 2.pi.fmax / cfmax = f (Q-1).
[0097]
(Ii) A method of determining the wave number kz as a constant multiple of the wave number k of
the sound source With β1 being an arbitrary constant larger than 1, it is calculated as kz (k) =
β1k. The value of β1 here is about 1 to several tens. In addition, since k is a value which
changes according to each frequency band f (q) from a formula (C '), kz also becomes a value
which changes according to each frequency band f (q) and k.
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[0098]
(Iii) A method of determining the wave number kz from the attenuation control term In the
evanescent wave equation (12), the exponential attenuation term in the r direction of P (r, φ, z)
is e <-kar> (provided that the subscript ka is If it represents ka),
[0099]
[0100]
Equation (20) indicates that the wavenumber kz in the axial direction can be determined from an
arbitrary attenuation amount and the wavenumber k of the sound source.
Therefore, the wave number calculation unit 180 calculates the wave number kz by equation
(20).
As to the value of ka to be specified, if it is too large, it will be attenuated immediately in the
vicinity of the device, so it is a standard to design with ka = 1 to several tens. As described above,
since k is a value that changes according to each frequency band f (q) according to equation (C
′), as in the case of (ii), kz is also added to each frequency band f (q) and k The value changes
accordingly.
[0101]
[0102]
Note that the sound can be reproduced as an evanescent wave from a spiral-shaped speaker
directed in the z-axis direction (axial direction of the cylindrical surface) by using both the axial
direction and the circumferential direction as the direction satisfying the evanescent wave
reproduction condition. it can.
[0103]
<Effects> With this configuration, the evanescent wave is reproduced using a cylindrical speaker
array, the listening area is made cylindrical different from the conventional one, and the range of
the attenuation effect can be expanded. Furthermore, not only the exponential attenuation An
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evanescent wave can be regenerated that has an attenuation characteristic that follows a power
function.
[0104]
<Other Modifications> When the direction satisfying the reproduction condition of the
evanescent wave is determined in advance, the wave number calculation unit 180 determines
which direction is input as the direction satisfying the reproduction condition of the evanescent
wave (see FIG. You do not have to do 12 s21).
When the wave number determination pattern is determined, processing may be performed
according to the wave number determination pattern.
[0105]
In the first embodiment, a speaker in a circular shape parallel to the xy plane is stacked in the zaxis direction as shown in FIG. 8 as the helical speaker, but as shown in FIG. May be arranged in
a spiral form in advance.
[0106]
In the first embodiment, the local reproduction apparatus 100 includes the filter coefficient
calculation unit 170 and the wave number calculation unit 180. However, the filter coefficient
determination unit 190 including the filter coefficient calculation unit 170 and the wave number
calculation unit 180 is a separate device You may provide.
The filter coefficient determination device 190 may be incorporated inside the local reproduction
device 100 or may be provided outside as a separate device.
The filter coefficient determination device 190 determines the filter coefficient using the
generation direction, the wave number determination pattern, and the position information of the
speaker, and outputs the filter coefficient to the filter multiplication unit 120 lm in the local
reproduction device 100.
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The contents of each process are as described in the first embodiment.
[0107]
The present invention is not limited to the above embodiments and modifications. For example,
the various processes described above may be performed not only in chronological order
according to the description, but also in parallel or individually depending on the processing
capability of the apparatus that executes the process or the necessity. In addition, changes can be
made as appropriate without departing from the spirit of the present invention.
[0108]
<Program and Recording Medium> The above-described local reproduction device or filter
coefficient determination device can also be functioned by a computer. In this case, a program
for causing a computer to function as a target device (a device having the functional
configuration shown in various embodiments) or a process of each processing procedure (as
shown in each embodiment) The program to be executed may be downloaded from a recording
medium such as a CD-ROM, a magnetic disk, a semiconductor storage device or the like into the
computer via a communication line, and the program may be executed.
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