JP2019039954A - Noise reduction device and construction machine - Google Patents

Abstract

To provide a noise reduction device and a construction machine, which can reduce noise from a low frequency band to a high frequency band with a simple structure.SOLUTION: In a noise reduction device 3, noise absorbers 9 are disposed at an inner wall of a duct 4 having a connection port 41 and an opening 42. The duct 4 is arranged in a construction machine 1 so that the connection port 41 is connected to a muffler of the construction machine 1. The duct 4 comprises a speaker 5 outputting control sound Y between the connection port 41 and the opening 42, and a microphone 6 is arranged between the speaker 5 and the opening 42. A controller 7 is connected to the microphone 6 and the speaker 5, receives a sound signal corresponding to residual noise Z2 from the microphone 6 and generates a control signal for controlling the control sound Y by inverting a phase of the sound signal to transmit the signal to the speaker 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a noise reduction device and a construction machine that reduce noise.

  Civil works and construction works are carried out using construction machines such as generators, air compressors, backhoes, mobile cranes and pumps. In recent years, noise generated by construction machines has become a problem. Conventional noise countermeasures include noise generated by construction machinery using passive noise countermeasures that reduce noise by using noise countermeasure products such as soundproofing sheets and sound-absorbing materials, and active noise control (ANC). Active noise countermeasures that electrically reduce noise are known. As a noise reduction device using ANC, for example, there are devices described in Patent Document 1 and Patent Document 2.

  For example, in the noise reduction device described in Patent Document 1, a bellows-like flexible duct opens at one end near the exhaust port of a construction machine and opens the other end at an intermediate portion between speakers arranged side by side. Are arranged as follows. Thereby, the noise which a construction machine generate | occur | produces is guide | induced to the intermediate part between several speakers by a flexible duct. The error microphone is provided corresponding to the speaker, and outputs an acoustic signal to the noise reduction device. The noise reduction device includes a band-pass filter that allows a signal in a specific frequency band (for example, 100 Hz or less) to pass through, and emits sound waves in a predetermined frequency band as a negative-phase wave of noise from a speaker. , Reduce noise. Patent Document 1 describes that a plurality of construction machines are covered with a soundproof sheet.

  For example, in the noise reduction device described in Patent Document 2, a noise detection microphone is arranged between the noise generation source side and the speaker. The evaluation microphone is disposed on the opposite side of the noise generation source with the speaker interposed therebetween. The noise reduction device outputs a control signal to the speaker so that the phase of the noise input from the noise detection microphone and the phase of the control sound input from the evaluation microphone are opposite to each other. At this time, the noise reduction device generates a control signal by removing the sound at the specific frequency from the noise and the control sound.

Japanese Patent Laying-Open No. 2015-169663 JP 2010-276773 A

  However, the above conventional technique has the following problems. That is, in order to block sound with a noise countermeasure product such as a soundproof sheet or a sound absorbing material, the soundproof sheet or the sound absorbing material needs to have a thickness of about one quarter of the wavelength of the noise. On the other hand, the thickness of the noise countermeasure product is limited in terms of installation space, workability, and handleability. Therefore, when passive noise countermeasures are performed, if noise countermeasure products are used to reduce noise in a low-frequency band having a long wavelength, the thickness of the soundproof sheet and the sound absorbing material becomes too large, and the feasibility is poor. Therefore, the conventional noise countermeasure product can reduce the noise level in the high frequency band as shown in P1 of FIG. 12, for example, but the noise level is low in the low frequency band as shown in P2 of FIG. Most of the sound was transmitted through the sound absorbing material, and the noise reduction effect was hardly obtained.

  On the other hand, with active noise countermeasures, it is possible to mute or reduce noise only with ANC when the noise wavelength is sufficiently long with respect to the muffling space. Therefore, as described in Patent Document 1 and Patent Document 2, the noise reduction device using only ANC can mute or reduce the low frequency band noise by the control sound generated from the speaker. As for the noise in the band, the silencing space (opening area of the duct) is insufficient, and it has been impossible to mute or reduce the noise by the control sound generated from the speaker.

  The present invention has been made to solve the above problems, and an object thereof is to provide a noise reduction device and a construction machine that can reduce noise from a low frequency band to a high frequency band with a simple configuration.

