JP5866142B2 - Active silencer - Google Patents

Description

  The present invention relates to an active silencer that reduces noise by generating sound waves having a phase opposite to that of noise in devices and apparatuses that generate noise, such as printing presses, automobiles, and air conditioners.

  2. Description of the Related Art Conventionally, active silencers have been applied to devices that generate noise, such as automobiles and coolers, which generate a signal with a phase opposite to that of the noise and output sound waves corresponding to the signal from a speaker. Yes.

  FIG. 7 is a block diagram showing a general configuration of a conventional active silencer (active noise control). As shown in FIG. 7, the conventional active silencer includes a noise source collecting microphone 1, an error detection microphone 2, an active noise control unit 3, and a cancellation speaker 4.

  The noise source collecting microphone 1 is a microphone that is installed on the upstream side (in the vicinity of the noise source) of an acoustic path through which noise generated in the apparatus passes and picks up the noise. The noise source collecting microphone 1 generates a noise signal based on the picked up noise and outputs the noise signal to an active noise control unit 3 described later.

  The error detection microphone 2 is installed on the downstream side of the acoustic path through which the noise generated in the apparatus passes (at least downstream of the canceling speaker 4), and picks up the noise and detects the result of the silencing. It is. The error detection microphone 2 outputs an error detection signal based on the picked up noise to the active noise control unit 3 described later.

  The active noise control unit 3 generates a mute signal having a phase opposite to that of the noise based on the noise signal generated by the noise source collecting microphone 1 and outputs the mute signal to the canceling speaker 4.

  The canceling speaker 4 outputs a sound wave having a phase opposite to that of the noise at a timing when the noise traveling wave reaches the installation position of the canceling speaker 4 based on the mute signal generated by the active noise control unit 3. Cancels the sound pressure.

  If the canceling speaker 4 always outputs a sound wave for silencing with a fixed conversion gain, the silencing effect is reduced. Therefore, the active noise control unit 3 detects a silencing effect based on the error detection signal generated by the error detection microphone 2 and generates a silencing signal controlled to an appropriate level. In other words, the active noise control unit 3 monitors the result of the silencing effect fed back through the error detection microphone 2, and generates and outputs a more efficient silencing signal.

  In Patent Document 1, it is possible to obtain a stable silencing effect even in an environment where sudden disturbances exist, and even when there are a plurality of noise sources that generate motor rotation noise or other pure sound system noise. Therefore, there is described a muffler for an image forming apparatus which has a problem of providing a muffling function for sufficiently muffing these noises.

  This silencer is generated even when there are multiple noise sources that generate pure tone noise, such as the rotational noise of the drive motor, scanner motor, etc., or the charging noise generated when the charging roller is driven with AC voltage. There are provided as many signal generation means as the number of noise sources that generate a signal correlated with the pure tone noise, and the signals for the plurality of noise sources obtained by the signal generation means are synthesized by the signal synthesis means. Sound waves that cancel each other out with the pure tone noise based on the synthesized signal are generated from the loudspeaker, so that a silencing effect can be obtained for the plurality of pure tone noises.

  Patent Document 2 describes an active silencer that easily detects an abnormal location and notifies a remote location of the abnormality even if the installation location is away from an operator or a service station.

  This active silencer is detected by a first noise detection means in a duct arranged on the noise source side, a means arranged on the downstream side of the duct to output a silence signal, and a first noise detection means. Computation means for calculating a mute signal having an antiphase with respect to the noise signal, and second noise detection means disposed downstream of the output means, and further detecting abnormality of the detection means and output means Because it has an alarm device that displays these and gives an alarm, when an abnormality occurs in the active silencer, it is possible to easily recognize the abnormal part and the faulty part at a remote place, It is possible to prevent the parts from being damaged by stopping them, and to take measures such as preparing a replacement for the failed part and repairing it.

JP-A-9-197921 JP 2001-222287 A

  However, the conventional active silencer has a problem in the convergence performance (real-time property) of the adaptive filter for optimizing the silencing effect. That is, in the conventional active silencer as shown in FIG. 7, a time lag occurs between the sound pick-up by the error detection microphone 2 and the feedback to the active noise control unit 3. Noise that cannot be fully generated occurs.

  The conventional active silencer shown in FIG. 7 can pick up true noise because the sound pressure output from the canceling speaker 4 returns to the noise source collecting microphone 1 to generate a howling phenomenon. It has the problem of becoming difficult.

