JP2005338759A - Method and device for controlling noise in duct - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable implementing active control of noise in a duct of high robustness. <P>SOLUTION: At a middle position of the duct 1 transmitting noise generated from a noise generation source 2, a noise control loudspeaker 3 is arranged and a sound pressure detecting microphone 4 is prepared near the position. A controller 5 is arranged for giving a necessary driving instruction to the noise control loudspeaker 3 according to the sound pressure of the acoustic field in the duct 1 detected by the sound pressure detecting microphone 4. Regarding the noise control loudspeaker 3 as a mechanical dynamic vibration reducer, the controller 5 calculates driving force to make an equation of motion in driving this by necessary force equivalent to an equation of motion in simultaneously tuning with an optional frequency, to drive the noise control loudspeaker 3 by this driving force. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a duct noise control method and apparatus used for reducing noise transmitted through a duct from a noise source and released.

In a factory facility or the like, various devices used become noise generation sources that generate noise, and noise generated from the noise generation source may be transmitted through a required air flow passage (duct) and emitted. For example, in a supercharger, a blower (blower), and the like, noise such as fan rotation noise may directly enter an intake duct or an exhaust duct and be transmitted after being transmitted through these ducts.

One of the measures to reduce the noise transmitted through this type of duct is as follows:
It is widely known to provide a Helmholtz resonator in the middle of a duct.

However, the Helmholtz resonator resonates at a certain frequency determined by its shape, size and the like. Therefore, a noise reduction effect can be expected only in a narrow frequency band near a specific frequency. Therefore, it is desired to be able to reduce noise in a wider frequency band.

By the way, in the technical field of controlling the vibration generated in the structure, a dynamic vibration absorber is installed on the upper part of the structure to be damped, and the mass (drive mass) of the dynamic vibration absorber is changed to that of the main structure. It has been considered to limit the vibration of the main structure by shifting the required phase with respect to the vibration, but when damping a structure using a dynamic vibration absorber as described above, The tuning frequency of the main structure and the dynamic vibration absorber is only a band near the fixed natural frequency of the driving mass, and the vibration damping effect can be obtained only in this band. In view of this, such a dynamic vibration absorber exhibits a vibration suppression effect over a wide band, i.e., even if there is some variation in parameters such as modeling error of the main structure to be controlled, natural frequency, etc. As a control theory for improving the robustness so as not to deteriorate, for example, a method using the H-infinity control theory to improve the robustness (property) of the vibration control of the main structure of the driving mass in the dynamic vibration absorber. It has been proposed to adopt (see, for example, Non-Patent Document 1).

Further, the inventor of the present invention is a vibration control method for suppressing the vibration of the main structure by vibrating the driving mass of the dynamic vibration absorber installed in the main structure. Calculate the driving force of the dynamic vibration absorber so that the natural frequency is not a fixed value but an arbitrary frequency, and further, calculate a force proportional to the speed of the main structure at the driving mass mounting position of the dynamic vibration absorber. A vibration control method for controlling a vibration by driving a dynamic vibration absorber with a driving force obtained by addition has been proposed (for example, see Patent Document 1).

JP 2003-206979 A Koike, Nonami, Nishimura, Satsuka, Tanida, Suzuki, “H∞ / μ bending and torsion control of flexible structures using two hybrid vibration control devices”, Japan Society of Mechanical Engineers, No. 95-28, Proceedings of the 4th Symposium on “Control of Motion and Vibration”, 1995, p. 209-212

However, in order to be able to reduce noise in a wide frequency band, the vibration control as described in Non-Patent Document 1 described above is performed by treating the noise transmitted through the duct from the noise generation source as air vibration. Considering that the method is applied to noise control, the vibration control method described in Non-Patent Document 1 determines the control law depending on the control object, and therefore, modeling error of the control object. The tolerance of fluctuations is not so large and the robustness cannot be so high.

That is, in the control law used in the vibration control method described in Non-Patent Document 1, the control effect is weakened along with the variation of the controlled object, and becomes unstable with the variation that the natural frequency changes by 20 to 30%. .

For this reason, there is a concern that problems such as deterioration of the control effect and unstable oscillation may occur due to modeling errors and fluctuations of the control target that are inevitable in practice.

Therefore, establishment of control (robust control) that does not cause such a problem is an important issue.

In addition, the vibration control method described in Patent Document 1 enables the dynamic vibration absorber to tune the driving force, which is one component of the force acting on the driving mass of the dynamic vibration absorber, to an arbitrary frequency. It is set so that it can exert a vibration absorbing effect on the vibration of the main structure that is the object of vibration suppression, and it is good even when the natural frequency of the main structure changes. Robust control can be performed. However, this is a vibration control method for a structure, and is not directly applicable to noise control.

Therefore, the present inventor has extended the highly robust vibration control method proposed in Patent Document 1 to a method for actively controlling the noise transmitted through the duct from the noise source,
The present invention was made in consideration of development.

Therefore, the object of the present invention is to improve the robustness,
It is an object of the present invention to provide a duct noise control method and apparatus capable of suppressing the possibility of problems associated with the collocation of sensors and actuators during active control of duct noise.

In order to solve the above-mentioned problems, the present invention corresponds to the invention according to claim 1, and is a motion for driving a noise control speaker provided at a required portion of a duct serving as a transmission path of noise from a noise source. The noise control method in the duct controls the noise by driving the noise control speaker with the driving force obtained so that the equation is equivalent to the equation of motion when simultaneously tuning to an arbitrary frequency.

