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JP2005142632

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DESCRIPTION JP2005142632
PROBLEM TO BE SOLVED: To reproduce low frequency sound with sufficient sound pressure in
an area to be reproduced using sound pressure and sound pressure gradient sensor having an
interval suitable for controlling divided frequency bands and higher Provided is a sound field
control method and apparatus capable of controlling up to frequency. SOLUTION: A sound field is
displayed by a primary sound source unit 31 that reproduces an input sound signal X (t) and a
secondary sound source unit 32 that reproduces a signal whose delay and frequency
characteristics are changed in the input sound signal X (t). In the sound field control method and
device to be controlled, the input sound signal X (t) supplied to the secondary sound source unit
32 is divided into N (N ≧ 2) frequency bands and installed on the boundary of the reproduction
area. By using the output signals of the sound pressure and sound pressure gradient sensors 4 to
4 selected for each frequency band signal, a signal for each frequency band is generated in which
the delay and frequency characteristics of the input sound signal X (t) are changed Sound field
control method and apparatus using the same for the secondary sound source unit 32. [Selected
figure] Figure 1
Sound field control method and device for implementing this method
[0001]
The present invention relates to a method of controlling a sound field and an apparatus for
carrying out the method, and an area limited loudspeaker that generates an audible sound only
in an arbitrary area by changing the sound field characteristic of a space such as an indoor area.
The present invention relates to a sound field control method for use in sound field control and
an apparatus for implementing the method.
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[0002]
When a sound is emitted using a loudspeaker, although there is an influence of the directional
characteristics of the speaker used for sound reproduction, the sound can be emitted from the
speaker in almost all directions for listening.
Therefore, when aiming at the construction of area limited reproduction, that is, aiming at the
construction of area limited reproduction, it is limited to a specific area only to reproduce the
sound and there is no leakage of the sound outside the area, It is necessary to devise
corresponding to this. A method of applying a sound field control method utilizing the property
of Kirchhoff-Helmholtz's integral equation can be considered as a method of this one realization
(see Non-Patent Document 1).
[0003]
The sound field control method utilizing the nature of the Kirchhoff-Helmholtz integral equation
controls the sound pressure and the sound pressure gradient on the boundary surface of any
given closed space, thereby closing the same shape at another place. The original sound field in
the space can be faithfully reproduced. In this control method, it is possible to use a horn, a
geometrical method of installing a speaker unit at the focal point of a reflector, or narrow
directivity characteristics of forming directivity by arranging a plurality of speakers in an array.
As compared with the case of reproducing the sound field only in a certain area using a speaker,
it can be realized in a small-scale system, and the control of the reproduction area is easier
compared to other methods. There is an advantage. However, in this control method, in order to
control the sound field over a wide frequency band, it is necessary to install a large number of
sensors for observing the sound pressure and the sound pressure gradient, and the number of
secondary sound sources in proportion to the number Also, if the system is actually operated, the
frequency band above the controllable frequency band increases. The limit is limited.
[0004]
In order to perform control to a higher frequency within this limited upper limit frequency, it is
effective to narrow the interval between the secondary sound source and the control point.
However, in particular, if the distance between the secondary sound sources is narrowed, control
can be performed for relatively high frequencies within the range that does not exceed the upper
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limit frequency, but sounds with relatively low frequencies are muted near the primary sound
source, The playback area becomes extremely small. As a result, sound reproduction can not be
performed with sufficient sound pressure in the desired reproduction area. Ise, Journal of the
Speech Society of Japan, Vol. 53. No. 9, pp. 706-713, 1977.
[0005]
As described above, in the area reproduction equation using the property of the KirchhoffHelmholtz integral equation, when trying to raise the upper limit frequency that can be
controlled, it becomes impossible to reproduce low frequency sound with sufficient sound
pressure. The present invention provides a sound field control method capable of reproducing
low frequency sound with sufficient sound pressure in a reproduction area and raising the upper
limit frequency that can be controlled, and an apparatus for implementing this method. is there.
[0006]
Claim 1: The primary sound source unit 31 for reproducing the input sound signal X (t) and the
secondary sound source unit 32 for reproducing a signal in which the delay and frequency
characteristics of the input sound signal X (t) are changed In the sound field control method to be
controlled, the input sound signal X (t) to be supplied to the secondary sound source unit 32 is
divided into N (N ≧ 2) frequency bands and installed on the boundary of the reproduction area.
Using the output signals of the sound pressure and sound pressure gradient sensors 41 to 4 n
selected for each signal, to generate a signal for each frequency band in which the delay and
frequency characteristics of the input sound signal X (t) are changed. A sound field control
method for loud-sound reproduction using the secondary sound source unit 32 is configured.