  The present invention solves the above-mentioned problems of the prior art, and enables a real-time silencing operation, and also prevents the oscillation phenomenon (howling) caused by the active silencing from interfering with the noise source collecting microphone, and the necessary active noise. It is an object of the present invention to provide an active silencer capable of securing a silence level.

  In order to solve the above problems, an active silencer according to the present invention includes an acoustic path for propagating a sound wave from a sound source, and a sound wave detection unit provided in the acoustic path for detecting the sound wave propagating through the acoustic path. A first silenced sound wave generator that is provided downstream of the sound wave detection unit in the acoustic path and generates a first silenced sound wave having an opposite phase to silence the sound wave from the sound source; and the sound wave detection unit A first control unit that controls the generation timing and volume of the first silencing sound wave based on the sound wave detected by the sound wave, and between the sound wave detection unit and the first silencing sound wave generation unit in the acoustic path. A second muffled sound wave generator provided to generate a second muffled sound wave having an opposite phase to mute the first muffled sound wave, and based on the sound wave detected by the sound wave detector, Occurrence timing and Characterized in that it comprises a second control unit for controlling the amount.

  In order to achieve the above object, the second feature of the active silencer according to the present invention is that the first control unit is configured such that the volume of the first silenced sound wave is based on the frequency of the sound wave detected by the sound wave detection unit. Is to control.

  In order to achieve the above object, a third feature of the active silencer according to the present invention is that the second control unit is configured such that the volume of the second silenced sound wave is based on the frequency of the sound wave detected by the sound wave detection unit. Is to control.

  In order to achieve the above object, a fourth feature of the active silencer according to the present invention is that the acoustic path has a smaller acoustic impedance than other openings that emit sound waves from the sound source to the outside. is there.

  In order to achieve the above object, a fifth feature of the active silencer according to the present invention is that the acoustic path has a shape in which a cross-sectional area gradually increases from the upstream side toward the downstream side.

  According to the first aspect of the present invention, a real-time silencing operation is possible, and an oscillation phenomenon (howling) due to interference of active silencing with the sound wave detection unit can be prevented to ensure a necessary active silencing level. it can.

  According to the second aspect of the present invention, by providing the first control unit, it is possible to control to an effective silencing level corresponding to the frequency of the sound wave from the sound source, and to converge by feedback control as in the prior art The mute operation can be performed in real time as compared with the case where the volume control is performed using the system.

  According to the invention described in claim 3, by providing the second control unit, an effective silencing level corresponding to the frequency of the sound wave from the sound source is obtained for the second silencing sound wave for muting the first silencing sound wave. Can be controlled.

  According to the fourth aspect of the present invention, by providing an acoustic path having an acoustic impedance smaller than that of the opening that cannot be sealed, the internal noise can be effectively guided to the acoustic path and active silencing can be performed.

  According to the invention described in claim 5, by providing the acoustic path having a shape in which the cross-sectional area gradually increases from the upstream side toward the downstream side (for example, a trumpet shape), the acoustic impedance is reduced, and the internal noise is effectively acoustically generated. Active mute can be performed by guiding to the road.

It is a block diagram which shows the structure of the active silencer of the form of Example 1 of this invention. It is an image figure which shows the structure at the time of applying the active silencer of the form of Example 1 of this invention to a printing press. It is a figure explaining operation | movement of the active silencer of the form of Example 1 of this invention. It is a figure which shows the volume coefficient by which the silencing effect is most acquired with respect to a noise frequency in the active silencing apparatus of the form of Example 1 of this invention about a 1st silencing sound wave and a 2nd silencing sound wave. It is a wave form diagram which shows the sound pressure frequency characteristic by the sweep sine wave of the active silencer of the form of Example 1 of this invention. It is a figure which shows the sound wave waveform of each part by the sweep sine wave of the active silencer of the form of Example 1 of this invention. It is a block diagram which shows the general structure of the conventional active silencer (active noise control).

  Embodiments of the active silencer of the present invention will be described below in detail with reference to the drawings.

  Embodiments of the present invention will be described below with reference to the drawings. First, the configuration of the present embodiment will be described. FIG. 1 is a block diagram illustrating a configuration of an active silencer according to a first embodiment of the present invention. Also. FIG. 2 is an image diagram showing a configuration when the active silencer of this embodiment is applied to a printing press. In this embodiment, the active silencer will be described as being applied to a printing press as shown in FIG. 2, but is not necessarily limited to a printing press and can be applied to various devices such as automobiles and air conditioner outdoor units. is there.

