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JP2008252625

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DESCRIPTION JP2008252625
PROBLEM TO BE SOLVED: To provide a directional speaker array in which control points for
reproduction are set in a main lobe direction and that reproduction sound is not deteriorated as a
design standard. SOLUTION: The directional speaker system according to the present invention
comprises a loudspeaker array 20 comprising a plurality of loudspeaker units arranged linearly
or in a plane, and a signal conditioning unit for regulating input signals to the plurality of
loudspeaker units. And 300, and control means 50 for controlling the signal adjustment means
300. The signal adjustment means 300 has digital filters 3 to 3 in which the filter coefficients are
set based on the boundary sound field control principle, and the control means 50 controls the
relationship between the plurality of suppression control points and the reproduction control
points and the boundary sound field control. The filter coefficients of the digital filters 3 to 3 are
calculated based on the principle of (1), and the filter coefficients of the digital filters 3 to 3 are
set. [Selected figure] Figure 4
Directional speaker system
[0001]
The present invention relates to a directional speaker system, and more particularly to a
directional speaker system to which a sound field localization technique is applied.
[0002]
In the last few decades, numerous loudspeaker systems have been proposed, many of which aim
to improve the quality of the reproduced signal.
09-05-2019
1
Of course, faithful reproduction of the original sound is an important issue. However, recently,
the quality is required for the ringing tone of the mobile phone, and various sounds are
overflowing in the city.
[0003]
On the other hand, the call quality that is supposed to be purpose is further deteriorated, and it is
difficult to talk with the other party unless the user makes a loud voice in the public space.
[0004]
Furthermore, announcements and broadcasts that are diffused due to lack of appropriate control
and are unclear and difficult to hear are made in various places and become a social problem.
[0005]
In view of such problems, a superdirective speaker system aiming at outputting voice and sound
signals only in a specific limited area has been researched and developed to guide visually
impaired persons, museums and museums. Is applied to the guidance system of (see Non-Patent
Document 1).
[0006]
These directional speaker systems can be roughly classified into two, a method using ultrasonic
waves (parametric speakers) and a speaker array using interference of sound waves.
In particular, parametric speakers have very sharp directivity and are expected to be applied to
various fields.
[0007]
However, it is necessary to emit a very large sound wave as compared to an acoustic signal
generated as an audible sound, and there is a concern about the problem of ultrasound exposure
(see Non-patent literature 2).
09-05-2019
2
[0008]
Moreover, in the case of a parametric speaker, since it becomes a new sound source without loss
of rectilinearity even if it is reflected on a wall or floor, it has excellent sound absorption
performance for the purpose of limiting the sound reproduction area when used indoors. It is
necessary to install the sound absorbing material around.
[0009]
On the other hand, the speaker array can be realized with a simple configuration using a normal
speaker unit.
However, generally speaking, in order to obtain sharp directivity in the low frequency range, it is
necessary to widen the spacing of the speaker units.
[0010]
So far, the present inventors have proposed a method of constructing a directional speaker
system (localized speaker) using sound field localization technology based on the principle of
boundary sound field control, and clarified its performance by numerical calculation and
experiment (Non-Patent Document 3).
Tsuneo Tanaka, Akihiro Furuta, "Development of speakers for art museums and museums,
narrowing directivity by array arrangement" Nikkei electronics, no. 587, pp. 155-165, Aug. 1993.
Kenichi Aoki, Tomoo Kamakura, Yoshiro Kumamoto, "Parametrics Speaker _ Application
Examples" Theory of Philosophy (A), Vol.
J76−A,PP.1127−1135,Aug.1993. Seigo Enomoto, Shiro Ise,
"Proposal of a Speaker System Using the Principle of Boundary Sound Field Control", Shingaku
Theory (A), Vol. J87−A,no.4,PP.431−438,Apr.2004.
