JP5164588B2 - Active silencer system - Google Patents

Description

  The present invention relates to an active silencing system that cancels noise propagating in a predetermined space.

  A plurality of speakers attached to a speaker duct that encloses the periphery of the sound source pipe, a differential pressure sensor that is disposed in front of the speaker duct and attached to the sound source pipe and detects only noise from the sound source, and a differential pressure sensor A first filter for attenuating an output signal of noise detected by the sound according to the frequency, a sound wave sensor disposed in front of the speaker duct and detecting an interference sound wave between the noise from the sound source and the muffled sound wave generated from the speaker; There is an active silencer formed of a second filter that attenuates an output signal of an interfering sound wave detected by a sensor according to a frequency, and a controller to which each sensor, speaker, and each filter are connected (see Patent Document 1). . The muffled sound wave generated from the speaker is a sound wave having an antiphase sound pressure with respect to noise. The first and second filters have a characteristic that the attenuation decreases as the frequency increases. The controller generates a mute signal that becomes a mute sound wave based on the output signal from the differential pressure sensor and the output signal from the sound wave sensor, and outputs the mute signal to the speaker.

This active silencer improves the signal-to-noise ratio of the signal by increasing the level of the output signal output from the first and second filters to the controller in the frequency region where the human hearing sensitivity is high, and has high hearing sensitivity. Silence can be effectively performed by increasing the output level of the silence signal in the frequency domain. In addition, since the output signal from the sound wave sensor is increased in the frequency region where human hearing sensitivity is increased and fed back to the controller, the insufficient point of the silencing action based on the output signal from the differential pressure sensor alone is corrected, and the sound is muted. The effect can be improved.
Japanese Patent Laid-Open No. 5-40489

  The active silencer disclosed in Patent Document 1 generates a silenced sound wave having an antiphase sound pressure with respect to noise in a sound source pipe from a speaker, and cancels the noise of the sound source pipe by causing the noise and the silenced sound wave to interfere with each other. However, the sound environment in the other sound source pipe that is different from the sound source pipe to be muted cannot be reproduced in the sound source pipe to be muted. The effect cannot be matched. Therefore, the sound environment of other sound source pipes cannot be applied to the sound source pipe to be muffled, and it is necessary to set a new sound environment unique to the sound source pipe to be mute. .

  The object of the present invention is to reproduce the acoustic environment of another space different from the space to be silenced in the space to be silenced, and to apply a good acoustic environment of the other space to the space to be silenced. It is to provide an active silencing system.

  The premise of the present invention for solving the above-mentioned problems is that the first sensor arranged at a predetermined distance from the noise source, the predetermined distance from the noise source across the first sensor, and the noise source A second sound wave generator that generates a second sound wave that interferes with a first sound wave that is generated and propagates in a predetermined first space, and a predetermined distance from the first sensor with the second sound wave generator interposed therebetween And a second interference sensor generating device that generates an interference signal to be a second sound wave and outputs the generated interference signal to the second sound wave generation device. The first sensor has a first sound wave. And the second synthesized sound wave is detected, the detected synthesized sound wave is output as a first signal, and the second sensor detects and detects the interfering sound wave generated by the interference between the first and second sound waves. An active silencing system that outputs interfering sound waves as a second signal.

  The feature of the present invention based on the above premise is that the active silencer system is disposed in the second space, which is separated from the noise source by a predetermined size, and is generated from the noise source. A silencer for reducing the first sound wave propagating in the second space, and a predetermined sound distance from the noise source with the silencer interposed therebetween, and the reduced sound wave of the first sound wave reduced by the silencer. A third sensor that outputs the sound-reduced sound wave as a third signal while detecting, a third signal received from the third sensor while receiving a second signal from the second sensor, and a third signal from the second signal A first subtractor that generates the removed error signal, and the interference signal generator generates an interference signal using the first signal received from the first sensor and the error signal received from the first subtractor. It is in.

  As an example of the present invention, the active silencing system includes a pseudo feedback signal generation filter that generates a pseudo feedback signal that estimates a second sound wave that reaches the first sensor from the second sound wave generator, and a first signal from the first sensor. And a second subtracting device that receives a pseudo feedback signal from the pseudo feedback signal generation filter and generates a fourth signal obtained by removing the pseudo feedback signal from the first signal. An interference signal is generated using the fourth signal received from the subtracting device and the error signal received from the first subtracting device.

  As another example of the present invention, an interference signal generation device updates an adaptive digital filter using an adaptive digital filter for generating an interference signal that minimizes the second signal and an error signal received from the second subtraction device. And an adaptive control arithmetic unit.

  As another example of the present invention, the interference signal generation device includes a digital filter that simulates a time-series transfer characteristic from the second sound wave generator to the second sensor, and the adaptive control arithmetic device transmits the time-series transmission in the digital filter. The adaptive digital filter is updated from the characteristics and the error signal received from the second subtractor.

  As another example of the present invention, the distance from the noise source to the third sensor is substantially the same as the distance from the noise source to the second sensor or longer than the distance from the noise source to the second sensor.

  As another example of the present invention, the distance from the noise source to the third sensor is shorter than the distance from the noise source to the second sensor, and the distance from the noise source to the third sensor is between the third sensor and the first subtractor. A time delay correction device that corrects a time delay until the reduced sound wave propagates to the three sensors is connected.

  As another example of the present invention, the sampling frequency in the active silencing system is in the range of 3 kHz to 40 kHz.

  As another example of the present invention, in the active silencing system, there are a plurality of first spaces that are independent of each other.

  As another example of the present invention, the first space and the second space are internal spaces of the air conditioning duct.

  According to the active silencing system of the present invention, the first subtracter generates an error signal obtained by removing the third signal from the second signal, and the interference signal generator receives the first signal received from the first sensor and the first signal. Since the interference signal is generated using the error signal received from the subtracting device, the error signal does not include the third signal output from the third sensor in the second space, and the second signal is reduced by the silencer. The sound waves in the first space can be canceled out by the second sound wave, which is output as the second signal from the second sensor, while the sound waves in the two spaces remain, and the acoustic environment of the second space is reproduced in the first space. can do. Since this active silencing system can apply the favorable acoustic environment of the second space adjusted by the silencer to the first space, it is not necessary to set the acoustic environment independently in the first space. Save time and effort.