  As shown in FIG. 1, the active silencer 3 of the present embodiment includes a noise source collecting microphone 1, cancellation speakers 4a and 4b, an opening 5, an acoustic path 6, a first signal delay unit 7, and a second signal delay. Unit 8, frequency detection unit 9, first volume control unit 10, and second volume control unit 11.

  The noise source collecting microphone 1 corresponds to the sound wave detection unit of the present invention, is provided in the acoustic path 6, and detects a sound wave propagating through the acoustic path 6. The noise source collecting microphone 1 is a microphone that is installed on the upstream side (in the vicinity of the noise source) of the acoustic path 6 through which noise generated in the printing machine passes and picks up the noise. This noise source collecting microphone 1 generates a noise signal based on the picked up noise and outputs it to the first signal delay unit 7 and the frequency detection unit 9.

  The acoustic path 6 propagates sound waves from a sound source (here, a noise source in the printing press). The acoustic path 6 constitutes a sound guiding path with a lighter acoustic load (impedance) than the opening 5 that cannot be sealed. Here, the opening 5 is not an essential component for the active silencer, but refers to a portion that cannot be sealed (must open) due to the nature of the device to which the active silencer is applied. For example, a printing machine as shown in FIG. 2 includes a paper feed unit that feeds paper and a paper discharge unit that discharges printed paper in the apparatus. On the other hand, noise generated in the printing press is emitted to the outside through the opening 5 and it is difficult to provide sound insulation.

  When applied to a device having such an opening 5, the active silencer of this embodiment has an effect of reducing noise emitted to the outside from the opening 5. That is, the acoustic path 6 has a smaller acoustic impedance than the other openings 5 that emit sound waves from the sound source to the outside. Specifically, the acoustic path 6 has a shape (for example, a trumpet shape) whose cross-sectional area gradually increases from the upstream side toward the downstream side. Thereby, the acoustic path 6 can reduce the acoustic impedance, and can induce internal noise into the acoustic path 6.

  In other words, it is desirable that the acoustic path 6 has a trumpet shape that can guide the acoustic load as much as possible toward the radiation port, and it is desirable that the acoustic load be sufficiently lighter than the opening 5 in order to disperse the noise energy.

  Here, A (z_o) is the acoustic impedance of the opening 5, A (z_r) is the acoustic impedance of the acoustic path 6, E (in) is the noise energy in the apparatus (here, the printing press), and E (out_o) Is the noise energy emitted from the opening 5, and E (out_r) is the energy emitted from the acoustic path 6 radiation port, the following equation is established.

E (in) = E (out_o) + E (out_r) (1)
E (out_o) / E (out_r) = A (z_r) / A (z_o) (2)
Equation (3) is obtained from Equation (1) and Equation (2).

E (out_o) = [A (z_r) / (A (z_o) + A (z_r))]. E (in) (3)
That is, by making the acoustic impedance of the acoustic path 6 smaller than the acoustic impedance of the opening 5 (lightening the acoustic load) (A (z_o)> A (z_r)), the noise energy E (out_o) emitted from the opening 5 ) Can be reduced. A more preferred form is A (z_o) >> A (z_r).

  The canceling speaker 4a corresponds to the first silenced sound wave generation unit of the present invention, and is provided in the acoustic path 6 on the downstream side of the noise source collecting microphone 1, and has a reverse phase for muting sound waves from the sound source. A first silencing sound wave is generated.

  The first signal delay unit 7, the frequency detection unit 9, and the first volume control unit 10 correspond to the first control unit of the present invention, and cancel the speaker based on the sound wave detected by the noise source collecting microphone 1. The generation timing and volume of the first silencing sound wave by 4a are controlled.

  Specifically, the first signal delay unit 7 delays the noise signal based on the sound wave detected by the noise source collecting microphone 1 for a predetermined time. The amount of delay by the first signal delay unit 7 includes a time until the first muffled sound wave is radiated (converted into sound pressure) by the canceling speaker 4a and a time during which the noise travels in the acoustic path 6. It is preset to match.

  Accordingly, the canceling speaker 4a generates the first silencing sound wave when the noise reaches the position of the canceling speaker 4a.

  That is, the first control unit in the active silencer of the present embodiment includes the first signal delay unit 7, so that the first silencer by the cancellation speaker 4 a is based on the sound wave detected by the noise source collecting microphone 1. Controls the timing of sound wave generation.