  The noise reduction device of the present invention made to solve the above problems is a noise reduction device that reduces noise generated from a noise source of a construction machine, has a cylindrical shape having a predetermined length, and communicates with the noise source. A first communication port, a duct having a second communication port communicating with the atmosphere, a noise absorber provided on an inner wall of the duct, and the first communication port and the second communication port. A speaker that outputs a control sound, a microphone that is disposed between the speaker and the second communication port, and that converts a residual noise after the noise and the control sound interfere with each other into an acoustic signal; and the microphone A control device that is connected to the speaker, receives the acoustic signal from the microphone, and generates a control signal for controlling the control sound by transmitting the acoustic signal to an opposite phase, and transmits the control signal to the speaker; Having To.

  In the above configuration, the duct covers the noise source, and the noise generated by the noise source propagates in the air from the first communication port of the duct toward the second communication port. The noise in the high frequency band collides with a noise absorbing material provided on the inner wall of the duct to absorb energy, and is silenced or reduced. On the other hand, the noise in the low frequency band interferes with the control sound output by the speaker between the first communication port and the second communication port, and is silenced or reduced. Therefore, according to the noise reduction device having the above-described configuration, noise from the low frequency band to the high frequency band can be reduced with a simple configuration in which the noise absorbing material is simply provided on the inner wall of the duct used in the ANC.

  In the noise reduction device having the above-described configuration, it is preferable that the microphone is disposed at a position where the sound wave becomes a uniform plane wave in a cross section perpendicular to the axial direction of the duct. According to this, since the microphone converts the representative point of the residual noise emitted from the duct to the atmosphere into an acoustic signal, it is possible to guarantee the silencing on the same plane.

  Moreover, in the noise reduction device having the above configuration, it is preferable that the duct is divided. It is known that the noise frequency is determined by the opening area of the duct. Therefore, in the above configuration, by dividing the duct, the opening area of the duct can be easily adjusted so that the frequency of the noise becomes a desired band suitable for noise reduction.

  Furthermore, the construction machine of the present invention made to solve the above-described problems is characterized by including a noise reduction device having any one of the above-described configurations. Such a construction machine can be used even at night, for example, because noise from a high frequency band to a low frequency band is reduced by the noise reduction device.

  Therefore, according to the present invention, it is possible to provide a noise reduction device and a construction machine that can reduce noise from a low frequency band to a high frequency band with a simple configuration.

It is a schematic block diagram of the noise reduction apparatus which concerns on embodiment of this invention. It is the figure which represented the sound level in the AA cross section of FIG. 1 visually. It is the figure which represented the sound level in the BB cross section of FIG. 1 visually. It is the figure which represented the sound level in CC cross section of FIG. 1 visually. It is a block diagram of a control apparatus. It is a figure which shows the relationship between the frequency of the acoustic signal which a band pass filter receives, and a sound level. It is a figure which shows the relationship between the frequency of the signal which a band pass filter transmits, and a sound level. It is a figure which shows typically the frequency of a noise, and the frequency of a control sound. It is a figure which illustrates acoustic interference typically. It is a figure which shows the result of having verified the noise reduction effect. It is a figure which shows the modification of a duct. It is a figure which shows the result of having verified the noise reduction effect.

  Hereinafter, embodiments of a noise reduction device and a construction machine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of the noise reduction device 3. A thick dotted line in the duct 4 in FIG. 1 schematically shows how the noise X propagates, and a thin dotted line schematically shows how the residual noise Z propagates. The noise X is attenuated by the acoustic propagation characteristic α of the propagation path from the connection port 41 to the speaker 5, and the residual noise Z is attenuated by the acoustic propagation characteristic β of the propagation path from the speaker 5 to the microphone 6. The state of the attenuation is expressed by the lengths of a thick dotted line and a thin dotted line, respectively. In this embodiment, the noise reduction device 3 is applied to the construction machine 1. Examples of the construction machine 1 include a generator, an air compressor, a backhoe, a mobile crane, and a pump. The construction machine 1 exhausts exhaust gas generated by an engine built in the main body 2 from a muffler, and noise X is generated from the muffler. An engine muffler is an example of a noise source.

  The noise reduction device 3 includes a duct 4, a noise absorbing material 9, a speaker 5, a microphone 6, and a control device 7. The noise reduction device 3 is configured to be retrofitted to the main body 2 of the construction machine 1.

