JP2019124867A - Method and apparatus for simulating active noise controlled sound field - Google Patents

Abstract

To provide a method and an apparatus for simulating an active noise controlled sound field in which noise reduction effects are verified by simulation, such as before installing a system at a site or the like, in the case where a control speaker is disposed at a position remote from a noise source in an ANC for a part of an open space.SOLUTION: From a sound pressure reduction condition in which an amplitude ratio of sound from a noise source N and a control speaker S at a simulation position of a control microphone P is 1 and a phase difference is π, a coefficient α representing the intensity of a sound source of the control speaker to the noise source and a phase difference φ of the control speaker with respect to the noise source are calculated, and then, an amplitude ratio Aj and a phase difference Δφj in the position coordinate of an evaluation point J of the noise and the control sound are calculated from the coefficient α and the phase difference φ, and then, a sound pressure E indicating the effect of the position coordinate of the evaluation point where the sound pressure is controlled is calculated, thereby obtaining the simulation result.SELECTED DRAWING: Figure 1

Description

  The present invention is an ANC targeting a partial area of an open space, and in the case where a control speaker is disposed at a position distant from a noise source, a noise reduction effect such as before installing a system in the field etc. The present invention relates to an active noise controlled sound field simulation method and simulation apparatus that can be verified by simulation.

  Patent documents 1-3 are known about the technology which reduces the noise from a noise source. In the "muffler" of Patent Document 1, two muffling speakers are provided to create a muffling area according to a specific range by overlapping of the emitted sound, and two sensor microphones are provided corresponding to each muffling speaker, An active controller is connected to an oscillator for freely setting the frequency range of noise to be extinguished.

  The "plant monitoring control system" of Patent Document 2 is a means for transmitting individual information without mounting a receiver, using an audio output method which is an information transmitting means effective for propagating a contingent event to an operator in a waiting state. The voice output device includes a speaker for outputting control information (fault, abnormality transmission), a unidirectional directivity speaker for muffling, a sound pressure detection microphone, and a sensor for acquiring plant (abnormality) information. , And an active sound field control unit.

  The "Position determination method of the noise detection means in the noise reduction system" of Patent Document 3 is a second noise that makes full use of the ANC technology to satisfactorily silence the noise generated from the noise source arranged in the three-dimensional closed space. With the task of obtaining a method of determining the position of the detection means and applying ANC technology in a three-dimensional closed space such as a basement, a plurality of high sound pressure level frequencies having high levels of noise generated from noise sources are determined. Wave acoustic analysis is performed in the three-dimensional closed space for each sound of high sound pressure level frequency, the acoustic state of the three-dimensional closed space is estimated, and the sound pressure level of the three-dimensional closed space is A position higher than the average sound pressure level in the space is set as a second position where the second noise detection means is disposed.

JP 9-160566 A Japanese Patent Laid-Open No. 10-27003 Unexamined-Japanese-Patent No. 2011-107673

  For example, although various noises exist in a factory, it is often impossible to take measures such as surrounding a noise source with a sound insulation wall or the like, which is a usual noise countermeasure, since it is necessary to visually check the production situation. For this reason, there is a demand to reduce the noise in the area where the 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 control methods, can reduce noise in a certain area without blocking the view. ANC sets the microphone position for control as the position where the above-mentioned worker is, and in order to reduce the target sound (noise) at this microphone position for control, the speaker for controlling the sound with the same amplitude and the opposite phase as the target sound. It is a method to output from.

  When a control speaker is disposed in the vicinity of a noise source, for example, as a measure for the engine noise of a construction heavy machine, the ANC can obtain a large noise reduction effect with one control speaker and one control microphone. However, as shown in FIG. 6, when the control speaker b is disposed at a position away from the noise source a, in order to reduce noise in the entire area such as the area where the worker c is located, a large number of control speakers And a control microphone is required, which is difficult to realize.

  ANC can be classified into three, a minimal area, an entire closed space, and a partial area in an open space, according to 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 in a factory are located, or an area where noise affects the neighborhood outdoors such as a construction site. Often there is. Some ANCs targeting noise in a part of the area are based on the principle of boundary sound field control to reduce noise passing through a certain surface, and to use a parametric speaker with a sharp directivity. In these ANCs, although a great effect is exhibited in the control microphone position and its surroundings in the target area, amplification may occur in other parts. In addition, it is difficult to reproduce a low frequency sound of about 200 Hz or less or a high sound pressure of 100 dB or more with a parametric speaker alone, and it may not be applicable to ANC.