  In addition, the 1st signal delay part 7 can be comprised by a FIR filter, for example. In this case, the first signal delay unit 7 can have not only a function of delaying the noise signal for a predetermined time but also a function of attenuating a band included in the noise source that cannot be actively silenced.

  The frequency detection unit 9 detects the noise frequency based on the sound signal of the sound wave detected by the noise source collecting microphone 1, and uses the detection result as a frequency signal to generate the first sound volume control unit 10 and the second sound volume control unit. 11 and output.

  The first volume control unit 10 sets a volume corresponding to the frequency of the noise based on the frequency signal output from the frequency detection unit 9, and controls the volume of the first mute sound wave from the canceling speaker 4a.

  That is, the first control unit in the active silencer of the present embodiment includes the frequency detection unit 9 and the first volume control unit 10, thereby canceling based on the frequency of the sound wave detected by the noise source collecting microphone 1. The volume of the first mute sound wave by the speaker 4a is controlled.

  The canceling speaker 4b corresponds to the second silenced sound wave generator of the present invention, and is provided in the acoustic path 6 between the noise source collecting microphone 1 and the canceling speaker 4a. A second muffled sound wave having an opposite phase to mute the muffled sound wave is generated.

  The second signal delay unit 8, the frequency detection unit 9, and the second volume control unit 11 correspond to the second control unit of the present invention, and cancel the speaker based on the sound wave detected by the noise source collecting microphone 1. The generation timing and volume of the second silencing sound wave by 4b are controlled.

  Specifically, the second signal delay unit 8 further delays the noise signal delayed by the first signal delay unit 7 for a predetermined time. The amount of delay by the second signal delay unit 8 depends on the time until the second muffled sound wave is radiated from the canceling speaker 4b and the first muffled sound wave travels in the acoustic path 6 from downstream to upstream. The time until the position of the cancellation speaker 4b is reached is set in advance.

  Accordingly, the canceling speaker 4b generates the second silencing sound wave when the first silencing sound wave reaches the position of the canceling speaker 4b.

  That is, the second control unit in the active silencer of the present embodiment includes the second signal delay unit 8, so that the second silencer by the canceling speaker 4 b is based on the sound wave detected by the noise source collecting microphone 1. Controls the timing of sound wave generation.

  The second signal delay unit 8 can be configured by a simple memory delay such as a FIFO delay.

  The second volume control unit 11 sets a volume corresponding to the frequency of the noise based on the frequency signal output from the frequency detection unit 9, and controls the volume of the second mute sound wave from the canceling speaker 4b.

  That is, the second control unit in the active silencer of the present embodiment includes the frequency detection unit 9 and the second volume control unit 11, thereby canceling based on the frequency of the sound wave detected by the noise source collecting microphone 1. The volume of the second silenced sound wave by the speaker 4b for control is controlled.

<Operation of active silencer>
Next, the operation of the present embodiment configured as described above will be described. FIG. 3 is a diagram for explaining the operation of the active silencer of this embodiment. First, the noise source pickup microphone 1 detects a sound wave propagating through the acoustic path 6, generates a noise signal based on the detected sound wave, and outputs the noise signal to the first signal delay unit 7 and the frequency detection unit 9.

  The first signal delay unit 7 delays the noise signal based on the sound wave detected by the noise source collecting microphone 1 for a predetermined time. As described above, the amount of delay by the first signal delay unit 7 depends on the time until the first muffled sound wave is radiated (converted into sound pressure) by the canceling speaker 4a and the noise in the acoustic path 6. The advance time is set in advance so as to match.

  That is, when the distance from the noise source collecting microphone 1 to the cancellation speaker 4a is L_1 and the sound traveling speed (about 340 m / sec) is Cs, the first signal delay unit 7 causes the noise source collecting microphone 1 to generate a sound wave. After t1 (= L_1 / Cs) has elapsed since the sound was picked up, the noise signal is delayed so that the canceling speaker 4a emits the first silenced sound wave.

  On the other hand, the frequency detector 9 detects the noise frequency based on the sound signal of the sound wave detected by the noise source collecting microphone 1. While the conventional active silencer converges the sound wave volume for silencing using the error detection microphone 2 to an appropriate value as shown in FIG. 7, the active silencer of this embodiment is In order to improve the performance and realize a real-time silencing operation, it is necessary to perform frequency detection.

