JP4125216B2 - Sound field control method and apparatus for implementing the method - Google Patents

Description

  The present invention relates to a sound field control method and an apparatus for performing the method, and relates to an area-limited loudspeaker for generating an audible sound only in an arbitrary area by changing a sound field characteristic of a space such as an indoor area, active noise control, and the like. The present invention relates to a sound field control method for use in sound field control and an apparatus for implementing this method.

  When sound is radiated using a loudspeaker, although there is an influence of the directivity characteristics of the speaker used for sound reproduction, the sound is radiated from the speaker in almost all directions and can be heard. Therefore, when the sound is reproduced only in a specific area and the sound is not leaked to the outside, that is, when aiming at the construction of the area limited reproduction, a loudspeaker such as a speaker or a reproducing device is used. It is necessary to devise correspondingly. As a method for realizing this, a method of applying a sound field control method using the property of the Kirchhoff-Helmholtz integral equation can be considered (see Non-Patent Document 1).

The sound field control method using the property of this Kirchhoff-Helmholtz integral equation is the same shape closed in another place by controlling the sound pressure and the sound pressure gradient on the boundary surface of an arbitrary closed space. The original sound field in the space can be faithfully reproduced.
This control method uses a horn, a geometric method of installing a speaker unit at the focal point of the reflector, or a narrow directivity characteristic of forming directivity by arranging a plurality of speakers in an array. Compared to the case where a sound field is reproduced only within a certain area using a speaker having the same, it can be realized with a small-scale system and the control of the reproduction area is easier than other methods. There are advantages. However, in this control method, in order to control the sound field over a wide frequency band, it is necessary to install many sensors for observing the sound pressure and the sound pressure gradient, and the number of secondary sound sources is proportional to the number of sensors. Therefore, when the system is actually operated, the upper limit of the controllable frequency band is limited.

In order to perform control up to a higher frequency within the 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 interval between the secondary sound sources is narrowed, it can be controlled for a relatively high frequency in a range not exceeding the upper limit frequency, but the sound of a relatively low frequency is muted in the vicinity of the primary sound source, The playback area becomes extremely small. As a result, it is not possible to reproduce sound with a sufficient sound pressure in the desired reproduction area.
Ise, Phonetic Society Journal Vol.53.No.9, pp.706-713, 1977.

As described above, the area reproduction method using the property of the Kirchhoff-Helmholtz integral equation cannot reproduce low-frequency sound with sufficient sound pressure if the upper limit frequency that can be controlled is increased.
The present invention provides a sound field control method capable of reproducing a low-frequency sound with a sufficient sound pressure in a reproduction area and increasing the upper limit frequency that can be controlled, and an apparatus for carrying out this method. is there.

A first sound source unit 31 that reproduces an input sound signal X (t) and a 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. 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 each frequency band is installed on the boundary of the reproduction area. By using the output signals of the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n selected for each signal, a signal for each frequency band in which the delay and frequency characteristics of the input sound signal X (t) are changed is generated. Thus, a sound field control method for reproducing the sound by using the secondary sound source unit 32 is configured.

According to a second aspect of the present invention, in the sound field control method according to the _{first aspect} , the number of the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n and the distance interval are different for each of the divided arbitrary frequency bands. A field control method was constructed.
Further, in the sound field control method according to claim 3, some of the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n are commonly used in a plurality of frequency bands. Configured.
In this case, the primary sound source unit 31 that reproduces the input sound signal X (t) and the secondary sound source unit 32 that reproduces the signal in which the delay and frequency characteristics of the input sound signal X (t) are changed. The sound field control device for controlling the sound field includes a frequency division unit 10 that divides the input sound signal X (t) supplied to the secondary sound source unit 32 into N (N ≧ 2) frequency bands, and includes a reproduction area. Is provided with a sound pressure / sound pressure gradient sensor unit 40 composed of sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n selected for each signal in each frequency band. Using the output signals of the sensors 4 ₁ to 4 _n, the input sound signal X (t) supplied from the frequency division unit 10 is generated with a signal to which a delay and a change in frequency characteristics are added and output to the secondary sound source unit 32. A sound field control device including the signal processing unit 20 was configured.

And, in the sound field control device according to claim 5, the signal processing unit has filter units 21 _{1 to} 21 _n corresponding to the divided frequency bands, and corresponds to the highest frequency band. The input of the filter unit 21 ₁ is connected to all the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n in the basic sensor arrangement, and the filter unit 21 _{2 and the} subsequent ones that process the next highest frequency band after this highest frequency band. The input is configured as a sound field control device that is selectively connected to a plurality of sound pressure / sound pressure gradient sensors in which the interval between the sound sensors 4 is coarser than the basic sensor arrangement.