  The pseudo feedback signal generation filter generates a pseudo feedback signal obtained by estimating the second sound wave reaching the first sensor from the second sound wave generator, and the second subtractor generates a fourth signal obtained by removing the pseudo feedback signal from the first signal. In the active silencing system in which the interference signal generating device generates the interference signal using the fourth signal received from the second subtracting device and the error signal received from the first subtracting device, the second subtracting device uses the synthesized signal. Since the fourth signal excluding the pseudo-feedback signal that can be estimated as the second sound wave is generated and the fourth signal is output to the interference signal generation device, the first signal is output to the fourth signal output to the interference signal generation device. The pseudo feedback signal that estimates the second sound wave that reaches is not included, and howling in the first sensor can be prevented. When the combined signal including the interference signal that becomes the second sound wave is output to the interference signal generation device as it is, an interference signal including a sound wave that cancels the interference signal is generated. In this active silencing system, Since the fourth signal excluding the pseudo feedback signal is output to the interference signal generation device, it is possible to prevent the interference signal from including a sound wave that cancels the interference signal. The active silencer system generates an interference signal using the fourth signal received from the second subtractor by the interference signal generator and the error signal received from the first subtractor, and the second signal is reduced by the silencer. The sound waves in the first space can be canceled out by the second sound wave, which is output as the second signal from the second sensor, while the sound waves in the two spaces remain, and the acoustic environment of the second space is reproduced in the first space. can do.

  In the active silencer system in which the interference signal generation device is formed of the adaptive digital filter and the adaptive control arithmetic device, the adaptive control arithmetic device updates the adaptive digital filter and the interference digital signal is generated by the adaptive digital filter. By using the second sound wave generated from the second sound wave generator while following the change in the noise and the target signal in the first space, the interfering sound wave except the reduced sound wave in the second space is surely canceled. be able to. This active silencer system can reliably reproduce the good acoustic environment of the second space adjusted by the silencer in the first space.

  In the active silencing system in which the interference signal generation device includes a digital filter, the time series transfer characteristic from the second sound wave generation device to the second sensor is used by the digital filter, so that the adaptive control arithmetic device is moved from the second sound wave generation device. The adaptive digital filter can be updated using the error signal in consideration of the time-series transfer characteristics up to the second sensor, and the second sound sensor can remove the sound-reduced sound wave in the second space at the position of the second sensor that is the mute position. The interference sound wave in one space can be canceled out reliably. This active silencer system can reliably reproduce the good acoustic environment of the second space adjusted by the silencer in the first space.

  An active silencing system in which the distance from the noise source to the third sensor is substantially the same as the distance from the noise source to the second sensor or longer than the distance from the noise source to the second sensor is output from the second sensor. Since the causality between the signal and the third signal output from the third sensor can be maintained, the second sensor outputs the second signal as the second signal while leaving the sound-reduced sound wave in the second space. The interference sound wave in one space can be canceled by the second sound wave reliably, and the good acoustic environment of the second space adjusted by the silencer can be reliably reproduced in the first space.

  A time delay correction device that corrects a time delay until the sound-reduced sound wave propagates from the noise source to the third sensor is shorter than the distance from the noise source to the third sensor. In the active silencing system connected between the sensor and the first subtracting device, the time delay until the reduced sound wave is propagated from the noise source to the third sensor is corrected by the time delay correcting device, and the second sound source from the noise source is corrected. The time until the first sound wave propagates to the sensor can coincide with the time until the reduced sound wave propagates from the noise source to the third sensor, and the second signal output from the second sensor and the third sensor The causality between the third signal output from the first signal and the third signal can be maintained. This active silencing system can reliably cancel the interfering sound wave of the first space output as the second signal from the second sensor by the second sound wave while leaving the sound-reduced sound wave of the third sensor. It is possible to reliably reproduce a good acoustic environment in the second space adjusted by the first space. This active silencing system is effective when the length of the second space is shorter than that of the first space and the third sensor must be installed at a position shorter than the distance from the noise source to the second sensor. It is.

  An active silencing system whose sampling frequency is in the range of 3 kHz to 40 kHz can be as close as possible to the sound wave of the opposite phase and the same sound pressure of the sound wave that the second sound wave is to be silenced because the system samples at that frequency within a unit time. In addition, by using the second sound wave generated from the second sound wave generator, the interference sound wave in the first space excluding the sound-reduced sound wave in the second space can be surely canceled.

  An active silencing system in which a plurality of first independent spaces exist can reproduce a good acoustic environment of the second space adjusted by the silencer in each of the first spaces, and the acoustic environment of the second space. Can be applied to all of these first spaces.

  The active silencing system according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a configuration diagram of an active silencing system 10A shown as an example, and FIG. 2 is a diagram illustrating response characteristics. In FIG. 1, the longitudinal direction is indicated by an arrow X, and the width direction is indicated by an arrow Y. This system 10A includes a first air conditioning duct 11 and a second air conditioning duct 12, a reference microphone 13 (first sensor) and an error microphone 14 (second sensor), a muffler speaker 15 (second sound wave generator), The silencer 16 includes a target microphone 17 (third sensor) and a controller 18. The reference microphone 13, the error microphone 14, the mute speaker 15, and the target microphone 17 are connected to the controller 18 through an interface. The sampling frequency in this system 10A is in the range of 3 kHz to 40 kHz, preferably in the range of 10 kHz to 40 kHz.

  The first air conditioning duct 11 and the second air conditioning duct 12 extend in the longitudinal direction in parallel with each other. The ducts 11 and 12 have substantially the same outer shape and width direction diameter, and the volume of the internal space per unit length is substantially the same. However, these ducts 11 and 12 are merely examples, and the outer shape of the ducts and the diameter in the width direction do not need to be the same, and further, the volume of the internal space per unit length need not be the same. In addition, the ducts do not need to exist in parallel. Therefore, those having different external shapes can be used for the first air-conditioning duct 11 and the second air-conditioning duct 12, and those having different internal space volumes per unit length can also be used. The first and second air conditioning ducts 11 and 12 may extend so as to intersect each other. In the first and second air conditioning ducts 11 and 12, the first sound wave (noise) generated from the same noise source 19 propagates in the longitudinal direction.

