JP6917914B2 - Active noise controlled sound field simulation method and simulation device - Google Patents

Description

The present invention is an ANC for a part of an open space, and when the control speaker is arranged at a position away from the noise source, the noise reduction effect can be obtained before installing the system at a site or the like. The present invention relates to a simulation method and a simulation device for an active noise-controlled sound field that can be verified by simulation.

Patent Documents 1 to 3 are known as techniques for reducing noise from a noise source. The "silencer" of Patent Document 1 is provided with two muffling speakers in order to create a muffling area in a specific range by overlapping emitted sounds, and is provided with two sensor microphones corresponding to each muffling speaker. , It is a means of connecting an oscillator that freely sets the frequency range of the noise to be eliminated to the active controller.

The "plant monitoring and control system" of Patent Document 2 is a means for transmitting individual information to an operator in a waiting state by using a sound output method, which is an effective information propagation means for propagating an accidental event, without attaching a receiver. The voice output device is a speaker that outputs control information (fault, abnormality transmission), a unidirectional speaker for muffling, a microphone for sound pressure detection, and a sensor that acquires plant (abnormality) information. , And an active sound field control unit.

The "method for determining the position of noise detecting means in a muffling system" of Patent Document 3 is a second noise in which ANC technology can be fully utilized to satisfactorily mute noise generated from a noise source arranged in a three-dimensional closed space. With the task of obtaining a method for determining the position of the detection means, in order to apply the ANC technology in a three-dimensional closed space such as a basement, a plurality of high sound pressure level frequencies having a high level of noise generated from a noise source are obtained, and the plurality of them are obtained. For each sound with a high sound pressure level frequency, wave acoustic analysis is performed in the three-dimensional closed space to estimate the acoustic state of the three-dimensional closed space, and the sound pressure level in the three-dimensional closed space is determined at the abdomen of the standing wave. A position higher than the average sound pressure level in the space is set as the second position where the second noise detecting means is arranged.

Japanese Unexamined Patent Publication No. 9-160566 Japanese Unexamined Patent Publication No. 10-27003 Japanese Unexamined Patent Publication No. 2011-107673

For example, although various noises are present in a factory, it is often impossible to take measures such as surrounding the noise source with a sound insulation wall or the like, which is a usual noise countermeasure, because it is necessary to visually check the production status. Therefore, there is a demand to reduce the noise in the area where workers are present without using a sound insulation wall or the like. Active noise control (hereinafter referred to as ANC), which is one of the noise countermeasure methods, can reduce noise in a certain area without obstructing the field of view. The ANC uses the control microphone position as the position where the worker is located, and in order to reduce the target sound (noise) at this control microphone position, the ANC is a speaker for controlling a sound having the same amplitude and opposite phase as the target sound. It is a method to output from.

In ANC, when a control speaker is arranged in the vicinity of a noise source, for example, as a countermeasure for engine noise of heavy construction machinery, a large noise reduction effect can be obtained with one control speaker and one control microphone. However, as shown in FIG. 6, when the control speaker b is arranged at a position away from the noise source a, in order to reduce the noise of the entire area such as the area where the worker c is present, a large number of control speakers are used. And a control microphone is required, which is difficult to realize.

ANC can be classified into three types, a minimum area, an entire closed space, and a part of an open space, depending on the size of the area to be controlled. The wider the area of interest, the more difficult it is to control the entire subject. This target area is a part of the whole area, such as a part of a large space such as a place where workers are in a factory, or an area where noise affects the neighborhood outdoors such as a construction site. Often there are. ANCs that target noise in some areas include those that reduce noise passing through a certain surface and those that use a parametric speaker with sharp directivity, based on the principle of boundary sound field control. In these ANCs, although they exert a great effect in the control microphone position and its surroundings in the target region, they may be amplified in other parts. Further, it is usually difficult for a parametric speaker alone to reproduce a low-pitched sound of about 200 Hz or less or a high-pitched sound of 100 dB or more, and it may not be applicable to ANC.

When the control speaker is arranged coaxially with the propagation direction of the noise in the target area, the noise and the control sound from the control speaker have the same amplitude and opposite phase (or a state close to it) in a wide range, and the noise is generated in the target area. Reduce. However, since it is not always possible to arrange them coaxially in an actual factory or the like, the control speakers may be arranged in a direction different from the noise propagation direction (which also means a position away from the noise source). Further, depending on the directivity of the control speaker, the noise reduction effect and the amplification position in the target area change.

