JP4125217B2 - 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 and an area-limited loudspeaker control for generating an audible sound only in an arbitrary area by changing a sound field characteristic of an indoor or other space. The present invention relates to a sound field control method used for the above and an apparatus for implementing this method.

When sound is radiated using a loudspeaker, although there is an influence of the directional 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 aiming at the construction of a limited area reproduction, that is, it is necessary to devise a speaker or other loudspeaker or a reproduction method when the sound is reproduced only in a specific area and the sound is not leaked outside. There is. One method is to apply a sound field control method (see Non-Patent Document 1) using the properties of Kirchhoff-Helmholtz integral equations.
The sound field control method using the properties of this Kirchhoff-Helmholtz integral equation is a closed space of the same shape in another place by controlling the sound pressure and the sound pressure gradient at the boundary surface of a certain closed space. It is a method that can reproduce the original sound field faithfully.

  This control method uses a horn or a geometric method in which a speaker unit is installed at the focal point of a reflector, or a narrow directivity characteristic in which directivity is formed by arranging a plurality of speakers in an array. Compared to the case where the sound field is reproduced only in a certain area using a speaker having the original sound field in a closed space with a small system, and the control of the reproduction area is compared with other methods. It has the advantage of being easy. However, in this control method, in order to control the sound field over a wide frequency band, it is necessary to install sensors for observing the sound pressure and the sound pressure gradient at many points. Since the number of sound sources also increases, the upper limit of the frequency band that can be controlled when operating as an actual system is limited.

In the case of performing control up to a higher frequency within the limited upper limit frequency band, it is effective to narrow the interval between the secondary sound source and the control point. However, in particular, by reducing the interval between the secondary sound sources, it is possible to control a relatively high frequency within a range not exceeding the upper limit frequency. The sound is muted in the vicinity and the playback area becomes extremely small. As a result, it is impossible to reproduce 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 if the upper limit frequency that can be controlled is increased. The present invention provides a sound field control method capable of increasing the upper limit frequency that can be controlled while reproducing low-frequency sound with a sufficient sound pressure in a reproduction area, and an apparatus that implements 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 input sound signal X (t) is delayed and changed in frequency characteristics. 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 the delay and frequency characteristics are divided for each of the divided frequency band signals. A sound field control method is generated in which a signal in which the sound is changed is generated, and the secondary sound source unit 32 is used to reproduce the sound for each of the generated signals.
And, in the sound field control method according to claim 2: in the sound source control method according to claim 1, based on the detection output signal from the sound pressure / sound pressure gradient sensor 43 set in advance at the boundary of the reproduction area, A sound field control method for controlling the delay and frequency characteristics of the supplied signal was constructed.

Further, in the sound field control method according to claim 3, in the sound field control method according to claim 1, sound having different numbers and distance intervals of the speakers 32 _n constituting the secondary sound source unit 32 for each divided arbitrary frequency band A field control method was constructed.
Furthermore, in the sound field control method according to claim 4, in the sound field control method according to claim 1, some of the speakers 32 _n constituting the secondary sound source unit 32 constitute a sound field control method commonly used in a plurality of frequency bands. did.
Claim 5: A primary sound source unit 31 for reproducing the input sound signal X (t) and a 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 device for controlling the sound field, the frequency dividing unit 10 divides the input sound signal X (t) supplied to the speaker 32 _n constituting the secondary sound source unit 32 into N (N ≧ 2) frequency bands. And a sound pressure / sound pressure gradient sensor unit 40 composed of a plurality of sound pressure / sound pressure gradient sensors 43 installed at the boundary of the reproduction area. A sound field control including a signal processing unit 20 that generates a signal obtained by adding a delay and a change in frequency characteristics to the input sound signal X (t) supplied from the frequency dividing unit 10 and outputs the signal to the secondary sound source unit 32. Configured the device.