  The duct 4 is attached to the upper surface of the main body 2 of the construction machine 1 in the figure, and forms an exhaust passage for exhaust gas discharged from the engine of the construction machine 1. For example, the duct 4 may be attached to the main body 2 via an attachment member such as a bolt, or may be attached to the main body 2 via a magnet or the like. The duct 4 is provided in a square cylindrical shape by four metal side plates 4A, and one end is closed by a metal closing plate 4B. That is, the duct 4 is formed in a box shape having a predetermined length. The other end of the duct 4 located on the side opposite to the closing plate 4B is opened, and an opening 42 is provided. The opening 42 is an example of a second communication port.

  Of the four side plates 4A, the side plate 4A located on the lower side in FIG. 1 is provided with a connection port 41 in the vicinity of the closing plate 4B. The connection port 41 is an example of a first communication port. The connection port 41 is connected to the exhaust port of the muffler of the construction machine 1. In the duct 4, the connection port 41 opens upward in FIG. 1, the opening 42 opens leftward in FIG. 1, and the opening 42 is different from the direction in which the noise X is emitted into the duct 4. It is provided in a direction (in this embodiment, 90 degrees different). A noise absorbing material 9 such as glass wool is attached to the inner wall of the duct 4. Thereby, when the noise X emitted upward in the figure in the duct 4 propagates through the internal space 43 from the connection port 41 toward the opening 42, it collides with the noise absorbing material 9 and is absorbed. Noise level is reduced.

  The opening area of the duct 4 is set so that the internal space 43 formed inside the noise absorbing material 9 forms a sufficient silencing space for the wavelength of the noise X in the low frequency band.

  The speaker 5 is fixed to a side plate 4A located above the duct 4 in FIG. The speaker 5 is disposed in a speaker attachment port 44 that opens at a position between the connection port 41 and the opening 42, and outputs a control sound Y to the internal space 43 of the duct 4. The speaker 5 emits a control sound Y downward in the figure. Noise X1 attenuated by the acoustic propagation characteristic α of the propagation path from the connection port 41 to the speaker 5 reaches the speaker 5. The control sound Y is output from the speaker 5 so as to mute or reduce the noise X1.

  The microphone 6 is disposed between the speaker 5 and the opening 42. The microphone 6 detects the residual noise Z1 after the noise X1 and the control sound Y interfere. The residual noise Z1 reaching the microphone 6 is attenuated by the acoustic propagation characteristic β of the propagation path from the speaker 5 to the microphone 6 as compared with the residual noise Z immediately after the noise X1 and the control sound Y interfere. That is, the noise X2 and the control sound Y1 included in the residual noise Z1 are attenuated by the acoustic propagation characteristic β from the noise X1 and the control sound Y included in the residual noise Z. The microphone 6 converts the detected residual noise Z1 into an acoustic signal and transmits it to the control device 7.

  The microphone 6 is disposed at a position where the sound wave becomes a uniform plane wave. That is, as shown in FIG. 2, in the duct 4, the noise level is not uniform between the upper surface of the duct and the lower surface of the duct and is unstable in the cross section near the connection port 41. This is because the sound wave of the noise X hits the noise absorber 9 and is disturbed. Further, as shown in FIG. 3, the duct 4 has a noise level that is more stable in the cross section between the connection port 41 and the speaker 5 than in the cross section in the vicinity of the connection port 41, but is still between the duct upper surface and the duct lower surface. It is not uniform. This is because the sound wave of the noise X is in the process of gradually stabilizing the waveform while being transmitted toward the opening 42. Further, the noise X1 and the control sound Y interfere with each other. As shown in FIG. 4, the duct 4 forms a plane sound field in which the noise level is uniform between the upper surface of the duct and the lower surface of the duct in the cross section between the speaker 5 and the opening 42. The microphone 6 is disposed at a position where this plane sound field is formed. Thereby, the microphone 6 can detect a representative point of a uniform plane wave of the residual noise Z1 actually emitted from the duct 4 to the atmosphere and convert it into an acoustic signal.

  The control device 7 is connected to the speaker 5 and the microphone 6. The control device 7 generates a control signal for controlling the control sound Y according to the acoustic signal received from the single microphone 6 and transmits the control signal to the speaker 5. That is, the control device 7 feedback-controls the control sound Y based on the residual noise Z1.

