JPH04500A - Active control type soundproofing device - Google Patents

Abstract

PURPOSE:To reduce a noise sound field in a soundproofing wall, etc., by detecting a sound wave which is made incident on nearby an edge of the soundproofing wall, etc., and calculating the amplitude and phase of the incident sound wave and emitting a sound wave for canceling the incident sound wave according to the calculation result. CONSTITUTION:The sound wave which is made incident on nearby the edge E of the wall B owing to a noise from a noise source S outside the soundproofing wall B, etc., is detected by a microphone 1 and passed through a preamplifier 2 to calculate the amplitude and phase of the incident sound wave by a computer 6 and a real-time computer 3. The amplitude and phase which minimize the sound wave at a sound reception point M in the wall B are determined according to the calculation results and a speaker 5 is controlled to cancel the noise nearby the edge E with the sound wave emitted by the speaker 5; and the noise sound field at the sound reception point M in the wall B is reduced to eliminate the noise excellently without making the wall, etc., high.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an actively controlled soundproofing device used in conjunction with a soundproofing fence or wall for preventing noise generated from substations, factories, high-speed trains, expressways, etc. .

[Summary of the Invention] The active control type soundproofing device of the present invention eliminates the sound field at the top edge of the soundproofing wall or wall caused by the incident sound waves from the noise source with the sound field caused by the sound source other than the noise source. Or, it is designed to reduce the sound field caused by noise behind the wall.

[Prior Art] Conventionally, in order to improve the noise reduction performance of a soundproof wall, it has been basically assumed that the height of the soundproof wall is increased.

On the other hand, methods for increasing only the noise reduction performance while leaving the height unchanged are (1) making the surface of the soundproof wall sound absorbing, (2) increasing the thickness of the soundproof wall, and (3) How to attach an acoustic lens to the edge and change the directivity, (4
1) There is a method of lowering the potential of the edge by attaching a sound-absorbing cylindrical object to the edge.

In method (1), the effect of the general soundproof fence usage situation Q is about 3 dB, and when used on expressways, this effect cannot be expected to secure the above predicted value, and it is simply a guarantee of the predicted value. 6 Method (2) is of course very effective, but in order to be effective it requires a thickness of at least several wavelengths of the target sound wave, and it is not commonly used. This effect cannot be expected with a soundproof wall that is 10 cm thick. Method (3) utilizes the interference of sound waves in the shadow of the soundproof wall and at a certain distance, so the effect varies greatly depending on the position of the sound receiving point. At present, I have not heard of any evaluation that this method is highly effective. (4
) method has started to attract attention in recent years, but the effect of a sound-absorbing cylinder attached to the edge of a soundproof fence is about 2.3 d.
B, and it is still difficult to keep the height of the soundproof fence low enough to enjoy the scenery from the window of a moving car or train using this method.

[Problem to be solved by the invention] As described above, it is difficult to keep the height of soundproof walls low with the conventional technology, and currently on expressways and high-speed railways,
Soundproof walls as high as SmxlOm are used at substations and other facilities.

However, if we focus on the last method (4) above, this method is characterized by lowering the potential at the edges of the soundproof fence, and relies on sound-absorbing cylinders to do so, making it impractical. It is inconsiderate and its effectiveness is questionable. By the way, there is another way to lower the same potential. In other words, the method of active control, which has recently been taken up in various fields, is to be adopted.

For example, a noise control method disclosed in Japanese Patent Application Laid-Open No. 63-276100 can be mentioned. However, this method concerns ducts, and the problem here of active control of soundproofing of fences or walls has not been solved.

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide a novel active control system for acoustic fences or walls.

[Means for Solving the Problems] In order to achieve the above object, an active control type soundproofing device according to the first invention suppresses the incidence of noise from a noise source near the upper edge of a fence or wall having a two-dimensional planar extent. 1st to detect sound waves
means for calculating the amplitude and phase of the incident sound wave from the detection signal of the means, and generating a sound wave signal having an amplitude capable of canceling the incident sound wave from the calculated value, and responding to the sound wave signal. and third means for emitting sound waves that cancel the incident sound waves.

