JP2003288079A - Active noise suppressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the noise in an aperture. <P>SOLUTION: The active noise suppressor is provided with a reference signal detecting section 3 which detects the signal having a correlation with the noise advancing through the aperture 1 from a noise source 2 disposed on the outer side of the aperture, a speaker 4 which is installed at the circumference of the aperture, a microphone 5 which detects at least either of the sound pressure and acoustic intensity advancing from the aperture installed on the circumference of the aperture, and a control circuit 6 which produces the sound of the anti-phase from the signal detected by the detecting section 3 from the speaker so as to minimize the signal detected by the microphone. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise canceling device for reducing sound entering through an opening, and more particularly to an active noise canceling device suitable for installation in a sound insulation wall or the like.

[0002]

2. Description of the Related Art In a place facing a road or a railroad with a large amount of traffic, the noise caused by the running noise of automobiles and railcars is great, and it becomes a serious problem especially in the residential areas at night and public facilities such as schools and hospitals. There is. A sound insulation wall is effective as a technique for reducing such noise, but it is difficult to obtain a sufficient effect because low-frequency sound of 500 Hz or less is transmitted by diffracting through the sound insulation wall. In addition, the sound insulation effect cannot be obtained in the middle and high floor buildings located higher than the sound insulation wall. Further, an opening such as a doorway or a ventilation opening may be provided in a part of the sound insulation wall, and noise propagates through the opening, resulting in a problem that a sufficient soundproof effect cannot be obtained.

As a measure against the building which receives the noise, there is a measure such as providing trees and sound insulating walls in the vicinity of the structure side. Therefore, the soundproof effect cannot be obtained. In addition, although measures such as double glazing have been taken for the windows of buildings, they have the drawback of not providing sufficient ventilation and ventilation.

[0004]

Generally, the purpose of installing the opening is to secure a passage for carrying people or objects or to provide a heat source outside the opening, and to exhaust heat and ventilate the air to cool it. is there. Therefore, it is desirable to place no obstacles in front of the opening as much as possible. Therefore, the most general and reliable sound insulation and noise absorption measures cannot be used in this case. Therefore, if the opening has a length in the propagation direction to some extent like a duct, ordinary passive countermeasures such as inserting a slit or changing the shape of the duct can be expected, but with this proposal. The defined opening is like a door frame (doors and windows are open), the length in the propagation direction is shorter than the size of the opening, and the duct effect cannot be expected. Not applicable. Especially, the sound source of the opening noise is not always
Since the sound source cannot be specified and, as mentioned above, no passive countermeasures can be taken, originally high and low frequency sounds also remain as noise.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an active silencer capable of reducing the noise at the opening.

[0006]

An active noise suppressor according to a first aspect of the present invention is a reference signal for detecting a signal correlated with noise entering through an opening from a noise source provided outside the opening. A detection unit, a speaker installed around the opening, a microphone installed around the opening for detecting at least one of sound pressure and sound intensity entering from the opening, and the microphone. And a control circuit for causing the speaker to emit a sound having a phase opposite to that of the signal detected by the reference signal detection unit so that the detected signal is minimized.

With such a structure, it is possible to effectively reduce the noise entering the opening with a relatively simple control structure.

It should be noted that the speaker has a linearly elongated emission surface, and the emitted sound waves have the same phase characteristics in the line direction (longitudinal direction of the speaker), and are upward and downward with respect to the sound wave emission direction. It may be configured to have a sharp directional characteristic in the horizontal direction and the horizontal direction.

With such a structure, it is possible to effectively reduce the noise entering the opening with a relatively simple control structure.

The microphones each have a first microphone and a second microphone for detecting a sound pressure, and the control circuit minimizes the sum of squares of the sound pressures detected by the two microphones. Is provided with an adaptive control filter that obtains a filter coefficient using only one filter, and a fixed control filter that holds the filter coefficient obtained by this adaptive control filter. The distance from the sound source to the first microphone is d1, the distance from the sound source to the second microphone is r
1, the distance from the speaker to the first microphone is d
2. The distance from the speaker to the second microphone is r
If it is set to 2, it may be configured to minimize a point separated by (d1 + r1) / 2 from the sound source and (d2 + r2) / 2 from the speaker.

With such a structure, it is possible to effectively reduce the noise coming into the opening with a relatively simple control structure.