Corresponding to the second aspect of the present invention, a noise control speaker is provided at a required portion of a duct serving as a transmission path of noise from a noise source, and a speaker installation position is provided in the vicinity of the noise control speaker. A sound pressure detecting microphone for detecting the sound pressure of the noise in the sound source, and a controller for processing a signal from the sound pressure detecting microphone and giving a drive command to the noise control speaker. A function for giving a driving force to the noise control speaker as a drive command so that the equation of motion when driving the noise control speaker with a required force is equivalent to the equation of motion when simultaneously tuning to an arbitrary frequency. It is set as the noise control apparatus in a duct which has the structure made into having.

Further, in the invention according to the second aspect, the sound absorbing material is attached to the inner wall surface of the duct in the vicinity of the sound pressure detecting microphone, and more specifically, the sound absorber is attached to the inner wall surface of the duct in the vicinity of the place where the sound pressure detecting microphone is installed. A sound pressure detecting microphone is provided on the surface of the sound absorbing material.

Further, the duct wall surface in the vicinity of the sound pressure detection microphone installation location in the invention according to claim 2 has a sound absorbing property, and the sound pressure is detected on the inner surface of the duct wall having the sound absorbing property. A microphone is provided.

According to the present invention, the following excellent effects are exhibited.
(1) The equation of motion for driving the noise control speaker provided at the required location of the duct, which is the transmission path of noise from the noise source, was determined to be equivalent to the equation of motion when simultaneously tuning to an arbitrary frequency. A noise control method for controlling noise by driving the noise control speaker with a driving force, and a noise control speaker provided at a required portion of the duct serving as a transmission path of noise from the noise generation source. A sound pressure detection microphone for detecting the sound pressure of the noise at the speaker installation position is provided in the vicinity of the speaker for sound, and further, a signal from the sound pressure detection microphone is processed to give a drive command to the noise control speaker. A controller for supplying the controller, and when the equation of motion for driving the speaker for noise control with a required force is simultaneously tuned to an arbitrary frequency Since it is a noise control device in a duct having a function of giving a driving force calculated to be equivalent to the equation of motion to the noise control speaker as a drive command, it is input to the controller from the sound pressure detection microphone. The controller gives a drive command to the noise control speaker according to the sound pressure of the noise in the duct, and drives the noise control speaker to tune to the noise in the duct to reduce the noise in the sound field in the duct. Can be reduced. At this time, since the driving force of the noise control speaker is calculated so that the noise control speaker is simultaneously tuned to an arbitrary frequency, the control action is exerted on the broadband noise in the duct. be able to. Therefore, it is possible to reduce noise emitted after being transmitted through the duct from the noise generation source.
(2) Furthermore, it is possible to control the noise in the duct using the sound pressure differential feedback as an attenuation element without causing the possibility of the control becoming unstable even if the gain is increased.
(3) Further, when calculating the driving force of the noise control speaker, a control input is added so that the noise control speaker can be tuned to an arbitrary frequency without using a mode equation relating to the sound pressure in the duct to be controlled. Therefore, even if a modeling error or fluctuation of the duct occurs, it is possible to perform noise control in a large number of modes with high robustness over a wide band with respect to noise transmitted through the duct.
(4) A structure in which a sound absorbing material is attached to the inner wall surface of the duct in the vicinity of the sound pressure detecting microphone, more specifically, a sound is applied to the surface of the sound absorbing material attached to the inner wall surface of the duct in the vicinity of the sound pressure detecting microphone installation location. By adopting a configuration in which a pressure detection microphone is provided, high-frequency sound is generated by repeating reciprocal propagation between the sound wave emitted from the noise control speaker and the duct wall faced, and the higher-order acoustic mode of the duct Can be less likely to be excited. In addition, howling can be reduced by causing the sound absorbing material to absorb sound at the inner wall surface of the duct near the sound pressure detecting microphone. That is, since the sound pressure detected around the microphone can be lowered by sound absorption by the sound absorbing material, the sound pressure detection microphone is provided in the vicinity of the noise control speaker. This contributes more to the detection signal of the sound pressure detection microphone than the acoustic mode reflecting the entire sound field in the duct, and the closed loop in which the operation of the noise control speaker is performed according to this detection signal is repeated. Howling can be made difficult to occur. Therefore, it is possible to suppress the possibility of problems such as excitation of higher-order acoustic modes of the ducts and howling problems associated with the collocation of the noise control speaker as the actuator and the sound pressure detection microphone as the sensor. become. Furthermore,
The mounting position of the sound absorbing material with respect to the inner wall surface of the duct can be freely set according to the installation location of the sound pressure detection microphone in the duct.
(5) The duct wall surface near the sound pressure detection microphone installation location shall have sound absorption,
By adopting a configuration in which a sound pressure detection microphone is provided on the inner surface of the duct wall having the sound absorbing property, a noise control speaker that serves as an actuator and a sound that serves as a sensor, as in (4) above. It is possible to suppress the problem that the higher-order acoustic mode of the duct associated with the collocation of the pressure detection microphone is easily excited and the possibility of howling.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

1 (a) and 1 (b) show an embodiment of a noise control apparatus in a duct used for carrying out a noise control method in a duct according to the present invention, and has the following configuration.