For this reason, when installing the ANC system in the actual field, the characteristics of one or more control speakers and the placement position of these control speakers and control microphones are repeatedly selected. It has to be repeated many times, and it is not always possible to obtain a sufficient noise reduction effect, and there is a problem that it is extremely difficult.

The present invention has been devised in view of the above-mentioned conventional problems, and is an ANC for a part of an open space, and when the control speaker is arranged at a position away from the noise source, the present invention is used. It is an object of the present invention to provide an active noise controlled sound field simulation method and a simulation device capable of verifying a noise reduction effect by simulation, such as before installing a system in a field or the like.

次に、上記係数α及び上記位相差φから、上記騒音源から伝搬される騒音と上記制御用スピーカから伝搬される制御音の上記評価点の位置座標における振幅比Ａｊ及び位相差Δφｊを、下記式（５）及び（７）より算定し、

次に、音圧が制御された上記評価点の位置座標での効果を示す音圧Ｅを、下記式（１５）により算定して、

シミュレーション結果を取得することを特徴とする。 The method for simulating an active noise-controlled sound field according to the present invention includes the position coordinates of a virtual noise source that emits noise for simulating the noise reduction effect, the following data of the noise, and a distance from the noise source. It is positioned at the simulation position that is set to be selectable, and fits in both the position coordinates of the virtual control speaker that emits the control sound to reduce the noise, the directional angle of the noise source, and the directional angle of the control speaker. The position coordinates of a virtual control microphone that is positioned at a simulation position that is selectably set in the area and receives sound propagated from both the noise source and the control speaker, and the noise that is set selectably. It is the control position of, and the position coordinates of the evaluation point indicating the reached sound pressure are used, and
The length of the second line segment (rNP) between the noise source and the control microphone, the length of the third line segment (rSP) between the control speaker and the control microphone, the noise source and the evaluation point. The length of the 4th line segment between (rNJ), the length of the 5th line segment between the control speaker and the evaluation point (rSJ), the 1st angle formed by the 2nd line segment and the 4th line segment. Using (θ1) and the second angle (θ2) formed by the third line segment and the fifth line segment,
First, the following equations (6) and (8) obtained from the sound pressure reduction conditions in which the amplitude ratio of the sound from the noise source and the control speaker at the simulation position of the control microphone is 1 and the phase difference is π. The coefficient α representing the strength of the sound source of the control speaker with respect to the noise source and the phase difference φ of the control speaker with respect to the noise source are calculated.

Next, from the coefficient α and the phase difference φ, the amplitude ratio Aj and the phase difference Δφj at the position coordinates of the evaluation points of the noise propagated from the noise source and the control sound propagated from the control speaker are described below. Calculated from equations (5) and (7)

Next, the sound pressure E indicating the effect at the position coordinates of the evaluation points whose sound pressure is controlled is calculated by the following equation (15).

It is characterized by acquiring simulation results.

The evaluation point is set at the center position of a plurality of areas in which the target area to be simulated is divided by a grid, and the simulation result is acquired by the distribution of sound pressure in the target area. ..

The noise source, the control speaker, the control microphone, and the evaluation points are arranged on the coordinates of the same two-dimensional plane, and the simulation result of the sound propagating in the plane is acquired.

The data of the noise propagated from the noise source is obtained in advance before performing the simulation.

上記係数α及び上記位相差φから、上記騒音源から伝搬される騒音と上記制御用スピーカから伝搬される制御音の上記評価点の位置座標における振幅比Ａｊ及び位相差Δφｊを、下記式（５）及び（７）より算定し、