  The reference microphone 13 is disposed in the internal space 20 (first space) of the first air conditioning duct 11 and is disposed at a position spaced apart from the noise source 19 by a predetermined dimension in the longitudinal direction. An amplifier 21 that amplifies the sound wave detected by the reference microphone 13 is connected to the reference microphone 13. Although not shown, an A / D conversion device is connected between the controller 18 and the amplifier 21. The reference microphone 13 detects and detects a synthesized sound wave of an analog first sound wave generated from the noise source 19 and propagating through the internal space 20 of the duct 11 and an analog second sound wave described later generated from the muffling speaker 15. The synthesized sound wave is output to the amplifier 21. However, when the system 10A is activated, the reference microphone 13 detects only the first sound wave. The synthesized sound wave is amplified by the amplifier 21 and then converted into a digital first input signal (first signal) by the A / D converter. The first input signal is output from the A / D converter to the controller 18.

  The muffler speaker 15 is disposed in the internal space 20 of the first air conditioning duct 11 and is installed at a position spaced apart from the noise source 19 by a predetermined dimension in the longitudinal direction with the reference microphone 13 interposed therebetween. The muffler speaker 15 generates a second sound wave that interferes with the first sound wave in the internal space 20 of the duct 11. An amplifier 22 that amplifies the second sound wave is connected to the mute speaker 15. Although not shown, a D / A converter is connected between the controller 18 and the amplifier 22.

  The error microphone 14 is disposed in the internal space 20 of the first air conditioning duct 11 and is disposed at a position spaced apart from the reference microphone 13 by a predetermined dimension across the mute speaker 15. An amplifier 23 that amplifies the detected sound wave is connected to the error microphone 14. Although not shown, an A / D conversion device is connected between the controller 18 and the amplifier 23. The error microphone 14 detects an interference sound wave (error sound wave) generated by the interference between the first sound wave and the second sound wave, and outputs the detected interference sound wave to the amplifier 23. However, the error microphone 14 detects only the first sound wave when the system 10A is activated. The interference sound wave is amplified by the amplifier 23 and then converted into a digital second input signal (second signal) by the A / D converter. The second input signal is output from the A / D converter to the controller 18.

  The silencer 16 is disposed in the internal space 24 (second space) of the second air conditioning duct 12 and is installed at a substantially intermediate position between the noise source 19 and the target microphone 17. The silencer 16 reduces the first sound wave generated from the noise source 19 and propagating through the internal space 24 of the duct 12. The first sound wave is reduced by the silencer 16 to become a reduced sound wave. The reduced sound wave propagates in the longitudinal direction from the silencer 16 toward the target microphone 17. A silencer silencer is used for the silencer 16. As a silencer silencer, at least the sound absorbing type that reduces the noise in the middle and high frequencies by passing air between the sound absorbing materials, or the expansion type that reduces the noise of a specific frequency by the internal resonance design One can be used. In addition to the silencer silencer 16, a silencer chamber whose interior is covered with a sound absorbing material or a right angle silencer elbow attached to a corner of a duct can also be used as the silencer 16. A plurality of silencers 16 may be attached between the noise source 19 of the duct 12 and the target microphone 17.

  The target microphone 17 is disposed in the internal space 24 of the second air conditioning duct 12 and is disposed at a position spaced apart from the noise source 19 by a predetermined dimension in the longitudinal direction with the silencer 16 interposed therebetween. An amplifier 25 that amplifies the detected sound wave is connected to the target microphone 17. Although not shown, an A / D conversion device is connected between the controller 18 and the amplifier 25. The target microphone 17 detects a reduced sound wave after the first sound wave has been reduced by the silencer 16, and outputs the detected reduced sound wave to the amplifier 25. The reduced sound wave is amplified by the amplifier 25 and then converted into a digital third input signal (third signal) by the A / D converter. The third input signal is output from the A / D converter to the controller 18. The distance M1 from the noise source 19 to the target microphone 17 is substantially the same as the distance M2 from the noise source 19 to the error microphone 14. The distance M1 from the noise source 19 to the target microphone 17 may be longer than the distance M2 from the noise source 19 to the error microphone 14.

  The controller 18 includes a pseudo feedback signal generation filter 26, a first subtraction device 27, an interference signal generation device 28, and a second subtraction device 29. Although not shown, the filter 26 and the devices 27, 28, 29 A central processing unit for executing various means and a memory for storing various types of data. The controller 18 uses a DSP (Digital Signal Processor) that processes convolution calculations at high speed, but a CPU (Central Processing Unit) or MPU (Micro Processing Unit) can also be used.

  The controller 18 generates a predetermined interference signal through the filter 26 and the devices 27, 28, and 29, and generates a second sound wave in the internal space 20 of the duct 11 through the mute speaker 15. The controller 18 makes the interference sound wave and the sound reduction sound wave the same by causing the interference sound wave and the second sound wave to make the remaining sound wave obtained by removing the sound reduction sound wave from the second sound wave (0). Cancel the remaining sound wave. Although not shown, the controller 18 is connected to an input device such as a keyboard and a mouse and an output device such as a display and a printer via an interface.

  The internal address file of the memory stores an application for causing the filter 26 and the devices 27, 28, and 29 to execute each unit of the system 10A via the central processing unit. The central processing unit of the controller 18 activates an application from the memory based on the control by the operating system stored in the memory, and executes the following means according to the activated application. The central processing unit causes the interference signal generation device 28 to generate a digital interference signal (interference signal generation means), and causes the pseudo feedback signal generation filter 26 to generate a digital pseudo feedback signal (pseudo feedback signal generation means).

  The central processing unit of the controller 18 causes the interference signal to be output from the interference signal generation device 28 to the mute speaker 15 (interference signal output means), and causes the pseudo feedback signal to be output from the pseudo feedback signal generation filter 26 to the second subtraction device 29. (Pseudo feedback signal output means). The interference signal is the interference sound wave from the target microphone 17 among the interference sound waves of the first sound wave (noise) generated from the noise source 19 and propagating through the space inside 20 of the duct 11 and the second sound wave generated by the muffling speaker 15. It is a signal that becomes a second sound wave having the same sound pressure as that of the remaining sound wave excluding the sound-reduced sound wave. The pseudo feedback signal is a signal that can be estimated (identified) as the second sound wave that reaches the reference microphone 13 from the mute speaker 15.

  The central processing unit of the controller 18 causes the second subtractor 29 to subtract the pseudo feedback signal from the first input signal to generate the fourth input signal (fourth signal) (fourth signal generating means), and the fourth input signal. Is output from the second subtractor 29 to the interference signal generator 28 (fourth signal output means). The central processing unit causes the first subtracting device 27 to subtract the third input signal from the second input signal to generate an error signal (error signal generating means), and the error signal from the first subtracting device 27 to the interference signal generating device 28. (Error signal output means).