  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 a different number of control points and sound pressure / sound pressure gradient sensors for each band. Here, the frequency of the sound to be reproduced is a frequency to be controlled by the area reproduction method according to the present invention. At this time, as the basic sound pressure / sound pressure gradient sensor arrangement, the sound pressure / sound pressure gradient sensor arrangement is a sound pressure / sound pressure gradient sensor arrangement in which the sound pressure / sound pressure gradient sensors are arranged most densely suitable for control of the highest frequency band. For frequency bands other than the highest frequency band, the sound pressure / sound pressure gradient sensor used for the highest frequency band control is used so that the interval between the sound pressure / sound pressure gradient sensors corresponds to the control of the frequency band to be controlled. A plurality of sound pressure / sound pressure gradient sensors are selected. In this way, the frequency band to be reproduced is divided into a plurality of frequency bands, and reproduction is performed by using a sound pressure / sound pressure gradient sensor having an interval suitable for controlling the divided frequency bands. The low frequency sound is reproduced with sufficient sound pressure in the power area, and control up to a higher frequency can be achieved.

The best mode for carrying out the invention will be described with reference to the embodiment of FIG.
FIG. 1 shows an area reproducing apparatus according to the present invention. In FIG. 1, reference numeral 10 denotes a frequency dividing unit, which is a part that divides an input sound signal X (t) into signals of a plurality of frequency bands. Reference numeral 20 denotes a signal processing unit, which is a part that processes a signal for each divided frequency band. An acoustic reproduction unit 30 reproduces the input sound signal X (t) and reproduces the processed signal as sound. Reference numeral 40 denotes a sound pressure / sound pressure gradient sensor unit, which is a part for observing the sound pressure and the sound pressure gradient of the reproduced sound.

In general, the sound pressure / sound pressure gradient sensor unit 40 can be constituted by sound pressure / sound pressure gradient sensors 4 ₁ to 4 _{n such as} microphones. The sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n are illustrated by one circle, but each is constituted by arranging a pair of sound pressure sensors close to each other. The output signal of any one of the sound pressure sensors is used as a sound pressure signal, and the sound gradient is obtained from the difference between the output signals of the pair of sound pressure sensors 4. The sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n are set and arranged at intervals suitable for sound control 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 21 ₁ corresponding to the highest frequency band is a detection signal connected to all the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n in the basic sensor arrangement. The input after the filter unit 21 ₂ that processes the next highest frequency band after the highest frequency band is a plurality of sound pressure / sound pressure gradient sensors in which the interval between the sound sensors 4 is coarser than the basic sensor arrangement. Select to connect. For example, as shown in the figure, by selecting the sound pressure / sound pressure gradient sensors 4 ₂ ,..., 4 _n−2 , 4 _n adjacent to each other from the basic sensor arrangement, the sound pressure / sound pressure gradients are selected. The sensor interval can be made coarse. In this way, as the frequency band to be processed becomes lower, a plurality of sound pressure / sound pressure gradient sensors arranged on the boundary of the reproduction area are arranged 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 when there is room for installing a large number of sound pressure / sound pressure gradient sensors on the boundary of the reproduction area.

Referring to FIG. 2, for the sake of simplicity, the case where the frequency band of the input sound signal is divided into two is controlled by using _seven sound pressure / sound pressure gradient sensors 4 ₁ to 4 _7. It is a figure explaining. Here, all the sound pressure / sound pressure gradient sensors 4 ₁ to 4 ₇ are used to control signals in the high frequency band of the two divided frequency bands. And in order to control the signal of a low frequency band, four adjacent sound pressure / sound pressure gradient sensors 4 ₁ , 4 ₃ , 4 ₅ , 4 ₇ are used. . Here, regarding the sound pressure / sound pressure gradient sensors 4 ₁ to 4 ₇ , the causality of the filter of the signal processing unit 20 used for the secondary sound source 32 is increased by disposing the primary sound source 31 farther than the secondary sound source 32. Can be satisfied. Alternatively, the causality of the filter can be satisfied even if the primary sound source 31 is output with a delay.