音圧が制御された上記評価点の位置座標での効果を示す音圧Ｅを、下記式（１５）により算定して、

シミュレーション結果を取得することを特徴とする。 The active noise controlled sound field simulation apparatus according to the present invention is separated from the above noise source by the position coordinates of a virtual noise source that emits noise for simulating the noise reduction effect and the following data of the noise. It is positioned at the simulation position that is set to be selectable, and fits in both the position coordinates of the virtual control speaker that emits the control sound to reduce the noise, the directional angle of the noise source, and the directional angle of the control speaker. The position coordinates of a virtual control microphone that is positioned at a simulation position that is selectably set in the area and receives sound propagated from both the noise source and the control speaker, and the noise that is set selectably. It is equipped with a calculator that inputs the position coordinates of the evaluation point indicating the reached sound pressure, which is the control position of.
The arithmetic unit has a second line segment length (rNP) between the noise source and the control microphone, a third line segment length (rSP) between the control speaker and the control microphone, and the noise. The length of the 4th line segment (rNJ) between the source and the evaluation points, the length of the 5th line segment (rSJ) between the control speaker and the evaluation points, the 2nd line segment and the 4th line segment. The first angle (θ1) formed by the line segment and the second angle (θ2) formed by the third line segment and the fifth line segment are calculated.
The arithmetic unit is further obtained from the sound pressure reduction condition in which the amplitude ratio of the sound from the noise source and the control speaker at the simulation position of the control microphone is 1 and the phase difference is π, according to the following equation (6). And (8), the coefficient α representing the strength of the sound source of the control speaker with respect to the noise source and the phase difference φ of the control speaker with respect to the noise source are calculated.

From the coefficient α and the phase difference φ, the amplitude ratio Aj and the phase difference Δφj at the position coordinates of the evaluation points of the noise propagated from the noise source and the control sound propagated from the control speaker are calculated by the following equation (5). ) And (7)

The sound pressure E indicating the effect at the position coordinates of the above evaluation points in which the sound pressure is controlled is calculated by the following equation (15).

It is characterized by acquiring simulation results.

In the simulation method and simulation device for an active noise-controlled sound field according to the present invention, the ANC is intended for a part of an open space, and a control speaker is arranged at a position away from the noise source. In this case, the noise reduction effect can be verified by simulation, such as before installing the system at the site.

It is explanatory drawing explaining one preferable embodiment of the simulation method and the simulation apparatus of the active noise controlled sound field which concerns on this invention. It is explanatory drawing explaining the experimental situation for comparing the result of the simulation based on the embodiment shown in FIG. 1 with the experimental value. It is a block diagram explaining the control method used in the experiment shown in FIG. It is explanatory drawing which compares the experimental value which concerns on Case 1 and the result of a simulation. It is explanatory drawing which compares the experimental value which concerns on Case 2 and the result of simulation. It is explanatory drawing explaining a mode that active noise control is performed by a control speaker arranged at a position away from a noise source.

Hereinafter, a preferred embodiment of the active noise controlled sound field simulation method and the simulation apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

The present invention allows the noise reduction effect to be verified by simulation when the control speaker is arranged at a distance from the noise source instead of near the noise source in the ANC targeting a part of the open space. By taking into account the predominant frequency and propagation direction of noise in the target area, it is possible to efficiently arrange control speakers and select an appropriate directivity, which is effective with a small amount of equipment. To reduce noise.

Specifically, when applying ANC to an actual space such as a factory, the position and propagation direction of the noise source and the frequency of the noise to be reduced can be limited. Therefore, by arranging the optimum control speakers for reducing noise and setting the optimum speaker radiation angle, even if the number of these control speakers and control microphones is several or single, the noise in the target area Can be effectively reduced.

The present invention is a method for predicting the noise reduction effect in consideration of the arrangement of control speakers and their directivity based on the concept of wave field synthesis (superposition of waves). In addition, the sound field due to noise can be represented by a plurality of evaluation points evenly arranged in the region, and the range in which the noise reduction effect can be obtained can be predicted by combining with the sound field due to the control sound from the control speaker. To do so.

The following embodiment makes it possible to evaluate the arrangement of the control speakers and their directivity by simulation in the case where the noise propagates to the target region from one direction.

FIG. 1 shows an explanatory diagram for explaining the concept of a sound field simulation method and a simulation device for active noise control (ANC) according to the present embodiment. The simulation is executed inside an arithmetic unit (not shown) using various set data, and the simulation result is acquired in the arithmetic unit.

In the arithmetic unit that executes the simulation, the noise source N is the position coordinate N (xN) of the virtual noise source (hereinafter, simply referred to as “noise source”) in the two-dimensional plane Cartesian coordinate system (XY Cartesian coordinate system). , YN) and the data of the noise emitted from the noise source N in order to simulate the noise reduction effect are input.