  The pseudo feedback signal generation filter 26 simulates the time series transfer characteristic (Hr) from the mute speaker 15 to the reference microphone 13. The filter 26 reflects the time-series transfer characteristic (Hr) (impulse response) between the mute speaker 15 and the reference microphone 13 estimated in advance, and the second subtractor 29 uses the pseudo feedback signal from the first input signal. Is fed forward to the second subtractor 29 so that can be subtracted. The time series transfer characteristic 55 is a response characteristic at the sound receiving point 53 when the sound wave 51 (pulse) generated from the sound source 50 propagates through the transmission path 52 and reaches the sound receiving point 53 as shown in FIG. is there. That is, the time-series transfer characteristic (Hr) indicates that the second sound wave generated from the muffling speaker 15 propagates through the internal space 20 of the duct 11 and reaches the reference microphone 13 when the second sound wave at the position of the microphone 13 is reached. The response characteristics are shown.

  The interference signal generation device 28 includes a digital filter 30, an adaptive digital filter 31 (adaptive digital filter), and an adaptive control arithmetic device 32 (Filtered-XLMS algorithm) that updates the adaptive digital filter 31. The digital filter 30 simulates time-series transfer characteristics (C) from the mute speaker 15 to the error microphone 14. In the filter 30, the adaptive control arithmetic unit 32 can update the adaptive digital filter 31 in a state in which the time-series transfer characteristic (C) (impulse response) between the muffler speaker 15 and the error microphone 14 estimated in advance is reflected. As described above, the feedforward control is performed on the adaptive control arithmetic device 32. The time series transfer characteristic (C) is a response characteristic of the second sound wave at the position of the microphone 14 when the second sound wave generated from the muffling speaker 15 propagates through the internal space 20 of the duct 11 and reaches the error microphone 14. Is shown.

  The interference signal generation device 28 updates the adaptive digital filter 31 based on the adaptive control algorithm. The adaptive digital filter 31 is an interference sound wave for equalizing the characteristic of the interference sound wave detected by the error microphone 14 and the characteristic of the sound reduction sound detected by the target microphone 17 in accordance with a change in the environment of the internal space 20 of the duct 11. A signal that minimizes the error signal).

  An example of the silencing process of the system 10A of FIG. 1 will be described as follows. When an air conditioner (not shown) is started, first sound waves (noise) are propagated from the noise source 19 of the air conditioner to the internal spaces 20 and 24 of the first and second air conditioning ducts 11 and 12. When the system 10A is activated, the controller 18 causes the filter 26 and the devices 27, 28, and 29 to execute various means according to the application stored in the memory. As indicated by an arrow f, the first sound wave reaches the reference microphone 13 while propagating through the internal space 20 of the first air conditioning duct 11, and then passes through the muffler speaker 15 and reaches the error microphone 14. Further, the sound enters the silencer 16 while propagating through the internal space 24 of the second air conditioning duct 12, and the sound is reduced by the silencer 16 to become a reduced sound wave. The reduced sound wave reaches the target microphone 17.

  At the time of activation of the system 10A, no second sound wave is generated from the muffling speaker 15, and the first sound wave (noise) detected by the reference microphone 13 propagates through the internal space 20 of the duct 11 and remains as the error microphone 14 as it is. The first sound wave is detected by the microphone 14. The reference microphone 13 that has detected the first sound wave outputs the first sound wave to the amplifier 21. The amplifier 21 amplifies the first sound wave and then outputs the first sound wave to the A / D converter. The A / D conversion device converts the first sound wave into a digital first input signal, and outputs the first input signal to the second subtraction device 29. The error microphone 14 that has detected the first sound wave outputs the first sound wave to the amplifier 23. The amplifier 23 amplifies the first sound wave and then outputs the first sound wave to the A / D converter. The A / D conversion device converts the first sound wave into a digital second input signal and outputs the second input signal to the first subtraction device 27. The target microphone 17 that has detected the reduced sound wave outputs the reduced sound wave to the amplifier 25. The amplifier 25 amplifies the reduced sound wave and then outputs the reduced sound wave to the A / D converter. The A / D converter converts the reduced sound wave into a digital third input signal and outputs the third input signal to the first subtractor 27.

  Since the pseudo feedback signal is not generated in the pseudo feedback signal generation filter 26 when the system 10A is activated, the output signal of the pseudo feedback signal output from the pseudo feedback signal generation filter 26 is (0). When the system 10A is activated, the second subtractor 29 subtracts the pseudo feedback signal (0) from the first input signal to generate a fourth input signal (a signal having the same value as the first input signal) (fourth signal). Signal generation means), and outputs the fourth input signal to the interference signal generation device 28 (fourth signal output means).

  When the system 10A is activated, the first subtractor 27 subtracts the third input signal from the second input signal representing the first sound wave to calculate an error signal (error signal generating means), and generates the error signal as an interference signal. It outputs to the apparatus 28 (error signal output means). When the system 10A is activated, the value of the error signal, which is the difference between the second input signal and the third input signal, is maximum. The digital filter 30 forming the interference signal generation device 28 uses a time series transfer characteristic (C) that simulates a response characteristic from the muffler speaker 15 to the error microphone 14 estimated in advance, and transmits the time series transfer to the fourth input signal. The characteristic (C) is subjected to a convolution operation, and the result is output to the adaptive control operation device 32 forming the interference signal generation device 28.

  The adaptive control arithmetic unit 32 updates the adaptive digital filter 31 using the error signal while considering the time-series transfer characteristic of the secondary path. Specifically, the adaptive control arithmetic unit generates a Δ adaptive digital filter (ΔADF) in time series at a predetermined time interval in accordance with a sampling frequency (3 kHz to 40 kHz), and the Δ adaptive digital filter is converted into a current adaptive digital filter (ADF). ) To update the adaptive digital filter from the present to the future.

  The interference signal generator 28 convolves the adaptive digital filter 31 with the fourth input signal output from the second subtractor 29, and generates an interference signal that minimizes the second input signal in time series (interference signal generation). means). The interference signal generation device 28 outputs the generated interference signal to the pseudo feedback signal generation filter 26 and the D / A converter (interference signal output means). The D / A converter converts the digital interference signal into an analog second sound wave, and outputs the second sound wave to the amplifier 22. The amplifier 22 amplifies the second sound wave and outputs the amplified second sound wave to the mute speaker 15.