The filter unit 21 generates and outputs the output based on the detection output supplied from the sound pressure / sound pressure gradient sensor 4 in each frequency band to be processed. Specifically, the input sound signal X (t) input from the frequency division unit 10 is convolved with the filter coefficient Wi (t) of the filter unit 21, and the result yi (t) is the sound reproduction unit. 30 is output. Here, i indicates the number of the divided frequency band. Here, the filter coefficient Wi (t) is set to 0 as the sound pressure observed by the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n installed at the boundary of the area for the frequency band, and the sound pressure gradient is set to 0. It is set as. Here, the sound pressure observed in the vicinity of the installation point of the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n and the sound pressure gradient of 0 indicate that there is no sound pressure. It means that there is. As an example of this setting method, the sound output from the sound reproducing 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 one of the microphones is observed. There is a method of obtaining the filter coefficient Wi (t + 1) used for the next output using the value of and the difference between them as the sound pressure gradient. The filter coefficient Wi (t + 1) is updated by, for example, the MEFX-LMS algorithm (Elliot et al. “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 reproducing unit 30 and each of the sound pressure / sound pressure gradient sensors 4 of the sound pressure / sound pressure gradient sensor unit 40 is obtained in advance, and a large number of examples are obtained from the transfer functions. It is also possible to obtain the filter coefficient Wi (t) so that the sound pressure becomes zero in each sound pressure / sound pressure gradient sensor 4 by a point radiation type sound pressure control device (see Japanese Patent Application Laid-Open No. Sho 61-212996). is there.

The filter coefficient Wi (t) of the filter unit 21 for each frequency band is obtained independently for each frequency band because the number of sound pressure / sound pressure gradient sensors 4 used for each filter unit is different.
The input sound signal convolved with the filter coefficient Wi (t) for each frequency band divided by frequency is reproduced and output from the secondary sound source unit 32, so that the sound pressure / sound pressure gradient sensors 4 ₁ to 4 _n Sound is reproduced with a sufficient sound pressure over a wide frequency band in a reproduction area with the arranged position as a boundary.

The block diagram explaining an Example. The figure explaining an example of the Example of FIG.

Explanation of symbols

10 frequency division unit 20 signal processing unit 21 ₁ through 21 _n filter unit 30 the sound reproducing unit 31 primary sound source 32 secondary source 40 sound pressure, sound pressure gradient sensor unit 4 ₁ to 4 _n sound pressure, sound pressure gradient sensor

Claims (5)

In a sound field control method for controlling a sound field by a primary sound source unit that reproduces an input sound signal and a secondary sound source unit that reproduces a signal in which the delay and frequency characteristics of the input sound signal are changed,
The input sound signal supplied to the secondary sound source section is divided into N frequency bands (N ≧ 2), and the sound pressure / sound pressure gradient selected for each signal in each frequency band installed on the boundary of the playback area A sound field control method characterized by generating a signal for each frequency band in which a delay and a frequency characteristic of an input sound signal are changed using an output signal of a sensor and reproducing the signal using a secondary sound source unit . In the sound field control method according to claim 1,
A sound field control method, characterized in that the number of sound pressure / sound pressure gradient sensors and the distance interval are different for each divided arbitrary frequency band. In the sound field control method according to claim 1,
A sound field control method characterized in that some of the sound pressure / sound pressure gradient sensors are commonly used in a plurality of frequency bands. In a sound field control device that controls a sound field by a primary sound source unit that reproduces an input sound signal and a secondary sound source unit that reproduces a signal in which the delay and frequency characteristics of the input sound signal are changed,
A frequency division unit for dividing an input sound signal supplied to the secondary sound source unit into N (N ≧ 2) frequency bands;
A sound pressure / sound pressure gradient sensor unit comprising a sound pressure / sound pressure gradient sensor installed on the boundary of the reproduction area and selected for each signal in each frequency band;
A signal processing unit that generates a signal in which a delay and a change in frequency characteristics are added to an input sound signal supplied from a frequency dividing unit using an output signal of a sound pressure / sound pressure gradient sensor and outputs the signal to a secondary sound source unit A sound field control device. In the sound field control device according to claim 4,
The signal processing unit has a filter unit corresponding to each divided frequency band,
The input of the filter unit corresponding to the highest frequency band is connected to all the sound pressure / sound pressure gradient sensors in the basic sensor arrangement, and the input after the filter unit that processes the next highest frequency band after this highest frequency band is A sound field control device, wherein the sound field control device is selectively connected to a plurality of sound pressure / sound pressure gradient sensors in which the interval between the sound pressure / sound pressure gradient sensors is coarser in the basic sensor arrangement.

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