  That is, the active silencer of the present embodiment detects the frequency of noise, sets the volume of the first silenced sound wave and the second silenced sound wave according to the frequency, and enables real-time operation. Here, the frequency detection unit 9 performs, for example, zero cross detection as a frequency detection method. In this case, the frequency detection unit 9 extracts a sign inversion part from the noise signal, counts the time (sampling period) of the inversion part, and uses the count value as a frequency signal to control the first volume control unit 10 and the second volume control. To the unit 11. The first volume control unit 10 calculates a volume coefficient for setting the volume based on the count value indicated by the frequency signal, and controls the volume of the first muted sound wave by the cancellation speaker 4a.

  FIG. 4 is a diagram illustrating the volume coefficient that provides the most silencing effect with respect to the noise frequency in the active silencing device of the present embodiment for the first silencing sound wave and the second silencing sound wave. However, “a wave” in FIG. 4 indicates the first silencing sound wave, and “b wave” indicates the second silencing sound wave.

  When realizing the active silencer of the present embodiment, a graph as shown in FIG. 4 can be created by experimentally obtaining in advance a volume coefficient value that maximizes the active silence effect. Based on this, The correction amount can also be determined.

  Although the first volume control unit 10 and the second volume control unit 11 have been described as calculating the volume coefficient, the frequency detection unit 9 may perform not only the frequency detection but also the calculation of the volume coefficient.

  In this way, the first signal delay unit 7 controls the generation timing of the first silenced sound wave, and the frequency detection unit 9 and the first volume control unit 10 control the volume of the first silenced sound wave, thereby canceling out the sound. The speaker 4a generates a first muffled sound wave having an opposite phase to mute sound waves from the sound source at an appropriate timing and volume.

  The second signal delay unit 8 further delays the noise signal delayed by the first signal delay unit 7 for a predetermined time. As described above, the delay amount by the second signal delay unit 8 includes the time until the second silencing sound wave is emitted from the canceling speaker 4b, and the first silencing sound wave in the acoustic path 6 from downstream to upstream. The time until the position of the canceling speaker 4b is reached in advance is set in advance.

  That is, if the distance from the canceling speaker 4a to the canceling speaker 4b is L_2 and the sound traveling speed is Cs, the second signal delay unit 8 is configured so that the noise source collecting microphone 1 picks up the sound wave. After t2 (= (L_1 + L_2) / Cs) has elapsed (that is, after L_2 / Cs has elapsed after the first muffled sound wave is emitted by the mute speaker 4a), the mute speaker 4b radiates the second muffled sound wave. Thus, the noise signal is delayed.

  Accordingly, the canceling speaker 4b generates the second silencing sound wave when the first silencing sound wave reaches the position of the canceling speaker 4b. The second silenced sound wave is in the opposite phase to the first silenced sound wave and in phase with the sound wave from the noise source.

  The second volume control unit 11 calculates a volume coefficient for setting the volume based on the count value indicated by the frequency signal, and controls the volume of the second muted sound wave by the cancellation speaker 4b.

  As described above, the second signal delay unit 8 controls the generation timing of the second sound dead sound wave, and the frequency detection unit 9 and the second sound volume control unit 11 control the sound volume of the second sound dead sound wave, thereby canceling the sound. The speaker 4b generates a second silencing sound wave having an opposite phase for silencing the first silencing sound wave at an appropriate timing and volume.

  As described above, according to the active silencer according to the first embodiment of the present invention, it is possible to prevent an oscillation phenomenon (howling) due to interference between the active silence and the sound wave detection unit (noise source collecting microphone 1). . Thereby, since the active silencer of a present Example has a high howling margin, it can ensure a required active silence level.

  Furthermore, since the active silencer of the present embodiment does not have a convergence system, a real-time silence operation is possible. That is, the active silencer of this embodiment can be processed with a simple algorithm (data delay and volume coefficient multiplication), and the processing device can be suppressed at low cost.

  FIG. 5 is a waveform diagram showing a sound pressure frequency characteristic by a sweep sine wave of the active silencer of the present embodiment. The sound pressure level picked up by the noise source pickup microphone 1 and provided at the radiation port of the acoustic path 6 (not shown). The sound pressure level picked up by the confirmation microphone is shown as being subjected to FFT analysis when the active silencer is operated and when it is not operated.

  Note that ANC in FIG. 5 indicates active noise control. That is, ANC_On is a waveform when the active silencer is operated, and ANC_Off is a waveform when the active silencer is not operated.

  As shown in FIG. 5, the sound pressure level picked up by the noise source collecting microphone 1 has no significant difference in frequency characteristics between when the active silencer is turned on and when it is turned off. However, the sound pressure that is confirmed at the radiation port of the acoustic path 6 is clearly reduced in the sound pressure level in the sound deadening effect band when the active sound deadening device is turned on, and the sound deadening effect is recognized.