  The mute speaker 15 generates a second sound wave in the internal space 20 of the duct 11. The second sound wave propagates from the speaker 15 toward the reference microphone 13 through the internal space 20 of the duct 11 and from the speaker 15 toward the error microphone 14 through the internal space 20. The second sound wave travels toward the error microphone 14 while interfering with the first sound wave, interferes with the sound wave of the frequency band attenuated by the silencer 16 of the second air conditioning duct 12 of the first sound wave, and the sound wave of the band is transmitted. Counteract. However, since the second sound wave does not include a sound wave of a frequency band that is not attenuated by the silencer 16 of the second air conditioning duct 12, the sound wave of the second air conditioning duct 12 is not canceled out. Sound waves having the same characteristics as the characteristics remain in the internal space 20 of the first air conditioning duct 11. When the system 10A is continuously operated, the error signal gradually decreases, and finally the error signal level becomes (0) and the error disappears. The disappearance of the error represents a state in which the sound wave in the frequency band attenuated by the silencer 16 is canceled.

  During the operation of the system 10 </ b> A, the second sound wave toward the reference microphone 13 is synthesized with the first sound wave, and these synthesized sound waves are detected by the reference microphone 13. Further, the second sound wave directed toward the error microphone 14 interferes with the first sound wave at the position of the microphone 14, and these interference sound waves are detected by the error microphone 14. The synthesized sound wave is amplified by the amplifier 21, converted to a digital first input signal by the A / D converter, and output to the second subtractor 29.

  The pseudo feedback signal generation filter 26 uses a time-series transfer characteristic (Hr) simulating a transmission path (tertiary path) from the muffler speaker 15 to the reference microphone 13 estimated in advance, and uses the time-series transfer characteristic (Hr) as an interference signal. ) To generate a pseudo feedback signal (pseudo feedback signal generating means). The pseudo feedback signal generation filter 26 outputs the generated pseudo feedback signal to the second subtraction device 29 (pseudo feedback signal output means). The second subtracting device 29 subtracts a pseudo feedback signal that can be estimated as an interference signal from the combined signal to generate a fourth input signal (fourth signal generating means), and sends the fourth input signal to the interference signal generating device 28. Output (fourth signal output means).

  The error microphone 14 that has detected the interfering sound wave during operation of the system 10 </ b> A outputs the interfering sound wave to the amplifier 23. The amplifier 23 amplifies the interference sound wave and then outputs the interference sound wave to the A / D converter. The A / D conversion device converts the interference sound wave into a second input signal and outputs the second input signal to the first subtraction device 27. The first subtractor 27 calculates an error signal by subtracting the third input signal from the second input signal representing the interfering sound wave (error signal generator), and outputs the error signal to the interference signal generator 28 (error). Signal output means). At this time, the output level of the error signal, which is the difference between the second input signal and the third input signal, is smaller than when the system 10A is activated.

  In the interference signal generation device 28, the adaptive control arithmetic device 32 updates the adaptive digital filter 31 using the error signal while taking into account the time delay of the secondary path and the transmission frequency characteristics. The interference signal generator 28 convolves the adaptive digital filter 31 with the fourth input signal output from the second subtractor 27, and generates an interference signal that minimizes the second input signal (interference signal generator). The interference signal generation device 28 outputs the generated interference signal to the pseudo feedback signal generation filter 26 and the D / A converter (interference signal output means). The D / A converter converts the digital interference signal into an analog second sound wave, and outputs the second sound wave to the amplifier 22. The amplifier 22 amplifies the second sound wave and then outputs the second sound wave to the muffler speaker 15. The mute speaker 15 generates a second sound wave in the internal space 20 of the duct 11.

  FIG. 3 is a diagram showing an example of the silencing effect (experimental result) by this system 10A, and FIG. 4 is a diagram showing another example of the silencing effect. In these figures, the frequency characteristic of the internal space 20 of the first air conditioning duct 11 when the system 10A is OFF is indicated by a one-dot chain line L1, the frequency characteristic of the internal space 20 of the duct 11 when the system 10A is ON is indicated by a solid line L2, and 2 The frequency characteristic of the internal space 24 of the air conditioning duct 12 is indicated by a one-dot chain line L3. In these figures, the vertical axis represents the sound pressure level, and the horizontal axis represents the frequency. In the system 10A, the frequency characteristics of the internal spaces 20 and 24 of the ducts 11 and 12 shown in the drawings can be monitored in time series via a display, and the monitored frequency characteristics can be output via a printer. . Further, the monitored frequency characteristics can be stored in the memory in time series.

  FIG. 3 shows a silencing effect in the system 10 </ b> A when the air-conditioning ducts 11 and 12 having substantially the same outer shape and diameter in the width direction and having substantially the same internal space volume per unit length are used. In the internal space 24 of the second air conditioning duct 12, as indicated by a dotted line L <b> 3 in FIG. 3, sound in the frequency band of 350 (Hz) to 550 (Hz) is reduced by the silencer 16. In the internal space 20 of the first air-conditioning duct 11 when the system 10A is OFF, there is no change in the sound pressure level in the frequency band of 350 (Hz) to 550 (Hz) as shown by a one-dot chain line L1 in FIG. Note that changes in the sound pressure level in other frequency bands are substantially the same in the first and second air conditioning ducts 11 and 12.

  When the system 10A is turned on, as indicated by a solid line L2 in FIG. 3, the sound in the frequency band of 350 (Hz) to 550 (Hz) is reduced in the internal space 20 of the first air conditioning duct 11, and the second air conditioning duct 12. The frequency characteristics of the internal space 20 of the first air conditioning duct 11 approximated to the frequency characteristics of the internal space 24 of the first air conditioning duct 11. As shown in FIG. 3, by using this system 10 </ b> A, the acoustic environment of the internal space 24 of the second air conditioning duct 12 could be reproduced in the internal space 20 of the first air conditioning duct 11.