In addition, the active control type soundproofing device according to the second invention is characterized in that the above-mentioned incident sound waves are generated based on the pre-calculated amplitude and phase of the incident sound waves from the noise source near the upper edge of a fence or wall having a two-dimensional planar extent. The present invention is characterized in that it includes a first means for generating a sound wave signal having an amplitude capable of canceling the incident sound wave, and a second means for emitting a sound wave that cancels the incident sound wave in response to the sound wave signal.

Furthermore, the active control type soundproofing device according to a third aspect of the present invention includes a first means for detecting an incident sound wave from a noise source near the top edge of a fence or wall having a two-dimensional planar extent and displaying the detected value. , a second means for generating a sound wave signal having an amplitude capable of canceling the incident sound wave based on the pre-calculated amplitude and phase of the incident sound wave corresponding to the detected value; and a third means for emitting sound waves for erasing.

[Function] According to the configuration of each of the inventions described above, it is possible to eliminate the sound field at the top edge of the soundproof wall or wall due to the incident sound waves from the noise source, and to eliminate the sound field caused by the incident sound waves behind the soundproof wall or wall. The sound field can be effectively reduced.

[Example 1] First, the principle of active control of the present invention will be explained. To make the discussion easier to understand, the explanation will be given using mathematical formulas and drawings, taking a two-dimensional sound field as an example.

Assume that a cylindrical wave is radiated from the noise source S toward the barrier B from the left side of the semi-infinite barrier 1fiB as shown in FIG. It is assumed that the sound receiving point M is on the opposite side from the noise source S, and the positional relationship among the barrier, the noise source, and the sound receiving point is as shown in the figure. Also, the noise source S
Let Si be the image sound source due to the barrier B, and k is the wave number = 2π/
It is λ. When the incident cylindrical wave is assumed, the diffracted sound wave at the sound receiving point M behind the barrier is given by, and now if another additional sound source S1 is placed near the upper edge of the barrier B while keeping the angle α the same as S, then , and the incident cylindrical wave from the sound #S', the diffracted sound wave at the sound receiving point M is given by.

The sum Cu of the diffracted sound waves at the sound receiving point M due to these two sound sources
By minimizing d+Ud'), the noise potential at the top edge of the acoustic fence or wall can be minimized by active control. Since the sum is , this sum can be minimized if the term including the coefficient A becomes zero. That is, the amplitude of the additional sound source S' is calculated as
yr)] By adjusting as in (6), the diffraction sound field behind the barrier B becomes zero, and theoretically an infinite noise reduction effect can be obtained.

This can also be explained from another perspective as follows. First, the contribution of the incident sound wave from the noise source S to the edge position is Jπ, and the contribution from the additional sound source S° is, so that equation (6) holds true as shown in equation (7).

This is equivalent to the sum of (8) becoming zero, that is, the noise potential at the upper edge of barrier B becoming zero.

FIG. 2 shows an embodiment of an active control type soundproofing device based on the principles of the present invention.

In the figure, l is a microphone installed near the top edge of soundproof fence B, 2 is a preamplifier, 3 is a digital signal processor (DPS), 4 is a power amplifier, and 5
6 is a speaker, 6 is a microphone for effect evaluation, 7 is a preamplifier, and 8 is a control computer.

Further, it is assumed that the noise source S is located at a certain distance from the upper edge E of the soundproof fence B, and that the sound receiving point M is located behind the soundproof fence B.

The microphone 1 detects a sound wave incident on the soundproof wall B from the noise source S, and the detection signal is inputted to the DPS 3. D
The PS 3 instantaneously calculates the amplitude and phase of the incident sound wave from this detection signal, generates a sound wave signal having the amplitude of equation (6) above based on the calculated value, and sends it to the speaker 5 installed near the edge. radiate a sound wave toward the noise source S to eliminate the noise potential at the edge.

In this way, the above-mentioned device predicts the incident sound wave from the noise source S at the upper edge of the soundproof fence B by real-time calculation, and based on this predicted value, a canceling sound wave is generated from the additional sound source. However, the effect of this erasure is
This is carried out while being confirmed using the effect evaluation microphone 6 installed in the area.

That is, the output signal of the microphone 6 is input to the DPS 3 via the preamplifier 7, and the DPS 3 evaluates the cancellation effect based on this output signal, and if this effect is insufficient, modifies the sound wave signal. At the same time, the noise potential at the edge will be eliminated.

A control computer 8 controls the operation of the DPS 3.