  If the control speaker is arranged coaxially with the noise propagation direction in the target area, the noise and the control sound from the control speaker will have the same amplitude and opposite phase (or near that) over a wide range, and the noise will Reduce. However, in an actual factory or the like, the control speaker may be disposed in a direction different from the propagation direction of the noise (which also means a position away from the noise source) because it can not necessarily be arranged coaxially. Furthermore, depending on the directivity of the control speaker, the noise reduction effect and the amplification position in the target area change.

  Therefore, when installing the ANC system on the actual site, it is necessary to select the characteristics of one or more control speakers and to select the arrangement positions of these control speakers and control microphones again and again. There is also a problem that it is difficult to obtain sufficient noise reduction effect even if it must be repeated.

  The present invention has been made in view of the above-described conventional problems, and is an ANC targeting a partial area of an open space, in which a control speaker is disposed at a position away from a noise source, It is an object of the present invention to provide a simulation method and a simulation apparatus of an active noise controlled sound field 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 simulation method of an active noise-controlled sound field according to the present invention comprises: position coordinates of a virtual noise source emitting noise for simulating a noise reduction effect, the following data of the noise, and a distance from the noise source Positioned at a simulation position that is set to be selectable, the position coordinates of a virtual control speaker that emits control sound for reducing the noise, and both the pointing angle of the noise source and the pointing angle of the control speaker The position coordinates of a virtual control microphone that is positioned at a simulation position that is set to be selectable in an area and that receives sound transmitted from both the noise source and the control speaker, and the noise that is set to be selectable. Using the position coordinates of the evaluation point that indicates the sound pressure that has been reached.
Length of second line segment (rNP) between the noise source and the control microphone, length of third segment (rSP) between the control speaker and the control microphone, the noise source, and the evaluation point The length of the fourth line segment (rNJ), the length of the fifth line segment (rSJ) between the control speaker and the evaluation point, the first angle formed by the second line segment and the fourth line segment Using (θ1) and a 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 condition that the amplitude ratio of the sound from each of the noise source and the control speaker at the simulation position of the control microphone is 1 and the phase difference is π Calculating 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,

Next, based on the coefficient α and the phase difference φ, the amplitude ratio Aj and the phase difference Δφj at the position coordinates of the evaluation point of the noise transmitted from the noise source and the control sound transmitted from the control speaker are Calculated from equations (5) and (7),

Next, the sound pressure E which shows the effect in the position coordinate of the said evaluation point by which sound pressure was controlled is calculated by following formula (15),

It is characterized by acquiring simulation results.

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

  The noise source, the control speaker, the control microphone, and the evaluation point are disposed on the coordinates of the same two-dimensional plane, and simulation results of sound propagating through the plane are obtained.

  The data of the noise transmitted from the noise source may be acquired in advance before the simulation is performed.

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 simulation apparatus for a sound field under active noise control according to the present invention comprises: position coordinates of a virtual noise source emitting noise for simulating a noise reduction effect, the following data of the noise, and a distance from the noise source Positioned at a simulation position that is set to be selectable, the position coordinates of a virtual control speaker that emits control sound for reducing the noise, and both the pointing angle of the noise source and the pointing angle of the control speaker The position coordinates of a virtual control microphone that is positioned at a simulation position that is set to be selectable in an area and that receives sound transmitted from both the noise source and the control speaker, and the noise that is set to be selectable. An arithmetic unit to which the position coordinates of the evaluation point indicating the sound pressure that has been reached are input.
The computing unit includes 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, the noise Length of the fourth segment between the source and the evaluation point (rNJ), length of the fifth segment between the control speaker and the evaluation point (rSJ), the second segment and the fourth segment Calculating a first angle (θ1) formed by the second line and a second angle (θ2) formed by the third line segment and the fifth line segment,
The arithmetic unit may further obtain the following equation (6) obtained from the sound pressure reduction condition that the amplitude ratio of the sound from each of the noise source and the control speaker at the simulation position of the control microphone is 1 and the phase difference is π. And (8) calculate a coefficient α representing the strength of the sound source of the control speaker with respect to the noise source and a phase difference φ of the control speaker with respect to the noise source,

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 point of the noise transmitted from the noise source and the control sound transmitted from the control speaker are given by Calculated from) and (7)

The sound pressure E which shows the effect in the position coordinate of the said evaluation point by which sound pressure was controlled is calculated by following formula (15),

It is characterized by acquiring simulation results.