09-05-2019
3
[0011]
The above-mentioned localized speakers are classified as one of directivity control methods using
sound wave interference as in the case of a speaker array, but the low frequency is particularly
low because the control of the flow of acoustic energy is a design criterion. The directivity can be
easily formed in the band as compared to the conventional speaker array.
[0012]
However, a virtual wall surface is installed only in the direction in which the flow of acoustic
energy is desired to be blocked, and the direction without the wall surface is used as the main
lobe, and the characteristics of the reproduction signal are unknown.
[0013]
An object of the present invention is to provide a directional speaker array in which control
points for reproduction are set in the main lobe direction and that the reproduction sound is not
deteriorated as a design standard.
[0014]
A directional loudspeaker system according to the present invention comprises a loudspeaker
array comprising a plurality of loudspeaker units arranged linearly or in a plane, a signal
conditioning unit for conditioning input signals to the plurality of loudspeaker units, and the
signal conditioning Control means for controlling means, the signal adjustment means having a
digital filter in which filter coefficients are set based on the boundary sound field control
principle, the control means comprising a plurality of suppression control points and
reproduction control The filter coefficients of the digital filter are calculated based on the
relationship between points and the principle of boundary sound field control, and the filter
coefficients of the digital filter are set.
[0015]
Further, the reproduction control point can be set at an arbitrary position of the boundary
surface.
The reproduction control point can be formed by deleting a part of the suppression control point.
09-05-2019
4
[0016]
Furthermore, the control means includes storage means for storing filter coefficients calculated
corresponding to reproduction control points having different directions, and the filter
coefficients are read out from the storage means based on the set reproduction control points,
and the digital It can be configured to set the filter coefficients of the filter.
[0017]
The present invention is characterized in that the flow of acoustic energy is controlled, so
directivity control can be easily performed in the low band.
Further, since the reproduction control point can be set at an arbitrary position, the reproduction
of the original signal can be performed at an arbitrary reproduction control point.
[0018]
Furthermore, according to the present invention, beam forming can be performed in a plurality
of directions.
[0019]
Embodiments of the present invention will be described in detail with reference to the drawings.
The same or corresponding portions in the drawings are denoted by the same reference
numerals, and the description thereof will not be repeated to avoid the repetition of the
description.
[0020]
First, the principle of three-dimensional sound field control based on boundary sound field
control will be described with reference to the drawings.
09-05-2019
5
The principle of boundary sound field control is a principle showing that the sound pressure
inside the boundary can be controlled by controlling the sound pressure and particle velocity on
the boundary surrounding an arbitrary area in the three-dimensional space.
FIG. 1 is a conceptual diagram of an active noise control system based on the principle of
boundary sound field control, and FIG. 2 is a conceptual diagram of a local reproduction system.
[0021]
As shown in FIG. 1, in an active noise control (ANC) system, sound pressure and particle velocity
from the speaker unit 10 as a primary source (Primary source) observed on a virtual boundary
surface (Notional boundary) 4 The sound pressure in the area surrounded by the boundary 4 can
be made zero by driving the speaker array 20 of the secondary source such that x is zero.
[0022]
The secondary sound source speaker array 20 is composed of a plurality of speaker units 21 to
2N.
Then, digital filters 31 to 3N having transfer functions (H1 to HN) calculated based on the
principle of boundary sound field control are provided in front of the respective speaker units 21
to 2N.
The input signal is given to the filter unit 30 including the speaker unit 10 and the digital filters
31 to 3N. An input signal is adjusted corresponding to each of the speakers 21 to 2N by each of
the digital filters 31 to 3N of the filter group 30. Each of the speakers 21 to 2N is driven based
on the adjusted signal.
[0023]
Thus, the sound pressure and particle velocity observed on the virtual boundary surface 4 can be
made zero by the sound pressure from the speaker unit 10 and the driving of the speaker array
20 of the secondary sound source.
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[0024]
As shown in FIG. 2, in the local reproduction system, the sound pressure on the interface 4 is
surrounded by the virtual interface 4 around the speakers 10 and the speaker array 20 of the
two-dimensional sound source as in the case of the ANC system. By making the particle velocity
zero and the particle velocity zero, the sound pressure in the region far from the interface 4 can
be zero.