Further, in the sound field control device according to claim 6, the signal processing unit 20 includes a filter unit 21 corresponding to each divided frequency band, and the output of the filter unit 21 ₁ having the highest frequency band. Are connected to all the speakers 32 _{1 to} 32 _n with the narrowest speaker interval, and the outputs of the filter units 21 _{2 to} 21 _n corresponding to the frequency band after the highest frequency band and the subsequent frequency band are The sound field control device is configured to connect to a plurality of selected speakers by sequentially increasing the speaker spacing.

  According to the present invention, by dividing the input sound signal into frequency bands and using the secondary sound source units selected and installed at different numbers and distance intervals, the input sound signal is processed and reproduced for each frequency band. In addition to area-limited reproduction up to a higher frequency, an input sound signal can be reproduced with sufficient sound pressure in the reproduction area even in a low frequency band.

The best mode for carrying out the invention will be described with reference to the embodiment of FIG.
FIG. 1 shows a sound field control 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 frequency band that is divided by the frequency dividing unit 10. Reference numeral 30 denotes an acoustic reproduction unit which reproduces the input sound signal X (t) and is processed by the signal processing unit 20 to reproduce the signal. A sound pressure / sound pressure gradient sensor unit 40 is a part for observing the sound pressure and the sound pressure gradient of the sound reproduced by the sound reproducing unit 30. The sound pressure / sound pressure gradient sensor unit 40 is generally configured by arranging sound pressure / sound pressure gradient sensors 43 formed of microphones as acoustic-electric converters on the boundary of the reproduction area. Here, the sound pressure / sound pressure gradient sensor 43 itself indicated by a circle is configured by arranging a pair of microphones close to each other. Here, either one of the pair of microphones of the sound pressure / sound pressure gradient sensor 43 is used as a sound pressure sensor, and a pair of adjacent microphones is used as a sound pressure gradient sensor to sound pressure between the two. Is the sound pressure gradient.

The sound reproducing unit 30 includes a primary sound source unit 31 and a secondary sound source unit 32. Specifically, these sound source units are configured by speakers. In the secondary sound source unit 32, each speaker is arranged and set at a speaker interval suitable for controlling a sound signal in the highest frequency band among the frequency bands divided by the frequency dividing unit 10. Here, the speaker arrangement at this interval is referred to as a basic speaker arrangement.
As shown in the figure, the output of the filter unit 21 ₁ having the highest frequency band is connected to all the speakers 32 _{1 to} 32 _n with the narrowest speaker interval in the basic speaker arrangement. The output of the filter unit 21 ₂ that processes the next highest frequency band after the highest frequency band is connected to a plurality of speakers selected by coarsening the speaker interval in the basic speaker arrangement. For example, as shown in the figure, by selecting _every other adjacent speaker 32 ₁ , 32 ₃ , 32 ₅ ... From the basic speaker arrangement, the speaker spacing can be halved. . In this way, as the frequency band to be processed becomes a lower frequency band, a plurality of speakers are selected with a coarser speaker interval, and the output of the filter unit 21 for each frequency band is connected. This embodiment is an example suitable for application when there is no room for installing a large number of sound pressure / sound pressure gradient sensors on the reproduction area. Instead, a large number of speakers are arranged closely.

Referring to FIG. 2, this shows a case where the sound field is controlled using a secondary sound source 32 composed of _seven speakers 32 _{1 to} 32 ₇ when the frequency band is divided into two for simplicity. Here, all the _seven speakers 32 _{1 to} 32 ₇ constituting the secondary sound source 32 are used to control the signal in the higher high frequency band of the divided frequency bands. Then, in order to control the lower signal in the low frequency band, _every other four speakers 32 adjacent to each other, which are shown in white among the _seven speakers 32 _{1 to} 32 ₇ constituting the secondary sound source 32. ₁ , 32 ₃ , 32 ₅ , and 32 ₇ are used. Here, regarding the sound pressure / sound pressure gradient sensor unit 40, the causality of the filter of the signal processing unit 20 used for the secondary sound source 32 can be satisfied by disposing the primary sound source 31 farther than the secondary sound source 32. it can. Alternatively, the causality of the filter can be satisfied even if the primary sound source 31 is output with a delay. Here, satisfying the causality means that there is no response in the filter before the pulse is input at time 0.