For the noise data propagated from the noise source N, sound data appropriately selected may be used in the experimental implementation, while observation in the space is observed in the simulation when ANC is applied to the actual space. The sound data obtained in advance may be used. The noise data propagated from the noise source N may be measured at any position within the target area, and may be acquired in advance before performing the simulation, such as on a desk or the like. It is preferable to input to the arithmetic unit of the above and perform the simulation. The noise data includes, for example, the (sound) intensity (volume velocity) Q0 of the noise source N, the wave number κ, the angular frequency ω, the period T, and the like.

The arithmetic unit includes the position coordinates S (xS, yS) of the virtual control speaker (hereinafter, simply referred to as "control speaker") in the two-dimensional plane orthogonal coordinate system for the control speaker S, and noise reduction. Control sound data for is input.

In particular, in the present invention, the control speaker S is positioned not in the vicinity of the noise source N but at a position separated from the noise source N and as a selectably set position as a simulation position.

As the control sound data, various sound data can be used in order to obtain the noise reduction effect. The sound data of the control sound includes, for example, a coefficient α representing the strength of the sound source of the control speaker S with respect to the noise source N, and the position of the control speaker S (control sound from) with respect to the noise source N (noise from). There is a phase difference φ etc.

The arithmetic unit is a virtual control microphone P that is used in an actual ANC and receives sound (noise and control sound) propagated from both the noise source N and the control speaker S in a two-dimensional plane orthogonal coordinate system. The position coordinates P (xP, yP) of the control microphone (hereinafter, simply referred to as “control microphone”) of the above are input.

The control microphone P is positioned as a simulation position at a position that can be selectably set on condition that the control microphone P is within a region within both the directivity angle of the noise emitted from the noise source N and the directivity angle of the control speaker S. ..

Further, in order to evaluate the noise reduction effect, the position of the evaluation point J indicating the reached sound pressure is input and set in the arithmetic unit as the position coordinates J (xJ, yJ) in the two-dimensional plane orthogonal coordinate system. .. The position coordinates J (xJ, yJ) of the evaluation point J correspond to information on the noise control position, for example, the position where the worker is required to reduce the noise as described above, and are in the two-dimensional plane orthogonal coordinate system. Set to be selectable.

In the present embodiment, in short, the noise source N, the control speaker S, the control microphone P, and the evaluation point J are arranged on the same two-dimensional plane Cartesian coordinate system, and the sound propagating in the plane by the arithmetic unit. Simulation result is acquired.

Further, in the present embodiment, the evaluation point J is set at the center position of a plurality of square areas in which the area to be simulated (hereinafter, simply referred to as “target area”) is divided by a grid. As a result, the simulation result by the arithmetic unit is calculated for a plurality of evaluation points J, acquired in the form of sound pressure distribution in the target region, and output to an output device such as a monitor or a printer. Will be done.

The arithmetic unit executes a simulation for predicting the effect of ANC by superimposing the sound propagating from the noise source N and the sound propagating from the control speaker S at the evaluation points J provided at equal intervals in the target region. do.

The arithmetic unit includes the input noise source N, the control speaker S, the control microphone P, and the position coordinates N (xN, yN), S (xS, yS), P (xP, yP), J of the evaluation point J. From (xJ, yJ), various numerical values shown in FIG. 1, specifically, the length of the first line segment (rNS) between the noise source N and the control speaker S, the noise source N, and the control speaker S. The length of the second line segment between the microphones P (rNP), the length of the third line segment between the control speaker S and the control microphone P (rSP), the fourth line segment between the noise source N and the evaluation point J. (RNJ), the length of the fifth line segment between the control speaker S and the evaluation point J (rSJ), the length of the sixth line segment between the control microphone P and the evaluation point J (rPJ), the first The first angle (θ1) formed by the 2nd line segment and the 4th line segment, the 2nd angle (θ2) formed by the 3rd line segment and the 5th line segment, and the 3rd angle formed by the 2nd line segment and the 6th line segment (θ2). It is configured to calculate θα) and the fourth angle (θβ) formed by the third line segment and the sixth line segment.

The effect simulated and predicted by the arithmetic unit is obtained according to the following logic.

(A) At the position coordinates P (xP, yP) of the control microphone, the velocity potentials δN, δS of the sound propagating from the noise source N and the control speaker S and arriving at the control microphone P are given by the equations (1) and δS. It is assumed that the equation (2) is obtained.

For the arithmetic unit, the noise from the noise source N shall be a sinusoidal wave, and the first angle θ1 and the second angle θ2 are larger than the directional angle of the noise source N and the directional angle of the control speaker S. In the case, the amplitude of the sound from the noise source N and the control speaker P at the evaluation point J is attenuated, and the attenuation characteristic of the amplitude is a value corresponding to the directional characteristics of the noise source N and the control speaker S. (Actual measurement value and specification data) is set.