[0025]
At this time, for example, the speaker units 10 and 21 to 2N are disposed on a straight line, and
the boundary surface 4 is disposed on a half circumference surrounding the speakers 10 and 21
to 2N. The sound pressure in all directions can be made zero.
In a local reproduction system, in practice, the sound pressure and the particle velocity do not
become zero rapidly near the interface, but gradually approach zero as they move away from the
speaker units 10 and 21 to 2N.
Therefore, the local reproduction system has a steep attenuation characteristic as compared with
a general speaker system, and only the vicinity of the speaker units 10 and 21 to 2N is the
reproduction area.
[0026]
The present invention proposes a directional speaker system in which a reproduction control
point is provided so that the reproduction signal can be controlled to a desired characteristic in
the main lobe direction, in addition to the design criteria of the conventional localized speaker
described above.
[0027]
According to the present invention, in addition to the suppression control point similar to that of
the conventional localized speaker, in the main lobe direction, a reproduction control point for
controlling the amplitude and phase of the reproduction signal is provided to control directivity.
[0028]
Next, the principle of control of the directional speaker system to which the localization
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7
technology is applied will be described.
[0029]
By deleting a part of the suppression control points constituting the virtual boundary 4 shown in
FIG. 2, a flow of acoustic energy is generated in the direction in which the control points are
deleted.
As will be described later, the suppression control point is provided with a microphone, and the
filter coefficients of the filter group 30 consisting of N digital filters 31 to 3N provided in front of
the speaker units 21 to 2N are calculated.
[0030]
As shown in FIG. 3, the directional speaker system according to the present invention comprises
N speaker units 21 to 2N as a speaker array 20 constituting a localized speaker, and digital
filters 31 to 3N provided in front of the speaker units. Ru.
[0031]
The filter coefficients of the digital filters 31 to 3N provided in front of the speaker units 21 to
2N are calculated based on the principle of boundary sound field control.
An embodiment for designing the digital filters 31 to 3N will be described with reference to FIG.
[0032]
When calculating the coefficients of the N digital filters 31 to 3N, M microphones are provided at
suppression control points in a range of 0 degrees to 180 degrees away from the speaker array
20 apart from the speaker array 20 Do.
In the following filter calculation, the number of speaker units 2 is 10, and the microphone 5 is
09-05-2019
8
configured of 13 microphones 50 to 50 180 divided every 15 degrees from 0 degree to 180
degrees.
[0033]
The calculation of the filter coefficients is as follows.
[0034]
The frequency transfer function from the j-th (j = 1,..., N) speaker unit 2 to the i-th (i = 1,..., M)
microphone 5 is Gij.
Then, assuming that an input signal to the speaker unit 2 is X and a signal measured at the
position of each microphone when output from the speaker unit is Y, the input / output system
of the system is expressed by the following equation (1).
[0035]
Y (ω) = {[G (ω)] · H (ω)} X (ω) (1) where [G (ω)] is between the j-th speaker unit 2 and the i-th
microphone 5 An M × N matrix having a frequency transfer function Gij (ω) as an element, and
Y (ω) has an element Yi (ω) measured at each microphone position as an element [Y0 (ω),. It is
assumed that Y 180 (ω)] <T> (T represents transposition).
[0036]
The coefficient H to (ω) of the filter that controls the desired directivity for an arbitrary input
signal X can be obtained by solving the following equation (2).
H ~ (ω) = [G (ω)] <-> · D (ω) (2) where D (ω) = [D0 (ω), ..., D180 (ω)] <T> It is a desired Mdimensional vector (object vector) at the position of the microphone, and [] <-> represents a
general inverse matrix.
Here, Di (ω) can be determined in consideration of the weight of each control point, but in this
embodiment, the response of the reproduction control point is 1 and the response of the
09-05-2019
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suppression control point is 0 for simplicity. .