  In the simulation method and simulation apparatus for an active noise-controlled sound field according to the present invention, an ANC targeting a partial area of an open space is provided, and a control speaker is disposed at a position away from a noise source. In this case, the noise reduction effect can be verified by simulation, for example, before installing the system at a site or the like.

It is an explanatory view explaining a suitable embodiment of a simulation method and simulation device of an active noise controlled sound field concerning the present invention. It is explanatory drawing explaining the experimental condition for comparing the result of simulation based on embodiment shown in FIG. 1 with an experimental value. It is a block diagram explaining the control method used for the experiment shown in FIG. It is explanatory drawing which compares the experimental value which concerns on case 1, and the result of 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 the speaker for control arrange | positioned in the position away from the noise source.

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

  According to the present invention, the noise reduction effect can be verified by simulation in the case of arranging the control speaker at a distance from the noise source instead of the vicinity of the noise source in the ANC for a partial area of the open space. And by taking into account the dominant frequency and propagation direction of noise in the target area, it is possible to efficiently arrange control speakers and select appropriate directivity, with less equipment and effects Noise can be reduced.

  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, even if the number of control speakers and the number of control microphones are several or single, the noise in the target area can be set by setting the optimum control speaker arrangement for reducing noise and the optimum speaker radiation angle. Can be effectively reduced.

  The present invention is a prediction method based on the concept of wavefront synthesis (superimposition of waves) on the noise reduction effect in consideration of the arrangement of control speakers and the directivity thereof. In addition, the sound field due to noise can be represented by a plurality of evaluation points evenly arranged in the area, 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. Let's do it.

  In the following embodiments, the arrangement of control speakers and the directivity thereof can be evaluated by simulation when noise propagates from one direction to a target area.

  FIG. 1 is an explanatory view for explaining the concept of a simulation method and simulation apparatus of a sound field subjected to active noise control (ANC) according to the present embodiment. The simulation is executed inside a computing unit (not shown) using various set data, and the computing unit obtains simulation results.

  In the computing unit that executes the simulation, position coordinates N (x N of virtual noise sources (hereinafter simply referred to as “noise sources”) in the two-dimensional planar orthogonal coordinate system (X-Y orthogonal coordinate system) for the noise source N , YN) and noise data generated from the noise source N in order to simulate the noise reduction effect.

  The data of the noise transmitted from the noise source N may use data of appropriately selected sound in the experimental implementation, while on the other hand, in the simulation in the case of applying ANC to the actual space, observation in the space concerned The sound data acquired in advance may be used. The data of the noise transmitted from the noise source N may be measured at any position within the target area, and may be obtained in advance before performing the simulation, such as on a desk or the like. It is preferable to perform simulation by inputting to the computing unit of The sound data of noise includes, for example, the (sound) strength (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 reduces, for the control speaker S, position coordinates S (xS, yS) of a virtual control speaker (hereinafter simply referred to as “control speaker”) in the two-dimensional plane orthogonal coordinate system and noise. Data of control sound is input.

  In the present invention, in particular, the control speaker S is not located near the noise source N, but is located at a distance from the noise source N and is set as a simulation position that is set to be selectable.

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

  For the control microphone P used in an actual ANC and receiving the sound (noise and control sound) transmitted from both the noise source N and the control speaker S, a virtual in a two-dimensional plane orthogonal coordinate system Position coordinates P (xP, yP) of the control microphone (hereinafter, simply referred to as "control microphone") are input.

  The control microphone P is positioned as a simulation position, which is set to be selectable, provided that the control microphone P is in a region that falls within both the directivity angle of noise emitted from the noise source N and the directivity angle of the control speaker S. .

  Furthermore, in order to evaluate the noise reduction effect, the position of the evaluation point J indicating the reached sound pressure is input to the computing unit as position coordinates J (xJ, yJ) in the two-dimensional plane orthogonal coordinate system and set. . The position coordinate J (xJ, yJ) of the evaluation point J corresponds to the information on the noise control position, for example, the position of the worker whose noise is required to be reduced, as described above. It is set to be selectable.

  In the present embodiment, the noise source N, the control speaker S, the control microphone P, and the evaluation point J are disposed on the same two-dimensional plane orthogonal coordinate system, and the sound propagating in the plane is calculated by the arithmetic unit. Simulation results of are obtained.

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

  The computing 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 area. Do.