That is, as shown in FIG. 1 (a), a noise generation source 2 such as various devices is connected to one end side, and the noise generated at the noise generation source 2 is transmitted to the middle position of the duct 1 at a middle position. A control speaker 3 is installed. A sound pressure detection microphone 4 for detecting the sound pressure of the noise transmitted through the duct 1 at the installation position of the noise control speaker 3 is provided in the vicinity of the noise control speaker 3. Furthermore, a controller 5 is provided which inputs a detection signal of the sound pressure of noise in the duct 1 detected by the sound pressure detection microphone 4 and gives a drive command to the noise control speaker 3 in accordance with a control law described later. .

As shown in FIG. 1B, the control law of the controller 5 is as follows. First, the noise control speaker 3 installed in the duct 1 is regarded as a mechanical vibration absorber, and the noise control speaker 3 is set to a required force. In addition to deriving an equation of motion when driven by (step 1: S1), an equation of motion when the noise control speaker 3 simultaneously tunes to an arbitrary frequency is derived (step 2: S2),
A driving force for equalizing the two is calculated (step 3: S3). Next, a controller transfer function from the detected sound pressure detected by the sound pressure detecting microphone 4 to the driving force calculated in step 3 is calculated (step 4: S4). Next, based on the calculated controller transfer function, the driving force according to the sound pressure in the duct 1 detected by the sound pressure detection microphone 4 is
The noise control speaker 3 is given a drive command (step 5: S5).

  This will be described in detail below.

First, as a model of the noise control apparatus in a duct according to the present invention, as shown in FIG. 2, a noise generating source 2 provided at one end of the duct 1 in the same configuration as FIG. Let us consider a case where it is indicated by the same reference numeral 2 as the generation source).

By the way, as will be described later, the control law used in the duct noise control method and apparatus according to the present invention is independent of the control target and does not use the mode equation relating to the sound pressure in the duct (control target) in the process of deriving the control law. The mode equation relating to the sound pressure in the duct is necessary for the explanation of the noise control method in the duct of the present invention and the numerical experiment in the embodiments described later. Let me state.

ここで、ｘ：ダクト１における騒音入射位置（図では加振用スピーカ２に接続してあるダ
クト１の左端部）を原点とするダクト１の長手方向の座標軸上の位置、ｐ：ダクト内音圧
、ｃ：音速、ｕ_０：加振用スピーカ振動板の変位、ｕ：騒音制御用スピーカ振動板の変位
、ρ_０：媒質密度、Ｓ：ダクト１の断面積、Ｓ_ａ：騒音制御用スピーカ３の振動板の面積
、Ｓ_ｅ：加振用スピーカ２の振動板の面積、Ｌ_ｓ：騒音制御用スピーカ３の位置（ｘ座標
）、をそれぞれ示す。なお、本明細書の各数式内にて上に・を付したパラメータは、該パ
ラメータの時間微分：ｄ／ｄｔを表し、又、上に‥を付したパラメータは、該パラメータ
の２回時間微分：ｄ^２／ｄｔ^２を表すものとする。 As shown in FIG. 2, the wave equation governing the sound pressure in the duct 1 in which the vibration speaker 2 and the noise control speaker 3 are installed is expressed as follows.

Here, x: position on the coordinate axis in the longitudinal direction of the duct 1 with the origin at the noise incident position in the duct 1 (the left end of the duct 1 connected to the vibration speaker 2 in the figure), p: sound in the duct Pressure, c: velocity of sound, u ₀ : displacement of speaker diaphragm for excitation, u: displacement of speaker diaphragm for noise control, ρ ₀ : medium density, S: cross-sectional area of duct 1, S _a : speaker for noise control 3 shows the area of the diaphragm 3, S _e : the area of the diaphragm of the vibration speaker 2, and L _s : the position (x coordinate) of the noise control speaker 3. In addition, in each mathematical expression of the present specification, a parameter with an upper symbol represents a time derivative of the parameter: d / dt, and a parameter with an upper symbol represents a time derivative of the parameter twice. : D ² / dt ²

となる。ここで、Ｘ_ｎ（ｘ）は次式によって与えられるダクト内音圧ｐのｎ次モードの固
有振動モード関数である（なお、次式におけるＬはダクト１の全長を表す）。

The right side of the above formula (1) represents the time differentiation of the discharge flow rate. To convert the equation (1) to the mode equations, the modal coordinate at the q _n, to represent the solution of equation (1) as a superposition of modes function,

It becomes. Here, X _n (x) is a natural vibration mode function of the n-order mode of the sound pressure p in the duct given by the following equation (L in the following equation represents the total length of the duct 1).

ここで、ε_ｎは

で表される積分値である。又、ω_ｎはダクト内音圧ｐのｎ次モードの固有振動数を示す。 Substituting equation (2) into equation (1), multiplying X _n (x) on both sides and integrating with 0 <x <L, a differential equation related to the mode coordinate is derived, and the n-order mode of the sound pressure p in the duct is calculated. When the damping ratio ζ _n is introduced, the required mode equation is derived as follows.

Where ε _n is

It is an integral value represented by. Further, ω _n represents the natural frequency of the n-th mode of the sound pressure p in the duct.

  Next, the control law in the duct noise control method and apparatus of the present invention will be described.

Now, when driving the noise control speaker 3 with a force proportional to the time derivative of the detected sound pressure,
That is, consider the case where sound pressure differential feedback control is performed.

