JP3233810B2 - Duct acoustic impedance controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to sound related to a duct such as a non-reflective end, a duct end, a duct wall, a lining material of a sound-absorbing duct, and the like of a test apparatus for measuring sound generated by a fan or the like provided in the duct. The present invention relates to a duct acoustic impedance control device for controlling impedance.

[0002]

2. Description of the Related Art In a conventional test apparatus for measuring a sound generated by a fan in a duct, it is specified by a standard that a non-reflective end provided with a sound absorbing material is installed in a duct having a gradually expanding shape.

FIG. 6 is a sectional view of a duct 41 to be tested and a non-reflective end 43 installed in the duct 41 in a conventional test apparatus of this type. As shown in FIG. 6, a fan 42 is installed in a duct 41, and a non-reflective end 43 is provided at the tip of the duct 41. The non-reflective end 43 has a configuration in which a sound absorbing material 432 and a sound absorbing material 433 are surrounded by a trumpet-shaped metal body 431 whose cross section gradually expands. The sound absorbing material 432 has a shape whose diameter gradually increases from the base end to the distal end of the non-reflective end 43, and a cylindrical sound absorbing material 433 is provided at a position where the diameter becomes maximum. The sound absorbing material 432 is made of a foam or a fiberglass having a density of about 24 kg / m ³ , and the sound absorbing material 433 is made of a fiberglass having a density of about 48 kg / m ³ . Further, a region of about 58% of the surface of the metal body 431 which is surrounded by the sound absorbing materials 432 and 433 is in a state where holes are formed.
The sound absorbing material 433 is provided for the duct 41 having a diameter of 0.46 m.
Is about three times the diameter of the duct 41, and the total length of the non-reflective end 43 is several meters.

[0004]

On the other hand, in a duct actually used, it is considered that a sound generated by a fan causes a considerably complicated acoustic impedance. However, it is impossible to realize such a practical situation by the test method using the above-described apparatus, and the test of the sound generated from the fan or the like cannot be performed under the same boundary condition as the actual one.

A conventional non-reflective end for this type of test is:
The configuration is very large as described above, and it cannot be easily installed due to problems such as its installation location and the price involved in manufacturing. Also, at present, the generated sound is tested using a duct that is different from the condition of the duct actually used, so the generated sound power under the condition where the non-reflective end is installed in the duct actually used is correctly It could not be measured.

Therefore, the complicated acoustic boundary condition of the duct, that is, the acoustic impedance, can be set in the same manner as the duct actually used, and the different non-reflection conditions for each duct can be easily realized without installing a non-reflection end. Realization of simple test equipment was required.

An object of the present invention is to provide an acoustic impedance control apparatus for a duct which can set the same acoustic impedance as that of a duct actually used and can easily realize a non-reflection condition different for each duct.

[0008]

Means for Solving the Problems To solve the above problems and achieve the object, an acoustic impedance control apparatus for a duct according to the present invention is configured as follows . An acoustic impedance control device for a duct according to the present invention is installed on an upstream side in a propagation path of a sound wave propagating from a sound source provided in the duct, and a pair of acoustic-electric converters for detecting a sound pressure error; An electro-acoustic transducer installed on the downstream side of the propagation path of the sound wave, measuring means for separating and measuring an incident sound pressure and a reflected sound pressure from outputs of the pair of sound-electric transducers, and a preset acoustic impedance A first calculating means for calculating an impulse response of the reflectance from the target value of the first parameter, and a reflection from the impulse response of the reflectance calculated by the first calculating means and the sound pressure of the incident wave measured by the measuring means. A second calculating means for calculating a target value of the wave sound pressure; and an error signal indicating a difference between the reflected wave sound pressure measured by the measuring means and the target value of the reflected wave sound pressure calculated by the second calculating means. When , The error signal is the electrical to minimize - is composed of a means for adaptively controlling the output of the acoustic transducer.