  The arithmetic unit receives 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), and 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 Length of second line segment (rNP) between microphones P, length of third line segment (rSP) between control speaker S and control microphone P, fourth line segment between noise source N and evaluation point J Length (rNJ), length of fifth line segment (rSJ) between control speaker S and evaluation point J, length of sixth line segment between control microphone P and evaluation point J (rPJ), A first angle (θ1) formed by the two line segments and the fourth line segment, a second angle (θ2) formed by the third line segment and the fifth line segment, and a third angle formed by the second line segment and the sixth line segment θ ), And configured such that the third segment and the sixth line segment is calculated fourth angle (.theta..beta) eggplant.

  The effects simulated and predicted by the computing unit are obtained according to the following logic.

  (A) At 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 expressed by Equation (1) and It is assumed that equation (2) is obtained.

  For the computing unit, the noise from the noise source N is a sine wave, and the first angle θ1 and the second angle θ2 are larger than the directivity angle of the noise source N and the directivity angle of the control speaker S In this 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 according to the directivity characteristic of the noise source N and the control speaker S The setting of (making it into an actual measurement value or specification data) is made.

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

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 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. If the conditions of the sound pressure of the propagation sound (noise) from the noise source N and the propagation sound (control sound) from the control speaker S at the position coordinates P (xP, yP) of the control microphone at this time are determined, As for the ratio, from the ratio of the part 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,

Thus, the coefficient α representing the strength of the sound source 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 calculated from the phases of 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 can be obtained by the length of a minute; rSJ), the distance between the noise source N and the control microphone P in each of the equations (6) and (8) (the length of the second line segment; The amplitude ratio at each evaluation point J is obtained by substituting the fourth line segment rNJ and the fifth line segment length rSJ as numerical values into the distance of the control microphone P (the third line segment length; rSP) AJ and the phase difference ΔφJ are determined by the following equations (5) and (7).

と求められる。 (F) Although the distance (rNJ, rSJ) between each of the noise source N and the control speaker S and each evaluation point J is out of the description of the procedure, it can be obtained as follows. In addition to the length rNP of the second line segment between the noise source N and the control microphone P described above and the length rSP of the third line segment between the control speaker S and the control microphone P, the control microphone P and evaluation The length rPJ of the sixth line segment between points J, the third angle (θα) formed by the second line segment and the sixth line segment, and the fourth angle (θβ) formed by the third line segment and the sixth line segment From the cosine theorem, using

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 formula (11),

The “D” and “C” in the equation (11) use the amplitude ratio Aj and the phase difference Δφj at the position coordinate J (xJ, yJ) of the evaluation point to determine the following equation (12) and equation (13) Can be represented.

  Note that “D” is a unit amplitude, and the amplitude of “C” is expressed by the amplitude ratio Aj at the evaluation point J, whereby the noise from the noise source N (propagation sound) and the control sound from the control speaker S ( Represents the amplitude ratio of the propagating sound). Thereby, the following equation (14) is obtained.

  Here, since the second 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.

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

  The effect E obtained by Formula (15) is a sound pressure, and a unit is Pa (pascal). By applying the following equation (16), it is possible to convert to dB unit.

  The equations (9) to (15) assume a two-dimensional space as described above. For example, in the case of a factory with a high ceiling, etc., simulation is performed assuming a two-dimensional space by setting the noise source N, the control speaker S, the control microphone P and the evaluation point J as the same height. 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, the two-dimensional space of the vertically oriented vertical plane including these two points is similarly set. Simulation can be performed.

  In the simulation method and simulation apparatus for an ANC sound field according to the present embodiment, the control speaker S is located at a position away from the noise source N, which is an ANC targeting a partial area of the open space. In the case of arrangement, the noise reduction effect can be verified by simulation, for example, before installing the system in the field or the like.

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

  In detail, in the computing unit, the position coordinates of the control speaker S and the control microphone P are freely moved as appropriate, and the control sound and directivity angle etc. of the control speaker S are arbitrarily changed to obtain the evaluation point J. The simulation result of the effect of ANC can be acquired, and the movement or change result can be easily and quickly acquired and evaluated.

  Then, by acquiring the simulation results, when installing the ANC system on the actual site, the selection of the characteristics of one or more control speakers, and the arrangement positions of these control speakers and control microphones It is possible to eliminate the need to repeat the selection process over and over again, and to efficiently design and install an ANC system that suits the actual situation of the installation location.

