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JP2006074442

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DESCRIPTION JP2006074442
The present invention provides an area limited reproduction system having good reproduction
characteristics by giving guidance to the arrangement of speakers and the arrangement of
microphones. SOLUTION: M (M ≧ 2) sensors are arranged around a space where sound is to be
reproduced, and sound to be reproduced from N (N ≧ 2) sound sources based on outputs from
these M sensors An area-limited loud-speaking method that reproduces sound in space by
controlling the delay between each other and the frequency characteristics, and the reproduced
sound is reproduced only in space by reducing energy outside the space The sound sources are
arranged at unequal intervals on a straight line. [Selected figure] Figure 1
Area limited loud-speaking method, filter characteristic setting method, area limited loudspeaking device, area limited loud-speaking program, filter characteristic setting program, and
recording medium recording the same
[0001]
The present invention relates to sound field control for changing the sound field characteristics
of a space such as a room, and in particular, an area limited loud-speaking method for generating
a sound field only in a specific area and a filter for setting filter characteristics used in this loudspeaking method The present invention relates to a characteristic setting method, an area limited
loudspeaker, and a method of realizing the above-mentioned loudspeaker method, a filter
characteristic setting method on a computer, and a recording medium in which the program is
recorded.
[0002]
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When a sound is emitted using a loudspeaker, it is possible to listen to the sound from almost all
directions with respect to the speaker, although there is an influence of the directivity
characteristic of the speaker used for reproduction.
Therefore, in the case of aiming at the construction of the loud-sounding method in which the
sound is reproduced only in a specific area and the sound does not leak outside, that is, the
construction of the area limited reproduction method, devise a loud-sounding device such as a
speaker or a reproduction method. There is a need to. If it becomes possible to reproduce the
sound by limiting it to only a specific area, it is possible to prevent this sound from becoming
noise to people other than the listener, for example, when performing communication by loud
voice, etc. It is possible to improve the secrecy of making others invisible. As one implementation
means of this area limited reproduction system, it is conceivable to use a directional speaker
system which mainly emits sound only in a desired direction. As such a speaker system, a method
of realizing directivity by the geometric shape of a horn or a reflector such as using a horn
speaker or installing a speaker unit at the focal point of a reflector, a plurality of speakers A
method of forming directivity by arranging in an array, or emitting a sound wave obtained by
amplitude-modulating a carrier wave having strong directivity with an audio band signal, and
reproducing the sound in the audio band by its own demodulation There is a way to
[0003]
Among them, the method of realizing directivity by geometrical shape requires the use of a large
aperture horn or a reflector of a large area in order to obtain sharp directivity especially at low
frequencies, and a large-scale system Become. Moreover, although the method of installing the
speakers on the array is smaller in scale than a system using a horn or the like, although a
certain degree of directivity can be obtained, the directivity characteristic is still not good. On the
other hand, in the method using an ultrasonic speaker, the directivity according to the ultrasonic
wave which is the carrier wave can be obtained, and it is possible to realize the directivity in a
narrow range, but it is low due to the restriction of the modulation / demodulation mechanism. In
the frequency range, sufficient reproduced sound pressure can not be obtained.
[0004]
Apart from the above-described method, a method of applying a sound field control method
(Non-Patent Document 1) utilizing the property of the Kirchhoff-Helmholtz integral equation is
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conceivable. The sound field control method using the nature of the Kirchhoff-Helmholtz integral
equation controls the sound pressure and the sound pressure gradient on the interface of any
given closed space, thereby closing the same shape in another place. This is a method that can
faithfully reproduce the original sound field in space. In this control method, narrow directivity
characteristics such as a geometric method using a horn or placing a speaker unit at the focal
point of a reflector, or a method of forming directivity by arranging a plurality of speakers on an
array It can be realized in a relatively small-scale system as compared with the case of
reproducing the sound field only in a certain area using a speaker, and there is an advantage that
control of the reproduction area is easier than other methods.
[0005]
However, the arrangement of the speakers or the microphones for measuring the sound pressure
and the sound pressure gradient on the boundary surface is not arbitrary, and the arrangement
provides good reproduction characteristics (sound can be reproduced only in a desired area).