  FIG. 4 shows a silencing effect in the system 10A when a silencer different from that in FIG. 3 is used. Other conditions are the same as those in FIG. In the internal space 24 of the second air conditioning duct 11, as indicated by a dotted line L <b> 3 in FIG. 4, sound in the frequency band of 150 (Hz) to 160 (Hz) is reduced by the silencer 16, and 250 (Hz) to 310. The sound in the frequency band of (Hz) is reduced, and the sound in the frequency band of 360 (Hz) to 690 (Hz) is reduced. Furthermore, the sound in the frequency band of 790 (Hz) to 870 (Hz) is reduced. In the internal space 20 of the first air-conditioning duct 11 when the system 10A is OFF, there is no change in the sound pressure level in those frequency bands, as indicated by the one-dot chain line L1 in FIG.

  When the system 10A is turned on, as indicated by a solid line L2 in FIG. 4, sounds in these frequency bands are reduced in the internal space 20 of the first air conditioning duct 11, and the frequency characteristics of the internal space 24 of the second air conditioning duct 12 are 1 The frequency characteristics of the internal space 20 of the air conditioning duct 11 are approximated. As shown in FIG. 4, by using this system 10 </ b> A, the acoustic environment of the internal space 24 of the second air conditioning duct 12 could be reproduced in the internal space 20 of the first air conditioning duct 11.

  In this active silencing system 10A, the first subtractor 27 generates an error signal obtained by removing the third input signal from the second input signal, and the interference signal generator 28 receives the fourth input signal received from the second subtractor 29. And the error signal received from the first subtractor 27, the interference signal is generated, so that the error signal does not include a signal in a frequency band that is not attenuated by the silencer 16 of the second air conditioning duct 11, and the frequency The sound wave of the frequency band includes the signal of the frequency band that is attenuated by the silencer 16 of the second air conditioning duct 11 while the sound wave of the band is left in the first air conditioning duct 12. 11 can be canceled. Therefore, the system 10 </ b> A can reproduce the acoustic environment of the internal space 20 of the second air conditioning duct 12 in the internal space 24 of the first air conditioning duct 11.

  This active silencing system 10 </ b> A can apply the good acoustic environment of the internal space 24 of the second air conditioning duct 12 adjusted by the silencer 16 to the internal space 20 of the first air conditioning duct 11. It is not necessary to set the acoustic environment independently in the duct 11, and the labor for that can be saved. This system 10A generates a fourth signal obtained by removing the pseudo feedback signal that can be estimated as the second sound wave from the synthesized signal by the second subtractor 29, and outputs the fourth signal to the interference signal generator 28. The fourth signal output to the signal generator 28 does not include a pseudo feedback signal, and howling in the reference microphone 13 can be prevented.

  In this system 10A, since the digital filter 30 uses the time-series transfer characteristic from the muffler speaker 15 to the error microphone 14 to the second sound wave, the adaptive control arithmetic device 32 is connected between the mute speaker 15 and the error microphone 14. The adaptive digital filter 31 can be updated using the error signal while taking into account the time-series transfer characteristics of the next path, while following changes in noise and target signals in the internal space 20 of the first air conditioning duct 11, The interfering sound wave can be canceled reliably at the position of the error microphone 14 that is the mute position. Since the sampling frequency of the system 10A is in the range of 3 kHz to 40 kHz, the second sound wave can be brought as close as possible to the sound wave having the opposite phase and the same sound pressure of the interference sound wave, and the second sound wave can be used to ensure the interference sound wave. Can be canceled.

  In this system 10A, since the distance from the noise source 19 to the target microphone 17 is substantially the same as the distance from the noise source 19 to the error microphone 14, the second input signal output from the error microphone 14 and the output from the target microphone 17 are output. The causality between the second input signal and the second input signal output from the error microphone 14 as the second input signal while leaving the sound-reduced sound wave in the internal space 20 of the second air conditioning duct 11 can be maintained. 1 Interference sound waves in the internal space 20 of the air conditioning duct 11 can be reliably canceled by the second sound waves.

  FIG. 5 is a configuration diagram of an active silencing system 10B shown as another example. The system 10B shown in FIG. 5 is different from that shown in FIG. 1 in that two first air conditioning ducts 11 exist. The air-conditioning ducts 11 and 12 are the same as the air-conditioning ducts 11 and 12 shown in FIG. 1, and the microphones 13, 14, and 17 installed in the air-conditioning ducts 11 and 12, the speaker 15, and the silencer 16 are shown in FIG. These are the same as those installed in the air conditioning ducts 11 and 12 shown. The configuration of the controller 18 is the same as that of the controller 18 shown in FIG. Therefore, the description of the ducts 11 and 12, the microphones 13, 14 and 17, the speaker 15, the silencer 16, and the controller 18 in the system 10 </ b> B is omitted by giving the same reference numerals as the system 10 </ b> A in FIG. 1.

  Although two first air conditioning ducts 11 are illustrated in FIG. 5, the number of the ducts 11 is not limited to two, and more than two ducts 11 may exist, The system 10B can also be used. Since the silencing process in the system 10B is the same as that of the system 10A in FIG. 1, the silencing process in the system 10A in FIG. 1 is used, and the description of the silencing process in the system 10B is omitted. The sampling frequency in this system 10B is the same as that of the system 10A in FIG. The distance M1 from the noise source 19 to the target microphone 17 is substantially the same as the distance M2 from the noise source 19 to the error microphone 14.

  In addition to the effect of the system 10A shown in FIG. 1, the system 10B shown in FIG. 5 can provide a good acoustic environment in the internal space 24 of the second air conditioning duct 12 adjusted by the silencer 16. 24, and the acoustic environment of the internal space 20 of the second air conditioning duct 12 can be applied to all of the first air conditioning ducts 11.

  FIG. 6 is a configuration diagram of an active silencing system 10C shown as another example. The system 10C shown in FIG. 6 differs from that shown in FIG. 1 in that the distance M1 from the noise source 19 to the target microphone 17 is shorter than the distance M2 from the noise source 19 to the error microphone 14, and A time delay correcting device 33 that corrects a time delay until the sound-reduced sound wave propagates is connected between the microphone 14 and the first subtracting device 27, and other configurations are those of the system 10A of FIG. Therefore, the same reference numerals as those of the system 10A in FIG.

  In this system 10 </ b> C, a time delay correction device 33 is interposed between the microphone 14 and the first subtraction device 27. The time delay correction device 33 corrects the time delay until the sound reduction sound wave propagates from the noise source 19 to the target microphone 17. An A / D conversion device is connected between the time delay correction device 33 and the first subtraction device 27, although not shown. The sampling frequency in this system 10B is the same as that of the system 10A in FIG.