[0037]
When generating the main lobe of the speaker array 20 in the 90 degree direction, the
microphones 5 installed at 0, 15, 30, 45, 90, 135, 150, 165, 180 degrees are used. Since the
main lobe is generated in the 90 degree direction, the reproduction control point is 90 degrees.
Therefore, [0, 0, 0, 0, 1, 0, 0, 0] is given to the vector D (ω), and the coefficients of the digital
filters 31 to 3N are calculated.
[0038]
When the main lobe of the speaker array 20 is generated in the 45 degree direction, the
microphones 5 installed at 0, 45, 90, 105, 120, 135, 150, 165, and 180 degrees are used. Since
the main lobe is generated in the 40 degree direction, the reproduction control point is 45
degrees. Therefore, [0, 1, 0, 0, 0, 0, 0, 0, 0] is given to the vector D (ω), and the coefficients of
the digital filters 31 to 3N are calculated.
[0039]
As to the microphones to be used, elements of the vector D (ω) are selected so as to be
appropriate in accordance with the direction of the target directivity.
[0040]
In the directional speaker system, the filter coefficient may be calculated each time the signal is
reproduced, but the system requires a microphone and the system configuration becomes
complicated.
Therefore, the direction of directivity can be switched by calculating the filter coefficient for each
direction of the main lobe in advance, storing the calculation result in a memory or the like, and
switching the filter coefficient.
09-05-2019
10
[0041]
Next, a directional speaker system according to the first embodiment of the present invention
using the filter coefficients calculated by the method described above will be described according
to FIG. FIG. 4 is a block diagram showing a directional speaker system according to a first
embodiment of the present invention.
[0042]
As shown in FIG. 4, in this embodiment, ten speaker units 21 to 210 are provided as a speaker
array 20 that constitutes a localized speaker. The speaker units 21 to 210 are linearly arranged.
At the front stage of the speaker array 20, a signal adjusting unit 300 is provided which adjusts
input signals to the speaker units 21 to 210.
[0043]
The signal adjusting means 300 converts the digital signal passed through the filter group 30
constituted by the digital filters 31 to 310 in which the filter coefficients calculated based on the
principle of boundary sound field control described above are set and the analog A digital /
analog (D / A) conversion circuit 7 for converting into a signal and an amplifier 8 are included.
[0044]
The filter coefficients (transfer function) calculated based on the principle of boundary sound
field control are set by the control device 50 as the filter coefficients in the digital filters 31 to
310.
According to FIG. 3 described above, filter coefficients are calculated in advance for each
direction of the main beam, and the calculation results are stored in storage means 51 formed of
a non-volatile memory or the like.
[0045]
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11
The boundary surface 4 is disposed on a half circumference surrounding the speaker units 21 to
210, and control points 60 to 6180 serving as a reproduction control point or a suppression
control point are set at predetermined angles on the half circumference. The reproduction
control point is set by the input means 52 from among the control points 60 to 6180. The
position set as the reproduction control point is the direction of the main beam. Control points
other than the reproduction control point are suppression control points. As the reproduction
control point, any one of control points 60 to 6180 can be set.
[0046]
The storage means 51 described above stores the filter coefficients calculated for each direction
of the main beam, and the control device 50 follows the reproduction control point set by the
input means 52, that is, the direction of the main beam, The corresponding filter coefficient is
read out from the storage means 51. The filter coefficients of the digital filters 31 to 310 are set
in accordance with the read filter coefficients.
[0047]
An input signal from the input signal source 60 is converted into a digital signal by an analog /
digital (A / D) conversion circuit 61, and is applied to digital filters 31 to 310. Each digital signal
is controlled according to the filter coefficient by the digital filters 31 to 310 and is supplied to
the D / A conversion circuit 7. Then, the signal is converted into an analog signal by the D / A
conversion circuit 7, amplified by the amplifier 8, and input to each of the speaker units 21 to
210. Then, by outputting the respective sounds from the respective speaker units 21 to 210, it is
possible to obtain an output having directivity toward the set reproduction control point.