Also, there are cases where sound leaks out to the outside of the desired area, and there is no
knowledge as to what arrangement can provide good reproduction characteristics. Shiro Ise,
Journal of the Acoustical Society of Japan, Vol. 53, NO. 9, PP. 706-713, 1997
[0006]
As described above, if it is intended to reproduce sound only in a specific area, using a sound
field control method utilizing the nature of the Kirchhoff-Helmholtz integral equation can make
the system smaller or control the reproduction area Although there are many advantages such as
easy to use, the speaker arrangement and the microphone arrangement for obtaining good
reproduction characteristics are limited. An object of the present invention is to provide an area
limited reproduction system having good reproduction characteristics by giving guidance to the
arrangement of speakers and the arrangement of microphones.
[0007]
The present invention arranges M (MM2) sensors around the space where the sound should be
reproduced, and based on the outputs from these M sensors, reproduces the sound from N (N ≧
2) sound sources. A method of area-limited loud-speaking method in which sound is reproduced
in space by controlling mutual delay and frequency characteristics, and energy of the reproduced
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sound is reduced outside the space so that sound is reproduced only in the space. In the above,
the sound sources are characterized in that the spaces are arranged at unequal intervals on a
straight line. The present invention is further characterized in that among the sound sources
arranged on a straight line, the space between the sound sources arranged at the center is the
smallest, and the space between the sound sources becomes larger toward the end.
[0008]
The invention is further characterized in that, of the M sensors, at least one is close to the sound
source and the other sensors are set to zero response. Further, according to the present
invention, the characteristic of the filter connected to the N sources is a matrix H whose elements
are transfer characteristics between the N sources and the M sensors, where W is a matrix whose
elements are the characteristics. Based on a squared error minimum scale using a generalized
inverse matrix using a matrix A having M desired transfer characteristics assumed for each
control point and W = (H <T> H) < It is characterized by calculating and setting −1> × H <T> A.
[0009]
In the present invention, when N filter characteristics are further determined using a generalized
inverse matrix, a matrix positive having a smaller positive constant as a diagonal element and the
other elements of 0 is added, and W = (H <T> It is characterized by calculating by H + (delta) l <1> xH <T> A.
[0010]
According to the present invention, it is possible to reproduce sound so as not to leak out from a
desired boundary.
That is, area limited reproduction is possible. By using this method, even when sound
reproduction is performed by loud-speaking, it is possible to eliminate the inconvenience that
noise is generated by people other than those who want to hear the sound, or to improve the
secrecy of communication by sound.
[0011]
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In the configuration of the area limited loudspeaker shown in FIG. 1, the A / D converter 10, the
FIR filters 201 to 20N, the D / A converter 30, the response recording unit 60, the desired
response recording unit 70, and the filter coefficient determination unit 80 The computer
implemented embodiment is the most desirable embodiment. In other words, the area limited
loud sound program of the present invention is implemented by installing the area limited loud
sound program or the filter characteristic setting program proposed in the present invention in a
computer and causing a central processing unit (CPU) provided in the computer to decode and
execute the program. A method or filter characteristic setting method is implemented.
[0012]
By realizing the present invention, a sound field can be generated in a predetermined space
including a sound source, and sound can be prevented from leaking out of the predetermined
space. Therefore, according to the area limited loud-speaking method according to the present
invention, noise caused by persons other than the person who wants to listen to the sound will
not be annoyed. Or, it is possible to improve the secrecy of communication by sound. The effects
and advantages of the present invention can be obtained.
[0013]
First, a method for obtaining an arbitrary response at a desired control point will be described by
taking the configuration shown in FIG. 1 as an example. First, as an initialization operation, the
FIR filters 201 to 20 N receive an impulse as an input signal x (t) as an all-band pass
characteristic. This input signal is discretized into a signal X (k) by the A / D converter 10, and
after being subjected to digital-analog conversion again by the D / A converter 30, output from
the speakers 401 to 40N serving as a sound source Ru. The control points are provided with
microphones 501 to 50M acting as sensors, and respective microphone outputs become impulse
responses from the respective speakers 401 to 40N to the microphones 501 to 50M. The N × M
impulse response vectors hij (i = 1, 2,..., N, j = 1, 2,..., M) are input to the response recorder 60
and recorded. On the other hand, in the desired response recording unit 70, desired impulse
response vectors aj (j = 1, 2,..., M) defined for each control point are recorded. The filter
coefficient determiner 80 is input together with the output. Here, zero response can also be set
as aj. In the filter coefficient determination unit 80, the coefficients of the respective filters are
determined by performing the operation represented by the equation (1) using the matrices H
and A having these inputs hij and aj as elements, and the respective FIR filters 201, It is set to
202 to 20N. Here, W is a matrix having filter coefficients of the FIR filters 201 to 20N as
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elements. Also, in order not to make the inverse matrix unstable, it is determined after adding δl
using a small positive constant δ. Here, l is an identity matrix.