  An example of the silencing process in the system 10C will be described as follows. At the time of activation of the system 10C, the second sound wave is not generated from the muffling speaker 15, and the first sound wave (noise) detected by the reference microphone 13 propagates through the internal space 20 of the duct 11 and remains in the error microphone 14 as it is. The first sound wave is detected by the microphone 14. The reference microphone 13 that has detected the first sound wave outputs the first sound wave to the amplifier 21. The amplifier 21 amplifies the first sound wave and then outputs the first sound wave to the A / D converter. The A / D conversion device converts the first sound wave into a digital first input signal, and outputs the first input signal to the second subtraction device 29. The error microphone 14 that has detected the first sound wave outputs the first sound wave to the amplifier 23. The amplifier 23 amplifies the first sound wave and then outputs the first sound wave to the A / D converter. The A / D conversion device converts the first sound wave into a digital second input signal and outputs the second input signal to the first subtraction device 27. The target microphone 17 that has detected the reduced sound wave outputs the reduced sound wave to the amplifier 25. The amplifier 25 amplifies the reduced sound wave and then outputs the reduced sound wave to the A / D converter. The A / D converter converts the reduced sound wave into a digital third input signal and outputs the third input signal to the first subtractor 27.

  Since the pseudo feedback signal is not generated in the pseudo feedback signal generation filter 26 when the system 10C is activated, the output signal of the pseudo feedback signal output from the pseudo feedback signal generation filter 26 is (0). When the system 10C is activated, the second subtractor 29 subtracts the pseudo feedback signal (0) from the first input signal to generate a fourth input signal (a signal having the same value as the first input signal) (fourth signal). Signal generation means), and outputs the fourth input signal to the interference signal generation device 28 (fourth signal output means).

  The error microphone 14 that has detected the first sound wave outputs the first sound wave to the amplifier 23. The amplifier 23 amplifies the first sound wave and then outputs the first sound wave to the A / D converter. The A / D conversion device converts the first sound wave into the second input signal, and then outputs the second input signal to the first subtraction device 27. The target microphone 17 that has detected the reduced sound wave outputs the reduced sound wave to the amplifier 25. The amplifier 25 amplifies the reduced sound wave, and then outputs the reduced sound wave to the time delay correction device 33. The time delay correction device 33 corrects the time delay until the sound reduction sound wave propagates from the noise source 19 to the target microphone 17. Specifically, the time taken for the reduced sound wave to propagate from the noise source 19 to the target microphone 17 is matched with the time taken for the first sound wave to propagate from the noise source 19 to the error microphone 14. The time delay correction device 33 outputs the sound-reduced sound wave with the time delay corrected to the A / D conversion device. The A / D conversion device converts the reduced sound wave into a third input signal, and then outputs the third input signal to the first subtraction device 27. When the system 10C is activated, the first subtractor 27 calculates an error signal by subtracting the third input signal from the second input signal (error signal generation means), and outputs the error signal to the interference signal generator 28. (Error signal output means).

  The digital filter 30 forming the interference signal generation device 28 uses a time-series transfer characteristic (C) that simulates the response characteristic of the transmission path from the muffler speaker 15 to the error microphone 14 estimated in advance, and uses it as the fourth input signal. The time series transfer characteristic (C) is convolutionally calculated, and the result is output to the adaptive control arithmetic unit 32 forming the interference signal generation unit 28. The adaptive control arithmetic unit 32 updates the adaptive digital filter 31 using the error signal while considering the time-series transfer characteristic of the secondary path.

  The interference signal generation device 28 performs a convolution operation with the adaptive digital filter 31 on the fourth input signal output from the second subtraction device 29, and generates an interference signal that minimizes the second input signal (interference signal generation means). The interference signal generation device 28 outputs the generated interference signal to the pseudo feedback signal generation filter 26 and the D / A converter (interference signal output means). The D / A converter converts the digital interference signal into an analog second sound wave, and outputs the second sound wave to the amplifier 22. The amplifier 22 amplifies the second sound wave and then outputs the second sound wave to the muffler speaker 15.

  The mute speaker 15 generates a second sound wave in the internal space 20 of the duct 11. The second sound wave propagates from the speaker 15 toward the reference microphone 13 through the internal space 20 of the duct 11 and from the speaker 15 toward the error microphone 14 through the internal space 20. The second sound wave travels toward the error microphone 14 while interfering with the first sound wave, interferes with the sound wave of the frequency band attenuated by the silencer 16 of the second air conditioning duct 12 of the first sound wave, and the sound wave of the band is transmitted. Counteract. However, since the second sound wave does not include a sound wave of a frequency band that is not attenuated by the silencer 16 of the second air conditioning duct 12, the sound wave of the second air conditioning duct 12 is not canceled out. Sound waves having the same characteristics as the characteristics remain in the internal space 20 of the first air conditioning duct 11. When the system 10C is continuously operated, the error signal gradually decreases, and finally the error signal level becomes (0) and the error disappears. The disappearance of the error represents a state in which the sound wave in the frequency band attenuated by the silencer 16 is canceled.

  During operation of the system 10 </ b> C, a synthesized sound wave of the first sound wave and the second sound wave is detected by the reference microphone 13. Further, an interference sound wave between the first sound wave and the second sound wave is detected by the error microphone 14. The synthesized sound wave is amplified by the amplifier 21, converted to a digital first input signal by the A / D converter, and output to the second subtractor 29. As in the system 10A of FIG. 1, the pseudo feedback signal generation filter 26 convolves the time series transfer characteristic (Hr) with the interference signal, generates a pseudo feedback signal (pseudo feedback signal generation means), and generates the pseudo feedback signal. Output to the second subtractor 29 (pseudo feedback signal output means). The second subtractor 29 subtracts the pseudo feedback signal from the synthesized signal to generate a fourth input signal (fourth signal generator), and outputs the fourth input signal to the interference signal generator 28 (fourth signal). Output means).

  The error microphone 14 that has detected the interference sound wave during operation of the system 10 </ b> C outputs the interference sound wave to the amplifier 23. The amplifier 23 amplifies the interference sound wave and then outputs the interference sound wave to the A / D converter. The A / D conversion device converts the interference sound wave into a second input signal and outputs the second input signal to the first subtraction device 27. The first subtractor 27 calculates an error signal by subtracting the third input signal from the second input signal (error signal generator), and outputs the error signal to the interference signal generator 28 (error signal output unit). .