Note that in the above embodiment, the speaker 5 as an additional sound source does not necessarily have to be installed near the edge E;
The closer the speaker 5 is to the edge E, the smaller the sound emitted from the speaker 5 will be, and therefore the less power it will need to supply.

Even when vehicles are lined up in a line, which can be considered as point noise sources, such as on an actual road, or when there is a relatively large noise source, such as a substation, the synthesized waves from those noise sources are
The noise potential at the top edge of the soundproof fence B can be predicted by measuring near the edge of the soundproof wall B, and a sound wave that cancels the potential can be emitted from the speaker, which is basically the same as in the case of a cylindrical wave. In reality, it is a three-dimensional sound field, so if you prepare an active control system for the two-dimensional sound field for each finite length along the length of the soundproof fence and minimize the edge sound field, good. For this purpose, the same number of detection and evaluation microphones as the speakers as additional sound sources are required, and these are linked by a computer in groups to eliminate the sound field along the edges.

FIG. 3 shows an example based on this concept, with Sl...SK...
... is each point noise source arranged in a line, 1-1.1-2゜l
-3,...1-k... are microphones for detecting incident sound waves, 2-1.2-2.2-3. ...2-k... are respective preamplifiers, 4-1.4-2.4-3. ...4-
k... is a power amplifier, 5-1.5-2.5-3.・・・
・5-k... is a speaker as an additional sound source, 6-1゜6-2.6-3. ...6-k... is a microphone for effect evaluation, 7-1.7-2.7-3. ...7-k...
In the vicinity of the upper edge E of the soundproof wall B, a plurality of sets of active control systems shown in FIG. 2 are installed in parallel along the edge. Each set of systems performs the above-mentioned cancellation operation under the control of the control computer 8 to cancel the noise potential at the top edge of the soundproof wall caused by each noise source.

The embodiments shown in FIGS. 2 and 3 described above have a configuration that can sufficiently cope with the case where the noise source is variable, but if the noise source is fixed to some extent, it is possible to obtain the sound wave signal for noise cancellation in advance. Therefore, even the extremely simple configuration shown in FIG. 4 can be expected to have significant practical effects.

In FIG. 4, 10 is a switch, 11 is a sound wave signal generator, and when the switch 10 is turned on, this device 11
A sound wave signal having a pre-calculated amplitude is sent to the speaker 5, and a sound wave for noise cancellation at the edge E is emitted. In this case, it is preferable that the device 11 is provided with a manual knob 12 so that the amplitude of the sound wave signal can be varied to some extent.

Alternatively, as shown in FIG. 5, the detection signal of the incident sound wave output from the microphone 1 may be displayed on the meter 13, and the above-mentioned knob may be adjusted in accordance with the displayed value.

In addition, the properties of the fence itself do not really matter for these soundproof fences, and the surface may be a sound-absorbing surface, a rigid reflective surface, or a soft reflective surface. In short, it is only necessary to make it possible to eliminate the sound field of the soundproof fence edge through active control.

Furthermore, the active control system of the present invention can be effectively applied not only to fences but also to the walls of buildings for soundproofing the interior of buildings.

In addition, in the above-mentioned explanation of the principles of the present invention, an approximate expression was used to express the diffraction field in order to make the discussion easier to understand.
In reality, the equation representing the sound field including the contribution of the noise source and the additional sound source is somewhat complicated as shown in equation (9).

Ud=PD(ρ,, α, ρ, β) 10F(a)= ,/',”exp(-jλ°)dλ+ R
+°・(p , +p )” Using this formula, Figure 6 shows the noise reduction effect behind the soundproof fence by using the soundproof fence according to the present invention in a two-dimensional sound field.The values shown in this figure is the sound pressure level difference behind the soundproof fence when the additional sound source is turned on and off.The frequency of the noise source was set to 5001-1x, which is representative in this field. The positional relationship is as shown in Figure 5. According to these results, an effect of more than 20 decibels can be expected behind the soundproof fence.

We attempted a 1/1O model experiment using the same positional relationships as in Figure 7 for the noise source, additional sound source, and soundproof fence. Since this is a model, the distance between the noise source and the edge of the soundproof fence is 50 marks, and the distance between the additional sound source and the edge is 10 cm.

The frequency of the noise source is 5kHz, which is 10 times higher. The results are shown in FIG. 8, and are in relatively good agreement with the calculated values in FIG. 6, except for the fact that standing waves were generated, confirming the effectiveness of the present invention.