[0009]

[Action] As a result of taking the above-mentioned hand stage, effects such as the following may occur. In the acoustic impedance control apparatus for a duct according to the present invention, a sound pressure error is detected by a pair of acoustic-electrical converters, and an incident wave sound pressure and a reflected wave sound pressure are separately measured from an output thereof, and a predetermined acoustic impedance is set. The target value of the reflected wave sound pressure is calculated from the impulse response of the reflectance calculated from the target value of the incident wave sound pressure and the target value of the reflected wave sound pressure is measured so that the difference between the separately measured reflected wave sound pressure and the target value becomes minimum. Since the output of the acoustic transducer is adaptively controlled, by appropriately operating the electro-acoustic transducer in accordance with the sound pressure of the incident wave, it becomes possible to arbitrarily control the sound wave reflection conditions on the cross section thereof, The non-reflection conditions that are different for each case can be realized more reliably.

[0010]

FIG. 1 is a diagram showing a configuration of a duct acoustic impedance control apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a duct to be measured in this embodiment, and a fan 2 serving as a sound source is provided in the duct 1. In FIG. 1, reference numerals 3 and 4 denote acoustic impedance setting cross sections in the duct 1.

On the lower surface of the duct 1, a detection microphone 11 and an error microphone 1 are sequentially arranged at predetermined intervals from a sound source, that is, a fan 2 to a downstream side of a sound wave propagation path.
2, 12 and a control speaker 13 are provided. The detection microphone 11 detects a reference signal from the sound generated by the fan 2. The error microphones 12, 12, which are a pair of acoustic-electric converters, are a pair of microphones, each of which performs sound pressure detection to detect the sound pressure error, and both are arranged with an interval Δr. In this embodiment, the sound pressures output from the error microphones 12 and 12 are P1 and P2, respectively. The control speaker 13, which is an electro-acoustic converter, controls the sound wave reflected from the downstream side of the sound wave propagation path to the upstream side, that is, the fan 2 side.

The detection microphone 11, the error microphones 12, 12, and the control speaker 13 are respectively provided with amplifier filters 21, 22, 22, 23 (and terminals a, b, c,
It is connected to the controller 100 via d). The measurement signals output from the detection microphone 11 and the error microphones 12 are
The data is input to the controller 100 via the terminals 2 and 22. An output signal from the controller 100 described later is output to the control speaker 13 via the amplifier filter 23.

The controller 100 performs general control of the acoustic impedance control device and various calculations for the control. Basically, the controller 100 performs calculation processing in accordance with the Filtered-X-LMS algorithm used for ordinary active acoustic control. Perform As will be described later, a target acoustic impedance Zx (f) is input to the controller 100 from outside.

FIG. 2A is a detailed block diagram of the controller 100. A / D in controller 100
The converters 31, 32, and 32 are connected to the amplifier filters 21, 22, and 22 shown in FIG. 1, respectively, and the D / A converter 33 is connected to the amplifier filter. A
The / D converter 31 is connected with a howling canceling filter 101 (not necessary depending on conditions), an error path compensation filter 102, and an adaptive filter 103 via a subtractor.
01 and the adaptive filter 103 are connected to the D / A converter 33. The error path compensation filter 102 and the adaptive filter 103 are connected to an LMS algorithm unit 104, and the filter coefficient of the adaptive filter 103 is LM
Updated by the S algorithm unit 104. On the other hand, A
/ D converters 32, 32 are connected to the first arithmetic unit 105,
Further, the first calculation unit 105 is connected to the second calculation unit 106. The first operation unit 105 and the second operation unit 106 are connected to the LMS algorithm unit 104 via a subtractor.