[0007]
And in the sound field control method according to the second aspect of the present invention,
sound field control in which the number of sound pressure / sound pressure gradient sensors 41
to 4 n and the distance interval are different for each of the divided arbitrary frequency bands. I
configured the method.
In the sound field control method according to claim 1, some of the sound pressure / sound
pressure gradient sensors 41 to 4 n constitute a sound field control method commonly used in a
plurality of frequency bands. did. Here, Claim 4: The primary sound source unit 31 that
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reproduces the input sound signal X (t), and the secondary sound source unit 32 that reproduces
a signal in which the delay and frequency characteristics of the input sound signal X (t) are
changed The sound field control apparatus for controlling the sound field includes the frequency
dividing unit 10 for dividing the input sound signal X (t) supplied to the secondary sound source
unit 32 into N (N ≧ 2) frequency bands, A sound pressure / sound pressure inclination sensor
unit 40 comprising sound pressure / sound pressure inclination sensors 41 to 4 n which are
installed on the boundary of each frequency band and selected; A signal processing unit 20 that
generates a signal obtained by adding a delay and a change in frequency characteristic to the
input sound signal X (t) supplied from the frequency dividing unit 10 using an output signal of ~
4n and outputting the signal to the secondary sound source unit 32 To construct a sound field
control device.
[0008]
In the sound field control device according to claim 4, the signal processing unit includes the
filter units 211 to 21 n corresponding to the divided frequency bands, and the filter unit
corresponding to the highest frequency band. The input of 211 is connected to all the sound
pressure and pressure gradient sensors 41 to 4 n in the basic sensor arrangement, and the input
after the filter unit 212 for processing the next higher frequency band of this highest frequency
band is of the basic sensor arrangement The sound field control device is configured to be
selectively connected to a plurality of sound pressure / sound pressure gradient sensors in which
the distance between the sound sensor 4 from the inside is made coarser.
[0009]
According to the present invention, the frequency of the sound to be reproduced is divided into
arbitrary frequency bands, and the reproduction area is controlled using different numbers of
control points and sound pressure / sound pressure gradient sensors for the respective bands.
Here, the frequency of the sound to be reproduced is a frequency at which control is performed
in the area reproduction method according to the present invention. In this case, as the basic
sound pressure / sound pressure inclination sensor arrangement, the sound pressure / sound
pressure inclination sensor is arranged as the sound pressure / sound pressure inclination sensor
arrangement in which the sound pressure / sound pressure inclination sensor is most closely
arranged suitable for control of the highest frequency band. Among frequency bands other than
the highest frequency band, among sound pressure and pressure gradient sensors used for
control of the highest frequency band so that the distance between the sound pressure and
pressure pressure sensor corresponds to control of the frequency band to be controlled. And
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select a plurality of sound pressure and sound pressure inclination sensors. As described above,
the frequency band to be reproduced is divided into a plurality of frequency bands, and the
sound pressure and sound pressure gradient sensor having an interval suitable for controlling
the divided frequency band is used to perform reproduction. In addition to reproducing low
frequency sound with sufficient sound pressure in the area to be controlled, it is possible to
control to higher frequencies.
[0010]
The best mode for carrying out the invention will be described with reference to the embodiment
shown in FIG. FIG. 1 shows an area reproduction apparatus according to the present invention. In
FIG. 1, reference numeral 10 denotes a frequency division unit, which is a portion that divides an
input sound signal X (t) into signals of a plurality of frequency bands. A signal processing unit 20
is a unit that processes a signal for each of the divided frequency bands. Reference numeral 30
denotes a sound reproduction unit, which reproduces the input sound signal X (t) and the
processed signal as sound. A sound pressure / sound pressure gradient sensor unit 40 is a part
for observing the sound pressure and the sound pressure gradient of the reproduced sound.
[0011]
In the sound pressure / sound pressure inclination sensor unit 40, in general, the acousticelectric signal converter can be constituted by sound pressure / sound pressure inclination
sensors 41 to 4n such as a microphone. The sound pressure and sound pressure gradient sensors
41 to 4n are illustrated by one circle, but each is configured by arranging a pair of sound
pressure sensors close to each other, and any one of the pair is used. The output signal of one
sound pressure sensor is used as a sound pressure signal, and the sound inclination is obtained
from the difference between the output signals of the pair of sound pressure sensors 4. The
sound pressure and sound pressure gradient sensors 41 to 4 n are set and arranged at intervals
suitable for control of sound in the highest frequency band among the frequency bands divided
by the frequency dividing unit 10. Here, this is called a basic sensor arrangement. The input of
the filter unit 211 corresponding to the highest frequency band is a detection signal connected to
all the sound pressure and sound pressure inclination sensors 41 to 4 n in the basic sensor
arrangement. The input after the filter unit 212 that processes the next highest frequency band
to the highest frequency band is a plurality of sound pressure / sound pressure gradient sensors
in which the distance between the sound sensor 4 is made coarse from the basic sensor
arrangement. It is selected and connected. For example, as shown in the drawing, the sound
pressure and sound pressure inclination sensor interval can be selected by selecting the sound
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pressure and sound pressure inclination sensor 42, ..., 4n-2, 4n adjacent to every other basic
sensor arrangement. It can be rough. Thus, as the frequency band to be processed becomes
lower, a plurality of sound pressure / sound pressure gradient sensors disposed on the boundary
of the reproduction area are placed so that the sound pressure / sound pressure gradient sensor
interval becomes coarser. And connected to the input of the filter unit 21 for each frequency
band. This embodiment is a preferred embodiment in the case where there are many sound
pressure / sound pressure gradient sensors installed on the boundary of the reproduction area.