(B) From the relationship between the velocity potential and the sound pressure, when the above equations (1) and (2) are differentiated with respect to time t and multiplied by the air density ρ0, the noise source N and the noise source N represented by the following equations (3) and (4) are obtained. The sound pressures of the control speaker S are PN and PS.

となり、制御用マイクの位置座標Ｐ（ｘＰ，ｙＰ）における振幅比Ａｒ＝１なので、

より、騒音源Ｎの音源強さに対する制御用スピーカＳの音源の強さを表す係数αが設定される。 (C) At the position coordinates P (xP, yP) of the control microphone, when the amplitude ratio of the noise from the noise source N and the control sound from the control speaker S is 1, and the phase difference is π, the noise is canceled. The sound pressure at the position coordinates P (xP, yP) of the control microphone is reduced. When the sound pressure conditions of the sound propagating sound (noise) from the noise source N and the sound propagating sound (control sound) from the control speaker S at the position coordinates P (xP, yP) of the control microphone at this time are obtained, the amplitude is obtained. Regarding the ratio, from the ratio of the parts related to the amplitude of equations (1) and (2),

Since the amplitude ratio Ar = 1 at the position coordinates P (xP, yP) of the control microphone,

Therefore, a coefficient α representing the sound source strength of the control speaker S with respect to the sound source strength of the noise source N is set.

となり、制御用マイクの位置座標Ｐ（ｘＰ，ｙＰ）における位相差Δφ＝πなので、

が求められる。 (D) Subsequently, the phase difference φ is determined from the phases of the equations (3) and (4).

Since the phase difference Δφ = π at the position coordinates P (xP, yP) of the control microphone,

Is required.

(E) The effect of ANC in the target area is the distance between the noise source N and each evaluation point J (the length of the fourth line segment; rNJ) and the distance between the control speaker S and each evaluation point J (the fifth line). Since it is obtained by the length of a minute; rSJ), the distance between the noise source N and the control microphone P (the length of the second line segment; rNP) and the control speaker S in each of the equations (6) and (8). By substituting the length rNJ of the fourth line segment and the length rSJ of the fifth line segment into the distances of the control microphones P (the length of the third line segment; rSP) as numerical values, the amplitude ratio at each evaluation point J AJ and the phase difference ΔφJ are obtained by the following equations (5) and (7).

と求められる。 (F) The distances (rNJ, rSJ) between each of the noise source N and the control speaker S and each evaluation point J can be obtained as follows, although they are out of the description of the procedure. In addition to the length rNP of the second line segment between the noise source N and the control microphone P and the length rSP of the third line segment between the control speaker S and the control microphone P described above, the control microphone P and the evaluation The length rPJ of the 6th line segment between the points J, the 3rd angle (θα) formed by the 2nd line segment and the 6th line segment, and the 4th angle (θβ) formed by the 3rd line segment and the 6th line segment. From the cosine theorem,

Is required.

当該式（１１）中の「Ｄ」及び「Ｃ」は、評価点の位置座標Ｊ（ｘＪ，ｙＪ）における振幅比Ａｊ及び位相差Δφｊを用いて、下記式（１２）及び式（１３）と表すことができる。 (G) Next, considering the effect of ANC at each evaluation point J as the following equation (11),

“D” and “C” in the equation (11) are the following equations (12) and (13) using the amplitude ratio Aj and the phase difference Δφj at the position coordinates J (xJ, yJ) of the evaluation points. Can be represented.

By expressing the amplitude of "C" as the unit amplitude of "D" and the amplitude ratio Aj at the evaluation point J, the noise (propagated sound) from the noise source N and the control sound (propagated sound) from the control speaker S ( Expresses the amplitude ratio of (propagated sound). As a result, the following equation (14) is obtained.

Here, since the latter half of the second term of the equation (14) is an effective value of a sine wave having a unit amplitude, the following equation (15) is obtained.

By evaluating the effect at the position coordinates J (xJ, yJ) of the evaluation point whose sound pressure is controlled by ANC according to the above equation (15), the noise source N, the control speaker S, and the control microphone P are evaluated. Obtain a simulation result that can predict the effect of ANC at the evaluation point J from the positional relationship between the respective position coordinates N (xN, yN), S (xS, yS), P (xP, yP) and the target area. can do.