ここで、騒音制御用スピーカ３の減衰比ζ_ａと固有振動数ω_ａはそれぞれ次式によって表
される。

上記式（６）の右辺はダクト内音圧（制御対象）が騒音制御用スピーカを押す力を表す
ものである。そこで、この右辺に更にダクト内音圧の時間微分に比例する力を駆動力とし
て

のように加え、この駆動力の反作用によって生じるダクト１への媒質流量（式（１）右辺
第２項）が、制御対象となるダクト内音圧に対して減衰効果をもたらすことを期待してみ
る。この期待の妥当性を調べるため、上記駆動力を表す式（８）の下での式（６）

を、ダクト内音圧に関するモード方程式（４）（ｎ＝１）と連成させた系の特性方程式を
導くと、以下のようになる。

ここで、

である。 As shown in FIG. 2, the noise control speaker 3, the speaker mass (mass), the spring constant, the attenuation constant, respectively m _a, k _a, sees mechanical dynamic vibration absorber according to c _a, displacement of the speaker mass m _a If u is u and the driving force is f, the equation of motion of the noise control speaker 3 is given by the following equation.

Here, the damping ratio ζ _a and the natural frequency ω _a of the noise control speaker 3 are respectively expressed by the following equations.

The right side of the above formula (6) represents the force with which the sound pressure in the duct (control target) pushes the noise control speaker. Therefore, on this right side, the force proportional to the time derivative of the sound pressure in the duct is used as the driving force.

In addition to the above, the medium flow rate to the duct 1 (second term on the right side of the equation (1)) generated by the reaction of the driving force is expected to have a damping effect on the sound pressure in the duct to be controlled. View. In order to examine the validity of this expectation, equation (6) below equation (8) representing the driving force is used.

When the characteristic equation of the system coupled with the mode equation (4) (n = 1) relating to the sound pressure in the duct is derived as follows.

here,

It is.

Since all the coefficients of the above characteristic equation are positive, the stability condition based on the Hurwitz determinant is given by

In the above, when the gain G is 0, it is clearly stable because it is an uncontrolled system with no driving force, and both inequalities (12a, 12b) are satisfied. On the other hand, the gain G Yuku increasing from 0, the gain G as can be seen from equation (11) is included as the first-order terms only a _1, because the coefficient of G in the formula in a ₁ is a positive value, the first The stability condition formula (12a) is satisfied, but the second stability condition formula (12b) is not satisfied. Therefore, the expectation that the above-described equation (8) is a stable damping controller is not satisfied. A solid line 6 shown in FIG. 3 indicates instability in the above-described sound pressure differential feedback control, and unit amplitude excitation acceleration sin (2π × 86 t) under the conditions in which each parameter is set as shown in the figure. This shows an example in which the response of sound pressure p (0.8 L, t) to oscillates unstablely. As a comparison, the broken line 7 with a small amplitude shows the case of no control. The instability reasons, that a ₄ is positive, i.e., which arises due to tune only to the frequency omega _a of the noise control speaker 3 is fixed.

Therefore, in the noise control method in the duct according to the present invention, the above-mentioned problem is solved and the sound pressure differential feedback control is stabilized, and the equation of the noise control speaker 3 is simultaneously tuned to an arbitrary frequency. A method of active control is introduced so that

とおき（図１（ロ）の制御則のステップ２）、これと一致するように駆動力を以下のよう
に決定する（図１（ロ）の制御則のステップ３）。

That is, the equation (6) (step 1 of the control law in FIG. 1 (b)) obtained in the same manner as described above for the excitation of an arbitrary frequency in which the time variation is given in the form of exp (iωt) In contrast to 9), a form simultaneously tuned to an arbitrary frequency gω (g is a constant satisfying a stability condition to be derived later, ζ _t and
Each _ωt is a required constant. ) The expression of the controller (target controller) to be

(Step 2 of the control law in FIG. 1 (b)), and the driving force is determined as follows (Step 3 of the control law in FIG. 1 (b)) to coincide with this.

なる置き換えをすることにより得られる方程式

を次式のようにラプラス変換表示し（各パラメータのラプラス変換表示は対応する大文字
により表す）、

この係数行列式ｄｅｔＡ_１を０とおいた以下の特性方程式（１８）が安定根を持つように
ｇの範囲を定める。

ここで、

である。 In order to realize Equation (13) of the target controller, the mode equation (4) (n = 1) regarding the sound pressure in the duct and Equation (13)

The equation obtained by replacing

Is displayed as Laplace conversion as in the following equation (Laplace conversion display of each parameter is indicated by the corresponding capital letter)

The range of g is determined so that the following characteristic equation (18) having the coefficient determinant detA ₁ as 0 has a stable root.

here,

It is.

The stability condition expression (12a) based on the Hurwitz determinant according to the above expression (19) indicates that a ₀ a ₃ with a negative sign cancels the product of the a ₁ first term and the a ₂ second term. The equation (12b) of the stability condition is satisfied because a ₄ = 0 as opposed to the equation (11).

の範囲にとっておけば、Ｇを大きくしても安定になる。又、０の特性根があって特性多項
式ｄｅｔＡ_１がｓを因子にもつが、周波数０の極限（ｓ→０）で解は有限であり不安定に
ならないことが、式（１７）の解

、及び、後述する実施例の時刻歴応答シミュレートによっても検証される。 Therefore, g is set so that a ₀ in the equation (19) is positive.

If it is within this range, it will be stable even if G is increased. The characteristic polynomial detA ₁ has a characteristic root of 0 and s as a factor, but the solution of the equation (17) is that the solution is finite and does not become unstable at the limit of frequency 0 (s → 0).

And it is also verified by a time history response simulation of an embodiment described later.