In the acoustic impedance control apparatus of this embodiment, as described above, the error microphones 12 and 12 are installed on the side closer to the sound source, that is, the fan 2 than the control speaker 13, and reflected to the upstream side of the sound wave propagation path. Control incoming sound waves. A particular problem is a relatively low frequency region where a plane wave propagates in the duct 1. However, the reflection is adjusted by operating a control speaker (electric-acoustic converter) 13 in accordance with the incident sound wave. Set the acoustic impedance to the target. The error microphones 12 and 12
From the two signals of sound pressures P1 and P2 detected at
The calculation unit 105 calculates the incident sound pressure Pi and the reflected sound pressure Pr. Further, the second calculation unit 106 calculates a target value Pr 'of the reflected wave from the incident sound pressure Pi and the reflection coefficient rx (τ) (shown in FIG. 1) given as a target. And then
The difference e = P between the reflected sound pressure Pr and the target value Pr '
r-Pr 'is input to the LMS algorithm unit 104 as the error signal 107. In order to operate the acoustic impedance control device as a non-reflection end, the target value Pr
'= 0, that is, the error signal 107 is e = Pr-0 = Pr
The control may be performed as follows.

A set cross section 3 in the duct 1, that is, x =
Let Rx (f) be the complex reflectivity, which represents the ratio of the reflected sound pressure Pr to the incident sound pressure Pi at x as a function of frequency, and its value is expressed as follows using the acoustic impedance Zx (f) at x = x. It can be expressed as in equation (1).

Rx (f) = − (1−Zx (f) / ρc) / (1 + Zx (f) / ρc) (1) ρ: gas density, c: sound speed Further, the incident sound pressure Pi and the reflected sound pressure If the waveform of Pr at time t is Pi (t) and Pr (t), it can be generally expressed by the following equation (2).

[0018]

(Equation 1) In Expression (2), rx (τ) is an impulse response of the reflectance Rx (f), and is obtained by performing an inverse Fourier transform on Rx (f) as shown in Expression (3).

Rx (τ) = FFT ⁻¹ (Rx (f)) (3) Then, given the target Rx (f), the target rx (τ) is obtained by equation (3), and the target rx (τ) is obtained. The time waveform Pr '(t) of the reflected wave is obtained from the measured time waveform Pi (t) of the incident wave by the following equation (4).

[0020]

(Equation 2)

On the other hand, the incident sound pressure Pi
(t), the calculation of the reflected sound pressure Pr (t) is as follows. Assuming that the sound pressure time waveforms detected at the two points of the error microphones 12 and 12 are P1 (t) and P2 (t), the sound pressure at x = x is Px (t) = (P1 (t) + P2 ( t)) / 2 (5), and the particle velocity at x = x is as shown in the following equation (6).

[0022]

(Equation 3) Here, Δr is the interval between the pair of error microphones 12, 12, as described above. The incident sound pressure Pi (t) and the reflected sound pressure Pr (t) are the sound pressure Px (t) at x = x and the particle velocity Ux
From (t), it can be expressed as follows.

Pi (t) = (Px (t) + ρcUx (t)) / 2 (7) Pr (t) = (Px (t) −ρcUx (t)) / 2 (8) (8) in FIG. (b) is a diagram for explaining the function of the control speaker 13 as an electro-acoustic converter and the relationship with the acoustic impedance. In the duct 1 shown in FIG. 2B, the sound pressure at the acoustic impedance setting position x = x is Px, the particle velocity is Ux, these incident wave components are Pix,
Uix, and the reflected wave components are Prx and Urx.
At the position x = 0 where is installed, the sound pressure P0,
Assuming the particle velocity U0, incident wave component Pi0, incident wave component Ui0, reflected wave component Pr0, and reflected wave component Ur0, the following equation (9)
To (14).