The effect E obtained by the formula (15) is sound pressure, and the unit is Pa (Pascal). By applying the following formula (16), it can be converted into dB units.

Equations (9) to (15) assume a two-dimensional space as described above. For example, in the case of a factory with a high ceiling, the noise source N, the control speaker S, the control microphone P, and the evaluation point J are set to have the same height, so that the simulation is performed assuming a two-dimensional space. be able to. On the other hand, for example, when the noise source N is on the second floor and the evaluation point J is on the first floor, a two-dimensional space of an oblique vertical plane including these two points can be set in the same manner. Simulation can be performed.

In the simulation method and simulation device of the sound field to be ANC according to the present embodiment, the ANC is intended for a part of the open space, and the control speaker S is installed at a position away from the noise source N. In the case of placement, the noise reduction effect can be verified by simulation, such as before installing the system at the site or the like.

In particular, if there is sound data of the noise source N, the simulation can be performed by the arithmetic processing by the arithmetic unit only by inputting the position where the control speaker S and the control microphone P can be installed in the actual space. Can be done. Therefore, not only can the arithmetic unit be brought into the actual space where noise is measured and the simulation can be performed, but also the simulation can be performed on a desk or the like even if it is not in the field.

Specifically, in the arithmetic unit, the position coordinates of the control speaker S and the control microphone P can be freely moved, and the control sound and the direction angle of the control speaker S can be arbitrarily changed to obtain the evaluation point J. The simulation result of the effect of ANC can be acquired, and the result of movement or change can be easily and quickly acquired and evaluated.

Then, by acquiring the simulation results, when installing the ANC system at the actual site, the characteristics of one or more control speakers can be selected, and the positions of these control speakers and control microphones can be arranged. It is possible to eliminate the need for the work of repeating the selection process over and over again, and it is possible to efficiently design and install the ANC system suitable for the actual condition of the installation location.

≪Comparison with experimental values≫
-Experimental conditions The comparison between the actually observed experimental values and the values of the simulation results will be described below. The experimental situation is shown in FIG. Since the actual site is supposed to be an open space, the laboratory is an anechoic chamber and is a space with little reflected sound. In order to obtain the experimental values, microphones corresponding to control microphones were installed at all evaluation points. In the experiment, the noise from the noise source speaker and the control sound from the control speaker propagate in the same direction (Case 1), and the radiated sound from the control speaker (control sound) with respect to the noise propagation direction. There are two cases of Case 2 in which the sound propagates at an angle. The experimental conditions are shown in Table-1.

騒音源（騒音源用スピーカ）に対する制御用スピーカの角度（以下、「放射角度」と称する）は、０°及び３０°とした。騒音源（騒音）に用いた正弦波は、６３Ｈｚ，１２５Ｈｚ，２５０Ｈｚ，５００Ｈｚの正弦波とした。また、制御用スピーカの指向角は周波数によって変化するため、事前の実測により指向角を決定した。実験に使用した制御用スピーカの周波数と指向角が表−２に示されている。

The angles of the control speaker (hereinafter referred to as “radiation angle”) with respect to the noise source (noise source speaker) were set to 0 ° and 30 °. The sine waves used as the noise source (noise) were 63 Hz, 125 Hz, 250 Hz, and 500 Hz sine waves. Moreover, since the directional angle of the control speaker changes depending on the frequency, the directional angle was determined by actual measurement in advance. The frequencies and directional angles of the control speakers used in the experiment are shown in Table-2.

The control speaker used in Case 1 was used in the experiment only when the reproducible frequency was 400 Hz or higher and the frequency of the noise source (noise) was 500 Hz. As shown in FIG. 2, the effect of reducing the sound pressure was confirmed at the evaluation points arranged at a pitch of 0.5 m, and the size of the target area for which the sound pressure was to be reduced was set in the range of 2 m × 2 m. The reduction effect was the difference in sound pressure level at each measurement point when the ANC was turned on and when it was turned off. In the figure, r1 is rNJ and r2 is rSJ.

-Control method The control method of ANC is shown in the block diagram of FIG. A known Filtered-X-LMS algorithm was used. In this control method, the sound pressure observed by the observation microphones shown in FIGS. 2 and 3 is controlled, and the output signal is controlled by an adaptive filter so as to minimize the sound pressure observed by the control microphone. This is the output method. The adaptive filter is identified by sequential calculation based on the target noise observed by the observation microphone and the sound observed by the control microphone.