Furthermore, when this is extended to a three-dimensional problem, FIG. 9 shows the numerical calculation results of the noise reduction effect distribution in the horizontal plane behind the soundproof fence. This value is the distribution in a plane 2 m below the edge on the sound receiving side. The basic diffraction equation used for calculation in this case is equation (10).

The noise source was located at a distance of 5 m from the soundproof wall, and the additional sound sources were arranged parallel to the edge at 1 m distance from the edge and 20 cm apart in a plane that included the soundproof wall edge and the noise source. Even in the three-dimensional case, there is a noise reduction effect of more than 20 decibels, and conventional soundproof walls would be too tall to achieve these effects.

22, R,”=(ρ+ρ,).

[Effects of the Invention] As is clear from the above description, according to the present invention, the sound field at the edge of a soundproof fence or wall can be minimized by the active control system, and the sound field at the shadow part is Because it depends on the sound field, a large noise reduction effect can be expected in the shaded area regardless of the height of the soundproof fence or wall. That is, if the soundproofing device according to the present invention is used, a greater reduction effect than before can be obtained as long as the sound source is hidden from the sound receiving point. Taking road traffic noise as an example, it is no longer necessary to have a soundproof fence that is over 3 meters long as in the past, and it may be as long as about 1 meter at most, depending on the position of the sound receiving point and the height of the sound source. This allows you to enjoy a good view of the scenery from the train window, and eliminates the need to emit noise into the surrounding area.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the principle of noise cancellation according to the present invention, FIG. 2 is a block diagram showing one embodiment of the present invention, and FIGS. 3, 4, and 5 each show other embodiments of the present invention. Block diagram shown, No. 6
The figure is a distribution diagram of the noise reduction effect behind the soundproof wall of the device of the present invention in a two-dimensional sound field. The figure is 1/1
Measured data diagram corresponding to the conditions in Figure 1 using the o model,
FIG. 9 is a horizontal distribution diagram of the noise reduction effect behind the soundproof fence of the present invention when the sound field is expanded in three dimensions. 1. Microphone 2: Preamplifier 3: DSP (real time computer) 4: Power amplifier 5: Speaker 6: Effect evaluation microphone 7: Preamplifier 8: Control computer, S: Sound source M: Sound receiving point B: Soundproofing Fence E: Soundproof Fence Edge Patent Applicant Kyoji Fujiwara Agent Patent Attorney Nagai 1) Takeshi Part 3 Figure 2 Figure 4 Figure 5 Figure Ile Figure 8 Figure 7 Figure 119 Figure

Claims (6)

[Claims] (1) A first means for detecting an incident sound wave from a noise source near the upper edge of a fence or wall having a two-dimensional planar extent, and calculating the amplitude and phase of the incident sound wave from the detection signal of the means. and a second means for generating a sound wave signal having an amplitude capable of canceling the incident sound wave based on the calculated value, and a third means for emitting a sound wave that cancels the incident sound wave in response to the sound wave signal. An active control type soundproofing device characterized by: (2) The active control type soundproofing device according to claim (1), characterized in that a plurality of first and third means are arranged in parallel along the fence or wall. (3) Generate a sound wave signal with an amplitude capable of canceling the incident sound wave based on the pre-calculated amplitude and phase of the sound wave incident from the noise source near the upper edge of a fence or wall with a two-dimensional planar extent. 1. An active control type soundproofing device comprising: first means for emitting sound waves that cancel the incident sound waves in response to the sound wave signals; and second means for emitting sound waves that cancel the incident sound waves in response to the sound wave signals. (4) The active control type soundproofing device according to claim (3), wherein the first means is configured to be able to vary the amplitude of the sound wave signal. (5) A first means for detecting an incident sound wave from a noise source near the upper edge of a fence or wall having a two-dimensional planar extent and displaying the detected value; and a second means for generating a sound wave signal having an amplitude capable of canceling the incident sound wave based on a pre-calculated amplitude and phase; and a third means for emitting a sound wave responsive to the sound wave signal canceling the incident sound wave. An active control type soundproofing device characterized by comprising: means. (6) The active control type soundproofing device according to claim (1), further comprising means for evaluating the effect of eliminating incident sound waves by the third means.