  In the interference signal generation device 28, the adaptive control arithmetic device 32 updates the adaptive digital filter 31 using the error signal while taking into account the time-series transfer characteristics of the secondary path. The interference signal generator 28 convolves the adaptive digital filter 31 with the fourth input signal output from the second subtractor 29, and generates an interference signal that minimizes the second input signal in time series (interference signal generation). means). The interference signal generation device 28 outputs the interference signal to the pseudo feedback signal generation filter 26 and the D / A conversion device (interference signal output means). The D / A conversion device converts the interference signal into a second sound wave and outputs the second sound wave to the amplifier 22. The amplifier 22 amplifies the second sound wave and outputs the amplified second sound wave to the mute speaker 15. The mute speaker 15 generates a second sound wave in the internal space 20 of the duct 11.

  In this system 10C, since the time delay until the reduced sound wave propagates from the noise source 19 to the target microphone 17 is corrected by the time delay correction device 33, the first sound wave propagates from the noise source 19 to the error microphone 14. And the second input signal output from the error microphone 14 and the third input output from the target microphone 17 can be made to coincide with the time until the reduced sound wave propagates from the noise source 19 to the target microphone 17. Causality between signals can be maintained. Further, in this system 10C, the length of the second air conditioning duct 12 is shorter than that of the first air conditioning duct 11, and the target microphone 17 must be installed at a position shorter than the distance from the noise source 19 to the error microphone 14. It is effective when it is necessary. The system 10C has the same effects as the system 10A of FIG. 1 in addition to the effects described above. However, the effects of the system 10A of FIG. 1 are used, and description of other effects of the system 10C is omitted.

  In the illustrated systems 10A, 10B, and 10C, microphones 13, 14, and 17 and speakers 15 are installed in the internal spaces 20 and 24 of the air conditioning ducts 11 and 12, and the acoustic environment of the second air conditioning duct 12 is defined as the first air conditioning duct 11. However, the system 10A, 10B, and 10C are not limited to the internal spaces 20 and 24 of the ducts 11 and 12, but the illustrated systems 10A, 10B, and 10C are ducted. It can also be used in other spaces.

The block diagram of the active silence system shown as an example. The figure explaining a frequency characteristic. The figure which shows an example of the silencing effect (experimental result) by a system. The figure which shows another example of the muffling effect (experiment result) by a system. The block diagram of the active silence system shown as another example. The block diagram of the active silence system shown as another example.

10A Active silencer system 10B Active silencer system 10C Active silencer system 11 First air conditioning duct 12 Second air conditioning duct 13 Reference microphone (first sensor)
14 Error microphone (second sensor)
15 Silencer speaker (second sound generator)
16 Silencer 17 Target microphone (third sensor)
18 Controller 19 Noise source 20 Internal space (first space)
24 Internal space (second space)
26 pseudo feedback signal generation filter 27 first subtraction device 28 interference signal generation device 29 second subtraction device 30 digital filter 31 active digital filter 32 adaptive control arithmetic device 33 time delay correction device

Claims (9)

A first sensor disposed at a predetermined distance from the noise source, and disposed at a predetermined distance from the noise source with the first sensor interposed therebetween, and is generated from the noise source and propagates through the predetermined first space. A second sound wave generator that generates a second sound wave that interferes with the first sound wave in the first space; and a second sensor that is spaced apart from the first sensor by a predetermined dimension across the second sound wave generator. An interference signal generation device that generates an interference signal to be the second sound wave and outputs the generated interference signal to the second sound wave generation device, wherein the first sensor includes the first sound wave and the second sound wave. And the detected synthesized sound wave is output as a first signal, and the second sensor detects the interference sound wave generated by the interference between the first sound wave and the second sound wave, and detects the detected interference. Active silencer system that outputs sound wave as second signal In,
The active silencing system is disposed in the second space that is different from the first space by a predetermined distance from the noise source, and is generated in the second space and is generated from the noise source. A silencer for reducing the propagating first sound wave, and a predetermined distance from the noise source with the silencer interposed therebetween, and detecting the reduced sound wave of the first sound wave reduced by the silencer A third sensor that outputs the sound-reduced sound wave as a third signal; a third signal received from the third sensor while receiving a second signal from the second sensor; and the third signal from the second signal A first subtractor that generates an error signal excluding
The active silencer system, wherein the interference signal generation device generates the interference signal using a first signal received from the first sensor and an error signal received from the first subtraction device.   The active silencing system receives a first signal from the first sensor and a pseudo feedback signal generation filter that generates a pseudo feedback signal that estimates a second sound wave that reaches the first sensor from the second sound generator. A second subtraction device that receives a pseudo feedback signal from the pseudo feedback signal generation filter and generates a fourth signal obtained by removing the pseudo feedback signal from the first signal, and the interference signal generation device includes: The active silencing system according to claim 1, wherein the interference signal is generated using a fourth signal received from a second subtractor and an error signal received from the first subtractor.   Adaptive control in which the interference signal generation device updates the adaptive digital filter by using an adaptive digital filter for generating the interference signal that minimizes the second signal and an error signal received from the second subtraction device The active silencing system according to claim 2, wherein the active silencing system is formed from an arithmetic unit.   The interference signal generation device includes a digital filter that simulates a time-series transfer characteristic from the second sound wave generation device to the second sensor, and the adaptive control arithmetic device includes the time-series transfer characteristic in the digital filter and the first filter. 4. The active silencer system of claim 3, wherein the adaptive digital filter is updated from an error signal received from a subtractor.   The distance from the noise source to the third sensor is substantially the same as the distance from the noise source to the second sensor or longer than the distance from the noise source to the second sensor. An active silencing system according to claim 1.   The distance from the noise source to the third sensor is shorter than the distance from the noise source to the second sensor, and the distance from the noise source to the first sensor is between the third sensor and the first subtractor. 5. The active silencing system according to claim 1, wherein a time delay correction device for correcting a time delay until the sound-reduced sound wave propagates to three sensors is connected.   The active silencing system according to any one of claims 1 to 6, wherein a sampling frequency in the active silencing system is in a range of 3 kHz to 40 kHz.   The active silencing system according to any one of claims 1 to 7, wherein in the active silencing system, there are a plurality of the first spaces that are independent of each other.   The active silencing system according to any one of claims 1 to 8, wherein the first space and the second space are internal spaces of an air conditioning duct.

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