If the higher limit mode is taken into consideration for the stability limit, it is difficult to analytically obtain g as in equation (20). However, the stability control is performed by simulating by making g slightly smaller than 1. If g that can be found is found, the allowable value of g can be easily found. As described above, the present control method which attempts to realize the equation (13) as a controller by the driving force represented by the equation (14) plays an important role in stabilizing the equation (8) of the differential feedback control of the sound pressure. .

Furthermore, the equation (14) for determining the driving force of the noise control speaker 3 is the displacement of the speaker 3,
The formula includes parameters of speed and acceleration, but it is converted to a form that can be mounted by detecting only sound pressure as follows, so that convenience can be enhanced.

を用いて以下のように表せる。

That is, first, since the expression (14) is an expression derived so that the residual between the expressions (6) and (13) becomes 0, the expressions (6) and (13) are obtained in the Laplace transform region. ) Characteristic polynomial on the left side of

Can be expressed as follows.

Next, when the Laplace transform is performed on Equation (13) and U is solved, it becomes as follows.

Next, when the above equation (24) is substituted into equation (23) to obtain the controller transfer function H (s) from the detected sound pressure to the driving force, the following equation is derived (step of the control law in FIG. 1 (b)): 4).

ここで、Ａは、

で示されるコントローラ伝達関数の極を定める定数である。 Substituting the characteristic polynomial of equation (22) into equation (25) above, the following modification is made.

Where A is

Is a constant that determines the pole of the controller transfer function.

  As a result, the above equation (26) can be implemented relatively easily with integral, differential, and primary elements.

と変形される。上記式（２８）より、騒音制御用スピーカ３が固定した周波数ω_ａにのみ
同調することに起因して不安定因子であったゲインＧの項が、本発明のダクト内騒音制御
方法によれば、ハイパスフィルタｓ／（ｓ＋Ａ）を介して音圧微分に比例した減衰項とし
てきくようになったことが分かる。 Therefore, the medium inflow term of the mode equation of the sound pressure in the duct of the equation (17) realized by the equation (13) of the target controller is obtained by using the equation (24):

And transformed. From the formula (28), the section gain G noise control speaker 3 was unstable factors due to be tuned only to a fixed frequency omega _a is, according to the duct noise control method of the present invention It can be seen that an attenuation term proportional to the sound pressure differential is obtained through the high-pass filter s / (s + A).

Therefore, when the noise generated from the noise source 2 is transmitted through the duct 1, the noise from the controller 5 is determined according to the sound pressure p in the duct input from the sound pressure detection microphone 4 to the controller 5. The controller transfer function H (s) of the above equation (26) to the control speaker 3
) (Step 5 of the control law in FIG. 1 (b)) is applied to the noise in the sound field in the duct 1 by driving the noise control speaker 3. ,
Since the medium flow rate in a state in which the noise control speaker 3 is driven to be simultaneously tuned to noise of an arbitrary frequency can be given, noise in the sound field in the duct 1 can be reduced. Therefore, it is possible to reduce noise emitted after being transmitted through the duct from the noise generating source 2.

Thus, according to the noise control method and apparatus in a duct of the present invention, the noise control speaker 3
Since the driving force of the noise control speaker 3 is calculated so as to be simultaneously tuned to an arbitrary frequency gω, the control action can be exerted on the broadband noise in the duct 1. Further, when performing sound pressure differential feedback control in which the force proportional to the time differential of the sound pressure in the duct is used as the driving force of the noise control speaker 3, unstable oscillation occurs as the gain G increases, etc. Although stable control could not be performed, in the duct noise control method and apparatus according to the present invention, the sound pressure differential feedback is attenuated without causing the possibility of unstable control even when the gain G increases. The noise in the duct can be controlled.

Further, when calculating the driving force formula (14) of the noise control speaker 3, the noise control speaker 3 is simultaneously tuned to an arbitrary frequency without using the mode equation (4) regarding the sound pressure in the duct to be controlled. Therefore, even if modeling errors or fluctuations occur in the duct 1, noise control in a large number of modes with high robustness over a wide band is possible for noise transmitted through the duct 1. It can be performed. This is also clear from the results of Examples described later.

Next, FIGS. 4A and 4B show another embodiment of the present invention. In the duct noise control method and apparatus similar to those shown in FIGS. 1A and 1B, FIG. (A) It is set as the structure attached to the inner wall surface of the duct near the installation location of the sound pressure detection microphone 4 in the same duct 1 as shown in (a) by stretching the sound absorbing material 8 or the like.

Specifically, the sound-absorbing material 8 is formed on the inner surface of the duct wall facing the noise control speaker 3 installed in the duct 1 in the longitudinal direction of the duct 1 with a diameter 2 to 2 of the noise control speaker 3. It is attached so as to cover an area about three times as large. Also, as shown in FIG. 4B, the required dimensions, for example, the noise control speaker 3, are also provided on the inner surfaces of the duct walls on both sides of the duct 1 that are connected to the duct wall opposite to the noise control speaker 3 in the circumferential direction. The sound-absorbing material 8 is attached so as to cover an area on the side of the wall surface opposite to the wall surface, and the sound pressure detecting microphone 4 is provided on the surface of the sound-absorbing material 8 attached to the inner wall surface of the duct. It is.

Other configurations are the same as those shown in FIGS. 1A and 1B, and the same components are denoted by the same reference numerals.