  Moreover, FIG. 6 is a figure which shows the sound wave waveform of each part by the sweep sine wave of the active silencer of a present Example. The two waveforms shown on the left side of FIG. 6 are sound source current waveforms when the active silencer is off (upper waveform) and on (lower waveform), and there is no difference between on and off. In this sound source, a pseudo noise source speaker is arranged as a noise source for experiments, and has a resonance frequency around 190 Hz as an electrical characteristic, so that it has a hollow waveform as shown in FIG. ing.

  The two waveforms shown in the middle of FIG. 6 are sound wave waveforms picked up by the noise source pickup microphone 1 when the active silencer is off (upper waveform) and on (lower waveform). As shown by the ON waveform, no oscillation phenomenon (howling) occurs.

  The two waveforms shown on the right side of FIG. 6 are sound wave waveforms at the sound path 6 emission port when the active silencer is off (upper waveform) and on (lower waveform). It can be seen that the level is reduced.

  Furthermore, the active silencer of the present embodiment includes the frequency detector 9 in the first controller, so that it can be controlled to an effective silence level corresponding to the frequency of the sound wave from the sound source. As compared with the case where the volume control is performed using the convergence system based on the feedback control as described above, the mute operation can be performed in real time.

  Moreover, the active silencer of a present Example is provided with the frequency detection part 9 in the 2nd control part, and respond | corresponds to the frequency of the sound wave from a sound source about the 2nd silence sound wave for silencing the 1st silence sound wave. The effective mute level can be controlled.

  Moreover, the active silencer of the present embodiment can effectively silence the internal noise by providing the acoustic path 6 having an acoustic impedance smaller than that of the opening 5 that cannot be sealed.

  Furthermore, the active silencer of the present embodiment includes an acoustic path 6 having a shape (for example, a trumpet shape) whose cross-sectional area gradually increases from the upstream side toward the downstream side, thereby reducing acoustic impedance and reducing internal noise. Active silencing can be performed by effectively guiding the acoustic path 6.

  The active silencer according to the present invention can be used for devices and devices that emit noise such as printing machines such as image forming apparatuses and stencil printing apparatuses, automobiles, coolers, and air conditioners.

DESCRIPTION OF SYMBOLS 1 Noise source pick-up microphone 2 Error detection microphone 3 Active noise control part 4, 4a, 4b Canceling speaker 5 Aperture part 6 Acoustic path 7 First signal delay part 8 Second signal delay part 9 Frequency detection part 10 First volume control Part 11 Second volume control unit

Claims (4)

An acoustic path for propagating sound waves from the sound source;
A sound wave detector provided in the acoustic path and detecting a sound wave propagating through the acoustic path;
A first silenced sound wave generator that is provided downstream of the sound wave detector in the acoustic path and generates a first silenced sound wave having an opposite phase to silence the sound wave from the sound source;
A first control unit that controls the generation timing and volume of the first mute sound wave based on the sound wave detected by the sound wave detection unit;
A second silenced sound wave generator that is provided between the sound wave detector and the first silenced sound wave generator in the acoustic path, and generates a second silenced sound wave having an opposite phase to silence the first silenced sound wave. When,
A second control unit that controls the generation timing and volume of the second silenced sound wave based on the sound wave detected by the sound wave detection unit;
With
The first control unit detects the frequency of the sound wave detected by the sound wave detection unit, and controls the volume of the first mute sound wave based on the detected frequency of the sound wave,
The second control unit detects the frequency of the sound wave detected by the sound wave detection unit, and controls the volume of the second muffled sound wave based on the detected frequency of the sound wave. apparatus.   2. The active silencer according to claim 1, wherein the acoustic path has a smaller acoustic impedance than other openings that emit sound waves from the sound source to the outside.   3. The active silencer according to claim 2, wherein the acoustic path has a shape in which a cross-sectional area gradually increases from the upstream side toward the downstream side.   The first control unit calculates a first volume coefficient corresponding to the frequency of the sound wave based on the frequency of the sound wave, and controls the volume of the first mute sound wave using the calculated first volume coefficient. ,
  The second control unit calculates a second volume coefficient according to the frequency of the sound wave based on the frequency of the sound wave, and controls the volume of the second silenced sound wave using the calculated second volume coefficient. The active silencer according to claim 1.

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