[0048]
Next, the control operation in the above-described first embodiment will be further described
according to the operation flowchart of FIG.
[0049]
When the reproduction control point is selected from the control points 60 to 6180 by the input
means 51, the control device 50 sets the selected control point as a reproduction control point
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(step S1).
Then, the control device 50 reads the corresponding filter coefficient from the storage means 51
based on the set reproduction control point (step S2).
[0050]
Thereafter, the control device 50 sets the filter coefficients read from the storage unit 51 in the
corresponding filters 31 to 310 (step S4).
[0051]
Subsequently, the input signal from the input signal source 60 is converted to a digital signal by
the A / D conversion circuit 61 and is applied to the digital filters 31 to 310.
Each digital signal is controlled according to the filter coefficient by the digital filters 31 to 310,
and the signal is converted to an analog signal by the D / A conversion circuit 7 and is applied to
the amplifier 8. The signal is amplified by the amplifier 8 and output from each of the speaker
units 21 to 210 (step S4).
[0052]
The process returns to step S4 until the end of the output is instructed, and the output is
continued, and when the end of the output is instructed, the operation is ended (step S5).
[0053]
Next, a directional speaker system according to a second embodiment of the present invention
will be described with reference to FIG.
FIG. 6 is a block diagram showing a directional speaker system according to a second
embodiment of the present invention. The same parts as those in the first embodiment are
denoted by the same reference numerals, and in order to avoid duplication of explanation, the
explanation is omitted here.
09-05-2019
13
[0054]
In FIG. 6, the speaker array 20, the control device 50, the storage unit 51, the input unit 52, and
the signal adjustment unit 300 are the same as those in the first embodiment described above. In
the second embodiment, the reproduction control point is configured to detect and set the
position of the listener. For this reason, detection devices 801 to 80M are installed along the
boundary surface 4.
[0055]
The detection device comprises, for example, an infrared light source and a reception device. The
detection means 81 detects the presence or absence of the listener based on the output from the
detection devices 801 to 80M. When the listener is located between the infrared source and the
receiver, the infrared is blocked. The detection means 81 detects the presence of the listener
based on the output when the infrared ray is blocked. The output from each detection means 81
is given to the control device 50, and the control device 50 determines which control point the
listener is present on the basis of the output from the detection means 81, and the control point
is used as a reproduction control point Set as.
[0056]
Then, according to the set reproduction control point, that is, the direction of the main beam, the
corresponding filter coefficient is read out from the storage means 51. The filter coefficients of
the digital filters 31 to 310 are set in accordance with the read filter coefficients.
[0057]
Next, the control operation in the above-described second embodiment will be further described
according to the operation flowchart of FIG.
[0058]
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14
The signal from the detection means 81 according to the signal output from the detection
apparatuses 801-80M is input into the control apparatus 50 (S11).
The control device 50 detects the reproduction control point based on the output of the detection
means 81, and sets the reproduction control point (step S12). Then, the control device 50 reads
the corresponding filter coefficient from the storage unit 51 based on the detected reproduction
control point (step S13).
[0059]
Thereafter, the control device 50 sets the filter coefficients read from the storage unit 51 in the
corresponding digital filters 31 to 310 (step S14).
[0060]
Subsequently, the input signal from the input signal source 60 is converted to a digital signal by
the A / D conversion circuit 61 and is applied to the digital filters 31 to 310.
Each digital signal is controlled according to the filter coefficient by the digital filters 31 to 310,
and the signal is converted to an analog signal by the D / A conversion circuit 7 and is applied to
the amplifier 8. The signal is amplified by the amplifier 8 and output from each of the speaker
units 21 to 210 (step S15).
[0061]
The process returns to step S15 until the end of the output is instructed, and the output is
continued, and when the end of the output is instructed, the operation is ended (step S16).
[0062]
In the second embodiment, the case where the infrared light source and the receiver thereof are
used as the detection device has been described, but the detection device is not limited to this.