The speaker is provided on one side of the opening, and a sound absorbing mechanism that absorbs sound emitted from the speaker is installed on the opposite side of the opening opposite to the one side, and the speaker emits the sound. As for the directional characteristic of the control sound wave, when the distance between one side where the speaker is installed and the side where the sound absorbing mechanism is provided is W and the width of the sound absorbing mechanism is d, an angle d / ( 2 W) radians or more may be configured to be 3 dB or less.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) An active silencer according to a first embodiment of the present invention will be described with reference to FIGS. 1 (a) and 1 (b). FIG. 1A is a block diagram showing the configuration of the active silencer of the first embodiment, and FIG. 1B is the active silencer of the first embodiment arranged in two rooms connected through an opening. It is a top view which shows the structure of a silencer. As shown in FIG. 1B, there is a noise source 2 outside the opening 1, and noise that enters through the opening 1 is targeted for reduction. The active silencer of this embodiment includes a reference signal detector 3, a speaker 4 installed around the opening 1, a microphone 5 installed around the opening, and a control circuit 6.

The reference signal detecting section 3 detects a signal having a correlation with the noise source 2 entering the opening 1. Even if the noise source 2 cannot be characterized, if the reference signal detection unit 3 is installed on the sound source side near the opening 1, a signal having a correlation with noise entering the opening 1 can be detected. Further, the sound pressure or sound intensity entering from the opening 1 is detected by the microphone 5 installed on the front side around the opening 1. Based on the signal detected by the reference signal detection unit 3, the control circuit 6 performs the feedforward control so that the sound pressure detected by the microphone 5 or the sound intensity is minimized, and the control circuit 6 controls the surroundings of the opening 1. The installed speaker 4 emits a sound having a phase opposite to the detection signal of the reference signal detection unit 3. Thereby, the sound that enters through the opening 1 can be reduced.

Although the noise source 2 is arranged in one of the two rooms connected by the opening 1 in the present embodiment, it is arranged outside the building or the room connected by the opening 1. May be.

(Second Embodiment) An active silencer according to a second embodiment of the present invention will be described with reference to FIGS. 2 to 11.

As shown in FIG. 2, the size of the opening (width a
(m) × height b (m)) is width 1 m to 1.3 m, height 1.
It is assumed that a person can go in and out from 8m to 2m. Then, if the noise source 2 is more than 3 m away from the opening,
As shown in (1), when the target sound has a frequency up to about 500 Hz, the height h is about 1.5 m within the half-wavelength within the opening, which can be regarded as the in-phase region. Regarding the lateral direction, the widths of 1 m to 1.3 m are also substantially in phase.

Therefore, as shown in FIG. 4 (a), the speaker 4 (hereinafter referred to as a line sound source speaker) arranged in a line having the same phase in the longitudinal direction (Z axis) has a sound source characteristic of the opening. It is installed upright in the direction shown in Fig. 5 (a) up to the height of the same phase region, and by causing antiphase radiation toward the center of the opening, sound interference is caused in this area to enter from the opening. It is possible to reduce noise. Also,
As shown in FIG. 4 (b), the line sound source speaker 4 has another feature that has a sharp attenuation (directivity angle of several degrees) in the vertical direction of the Z axis from the radiation surface, and thus has a height of 1.5 m. Area where the above phases are inverted (“−” display surface in FIG. 5B)
With regard to, the sound propagation characteristics are deteriorated, so that the interference is weakened and the sound is not amplified.

On the other hand, in the lateral direction, the width is from 1 m to 1.
Similarly, at 3 m, since the phases are almost the same, the speaker 4
When the sound emitted from the speaker is oriented in the direction shown in FIG. 6, the sound emitted from the speaker 4 is phase-reversed above the opening (“−” display surface in FIG. 5B) due to the wavelength. Therefore, as a result, the sound pressure may increase in the upper part, but if the sound pressure is reduced in the region up to the height of the opening of about 1.5 m, even if the upper part is increased, the sound deadening effect is sufficiently realized. it can.

To confirm the above, FIG. 7 (a)
A simple test was performed using the experimental apparatus shown in. FIG. 7B shows a plan view in which this experimental device is arranged in two rooms connected through an opening.