«Comparison with experimental values»
Experimental conditions The comparison of the actually observed experimental values with the values of the simulation results will be described below. The experimental situation is shown in FIG. The laboratory is an anechoic room and a space with little reflected sound, since it is assumed that the actual site is an open space. In order to obtain experimental values, microphones corresponding to control microphones were placed at all evaluation points. In the experiment, Case 1 (Case 1) in which the noise from the noise source speaker and the control sound from the control speaker propagate in the same direction, and the radiated sound from the control speaker (control sound) with respect to the noise propagation direction Are two cases of Case 2 (Case 2) propagating with 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 with respect to the noise source (speaker for noise source) (hereinafter, referred to as “radiation angle”) were 0 ° and 30 °. The sine wave used for the noise source (noise) was a sine wave of 63 Hz, 125 Hz, 250 Hz and 500 Hz. In addition, since the directivity angle of the control speaker changes with the frequency, the directivity angle was determined in advance by actual measurement. Table 2 shows the frequency and directivity angle of the control speaker used in the experiment.

  The control speaker used in Case 1 was used in the experiments only when the reproducible frequency was 400 Hz or more and the frequency of the noise source (noise) was 500 Hz. The sound pressure reduction effect was confirmed at an evaluation point arranged at a 0.5 m pitch as shown in FIG. 2, and the size of the target area for which the sound pressure was desired to be reduced was in the range of 2 m × 2 m. The reduction effect was the sound pressure level difference at each measurement point when 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. The known Filtered-X-LMS algorithm was used. This control method controls the output signal by an adaptive filter so that the sound pressure observed by the observation microphone shown in FIG. 2 and FIG. 3 is an object of control, and the sound pressure observed by the control microphone is minimized. It is a method of outputting. In the adaptive filter, 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.

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

  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 directivity angle of the noise source speaker is 60 °, and the directivity angle of the control speaker is 30 ° and 2 ° The effects of the experimental and simulation results are shown in FIG. 4 (case 1). The value of the experimental value (maximum effect) in the vicinity of the control microphone was taken as the effect of the position of the control microphone in the simulation.

  As shown in FIG. 4A, since the directivity angle of the control speaker is small, the range in which an effect of 5 dB or more (a difference allowing a human to feel the human body) can be obtained is also narrow. In addition, although the experimental value is slightly smaller in the range where the effect of 5 dB or more appears, the effect is obtained in a range almost equivalent to the simulation result (predicted value: the same as below). As shown in FIG. 4B, when the directivity angle of the control speaker is increased, the range in which the effect of 5 dB or more can be obtained is also expanded. Moreover, although the experimental value became larger in the range where the effect of 5 dB or more can be obtained, the influence of the attenuation characteristic of the control speaker can be considered as the reason. In the simulation, the attenuation characteristic of the sound source was given as a point sound source, but depending on the characteristics of the noise source speaker and the control speaker and the distance from the evaluation point, it may be the attenuation characteristic of the plane sound source. In Case 1, the distance between the noise source speaker and the target area was four or more wavelengths, but the distance between the control speaker and the target area was close to one wavelength. Considering the radiation area of the control speaker, the attenuation characteristics according to the distance between the target area and each speaker are different between experiment and simulation, and there is a difference in amplitude, so some differences between the experimental value and the simulation result Conceivable.

  The experimental values and the simulation results when the radiation angle is 30 ° are shown in FIG. 5 (case 2). As in FIG. 4, the value of the experimental value (maximum effect) near the control microphone is taken as the effect of the position of the control microphone in the simulation.

  As shown in FIG. 5A, although the directivity angle of the control speaker is 50 °, which is wider than that of the case 1, there is a radiation angle, and a range where an effect of 5 dB or more can be obtained appears in a band along the radiation angle. The range where the effect of 5 dB or more was obtained was slightly larger in the experimental value, but the difference with the simulation result was small and almost equal. From FIG. 5 (b), the effect appeared along the radiation angle as in FIG. 5 (a). In addition, the experimental value and the simulation result almost agree with each other in the range where the effect of 5 dB or more can be obtained and the amplification range, and the validity of the simulation method is confirmed.

  In order 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 to obtain a representative experimental value, and the noise of all evaluation points in the target area is assumed to be the same as the experimental value, and the value of the simulation result is obtained. You may draw a

  From the comparison of experimental values and simulation results, regardless of the radiation angle, regardless of the frequency of the sound source and the directivity angle of the control speaker, the ANC effect appears along the radiation direction of the control speaker, and an effect of 5 dB or more The range of obtaining was almost equal, and the distribution of effects could be reproduced with high accuracy. The difference between the simulation results and the experimental values was also less than 5 dB at all evaluation points (measurement points). Although the experimental values and the simulation results tend to be slightly different due to the influence of the attenuation characteristics of the control speaker at a distance from the control speaker, it is about several dB, which is considered to be sufficiently applicable in practice. .