For example, a monitoring camera or an ultrasonic sensor can be used as a detection device.
09-05-2019
15
[0063]
Next, the characteristics of the directional speaker system according to the embodiment of the
present invention will be described based on a specific example. The basic arrangement of the
speaker array 20 etc. is as shown in FIG. In this example, the speaker array 20 is an equidistant
linear array of several 10 speaker units and 17 cm between speaker units. Also, the microphones
forming the virtual interface 4 are arranged at intervals of 15 degrees on a half circumference of
a radius of 2 m from the center of the speaker array 20. However, the microphone used differs
depending on the direction of the main lobe. The calculation was performed at each frequency of
250 Hz, 500 Hz, 1 kHz, and 2 kHz. That is, the respective wavelengths are 1⁄8, 1⁄4, 1⁄2 and 1 ×
with respect to the speaker unit interval.
[0064]
First, the characteristics of the main lobe in one direction will be described.
[0065]
In this example, directivity characteristics when the main lobe direction is set to 90 degrees are
shown in FIG.
When the 90 degree direction is set as the main lobe, ten points of 15 degrees from 0 degree to
60 degrees and 120 degrees to 180 degrees are set as the suppression control point, and 90
degrees is set as the reproduction control point. The vertical axis in FIG. 8 is the gain at a
distance of 2 m from the center of the speaker array 20. Therefore, in this condition, the
directivity characteristic on the semicircle where the control point is placed is obtained. The gain
representing the directivity is normalized so that the maximum value is 1 for each frequency. The
horizontal axis is the angle.
[0066]
Further, the execution lines, the broken lines, the alternate long and short dash lines, and the
dotted lines in the figure are directivity characteristics in the case of 250 Hz, 500 Hz, 1 kHz, and
2 kHz.
09-05-2019
16
[0067]
It can be seen from FIG. 8 that although the beam width gradually decreases from 250 Hz to 1
kHz, substantially equal main lobes are formed.
Further, when the frequency is 2 kHz, the main lobe is not formed in the 90 ° direction, and the
sound is emitted in the other direction.
[0068]
The directivity characteristic when the direction of the main lobe is set to 60 degrees is shown in
FIG. When the 60 degree direction is set as the main lobe, ten points from 0 degree to 30
degrees and 90 degrees to 180 degrees are set as the suppression control point, and the 60
degree direction is set as the reproduction control point. It can be seen from FIG. 9 that the main
lobe is formed in the target direction up to 1 kHz, as in the case where the 90.degree. Direction is
the main lobe. However, as the frequency increases, the direction of the main lobe is shifted by
90 degrees.
[0069]
The directivity characteristic when the direction of the main lobe is set to 30 degrees is shown in
FIG. When the 30 degree direction is set as the main lobe, 10 points from 0 degree and 60
degrees to 180 degrees are set as the suppression control point, and the 30 degree direction is
set as the reproduction control point. It can be understood from FIG. 10 that the main lobe is
formed in the target direction up to 1 kHz, as in the case where the 90 ° direction and the 60 °
direction are used as the main lobe. However, in the case of 1 kHz, the direction of the main lobe
is largely shifted in the 90 ° direction from the set 30 ° direction, and is about 45 °. In
addition, the gain of the side lobe is also larger compared to other conditions.
[0070]
In the present invention, the arrangement of the speaker unit and the arrangement of the control
09-05-2019
17
points are strongly influenced, but the combination of the reproduction control point and the
suppression control point and the weighting of each control point in calculating the filter can in
principle be any shape. It is conceivable to form the main lobe of Therefore, as an example,
directivity characteristics in the case where the directions of 60 degrees and 105 degrees and
the directions of 60 degrees and 120 degrees are set as the main lobe are shown in FIGS. 11 and
12, respectively. The directivity characteristics were calculated on a half circle of 2 m from the
center of the speaker array 20 for the frequencies of 250 Hz, 500 Hz, 1 kHz and 2 kHz as
described above. The practical lines in the figure, the broken lines, the alternate long and short
dash lines, and the dotted lines are directivity characteristics in the case of 250 Hz, 500 Hz, 1
kHz, and 2 kHz.