The simulated sound source uses a cone type speaker 7,
It was arranged at L = 1.3 m from the center of the opening. As the speaker 8, a linear sound source speaker 4 (having a length corresponding to the width of the opening) having the same phase characteristic in the longitudinal direction was used, and the speaker 8 was installed on the floor with the radiation surface facing upward. A sound of 180 Hz was generated from the oscillator 9 and the amplitude / phase adjuster 10 was used to minimize the sound pressure at the microphone 11 installed 1 m before the center of the opening 1. Sound source position L and opening size (width 1.2m x height 2
From the relationship of m), the phase of the sound source entering the opening 1 is almost the same phase up to the height of the opening of about 1.5 m. On the other hand, the control line sound source speaker 8 has a height of about 0.9 m (for a half wavelength).
Up to the same phase. Therefore, the phases of the two are shifted by about 0.6 m in height, and in the calculation, the upper part does not decrease.
Certainly, in the area A part (parallel to the opening) that is about 20 cm into the room side from the opening as shown in FIG. 8, the sound pressure distribution reduction amount before and after the control is as shown in FIG. 9, and the height is 1.4 m. Although it did not decrease from the vicinity to the upper part, the maximum noise reduction amount of 10 dB or more was obtained up to a height of about 1.4 m, and the noise reduction amount was reduced to a good audibility. Locally, there was also a portion where it was reduced by nearly 15 dB.

Further, as shown in FIG. 10 (a), a measurement point shown in FIG. 11 (a) in a region B (height 1 m) further entering the room side by 50 cm or more from the linear sound source speaker 8 installed in the opening. The sound pressure distribution (discrete 12-point measurement) at the position is
The results are shown in FIGS. 11 (b) and 11 (c). Figure 1
1 (b) and (c) are control OFs by the line sound source speaker 8.
It is a figure which shows each sound pressure level (dB) at the time of F and ON. The sound pressure level, which was 61 dB to 66 dB, is 47 dB.
It was possible to confirm a sufficient reduction effect without decreasing the sound to 58 dB and increasing the sound.

Therefore, as described above, the size of the opening 1 is 1 m to 1.3 m in width and 1.8 m to 2 in height.
If it is limited to about m, from the relationship between the position of the sound source and the size of the opening, it is possible to reduce to about 500 Hz with one line sound source speaker.

(Third Embodiment) Next, an active silencer according to a third embodiment of the present invention will be described with reference to FIG. FIG. 12 is a block diagram showing the configuration of part of the active silencer of this embodiment. The active silencer of this embodiment is configured such that, instead of the microphone 5, two microphones 12 and 13 are used to detect sound pressures in the active silencer of the first embodiment. The speaker 4
Use only one. Therefore, the control circuit 6 holds one adaptive control filter 14 which is operated so as to minimize the sum of squares of the sound pressure detected by the two microphones 12 and 13, and the filter coefficient calculated by this filter 14. And one fixed control filter 15.

For example, consider a case where the sound source 2, the speaker 4, and the microphones 12 and 13 are installed as shown in FIG. For simplicity, there is no attenuation due to distance. At this time, the error signals e1 and e2 detected by the microphones 12 and 13 are as shown below.

[Equation 1]

Here, d1 and r1 indicate the distances from the sound source 2 to the microphones 12 and 13, respectively, and d2 and r2 are
The distances from the speaker 4 to the microphones 12 and 13 are shown respectively, and θ shows the phase of the speaker 4 with respect to the sound source 2.

At this time, the two microphones 1 shown in FIG.
Assuming that the sum of squares of the sound pressure detected in 2 and 13 is the evaluation function J, this is minimized by only one filter,
This value is the minimum in the case of the phase shown by the following equation. When the sound pressure square sum is minimized by the two filters, the following equation is not obtained, and as a result, points other than the point where the microphone is installed cannot be minimized.

[Equation 2]

Therefore, this is from the sound source 2 to (d1 + r
1) / 2, from the control speaker 4 to (d2 + r2) / 2
At a distance, that is, the position of the two microphones 12 and 13 above
It means that the points other than the positions can be minimized. Because
For example, from sound source 2 to (d1 + r1) / 2, control speaker 4
The error signal at a point (d2 + r2) / 2 away from e_p
Then, this is the error signal e transmitted from the sound source._a, Additional sound
Error signal e transmitted from the source _bIs expressed as the sum of and
Assuming that the amplitude attenuation term is ignored, the sound pressure is
It becomes 0.

[Equation 3]

This sound pressure 0 portion is (d1 + r) from the sound source.
1) / 2, since it is a locus of points that are (d2 + r2) / 2 away from the control speaker, except for certain cases (contact points),
It becomes a circle (tangential line between spheres with these as radii).

Since the speaker 4 and the sound source 2 used in this embodiment actually have distance attenuation, the sound pressure is 0.
When the sound pressures from the sound source 2 and the speaker 4 at the (error signal e _p ) point are P1 and P2, they are expressed by the following equation.

