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JP2013236217

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DESCRIPTION JP2013236217
Abstract: A local reproduction device capable of reproducing evanescent waves without using a
plurality of filters is provided. A local reproduction apparatus according to the present invention
includes a speaker array and a signal generation unit. The speaker array is configured by
alternately arranging two or more of two types of speakers with different phases of the
reproduced signal by 180 degrees at equal intervals and on the circumference of the radius r,
and the signal generation unit When the sound velocity is c, the input signal is converted into a
signal of a frequency such that f = Nc / 4πr determined by the number N of the speakers. With
this configuration, it is possible to enable local regeneration without using the filter group (the
part by which each filter coefficient is multiplied) required in the prior art. [Selected figure]
Figure 4
Local playback device
[0001]
The present invention relates to a local reproduction device capable of transmitting sound only
to listeners who are present in a specific place (near the device).
[0002]
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.
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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.
[0003]
If it is possible to transmit the sound only to people in a specific place, the reproduced sound will
not be a noise for people other than the listener, such as when performing communication by
loud voice, and the communication content will not leak around It is possible to protect privacy.
[0004]
As a means for realizing this local reproduction method, there is a method of reproducing an
evanescent wave having a steep distance attenuation characteristic (Non-Patent Document 1).
This is to reproduce an evanescent wave by changing a phase of a signal reproduced from each
speaker based on a certain condition using a plurality of concentrically and discretely arranged
speakers. An evanescent wave is a special wave whose power decays exponentially in the
direction perpendicular to the traveling direction.
[0005]
FIG. 8 shows a functional configuration of a reproduction apparatus 900 for reproducing an
evanescent wave according to the prior art. The playback apparatus 900 is configured of a
speaker group 901 including a plurality of speakers arranged in a circular array on an xy plane,
and a plurality of filter groups 902 connected to the plurality of speakers.
[0006]
In order to reproduce the evanescent wave in the circular speaker array, the drive signal (time
frequency domain) of the speaker may be given by the following equation.
[0007]
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[0008]
Where ω is the angular frequency of the input signal, φ 0 is the circumferential position of the
loudspeaker, C (ω) is a constant uniquely determined by ω, neva is the wave number in the
circumferential direction, j = ((-1) is the imaginary unit , S (ω) represent input signals input to the
signal input terminal 903.
[0009]
FIG. 9 shows an example of a speaker drive signal in the playback apparatus 900.
In FIG. 9, the representation of the loudspeakers constituting the loudspeaker group 901 is
omitted.
In the drawing, ◎ and a waveform represent a speaker drive signal supplied to each speaker of a
speaker group in which, for example, 20 speakers are arranged on the xy plane.
The horizontal direction represents time t, and the vertical direction represents amplitude.
[0010]
In FIG. 9, for the speaker drive signal supplied to the speaker disposed in the range of the
deflection angle φ = 45 degrees to 135 degrees when the deflection angle φ = 0 degree of the
cylindrical coordinate system is defined on the −x axis. An example is shown. Based on the
phase of the speaker drive signal supplied to the speakers (r0, φ135, z0), the input signal input
to the signal input terminal 903 is delayed and supplied by the filter group 902, for example by
π / 2 radians. Ru.
[0011]
Hiroaki Ito, Kenichi Furuya, Yoichi Haneda "On the Evanescent Wave Reproduction Method Using
a Circular Loudspeaker Array" Proceedings of the Acoustical Society of Japan (Autumn), pp. 713714, 2011.
09-05-2019
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[0012]
In the conventional local reproduction device 900, since the phase change of the speaker drive
signal is performed by the filter, there is a problem that the device scale becomes large.
[0013]
This invention is made in view of such a subject, and an object of the present invention is to
provide a local reproduction device which can reproduce an evanescent wave, without requiring
the above-mentioned filter group 902.
[0014]
The local reproduction apparatus of the present invention comprises a speaker array and a signal
generation unit.
The speaker array is configured by arranging two or more of each of two types of speakers
whose phases to be reproduced are different by 180 degrees, alternately at equal intervals and
on the circumference of the radius r0.
The signal generation unit converts the input signal into a signal of a frequency such that fmax =
Nc / 4πr0 determined by the number N of the speakers when the sound velocity c is set.
[0015]
According to the local regeneration device of the present invention, it is possible to enable the
regeneration of evanescent waves without using a filter group.
[0016]
The figure which shows a cylindrical coordinate system.
It is a figure for demonstrating the principle of this invention, and is a figure which shows the
drive signal for speakers supplied to a speaker array.