The duct noise control apparatus according to the present embodiment is detected by the sound pressure detection microphone 4 based on a controller transfer function calculated based on a control law similar to that shown in FIGS. The noise control in the duct 1 is performed by applying a driving force corresponding to the sound pressure in the duct to the noise control speaker 3 as a driving command and operating the same.

When noise control in the duct 1 is performed in this way, the sound pressure detection microphone 4 that is a sensor for detecting sound pressure is in the vicinity of the noise control speaker 3 that is a noise control actuator. Due to the fact that it is provided on the inner wall surface of the duct facing the control speaker 3, the noise control speaker 3 located in the immediate vicinity of the sound pressure detection microphone 4 from the acoustic mode reflecting the sound field in the entire area of the duct 1. The sound field (near field) radiated from the sound field contributes more to the detection signal from the sound pressure detection microphone 4, and howling occurs due to repeated closed loops in which the noise control speaker 3 is activated according to this detection signal. In such a case,
According to the present embodiment, howling can be made difficult to occur. That is, the sound absorbing material 8 is attached to the inner wall surface of the duct in the vicinity of the sound pressure detecting microphone 4, and the sound pressure detecting microphone 4
If the nearby inner wall surface of the duct has a sound absorbing property, the sound pressure detected by the sound pressure detecting microphone 4 can be lowered, and the occurrence of the above-described howling can be reduced.

More specifically, when the sound absorbing material 8 is not attached to the inner wall surface of the duct, the inner wall surface of the duct functions as a rigid wall surface, whereas in the present embodiment, the inner wall surface of the duct near the sound pressure detecting microphone 4 is used. Since the sound absorbing material 8 is provided, the boundary condition that the sound pressure is maximized at the duct wall surface, which is a rigid wall surface, is relaxed by the sound absorbing material 8, so that the periphery of the sound pressure detecting microphone 4 caused by the near field is detected. Sound pressure decreases. For this reason, howling is unlikely to occur.

Also, the noise control problem in the duct is usually discussed under the one-dimensional medium motion equation,
The same applies to the noise control described in the embodiment of FIGS. However, Fig. 1 (a)
As shown in FIG. 2, the noise control speaker 3 is provided in the middle of the duct 1 so as to face the inside of the duct 1, and the sound pressure detection microphone 4 is provided on the duct wall facing the noise control speaker 3 in the duct 1. In the case where it is provided, since the medium flow rate injected by the noise control speaker 3 is perpendicular to the longitudinal direction of the duct 1, the vicinity of the sound pressure detection microphone 4 (near field) is a complex multidimensional sound field. It becomes. Also, in the hard reverberant duct 1, sound waves emitted from the noise control speaker 3 are reflected by the facing duct wall surface and reciprocate in a narrow space between the noise control speaker 3 and the facing duct wall surface. As a result of repetition, there is a concern that high-frequency sound is generated and the higher-order acoustic mode of the duct 1 is likely to be excited. However, in the present embodiment, FIG.
(B) Since the sound absorbing material 8 is provided on the inner wall surface of the duct facing the noise control speaker 3 as shown in (b), the sound wave emitted from the noise control speaker 3 as described above is between the duct wall surface facing the noise control speaker 3. The possibility that high-frequency sound is generated by repeating reciprocating propagation in a narrow space and the higher-order acoustic mode of the duct 1 is excited is alleviated.

Thus, according to the present embodiment, the above-described howling occurs due to the collocation of the sound pressure detecting microphone 4 and the noise control speaker 3 when performing noise control in the duct, or the higher order acoustic mode of the duct 1 It is possible to reduce the possibility of the problem of being excited.

Furthermore, the sound absorbing material 8 is provided only in a very small part of the entire section of the duct 1, and the sound absorbing effect of the sound absorbing material 8 is exhibited in a high frequency range of 500 Hz or more, and is subject to active control below that. In the present embodiment, the sound absorbing effect is small, and therefore, the effect of the sound absorbing material 8 directly reducing the low-order acoustic mode to be actively controlled is small. The effect of active control can be further enhanced.

Next, FIG. 5 shows still another embodiment of the present invention. In the same configuration as shown in FIGS. 4 (a) and 4 (b), a duct near the installation location of the sound pressure detection microphone 4 in the duct 1 is shown. Instead of attaching the sound absorbing material 8 to the inner wall surface, the duct wall surface near the installation location of the sound pressure detecting microphone 4 in the duct 1 has sound absorbing properties, and the duct wall 9 having the sound absorbing properties is provided.
The sound pressure detecting microphone 4 is provided on the inner surface of the.

Specifically, the installation location of the sound pressure detection microphone 4 and a part of the duct wall in the vicinity thereof are used as a duct wall 9 made of a sound-absorbing material, and the duct wall 9 in the vicinity of the installation location of the sound pressure detection microphone 4 is used. The sound pressure detection microphone 4 is installed on the inner surface of the duct wall 9 to which the sound absorbing property is given. The portion of the duct 1 which is the duct wall 9 having the sound absorbing property is the noise control installed in the duct 1 as in the region where the sound absorbing material 8 is attached to the duct 1 as shown in FIGS. A portion of a region about 2 to 3 times the diameter of the noise control speaker 3 in the longitudinal direction of the duct 1 on the duct wall facing the speaker 3 for use;
In addition, if the duct wall on both sides of the duct 1 facing the noise control speaker 3 in the circumferential direction in the duct 1 is a portion of the area on the side of the wall facing the noise control speaker 3 on both sides of the duct wall, Good.