Filtered-X-LMS algorithm control has a high degree of freedom, although the effect of ANC changes depending on the arrangement of the control speaker, observation microphone, and control microphone. In the examination of the effect of ANC, in order to change the position of the control speaker, ANC by the Filtered-X-LMS algorithm control method was applied and an experiment was conducted.

When the radiation angle of the control speaker with respect to the noise source is 0 °, the frequency of the noise source (noise) is 500 Hz, the directional angle of the noise source speaker is 60 °, and the directional angle of the control speaker is 30 ° and 2 °. The effects of the experimental and simulated results are shown in FIG. 4 (Case 1). The experimental value (maximum effect) in the vicinity of the control microphone was used as the effect of the position of the control microphone in the simulation.

From FIG. 4A, since the directivity angle of the control speaker is small, the range in which an effect of 5 dB or more (difference that can be perceived by humans) can be obtained is narrow and has a band shape. In addition, although the experimental value was slightly smaller in the range where the effect of 5 dB or more appeared, the effect was obtained in a range almost equal to the simulation result (predicted value: hereinafter, the same). From FIG. 4B, as the directional angle of the control speaker increases, the range in which the effect of 5 dB or more can be obtained becomes wider. Further, the range in which the effect of 5 dB or more can be obtained is larger in the experimental value, and the reason for this is considered to be the influence of the attenuation characteristic of the control speaker. In the simulation, the attenuation characteristic of the sound source was given as a point sound source, but it is possible that it was the attenuation characteristic of the surface sound source depending on the characteristics of the noise source speaker and the control speaker and the distance from the evaluation point. In Case 1, the distance between the noise source speaker and the target region was 4 wavelengths or more, but the distance between the control speaker and the target region was as close as 1 wavelength. Considering the radiation area of the control speaker, the attenuation characteristics according to the distance between the target area and each speaker differed between the experiment and the simulation, and there was a difference in amplitude, so there was a slight difference between the experimental value and the simulation result. Conceivable.

The experimental values and simulation results when the radiation angle is 30 ° are shown in FIG. 5 (Case 2). Similar to FIG. 4, the experimental value (maximum effect) in the vicinity of the control microphone was used as the effect of the position of the control microphone in the simulation.

From FIG. 5A, although the directivity angle of the control speaker is 50 °, which is wider than that of Case 1, the range in which the effect of 5 dB or more can be obtained appears in a band shape along the radiation angle because of the radiation angle. The range in which the effect of 5 dB or more can be obtained is slightly larger in the experimental value, but the difference from the simulation result is small and almost the same. From FIG. 5 (b), the effect appeared along the radiation angle as in FIG. 5 (a). In addition, the experimental values and the simulation results were almost the same in both the range in which the effect of 5 dB or more was obtained and the range in which the amplification was achieved, confirming the validity of the simulation method.

To obtain the distribution of sound pressure due to noise in the target area, a control microphone may be installed at a position corresponding to the evaluation point, and the value of the simulation result may be subtracted from the experimental value. Alternatively, a control microphone is installed near the center of the target area, a representative experimental value is obtained, and the noise of all the evaluation points in the target area is the same as this experimental value, and the value of the simulation result. You may try to draw.

From the comparison between the experimental values and the simulation results, the effect of ANC appears along the radiation direction of the control speaker regardless of the radiation angle, the frequency of the sound source, and the direction angle of the control speaker, and the effect is 5 dB or more. The range in which the results can be obtained is almost the same, and the distribution of the effects can be reproduced accurately. The difference between the simulation results and the experimental values was also less than 5 dB at all evaluation points (measurement points). At a position away from the control speaker, the experimental value and the simulation result tend to be slightly different due to the influence of the damping characteristics of the control speaker, but it is about several dB, which is considered to be sufficiently applicable in practice. ..

In the region outside the directional angle of the control speaker, the effect may be discounted for determination. This discount may be judged empirically, and in the analysis illustrated this time, 30% of the inside of the directional angle is considered to be an effective value. If the directional angle of the noise source can be specified, it can be considered that the influence on the outside of the directional angle is reduced to the same extent.