[0014]
W = (H <T> H + δl) <− 1> × H <T> A (1) When calculating the filter coefficient using the
equation (1), a time stretching pulse is used as the input signal x (t), N × M impulse response
vectors hij can also be determined by the impulse response measurement method described in
Japanese Patent No. 2725838. After the end of the initial operation, filter coefficients are set to
the filters 201 to 20N. In this state, the input signal x (t) is supplied from the input terminal to
the A / D converter 10, and the signal X (k) obtained by the input signal x (t) being discretized by
the A / D converter 10 is N The FIR filters 201 to 20N (i = 1, 2,..., N) are respectively input. The
signals filtered here are subjected to digital-to-analog conversion by the D / A converter 30, and
then output from the speakers 401 to 40N. Thereby, desired responses can be obtained at M
control points 501 to 50M.
[0015]
Next, a method of area limited reproduction using the control method described above will be
described. FIG. 2 shows the arrangement of speakers in the case where speakers are used as four
sound sources, and the arrangement of control points (sensors) (indicated by □ and Δ in the
drawing). Here, the control points 501 to 50M-1 indicated by □ in the figure act as zero control
points, and in the recording portion corresponding to each of the control points 501 to 50M-1
provided in the desired response recording unit 70 A zero response was set as aj as the desired
response. On the other hand, the control point 50M indicated by Δ in the drawing acts as a
response control point, and only the speaker 1 shown in FIG. 4 is used as the recording unit in
the desired response recorder 70 corresponding to the control point 50M. The impulse response
from the speaker to the response control point 50M was set as the desired response. Further, the
distance between the response control point 50M and the speaker is set to be smaller than the
distance between the zero control points 501 to 50M-1 and the speaker. On the other hand, as
the speakers, four speakers 401 to 404 are used. When the distance between each of the four
speakers 401 to 404 is 16.5 cm between 401 and 402, 5.4 cm between 402 and 403, and 13.8
cm between 403 and 404, respectively. Indicates That is, the distance between the two central
speakers 402 and 403 is set to be smaller than the distance between the two speakers 401 and
404 on both sides. The result of having performed simulation about sound pressure analysis in
case a frequency is 1000 Hz on this condition is shown in FIG. FIG. 4 shows the sound pressure
distribution when one speaker is used for comparison. As apparent from FIGS. 3 and 4, when the
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sound is reproduced using the area limited loud-speaking method according to the present
invention, the sound is reproduced without performing control outside the zero response control
points 501 to 50M-1. The sound pressure is clearly smaller than in the comparison, and it can be
seen that no sound leaks to the outside. On the other hand, at the control point 50M in which the
response of only one speaker is the desired response, it can be seen that the sound is reproduced
with almost the same sound pressure in both cases.
[0016]
Since the present invention can reproduce sound only in a limited area, it is used in the field of a
speech communication system or a voice conference system.
[0017]
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram for explaining an embodiment
of an area limited loudspeaker according to the present invention.
FIG. 6 is a layout diagram for explaining an example of the layout of speakers and control points
for explaining the effects of the present invention. The graph for demonstrating the sound
pressure distribution obtained by the arrangement | positioning shown in FIG. The graph for
demonstrating the sound pressure distribution at the time of making a speaker into one.
Explanation of sign
[0018]
10 A / D converter 60 response recorder 201 to 20 NFIR filter 70 desired response recorder 301
to 30 ND / A converter 80 filter coefficient determiner 401 to 40 N speaker 501 to 50 M
microphone
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