Other configurations are the same as those shown in FIGS. 1A and 1B, and the same components are denoted by the same reference numerals.

According to the present embodiment, the sound in the duct detected by the sound pressure detection microphone 4 based on the controller transfer function calculated based on the control law similar to that shown in FIGS. By applying a driving force corresponding to the pressure as a driving command to the speaker 3 for noise control,
Noise control in the duct 1 can be performed, and when the noise control in the duct 1 is performed, the duct wall 9 in the vicinity of the sound pressure detection microphone 4 has sound absorbing properties, so that FIG. ) (
B), the sound pressure detected by the sound pressure detection microphone 4 can be reduced,
Howling can be reduced. In the hard reverberant duct 1, sound waves emitted from the noise control speaker 3 are reflected by the facing duct wall surface, and travels back and forth in a narrow space between the noise control speaker 3 and the facing duct wall surface. Repeatedly, high frequency sound is generated and duct 1
The possibility that the higher order acoustic mode is excited is also alleviated. Therefore, there is a possibility that the above-described howling occurs or the higher-order acoustic mode of the duct 1 is excited due to the collocation of the sound pressure detection microphone 4 and the noise control speaker 3 when performing the noise control in the duct. Can be reduced.

Furthermore, the duct wall 9 having the sound absorbing property is provided only in a part of the entire section of the duct 1, and the sound absorbing effect by the duct wall 9 having the sound absorbing property is exhibited in a high frequency range of 500 Hz or more. Since the sound absorbing effect is small in the band that is the target of active control below that, the duct wall 9 having the sound absorbing property has a small effect of directly reducing the low-order acoustic mode that is the target of active control. As in the embodiment shown in FIGS. 4A and 4B, the effect of active control can be enhanced through near-field sound field prevention.

The present invention is not limited to the above-described embodiment. For example, it is desired to reduce the noise emitted from the noise generating source 2 and transmitted through the duct 1. If there is any noise source 2, any equipment other than a supercharger or blower (fan),
Alternatively, a sound source such as a speaker may be used. In addition, the present invention can be applied to the duct 1 in which the noise control speaker 3 and the sound pressure detection microphone 4 can be installed in the middle of the noise generation source 2 side and the noise emission side. It can be applied to any length, and if it is duct-shaped with an internal space for transmitting the noise generated from the noise source 1, air is actively circulated like an intake duct or an exhaust duct. It is applicable also to things other than the duct 1 to be made. Further, the duct 1 can be applied as long as noise transmitted from the noise generating source 2 existing in the external position on one end side to the inside of the duct 1 is emitted from the other end side through the inside of the duct 1. The case where the noise generation source 2 is not directly connected to one end may be sufficient. In the embodiment shown in FIGS. 4 (a) and 4 (b), the region where the sound absorbing material 8 is provided on the duct wall surface, and FIG.
In the embodiment, the portion of the duct 1 which is the duct wall 9 having sound absorbing properties may be appropriately changed according to the size and shape of the duct 1, the diameter of the noise control speaker 3, and the like. Figure 4 (a)
In the embodiment of (b), the sound absorbing material 8 is attached to the inner wall surface of the duct and the sound pressure detecting microphone 4 is provided on the surface of the sound absorbing material 8, but the sound pressure detecting microphone 4 is provided on the inner wall surface of the duct. The sound absorbing material 8 may be attached to the inner wall surface of the duct near the sound pressure detecting microphone 4. Of course, various changes can be made without departing from the scope of the present invention.

  Hereinafter, numerical simulations and experimental results performed by the present inventors will be described.

(1)
Using a device model similar to that shown in FIG. 2, the effect of noise control by the duct noise control method and device of the present invention is expressed as a frequency response over a wide band of about 50 to 800 Hz.
The length dimension L was verified under two conditions of 1 m and 1.8 m, respectively. The setting of each parameter other than the length dimension L of the duct 1 is the same, and the numerical values of the individual parameters are shown in FIGS. 6A and 6B together with the results.

In this numerical simulation, in order to verify that there is no unstable oscillation of the control, the frequency response is a method in the frequency domain in which a steady amplitude is obtained by solving an algebraic equation related to the amplitude in a form proportional to e ^iωt. Regardless, the time history response analysis is performed in the time domain. In other words, the time response at a certain excitation frequency
Numerical calculation was performed until the steady amplitude was reached by the Kutta-Gill method, and the amplitude when the steady amplitude was reached was plotted as a function of the excitation frequency. In this method, if the control is unstable, it oscillates and does not reach the steady amplitude, and it is not possible to draw a frequency response curve as shown in FIGS.
It is effective for stability verification.

The result of the frequency response when the length L of the duct 1 is 1 m is shown by a solid line 10 in FIG. 6 (a) shows a frequency response in the case of no control in the duct 1 having the same dimensions as a comparison. As a result, when the noise control method and apparatus in the duct of the present invention is applied (solid line 10), a noise control effect (noise reduction effect) that can be achieved in a wide frequency range of many modes as compared to the case of no control (dashed line 11). ).

The result of frequency response when the length of the duct 1 is 1.8 m is shown by a solid line 12 in FIG. 6 (b) shows a frequency response in the case of no control in the duct 1 having the same dimensions as a comparison. Also in this case, when the noise control method and apparatus in the duct of the present invention is applied (solid line 12), a good noise control effect can be obtained in a wide frequency range of many modes as compared with the case of no control (broken line 13). Turned out to be possible.