Px = Pix + Prx (9) Ux = Uix + Urx = Pix / ρc-Prx / ρc (10) ρ: Density, c: Sound speed P0 = Pi0 + Pr0 (11) U0 = Ui0 + Ur0 = Pi0 / ρc-Pr0 / ρc ... (12) Pix = Pi0e ^-ikx ... (13) k: wave number Prx = Pr0eikx ... (14) ^{Assuming that} the target acoustic impedance at x = x is Zx, Zx = Px / Ux = (Pix + Prx) / (Pix / ρc−Prx / ρc) = ρc (1 + rx) / (1−rx) (15) Here, reflectance at x = x is, rx = Prx / Pix = Pr0e ikx / Pi0e -ikx = r0 e 2ikx ... (16) reflectance at x = 0 is, r0 = Pr0 / Pi0 = rx e - ^2ikx ... (17) Rx =-(1−Zx / ρc) / (1 + Zx / ρc) (18) On the other hand, from equation (12), U0 = Pi0 / pc (1-r0) = ^Pixeikx / ^pc (1- ^rxe - ^2ikx ) = Pix / ^pc ( ^eikx- rxe- ^ikx ) (19) . Therefore, when the target acoustic impedance Zx at x = x is determined, rx is determined from Expression (18), and Ux given by Expression (19) according to the measured incident sound pressure Pix
It is sufficient to operate the diagram of the control speaker 13 as shown in FIG. That is, by operating the control speaker 13 according to the relationship of Expression (19), the acoustic impedance at the point x = x can be set to Zx as desired.

In FIG. 2A, a detection microphone is installed so that a normal adaptive control algorithm can be used to detect a reference signal. However, for a sound synchronized with the rotation of the fan, a rotation pulse is referred to. You may. In the case of controlling a sound synchronized with the rotation of the fan or a narrow band random sound, one of the sound pressures P1 and P2 may be used as a reference signal after operating a howling canceller. Further, when the sound source is a speaker, a signal input to the speaker may be branched and used as a reference signal.

3 to 5 show the results obtained by applying the acoustic impedance control device of the present invention to an actual duct. 3 shows the sound pressure reflectance and the acoustic impedance when the acoustic impedance control device is not operated, FIG. 4 shows the case where the non-reflection end condition is set, and FIG. 5 shows the case where the completely rigid wall end is set. Both the sound pressure reflectance shown in FIG. 3A and the acoustic impedance shown in FIG.
It is a complex function with respect to frequency, and is a graph in which the complex amount is represented by an amplitude (Gain) and a phase (Phase) for each frequency.

As shown in FIG. 3, the original characteristics of the duct when the acoustic impedance control device is not operated are shown as they are. Further, as shown in FIG. 4, when the non-reflection end condition is set, the gain of the reflectance is substantially zero in the controlled frequency range as a result, and the target non-reflection condition control is performed. Further, as shown in FIG. 5, when the perfect hard wall end is set, the reflectance gain is substantially “1” in the controlled frequency range as a result, and the perfect reflection condition is satisfied as intended.

(Summary of Embodiment) The configuration, operation and effect shown in the embodiment are summarized as follows. [1] The acoustic impedance control apparatus for a duct shown in the embodiment is installed on the upstream side in the propagation path of a sound wave propagating from a sound source (2) provided in the duct 1, and is used for detecting a sound pressure error. Sound-electric converters (12, 1
2), an electro-acoustic converter (13) installed downstream of the sound wave propagation path, and an output of the duct 1 based on outputs from the pair of acoustic-electric converters (12, 12). A calculating means (100) for calculating the acoustic impedance in the cross section, and the electro-acoustic transducer (13) is operated so that the acoustic impedance calculated by the calculating means (100) becomes a preset target value. Means (100).

As described above, in the acoustic impedance control device for the duct, the sound pressure error is detected by the pair of acoustic-electric converters (12, 12) installed on the upstream side in the propagation path of the sound wave, and the output is output. The electro-acoustic converter (13) installed on the downstream side of the sound wave propagation path is operated so that the acoustic impedance in the duct cross section calculated based on the above becomes a predetermined target value. By setting the target value to the condition of the duct 1, the same acoustic impedance as that of the duct 1 actually used can be set, and the non-reflection condition that is different for each duct 1 can be simplified without installing a non-reflection end. It can be realized with a simple configuration. [2] The duct acoustic impedance control apparatus shown in the embodiment is installed on the upstream side in the propagation path of the sound wave propagating from the sound source (2) provided in the duct 1, and is used for detecting a sound pressure error. Sound-electric converters (12, 1
2), an electro-acoustic converter (13) installed on the downstream side in the sound wave propagation path, and the incident sound pressure and the reflected wave sound pressure from the outputs of the pair of sound-electric converters (12, 12). Measuring means (105) for separating and measuring the reflectance, first calculating means for calculating the impulse response of the reflectance from a preset target value of the acoustic impedance, and measuring the reflectance of the reflectance calculated by the first calculating means. Second calculating means (106) for calculating a target value of the reflected wave sound pressure from the impulse response and the incident wave sound pressure measured by the measuring means (105); and the reflection measured by the measuring means (105). The difference between the wave sound pressure and the target value of the reflected sound pressure calculated by the second calculating means (106) is used as an error signal, and the electro-acoustic converter (103) is controlled so that the error signal is minimized. Means for adaptively controlling the output (1 And it is configured from 0).