  In the area outside the directivity angle of the control speaker, the effect may be discounted and determined. This discount may be determined empirically, and in the analysis exemplified in this example, it is assumed that 30% inside the directivity angle is a valid value. If the pointing angle of the noise source can be identified, it can be considered that the influence on the outside of the pointing angle is equally reduced.

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

Claims (5)

The position coordinates of a noise-generating virtual noise source for simulating the noise reduction effect and the following data of the noise,
Position coordinates of a virtual control speaker that is positioned at a simulation position that is set to be selectable at a distance from the noise source and emits a control sound for reducing the noise;
A virtual position that is positioned at a simulation position that is selectively set in a region that falls within both the directivity angle of the noise source and the directivity angle of the control speaker, and receives sound transmitted from both the noise source and the control speaker Position coordinates of the control microphone, and
The control position of the noise, which is set to be selectable, uses position coordinates of an evaluation point indicating a sound pressure that has arrived, and
Length of second line segment (rNP) between the noise source and the control microphone,
Length of third line segment (rSP) between the control speaker and the control microphone,
Length (rNJ) of the fourth line segment between the noise source and the evaluation point,
Length of the fifth line segment (rSJ) between the control speaker and the evaluation point,
Using a first angle (θ1) formed by the second line segment and the fourth line segment, and a 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 condition that the amplitude ratio of the sound from each of the noise source and the control speaker at the simulation position of the control microphone is 1 and the phase difference is π Calculating 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,

Next, based on the coefficient α and the phase difference φ, the amplitude ratio Aj and the phase difference Δφj at the position coordinates of the evaluation point of the noise transmitted from the noise source and the control sound transmitted from the control speaker are Calculated from equations (5) and (7),

Next, the sound pressure E which shows the effect in the position coordinate of the said evaluation point by which sound pressure was controlled is calculated by following formula (15),

A method of simulating an active noise controlled sound field characterized in that simulation results are obtained.   The evaluation point is set at a central position of a plurality of areas divided by a grid into a target area to be simulated, and the simulation result is obtained by the distribution of sound pressure in the target area. The simulation method of the sound field by active noise control according to claim 1.   The noise source, the control speaker, the control microphone, and the evaluation point are disposed on the coordinates of the same two-dimensional plane, and simulation results of sound propagating through the plane are acquired. The simulation method of the sound field by active noise control according to 1 or 2.   The sound according to any one of claims 1 to 3, wherein the data of the noise transmitted from the noise source is obtained in advance before the simulation is performed. How to simulate the field. The position coordinates of a noise-generating virtual noise source for simulating the noise reduction effect and the following data of the noise,
Position coordinates of a virtual control speaker that is positioned at a simulation position that is set to be selectable at a distance from the noise source and emits a control sound for reducing the noise;
A virtual position that is positioned at a simulation position that is selectively set in a region that falls within both the directivity angle of the noise source and the directivity angle of the control speaker, and receives sound transmitted from both the noise source and the control speaker Position coordinates of the control microphone, and
The arithmetic control unit to which the position control of the evaluation point indicating the sound pressure that is the control position of the noise set to be selectable is input.
The computing unit is
Length of second line segment (rNP) between the noise source and the control microphone,
Length of third line segment (rSP) between the control speaker and the control microphone,
Length (rNJ) of the fourth line segment between the noise source and the evaluation point,
Length of the fifth line segment (rSJ) between the control speaker and the evaluation point,
Calculating a first angle (θ1) formed by the second line segment and the fourth line segment, and a second angle (θ2) formed by the third line segment and the fifth line segment;
The above computing unit is further
By the following equations (6) and (8) obtained from the sound pressure reduction condition that the amplitude ratio of the sound from each of the noise source and the control speaker at the simulation position of the control microphone is 1 and the phase difference is π: Calculating a coefficient α representing the strength of the sound source of the control speaker with respect to the noise source and a phase difference φ of the control speaker with respect to the noise source,

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 point of the noise transmitted from the noise source and the control sound transmitted from the control speaker are given by Calculated from) and (7)

The sound pressure E which shows the effect in the position coordinate of the said evaluation point by which sound pressure was controlled is calculated by following formula (15),

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

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