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FIG. 3 is a diagram showing a sound pressure waveform at time t = 0 of the speaker drive signal
shown in FIG. 2; FIG. 1 is a diagram showing an example of a functional configuration of a local
reproduction device 100 of the present invention. The figure which shows the simulation result
of the sound pressure distribution of the local reproduction | regeneration apparatus of this
invention. The figure which shows the simulation result of the sound pressure distribution of a
single speaker. FIG. 6 is a diagram showing the relationship between the distance r from the
origin of the simulation result shown in FIG. 5 and the sound pressure. FIG. 16 is a diagram
showing an example of a functional configuration of a conventional local reproduction device
900. FIG. 16 shows an example of a speaker drive signal of the local reproduction device 900.
[0017]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings. The same reference numerals are given to the same components in the drawings, and
the description will not be repeated. Before describing the embodiments, the principle of the
present invention will be described. For the theory of evanescent waves, see, for example,
reference (EG. See Williams, Shigeru Yoshikawa and Ken Nishijima, "Fourier Acoustics", Springer
Japan Ltd.
[0018]
[Principle of the Invention] In the present invention, the evanescent wave is reproduced by
supplying the speaker driving signal whose phase is reversed to the adjacent speakers of the
circular speaker array in which the speakers are arranged in a circular shape.
[0019]
In the following description of the embodiment, the speaker arrangement is expressed using a
cylindrical coordinate system.
FIG. 1 shows a cylindrical coordinate system. The cylindrical coordinate system represents
coordinates on the xy plane by the radius r from the origin and the deflection angle φ, and adds
the z axis to it to represent the xyz space.
09-05-2019
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[0020]
FIG. 2 shows a speaker drive signal supplied to the speaker array according to the present
invention. As shown in FIG. 2, + (indicated by a circle in the drawing) represents the phase of the
output signal reproduced from the speaker disposed at that position. Similarly,-(shown in a circle
in the figure) indicates that the phase of the output signal reproduced from the speaker placed at
that position differs by 180 degrees.
[0021]
The circular speaker array shown in FIG. 2 is an example in which the total number N of speakers
is N = 8 and the array radius is r0. In FIG. 2, assuming that the argument angle φ = 0 degree on
the −x axis, 3 arranged at the coordinates of (r0, φ225, z0), (r0, φ270, z0), and (r0, φ315, z0)
The representation of the output signal of this speaker is omitted.
[0022]
In the example shown in FIG. 2, the wavelength of the sound wave present in the circumferential
direction has a length obtained by equally dividing the circumference by N (equation (2)).
[0023]
[0024]
The wave number neva in the circumferential direction represents how many waves of
wavelength λ r exist on the circumference, so the wave number neva can be expressed by
equation (3).
[0025]
[0026]
In order to regenerate the evanescent wave, it is necessary to set the wave number in the
circumferential direction to the following condition.
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[0027]
[0028]
Here, k is the fraction of the input signal, and r is the distance from the origin to the observation
point.
It does not matter if r = r0.
[0029]
Assuming that the sound velocity is c and the frequency of the input signal is f, the wave number
k of the input signal can be expressed by equation (5).
[0030]
[0031]
Therefore, the wave number neva in the circumferential direction needs to satisfy the following
equation.
[0032]
[0033]
The frequency band fmax satisfying the condition of equation (6) is equation (7).
[0034]
[0035]
In FIG. 3, the sound pressure distribution at time t = 0 when the speaker drive signal meeting the
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above-described conditions is input to the speaker array having the total number N = 8 of
speakers is indicated by an alternate long and short dash line.
It can be seen that the wave number neva in the circumferential direction is four.
The evanescent wave can be reproduced by realizing such a sound pressure distribution.
[0036]
Formula (2)-Formula (7) arranges N speakers on a circle at equal intervals, where N is the total
number of speakers of a circular speaker array, radius r0 of the array of circular speaker arrays,
and sound speed c. By alternately changing the phases of the output signals output from the N
speakers by 180 degrees, it is indicated that sound waves having frequencies below the
frequency band fmax become evanescent waves.
[0037]
That is, the present invention enables the reproduction of the evanescent wave without using the
filter group required in the prior art by reproducing the sound wave under the conditions
described above.
[0038]
FIG. 4 shows an example of a functional configuration of the local reproduction device 100 of the
present invention.
The local reproduction device 100 includes a speaker array 40 and a signal generation unit 50.
The speaker array 40 is configured by arranging two or more of each of two types of speakers
whose phases to be reproduced are different by 180 degrees, alternately at equal intervals and
on the circumference of the radius r0.