J Evaluation point N Noise source P Control microphone S Control speaker

Claims (5)

The position coordinates of a virtual noise source that emits noise for simulating the noise reduction effect, the following data of the noise, and
The position coordinates of a virtual control speaker that is positioned at a simulation position that is selectably set at a distance from the noise source and emits a control sound to reduce the noise, and
A virtual position that is positioned at a simulation position that is selectably set in a region that fits in both the directional angle of the noise source and the directional angle of the control speaker, and receives sound propagated from both the noise source and the control speaker. The position coordinates of the control microphone and
It is the control position of the noise that is set to be selectable, and the position coordinates of the evaluation point indicating the reached sound pressure are used, and the control position of the noise is used.
The length of the second line segment (rNP) between the noise source and the control microphone,
The length of the third line segment (rSP) between the control speaker and the control microphone,
The length of the fourth line segment (rNJ) between the noise source and the evaluation points,
The length of the fifth line segment (rSJ) between the control speaker and the evaluation points,
Using the first angle (θ1) formed by the second line segment and the fourth line segment, and the second angle (θ2) formed by the third line segment and the fifth line segment,
First, the following equations (6) and (8) obtained from the sound pressure reduction conditions in which the amplitude ratio of the sound from the noise source and the control speaker at the simulation position of the control microphone is 1 and the phase difference is π. The coefficient α representing the strength of the sound source of the control speaker with respect to the noise source and the phase difference φ of the control speaker with respect to the noise source are calculated.

Next, from the coefficient α and the phase difference φ, the amplitude ratio Aj and the phase difference Δφj at the position coordinates of the evaluation points of the noise propagated from the noise source and the control sound propagated from the control speaker are described below. Calculated from equations (5) and (7)

Next, the sound pressure E indicating the effect at the position coordinates of the evaluation points whose sound pressure is controlled is calculated by the following equation (15).

A method of simulating an active noise-controlled sound field, characterized by acquiring simulation results. The evaluation point is set at the center position of a plurality of areas in which the target area to be simulated is divided by a grid, and the simulation result is acquired by the distribution of sound pressure in the target area. The method for simulating a sound field by the active noise control according to claim 1. The claim is characterized in that the noise source, the control speaker, the control microphone, and the evaluation points are arranged on the coordinates of the same two-dimensional plane, and the simulation result of the sound propagating in the plane is acquired. The method for simulating a sound field by the active noise control according to 1 or 2. The sound by the active noise control according to any one of claims 1 to 3, wherein the data of the noise propagated from the noise source is acquired in advance before performing the simulation. Field simulation method. The position coordinates of a virtual noise source that emits noise for simulating the noise reduction effect, the following data of the noise, and
The position coordinates of a virtual control speaker that is positioned at a simulation position that is selectably set at a distance from the noise source and emits a control sound to reduce the noise, and
A virtual position that is positioned at a simulation position that is selectably set in a region that fits in both the directional angle of the noise source and the directional angle of the control speaker, and receives sound propagated from both the noise source and the control speaker. The position coordinates of the control microphone and
It is provided with an arithmetic unit for inputting the position coordinates of the evaluation point indicating the reached sound pressure, which is the control position of the noise set to be selectable.
The arithmetic unit is
The length of the second line segment (rNP) between the noise source and the control microphone,
The length of the third line segment (rSP) between the control speaker and the control microphone,
The length of the fourth line segment (rNJ) between the noise source and the evaluation points,
The length of the fifth line segment (rSJ) between the control speaker and the evaluation points,
The first angle (θ1) formed by the second line segment and the fourth line segment, and the second angle (θ2) formed by the third line segment and the fifth line segment are calculated.
The above arithmetic unit is further
According to the following equations (6) and (8) obtained from the sound pressure reduction conditions in which the amplitude ratio of the sound from the noise source and the control speaker at the simulation position of the control microphone is 1, and the phase difference is π. The coefficient α representing the strength of the sound source of the control speaker with respect to the noise source and the phase difference φ of the control speaker with respect to the noise source are calculated.

From the coefficient α and the phase difference φ, the amplitude ratio Aj and the phase difference Δφj at the position coordinates of the evaluation points of the noise propagated from the noise source and the control sound propagated from the control speaker are calculated by the following equation (5). ) And (7)

The sound pressure E indicating the effect at the position coordinates of the above evaluation points in which the sound pressure is controlled is calculated by the following equation (15).

An active noise controlled sound field simulation device characterized by acquiring simulation results.

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