Further, the length dimension of the duct 1 is greatly changed to 1 m and 1.8 m, and the resonance frequency at the time of non-control shown by the broken line 11 in FIG. 6A and the broken line 13 in FIG. As can be seen from the change, it has been found that even if the characteristics of the controlled object are greatly changed, the control effect is maintained under the condition that the parameters of the control law are the same, and that the robustness is high.

7 (A) and 7 (B), the noise control speaker 3 in the model diagram shown in FIG. 2 is attached to the duct 1 whose length is set to 1 m and 1.8 m in the same manner as described above. Regarding the control effect in the case where the required Helmholtz resonator is attached in place of the noise control speaker 3 to perform passive control, the frequency response is obtained in the same manner as shown in FIGS. Each is shown. In FIG. 7 (a), the tuning frequency of the Helmholtz resonator to be installed is ω _r / 2π = 255 Hz, and in FIG. 7 (b), the tuning frequency is ω
_r / 2π = 142 Hz. The other parameters are shown in FIGS. 7A and 7B.

From the results shown in FIGS. 7 (a) and 7 (b), the passive control by the installation of the Helmholtz resonator can obtain the control effect only in a narrow band near the tuning frequency of the Helmholtz resonator to be installed. I understand.

(2)
In the same apparatus model as shown in FIG. 2 of the above embodiment (1), the sound absorbing material 8 is attached to the duct wall facing the noise control speaker 3 in the same manner as shown in FIGS. Using an experimental apparatus model having a configuration in which the sound pressure detecting microphone 4 is provided on the surface of the sound absorbing material 8, the noise control effect by the noise control method and apparatus in the duct of the present invention covers a wide band of about 50 to 500 Hz. The frequency response was verified under the condition that the length L of the duct 1 was 1 m. The frequency response was measured by applying a broadband sine wave excitation input with an FFT spectrum analyzer. The setting of each parameter other than the length dimension L of the duct 1 and the numerical values of the individual parameters are shown in FIG. 8 together with the results.

The resulting frequency response is shown by the solid line 14 in FIG. 8 shows a frequency response in the case of no control in the duct 1 having the same dimensions as a comparison. As a result, even when the embodiment shown in FIGS. 4A and 4B is applied (solid line 14), the results of the above-described embodiment (1) shown in FIGS. Similarly, it has been found that a good noise control effect can be obtained in a wide frequency range of many modes as compared with the case of no control (broken line 15). In the case of the present embodiment (solid line 14), the resonance peak can be reduced by about 14 to 15 dB as compared with the case of no control (broken line 15). However, it has been found that the reduction effect is improved by about 5 to 6 dB compared to the amount of decrease in the resonance peak obtained compared to the case of no control when no sound absorbing material is inserted.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a duct noise control apparatus used in the implementation of the duct noise control method of the present invention. FIG. 2 is a schematic diagram showing a device model used for deriving a control law in a duct noise control method and device according to the present invention, and showing a case where a vibration speaker is connected to the duct as a noise generation source. It is a figure which shows the instability of sound pressure differential feedback control. The other form of implementation of this invention is shown, (A) is a schematic diagram, (B) is an AA direction arrow line view of (A). It is a schematic diagram which shows other form of implementation of this invention. FIG. 2 shows the result of verifying the control effect by the noise control method and apparatus in the duct of FIG. 1, where (b) is 1 m of the duct length dimension and (b) is 1.8 m of the duct length dimension. It is a figure which respectively shows the frequency response in the case of having assumed. This shows the control effect when a Helmholtz resonator is attached to the duct to allow passive control of noise. (A) is the length of the duct is 1 m, (b) is the length of the duct is 1 It is a figure which shows the frequency response in the case of set to .8 m, respectively. It is a figure which shows a frequency response as a result of carrying out experiment verification of the control effect by employ | adopting the structure of FIG.

Explanation of symbols

1 Duct 2 Speaker for vibration (noise source)
3 Speaker for noise control 4 Sound pressure detection microphone 5 Controller 8 Sound absorbing material 9 Duct wall having sound absorbing property

Claims (5)

With the driving force calculated so that the equation of motion that drives the speaker for noise control provided at the required location of the duct that is the transmission path of noise from the noise source is equivalent to the equation of motion when simultaneously tuning to an arbitrary frequency A noise control method in a duct, wherein the noise control speaker is driven to control noise. Sound pressure detection for detecting the sound pressure of the noise at the speaker installation position in the vicinity of the noise control speaker, provided with a noise control speaker at a required portion of the duct as a transmission path of noise from the noise source. A microphone is provided, and further includes a controller that processes a signal from the sound pressure detection microphone and gives a drive command to the noise control speaker. The controller drives the noise control speaker with a required force. It is characterized in that it has a function to give a driving force as a drive command to the noise control speaker so that the equation of motion is equivalent to the equation of motion when simultaneously tuning to an arbitrary frequency. Duct noise control device. The noise control device in a duct according to claim 2, wherein a sound absorbing material is attached to the inner wall surface of the duct in the vicinity of the sound pressure detection microphone. The in-duct noise control device according to claim 3, wherein the sound pressure detection microphone is provided on the surface of the sound absorbing material attached to the inner wall surface of the duct in the vicinity of the place where the sound pressure detection microphone is installed. The duct wall surface in the vicinity of the sound pressure detection microphone installation location has a sound absorption property, and a sound pressure detection microphone is provided on the inner surface of the duct wall having the sound absorption property. In-duct noise control device.

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