[Equation 4]

In other words, the microphone 12 is installed at a distance d1 from the sound source 2 and d2 from the control speaker 4, and the microphone 13 is installed at a distance r1 from the sound source and r2 from the control speaker. When control is performed to minimize the sum of squares of pressure, the speaker 4 outputs an additional sound source that is (d2 + r2) / (d1 + r1) times the volume velocity of the sound source, and as a result, as shown in FIG. d1 + L
1) / 2, a new sound pressure minimum point is created at a point 20 distant from the control speaker 4 by (d2 + L2) / 2.

In order to confirm this principle, the sound source 2, the speaker (additional sound source) 4 and the two microphones 12 and 13 are installed in the free space of the three-dimensional space, and the XY plane (Z =
The results of calculating the sound pressure distribution in 0) are shown in FIGS.
Shown in. FIG. 15 is a perspective view of sound pressure, and FIG. 16 is a plan view showing the sound pressure shown in FIG. 15 by isobars. FIG. 17 is a perspective view of sound pressure, and FIG. 18 is a plan view showing the sound pressure shown in FIG. 17 by isobars. Note that FIGS. 15 and 16 and FIGS. 17 and 18 show calculation results when the relative positions of the sound source 2 and the speaker 4 are changed. From sound source 2 (d1 + r1) /
2. It can be seen that the sound pressure becomes minimum at the point 20 (d2 + r2) / 2 away from the control speaker 4, and the sound pressure is reduced to the position of the two microphones 12 and 13 or more.

Therefore, the active silencer of this embodiment has the configuration shown in FIG. FIG. 19A is a block diagram showing the configuration of the active silencer of this embodiment.
(B) is a top view when the active silencer of this embodiment is arranged in two rooms connected via an opening. Assuming that a person enters and leaves the opening 1,
In the embodiment, the microphone 5 is an obstacle to entry and exit, and FIG.
The microphone 5 cannot be installed at the ideal position in front of the opening shown by. Therefore, as in this embodiment,
By installing the two microphones 12 and 13 on both sides of the opening, it is possible to arbitrarily create a sound pressure minimum point in the space 20 of the opening 1 and to reduce the opening noise from a practical aspect. It can be effectively reduced in consideration of the above.

(Fourth Embodiment) Next, an active silencer according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 20A shows the configuration of the active silencer of this embodiment.
Shown in. FIG. 20B shows the active silencer of the present embodiment,
It is a top view when it is arranged in two rooms connected via an opening.

In the second embodiment, one of the factors that reduce the sound deadening effect is that the sound wave from the speaker 8 leaks out of the opening or is reflected / scattered on the partition wall or the like. Therefore, in the active silencer of this embodiment shown in FIG. 20, in the first embodiment, the line sound source speaker 4 shown in the second embodiment has the floor surface of the opening 1 (width a, height b, depth c). The sound absorbing material 21 is provided on the ceiling surface opposite to the above. The length of the linear sound source speaker 4 in the longitudinal direction is the opening 1
Is almost equal to the width a of the sound absorbing material 21 and the sound absorbing material 21 is provided in the full depth of the opening 1.

The acoustic emission characteristics of the line sound source speaker 4 are radiated in the same phase in the longitudinal direction, and the directional characteristics of the opening 1 in the depth direction are as shown in FIG.
At (2b) and above, the sound pressure is set to decrease by 3 dB or more as compared with the sound pressure in the central direction.

Since the directional characteristics of the line sound source speaker 4 are set as described above, the sound wave radiated from the line sound source speaker 4 hardly leaks to the outside of the opening, and the noise that efficiently enters the opening 1 is reduced. The sound absorbing material 21 also absorbs the sound waves from the linear sound source speaker 4 that reach the ceiling and interfere with the sound waves, so that the reflection / scattering is small.

In FIG. 20, the line sound source speaker 4 and the sound absorbing material 2 are shown.
Although 1 is provided on the floor and the ceiling, respectively, the same effect can be obtained by providing the line sound source speaker 4 on the ceiling and the sound absorbing material 21 on the floor.

The line sound source speaker 4 may be provided on the side wall of the opening 1 and the sound absorbing material 21 may be provided on the opposite side wall. In that case, the directional characteristic of the opening 1 of the line sound source speaker 4 in the depth direction is given by the following formula, where d is the width of the sound absorbing material 21 in the depth direction.
When the angle is d / (2a) or more, it is 3d compared to the sound pressure in the central direction.
It is set so as to decrease by B or more. In short, it is important to design the directional characteristics of the line sound source speaker 4 so that sound is strongly radiated only into the opening 1.

Needless to say, when the ceiling of the opening 1 is a through-hole, the directivity of the line sound source speaker 4 can be designed by regarding the through-hole as a sound absorbing section.