The sound pressure and sound pressure gradient signal detected and output by the sound pressure / sound pressure gradient sensor 43 are input to the filter units 21 _{1 to} 21 _n constituting the signal processing unit 20. Specifically, the input sound signal X (t) supplied from the frequency division unit 10 is subjected to a convolution operation process with the filter coefficients W _i (t) of the filter units 21 _{1 to} 21 _n , and as a result, A certain y _i (t) is output to the sound reproducing unit 30. Here, i indicates the number of the divided frequency band. Here, the filter coefficient W _i (t) is set so that the sound pressure observed by the sound pressure / sound pressure gradient sensor 43 installed at the boundary of the area to be reproduced is 0 and the sound pressure gradient is 0. Is done. Here, the sound pressure near the installation point of the sound pressure / sound pressure gradient sensor 43 being 0 and the sound pressure gradient being 0 mean that there is no sound in the vicinity. As an example of this setting method, the sound output from the sound reproducing unit 30 is observed by a sound pressure / sound pressure gradient sensor 43 installed on the boundary of the reproduction area, and a filter used for the next output using the observed value. There is a method for obtaining the coefficient W _i (t + 1). The filter coefficient W _i (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 secondary sound source unit 32 of the sound reproduction unit 30 and each sound pressure / sound pressure gradient sensor of the sound pressure / sound pressure gradient sensor unit 40 is obtained in advance, and from this transfer function, for example, There is also a method of obtaining the filter coefficient W _i (t) so that the sound pressure becomes zero in each sound pressure / sound pressure gradient sensor 43 by a multi-point radiation type sound pressure control device (Japanese Patent Laid-Open No. Sho 61-212996).

The filter coefficient W _i (t) of the filter unit 21 for each frequency band is obtained independently for each frequency band because the number of secondary sound source units 32 used for each frequency band is different.
The signal divided and convolved with W _i (t) for each frequency band is output from a predetermined secondary sound source unit 32, so that the position where the sound pressure / sound pressure gradient sensor 43 is arranged is bounded. Are reproduced with sufficient sound pressure over a wide frequency band.

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 tone generator 32 secondary source unit 32 ₁ to 32 _n speakers 40 sound pressure, sound pressure gradient sensor unit 43 the sound pressure, sound pressure gradient Sensor

Claims (6)

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 input sound signal is delayed and changed in frequency characteristics,
The input sound signal supplied to the secondary sound source unit is divided into N (N ≧ 2) frequency bands, and a signal in which the delay and frequency characteristics are changed is generated for each of the divided frequency bands. A sound field control method, wherein a secondary sound source unit is used for each signal to perform loud sound reproduction. In the sound field control method according to claim 1,
A sound field control method for controlling delay and frequency characteristics of a signal supplied to a secondary sound source unit based on a detection output signal from a sound pressure / sound pressure gradient sensor installed in advance at a boundary of a reproduction area . In the sound field control method according to claim 1,
A sound field control method, characterized in that the number and distance interval of speakers constituting the secondary sound source section are made different for each divided arbitrary frequency band. In the sound field control method according to claim 1,
A sound field control method, wherein some of the speakers constituting the secondary sound source unit are used in common for 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 a speaker constituting the secondary sound source unit into N (N ≧ 2) frequency bands;
A sound pressure / sound pressure gradient sensor unit comprising a plurality of sound pressure / sound pressure gradient sensors installed at the boundary of the reproduction area,
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 division unit using a detection 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 comprising: In the sound field control device according to claim 5,
The signal processing unit includes a filter unit corresponding to each divided frequency band,
The output of the filter part of the highest frequency band is connected to all speakers with the speaker interval being the tightest,
The output of the filter unit corresponding to the frequency band after the highest frequency band after this highest frequency band is connected to a plurality of speakers selected by sequentially increasing the speaker spacing. Control device.

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