The signal generation unit 50 sets the input signal S (ω) input to the signal input terminal 60 to
fmax = Nc / 4πr0 (equation (7)) determined by the number N of the speakers when the sound
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speed c is set. Convert to frequency signal.
The signal generation unit 50 can be easily realized by, for example, a low pass filter of a digital
filter.
[0039]
The speaker array 40 is an example in which the total number N of speakers is 8, and
coordinates (r0, φ0, z0), (r0, φ45, z0), (r0, and r0) obtained by dividing the circumference of the
radius r0 into eight at equal intervals. The speakers 41 to 48 are arranged on φ90, z0),..., (r0,
φ315, z0), respectively.
The signal generation unit 50 converts the input signal S (ω) input to the signal input terminal
60 into a frequency band signal fmax such that the equation (7) described above is obtained.
The frequency band signal fmax is input to two types of speakers 180 degrees out of phase.
As a specific example, it can be realized by making the connection between the speaker and the
amplifier positive and vice versa.
[0040]
In FIG. 4, this is performed by alternately inverting the relationship between the output polarity
of the amplifier 70 (71 to 78) corresponding to the number of speakers driving each speaker and
the polarity of the input terminal of the speaker.
The positive output terminal of the amplifier 75 is connected to the positive terminal of the input
terminal of the speaker 45 arranged on the coordinates (r0, φ180, z0), and the negative output
terminal of the amplifier 75 is connected to the negative terminal of the input terminal of the
speaker 45 .
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The negative output terminal of the amplifier 74 is connected to the positive terminal of the
input terminal of the speaker 44 adjacent in the clockwise direction, and the positive output
terminal of the amplifier 74 is connected to the negative terminal of the input terminal of the
speaker 44.
The same polarity inversion is performed between the adjacent speakers to configure the local
reproduction device 100.
[0041]
As apparent from the equation (7), it is possible to increase the frequency band fmax as the
radius r0 increases and as the total number N of speakers increases.
[0042]
[Simulation Results] For the purpose of confirming the effects of the present invention,
simulation experiments were performed under the condition of 500 Hz with the total number of
loudspeakers N = 24, radius r0 = 0.3 m, sound velocity c = 346.16 m / s, went.
[0043]
FIG. 5 shows the sound pressure distribution on the xy plane (z = z0) under the conditions.
It can be seen that the sound pressure at r = 1 m is greatly attenuated to -60 dB.
The sound pressure in the range of r0 = 0.3 m from the origin (x = 0, y = 0) is not calculated.
The sound pressure distribution in the case of one speaker is shown in FIG. 6 for reference. It can
be seen that the sound pressure does not attenuate below -10 dB even if r0 = 1.0 m away from
the origin (x = 0, y = 0).
[0044]
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FIG. 7 shows the relationship between the distance r from the origin of the local reproduction
device configured under the above conditions and the sound pressure. The horizontal axis in FIG.
7 is the distance r from the origin, and the vertical axis is the sound pressure [dB]. The sound
pressure of the local reproduction apparatus of the present invention exhibits a sharp
attenuation characteristic of about −20 dB at r = 0.6 m, about −57 dB at r = 0.8 m, and about
−60 dB at r = 0.92 m. Attenuation characteristics of sound pressure in the case of a single
speaker are shown by a broken line. Even at r = 0.9 m, the attenuation is only about -5 dB.
[0045]
As described above, according to the local regeneration device of the present invention, the
evanescent wave can be regenerated without using a filter group.
[0046]
In the above-described embodiment, the signal generation unit 50 is described as an example in
which the low pass filter is a digital filter. However, the digital filter does not have to be a digital
filter.
The signal generation unit 50 may be configured by a filter configured by a combination of an
active element by an operational amplifier, a passive element by a resistor R and a capacitor C.
[0047]
Further, although the example in which the amplifiers 70 are configured by eight amplifiers
respectively corresponding to the speakers 41 to 48 has been described, the number of
amplifiers may be any number within the range of one to eight. Thus, the local reproduction
apparatus of the present invention is not limited to the above-described embodiment. The
speaker array is composed of two or more speakers each of two types of speakers 180 degrees
out of phase with each other, that is, at least four speakers, and the local playback device of the
present invention is configured if the number is more than that. can do.
[0048]
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The above-described local regeneration device enables local regeneration without using a filter
group (a portion by which each filter coefficient is multiplied) required in the prior art. Therefore,
the device scale of the local reproduction device can be reduced and simplified.
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