[0012]
Referring to FIG. 2, for simplicity, the case where the frequency band of the sound signal to be
input is divided into two will be described in the case where control is performed using seven
sound pressure and pressure gradient sensors 41 to 47. FIG. Here, in order to control the signal
of the high frequency band in the frequency band divided into two, all sound pressure and sound
pressure inclination sensors 41 to 47 are used. And, in order to control the signal of the low
frequency band, four sound pressure and pressure gradient sensors 41, 43, 45, 47 adjacent to
every other one of these sensors are used. Here, regarding the sound pressure and sound
pressure gradient sensors 41 to 47, by arranging the primary sound source 31 farther than the
secondary sound source 32, the causality of the filter of the signal processing unit 20 used for
the secondary sound source 32 is satisfied. Can. Alternatively, the causality of the filter can be
satisfied also by delaying the primary sound source 31 and outputting a signal.
[0013]
The filter unit 21 generates and outputs an output based on the detection output supplied from
the sound pressure / sound pressure gradient sensor 4 of each frequency band to be processed.
Specifically, the input sound signal X (t) input from the frequency dividing unit 10 is convoluted
with the filter coefficient Wi (t) of the filter unit 21 and the result yi (t) is the sound reproducing
unit. Output to 30. However, i shows the number of the divided frequency band. Here, the filter
coefficient Wi (t) is assumed to be the sound pressure 0 observed by the sound pressure / sound
pressure gradient sensors 41 to 4 n installed at the boundary of the area for the frequency band
and the sound pressure gradient to be 0. It is set. Here, the fact that the sound pressure is 0 and
the sound pressure gradient is 0 observed near the installation point of the sound pressure /
sound pressure gradient sensors 41 to 4 n is that there is no sound pressure here. Means. As an
example of the setting method, the sound output from the sound reproduction unit 30 is
observed by a pair of microphones constituting the sound pressure / sound pressure gradient
sensor 4 installed on the boundary of the reproduction area, and either one of the microphones
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There is a way to obtain the filter coefficient Wi (t + 1) to be used for the next output by using
the value of and the difference between the two as the sound pressure gradient. As an example,
the MEFX-LMS algorithm (Elliot et al.) Is used to update the filter coefficient Wi (t + 1). Amultiple
error LMS algorithm and its application to active control of sound and vibration, "IEEE Trans.
Acoust. Speech Signal Proc., Vol. ASSP-35 (10), pp. 1423-1434, 1987) can be used. Alternatively,
an acoustic transfer function between each of the secondary sound source units 32 of the
reproduction unit 30 and each of the sound pressure and sound pressure gradient sensors 4 of
the sound pressure and sound pressure gradient sensor unit 40 is obtained in advance. How to
determine the filter coefficient Wi (t) so that the sound pressure becomes 0 in each sound
pressure and sound pressure gradient sensor 4 by a point radiation type sound pressure control
device (refer to JP-A-61-212996) is there.
[0014]
The filter coefficients Wi (t) of the filter unit 21 for each frequency band are obtained
independently for each frequency band, since the number of sound pressure / sound pressure
gradient sensors 4 used for each filter unit is different. The input sound signal convoluted with
the filter coefficient Wi (t) for each frequency band whose frequency is divided is reproduced and
output from the secondary sound source unit 32, whereby the sound pressure / sound pressure
gradient sensors 41 to 4n are arrayed. Sound is reproduced with a sufficient sound pressure over
a wide frequency band within the reproduction area bounded by the position.
[0015]
The block diagram explaining an Example. FIG. 2 is a view for explaining an example of the
embodiment of FIG. 1;
Explanation of sign
[0016]
DESCRIPTION OF REFERENCE NUMERALS 10 frequency dividing unit 20 signal processing unit
211 to 21 n filter unit 30 sound reproducing unit 31 primary sound source 32 secondary sound
source 40 sound pressure / sound pressure inclination sensor unit 41 to 4 n sound pressure /
sound pressure inclination sensor
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