[0071]
When the 60 ° and 105 ° directions are set as the main lobe, 9 points of 0 ° to 30 °, every
15 ° from 135 ° to 180 °, and 75 ° and 90 ° are set as the suppression point control point,
60 And 105 degrees were used as reproduction control points.
[0072]
As described above, according to the present invention, an output having directivity for any
reproduction control point can be obtained.
[0073]
The distance between the speaker units and the distance between the control points of the
speaker array should be determined from the upper limit frequency and the lower limit
frequency of the controlled band.
When the speaker unit spacing is 1⁄2 times the wavelength, there is a tendency to shift in the 90
° direction from the direction of the reproduction control point where the main lobe direction is
set, especially in the direction near 0 ° and 180 ° .
Therefore, if possible, it is desirable to set the speaker unit interval to 1/4 or less of the
wavelength of the upper limit frequency of the controlled band.
[0074]
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18
In the above embodiment, the case where the speaker array is linearly arranged is described.
However, the present invention can be applied to a case where the speaker units are arranged
planarly to constitute the speaker array. it can.
[0075]
In general, the aperture of a speaker unit capable of reproducing to low frequencies is large, and
as a result, it is necessary to increase the speaker unit interval.
In addition, in the case of realization as a closed type speaker system, since an enclosure having a
sufficient size in the back is required, the system configuration of the directional speaker array
becomes an important issue. Therefore, in this embodiment, it is possible to output up to a
relatively low frequency range, and AURA SOUND NS3-193-8A (reproduction frequency band F0
(= 80 Hz) -15 kHz, aperture 70 mm) is selected as a speaker unit having a small aperture. Then, I
made a prototype of a speaker system with an enclosure of about 11 cm in height and width and
1 m in depth behind it. Therefore, when the speaker units are arranged without gaps, the speaker
unit spacing of the speaker array 20 is about 11 cm. The speaker system can be configured with
a common enclosure for a plurality of units, can be thinned in shape, etc. In this embodiment, (1)
making each unit independent, (2) The shape of the speaker array is made to be freely
changeable.
[0076]
(Experimental conditions) In order to confirm the performance of the prototype speaker system,
the spatial sound pressure distribution of the speaker system was measured in the anechoic
chamber. The sound pressure distribution was measured in the same plane including the
loudspeaker system and the control points. The number of units of the speaker array 20 is four.
In this experiment, first, an impulse response every 15 degrees from 0 degrees to 180 degrees
on a half circumference of 2 m from the center of the speaker array 20 is first measured, and in
the frequency domain according to equation (2) The filter Hj (ω) was calculated. However, the
front of the array was 90 degrees, the right direction was 0 degrees, and the left direction was
180 degrees. Next, measure the impulse response on the grid point obtained by dividing the 3.6
m × 2.6 m area on the front of the speaker array 20 into 60 cm × 65 cm, and convolute with
the calculated filter coefficients to obtain spatial sound of the speaker system. Pressure
distribution was determined. The sampling frequency is 48 kHz and the number of quantization
bits is 24 bits. An outline of the experimental system is shown in FIG.
09-05-2019
19
[0077]
(Experimental Results) FIGS. 14 to 16 show sound pressure distributions of the speaker system
when the main lobe is set to 90 degrees. FIG. 14 shows the sound pressure distribution of the
directional (localized) speaker system of the present invention. Also, for comparison, FIG. 15
shows the sound pressure distribution of the conventional speaker array (delay-sum array), and
FIG. 16 shows the case where only one speaker unit (speaker # 3) is output from the speaker
array 20 shown in FIG. Sound pressure distribution is shown.