As described above, in the duct acoustic impedance control apparatus, the pair of acoustic-electric converters (1)
In step 2 and 12), a sound pressure error is detected, and the sound pressure of the incident wave and the sound pressure of the reflected wave are separately measured from the output. The impulse response of the reflectance calculated from a preset target value of the acoustic impedance and the sound wave The target value of the reflected wave sound pressure is calculated from the pressure and the output of the electro-acoustic converter (13) is adaptively controlled so that the difference between the separately measured reflected wave sound pressure and the target value is minimized. Therefore, by appropriately operating the electro-acoustic transducer (13) in accordance with the sound pressure of the incident wave, it is possible to arbitrarily control the reflection condition of the sound wave in the cross section, and to reduce the non-reflection condition different for each duct 1. It can be realized accurately.

[0031]

According to the present invention, the same acoustic impedance as that of a duct actually used can be set,
It is possible to provide a duct acoustic impedance control device that can easily realize a non-reflection condition different for each duct.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a duct acoustic impedance control device according to an embodiment of the present invention.

FIGS. 2A and 2B are diagrams according to an embodiment of the present invention, in which FIG. 2A is a detailed block diagram of a controller, and FIG. FIG.

FIG. 3 is a diagram showing a result of applying the acoustic impedance control device according to one embodiment of the present invention.

FIG. 4 is a diagram showing a result of applying the acoustic impedance control device according to one embodiment of the present invention.

FIG. 5 is a diagram showing a result of applying the acoustic impedance control device according to one embodiment of the present invention.

FIG. 6 is a diagram showing a conventional test apparatus for measuring a sound generated by a fan in a duct.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Duct 2 ... Fan 3 ... Acoustic impedance setting cross section 4 ... Acoustic impedance setting cross section 11 ... Detection microphone 12 ... Error microphone 13 ... Control speaker 21 ... Amp filter 22 ... Amp filter 23 ... Amp filter 100 ... Controller 101 ... Howling canceling Filter 102: Error path compensation filter 103: Adaptive filter 104: LMS algorithm unit 105: First calculation unit 106: Second calculation unit 107: Error signal 108: Reference signal

Continuation of the front page (56) References JP-A-7-20880 (JP, A) JP-A-4-127697 (JP, A) JP-A-5-223334 (JP, A) JP-A-57-169634 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G10K 11/178 G01H 15/00 G10K 11/16

Claims (1)

(57) [Claims] A sound wave propagating from a sound source provided in a duct
Installed on the upstream side of the propagation path of
A pair of acoustic-electrical converters for performing the electric wave, and electric-
An acoustic transducer, and the output of the pair of acoustic-electrical transducers determines the incident wave sound pressure
Measuring means for separating and measuring the sound pressure of the radiation, and the reflectance from a preset acoustic impedance target value
Calculating means for calculating the impulse response of the first and second impulse responses; and the impulse of the reflectance calculated by the first calculating means.
From the response and the incident wave sound pressure measured by the measuring means,
A second calculating means for calculating a target value of the reflected wave sound pressure; and a second calculating means for calculating the reflected wave sound pressure measured by the measuring means.
The difference between the reflected wave sound pressure calculated by the
The electric signal so that the error signal is minimized.
Means for adaptively controlling the output of the acoustic transducer .