[0042]

As described above, according to the present invention, an effective silencing effect can be achieved without installing a structure that obstructs ventilation or passage in the opening.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an active silencer according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an active silencer according to a second embodiment.

FIG. 3 is an explanatory diagram regarding a noise phase distribution of the second embodiment.

FIG. 4 is an explanatory diagram of a speaker used in the second embodiment.

FIG. 5 is an explanatory diagram regarding an installation situation of a speaker used in the second embodiment.

FIG. 6 is an explanatory diagram regarding another installation situation of the speaker of the second embodiment.

FIG. 7 is a diagram showing the configuration of an experimental device for demonstrating the effects of the second embodiment.

8 is an explanatory diagram relating to a sound deadening effect experiment performed using the experimental apparatus shown in FIG. 7.

9A and 9B are views for explaining the effect of a muffling experiment performed using the experimental apparatus shown in FIG.

FIG. 10 is an explanatory diagram of another silencing effect experiment conducted using the experimental apparatus shown in FIG. 7.

FIG. 11 is a diagram illustrating the effect of another silencing experiment performed using the experimental apparatus shown in FIG. 7.

FIG. 12 is a block diagram showing a configuration of a control circuit according to a third embodiment of the present invention.

FIG. 13 is a diagram showing a positional relationship between a microphone, a noise source, and a speaker according to a third embodiment.

FIG. 14 is a diagram for explaining the effect of the third embodiment.

FIG. 15 is a perspective view showing a sound pressure distribution obtained by the active silencer of the third embodiment.

FIG. 16 is a plan view showing a sound pressure distribution obtained by the active silencer of the third embodiment.

FIG. 17 is a perspective view showing a sound pressure distribution obtained by the active silencer of the third embodiment.

FIG. 18 is a plan view showing a sound pressure distribution obtained by the active silencer of the third embodiment.

FIG. 19 is a diagram showing a configuration of an active silencer of a third embodiment.

FIG. 20 is a diagram showing the configuration of an active silencer according to a fourth embodiment of the present invention.

FIG. 21 is a diagram illustrating characteristics of the speaker according to the fourth embodiment.

[Explanation of symbols]

1 opening 2 noise sources 3 Reference signal detector 4 speakers 5 microphone 6 control circuit 7 Cone type speaker for simulated sound source 8 speakers 9 oscillators 10 Amplitude and phase adjuster 11 microphone 12 microphone 13 microphone 14 Adaptive filter 15 Fixed filter 20 Sound pressure minimum position 21 Sound absorbing material

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuichi Morikawa             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center (72) Inventor Osamu Nishimura             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center (72) Inventor Hosaka Rinka             1st Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa             Inside the Toshiba Research and Development Center F-term (reference) 5D061 FF02

Claims (4)

[Claims] 1. A reference signal detection unit for detecting a signal correlated with noise entering through the opening from a noise source provided outside the opening, a speaker installed around the opening, A microphone installed around the opening to detect at least one of sound pressure and sound intensity entering from the opening, and the reference signal detection from the speaker so that the signal detected by the microphone is minimized. An active muffling apparatus, comprising: a control circuit that emits a sound having a phase opposite to that of a signal detected by the unit. 2. The speaker has a linearly elongated emission surface, and emitted sound waves have the same phase characteristics in the line direction (longitudinal direction of the speaker), and are vertically arranged with respect to the sound wave emission direction. 2. The active muffling device according to claim 1, wherein the active muffling device has sharp directional characteristics in the horizontal and horizontal directions. 3. The microphone has a first microphone and a second microphone, each of which detects sound pressure, and the control circuit minimizes a sum of squares of sound pressure detected by the two microphones. Is provided with an adaptive control filter that obtains a filter coefficient using only one filter, and a fixed control filter that holds the filter coefficient obtained by this adaptive control filter. The distance from the sound source to the first microphone is d
1, the distance from the sound source to the second microphone is r1,
The distance from the speaker to the first microphone is d2,
3. A point separated by (d1 + r1) / 2 from the sound source and (d2 + r2) / 2 from the speaker is minimized, where r2 is the distance from the speaker to the second microphone. The active silencer described. 4. The speaker is provided on one side of the opening, and a sound absorbing mechanism for absorbing sound emitted from the speaker is installed on the opposite side of the opening opposite to the one side.
The directional characteristic of the control sound wave emitted from the speaker is
When the distance between the one side where the speaker is installed and the one side where the sound absorbing mechanism is provided is W and the width of the sound absorbing mechanism is d, 3 dB or less for the angle d / (2W) radian or more from the center The active muffler according to claim 1 or 2, wherein