[0078]
The sound pressure distribution is an average value in the band of 350 Hz to 1.5 kHz, and is
normalized so that the maximum value is 0 dB. In the directional speaker system according to the
present invention, ten points of 0 degree to 60 degrees and 120 points of 15 degrees of 120
degrees to 180 degrees are used as suppression control points, and 90 degrees are used as
reproduction control points. From FIG. 15, it can be seen that the prototyped speaker system
forms sharp directivity even when the conventional array processing is performed. However, as
shown in FIG. 14, it can be seen that the directional (localized) speaker system of the present
invention provides a sharper directivity than conventional array processing.
[0079]
The sound pressure distributions on the axes separated by 80 cm and 1.45 m in parallel with the
speaker system are shown in FIGS. The number of units of the speaker array 20 in this example
is four. The straight line, the broken line and the dotted line in the figure are the sound pressure
distributions of the localized speaker (Proposed system), the delay-and-sum speaker array (Delay
and sum array), and the single speaker (Single speaker) of the present invention, respectively. In
FIG. 17 and FIG. 18, the axis perpendicular to the array passing through the center of the speaker
array is 0 m, and the maximum value is normalized to 0 dB. It can be seen that in both cases of
80 cm and 1.45 m, sharper directivity is obtained than in the delay-and-sum speaker array.
[0080]
09-05-2019
20
It should be understood that the embodiments disclosed herein are illustrative and nonrestrictive in every respect. The scope of the present invention is shown not by the above
description of the embodiment but by the scope of claims, and is intended to include all
modifications within the meaning and scope equivalent to the scope of claims.
[0081]
It can be applied to guidance of visually impaired persons, guidance systems for art museums
and museums, etc.
[0082]
It is a conceptual diagram of the active noise control system based on the principle of boundary
sound field control.
It is a conceptual diagram of a local reproduction system based on the principle of boundary
sound field control. It is a conceptual diagram which shows the principle of the directional
loudspeaker system in this invention. FIG. 1 is a block diagram showing a directional speaker
system according to a first embodiment of the present invention. It is a flowchart which shows
the control action of the directional loudspeaker system concerning 1st Embodiment of this
invention. It is a block diagram showing a directional loudspeaker system concerning a 2nd
embodiment of this invention. It is a flowchart which shows the control action of the directional
loudspeaker system concerning 2nd Embodiment of this invention. In the directional speaker
system of this invention, it is a figure which shows the directional characteristic at the time of
setting the main lobe direction to 90 degree. In the directional speaker system of this invention,
it is a figure which shows the directional characteristic at the time of setting the main lobe
direction to 60 degree | times. In the directional speaker system of this invention, it is a figure
which shows the directional characteristic at the time of setting the main lobe direction to 30
degree | times. In the directional speaker system of this invention, it is a figure which shows the
directional characteristic at the time of setting the main lobe direction to 60 degree | times and
105 degree | times. In the directional speaker system of this invention, it is a figure which shows
the directional characteristic at the time of setting the main lobe direction to 60 degree | times
and 120 degree | times. It is the schematic which shows the experiment system of the directional
loudspeaker system of this invention. In the directional speaker system of this invention, it is a
figure which shows sound pressure distribution at the time of setting the main lobe to 90 degree
direction. It is a figure which shows sound pressure distribution of the conventional speaker
array (delay sum array). It is a figure which shows sound pressure distribution when only one
09-05-2019
21
speaker unit (speaker # 3) is output out of a speaker array. It is a figure which shows the sound
pressure distribution normalized so that the axis | shaft perpendicular | vertical to the array
passing through the center of a speaker array may be 0 m, and the maximum value may be 0 dB.
It is a figure which shows the sound pressure distribution normalized so that the axis | shaft
perpendicular | vertical to the array passing through the center of a speaker array may be 0 m,
and the maximum value may be 0 dB.
Explanation of sign
[0083]
2, 21 to 210 speaker units, 31 to 310 digital filters, 20 speaker arrays, 50 controllers, 51 storage
means, 300 signal conditioning means.
09-05-2019
22
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