  FIG. 5 is a block diagram of the control device 7. The control device 7 includes a bandpass filter 71, a subtractor 74, an antiphase filter 72, a first propagation path filter 73, a second propagation path filter 75, and a filter update calculator 76.

  The band pass filter 71 is connected to the microphone 6 and is configured to extract a signal in a frequency band corresponding to the control sound Y that can be output from the speaker 5 from the acoustic signal received from the microphone 6. That is, for example, when the speaker 5 can output the control sound Y in a band of 10 Hz or more and 750 Hz or less, the acoustic signal shown in FIG. 6 passes through the band-pass filter 71, and as shown in FIG. A signal belonging to a band of 750 Hz or less is extracted. By providing the bandpass filter 71, the control device 7 can generate a control signal that matches the output performance of the speaker 5.

  The anti-phase filter 72 is connected to the band pass filter 71 via a subtracter 74. The anti-phase filter 72 is connected to the speaker 5, generates a control signal by processing a signal received from the band pass filter 71 side using a filter coefficient, and transmits the control signal to the speaker 5.

  The negative phase filter 72 is also connected to the first propagation path filter 73. The first propagation path filter 73 changes from the control signal transmitted from the antiphase filter 72 to the speaker 5 until the control sound Y output from the speaker 5 propagates (arrives) to the microphone 6, that is, the speaker 5. The first sound signal equivalent to the control sound Y1 reaching the microphone 6 is generated by attenuating the acoustic propagation characteristic β of the propagation path from the microphone 6 to the microphone 6.

  The subtracter 74 is connected to the first propagation path filter 73 and the band pass filter 71. The subtracter 74 subtracts the first signal received from the first propagation path filter 73 from the signal received from the bandpass filter 71, thereby generating a second sound signal equivalent to the noise X2 reaching the microphone 6. .

  Here, the residual noise Z1 detected by the microphone 6 includes the control sound Y1 reaching the microphone 6 from the speaker 5 and the noise X2 reaching the microphone 6 from the speaker 5. Similarly to the control sound Y1, the noise X2 is also attenuated by the acoustic propagation characteristic β in the propagation path from the speaker 5 to the microphone 6. Therefore, when the control signal is generated based on the noise X2, the reduction of the noise is delayed by the acoustic propagation characteristic β. Therefore, when the control sound Y is emitted from the speaker 5, it is necessary to supplement the acoustic propagation characteristic β.

  Therefore, a second propagation path filter 75 is connected to the subtracter 74. The second propagation path filter 75 is a change of the propagation path from the second sound signal received from the subtractor 74 until the noise reaches the microphone 6 from the speaker 5, that is, the propagation path from the speaker 5 to the microphone 6. By amplifying the acoustic propagation characteristic β, a third sound signal equivalent to the noise X1 reaching the speaker 5 is generated.

  The filter update calculator 76 is connected to the second propagation path filter 75. The filter update calculator 76 receives the third sound signal from the second propagation path filter 75 and calculates a filter coefficient based only on the third sound signal.

  The negative phase filter 72 is connected to the filter update calculator 76. The anti-phase filter 72 generates a control signal using the filter coefficient calculated by the filter update calculator 76 and transmits the control signal to the speaker 5. Therefore, as shown in FIG. 8, the speaker 5 can output a control sound Y having substantially the same level as the noise X1 propagated from the noise source to the speaker 5. In this case, as shown in FIG. 9, the noise X1 and the control sound Y interfere with each other, and a residual noise Z is generated. If the noise X1 and the control sound Y completely match, the noise X1 is completely eliminated by the control sound Y. That is, the residual noise Z becomes zero. Even if the noise X1 and the control sound Y do not completely coincide with each other, the residual noise Z can be reduced as much as possible because the control sound Y is almost at the same level as the noise X1.

  Then, operation | movement of the noise reduction apparatus 3 of this embodiment is demonstrated.

  The construction machine 1 operates by driving an engine in the main body 2. Exhaust gas generated from the engine is released to the atmosphere from the muffler of the engine through the duct 4 of the noise reduction device 3.

  Noise X generated from the muffler of the engine is emitted in a radial pattern into the internal space 43 of the duct 4 around the connection port 41 of the duct 4 and propagates in the air along the duct 4. The duct 4 is provided with an opening 42 in a direction different from the direction in which the noise X is emitted into the internal space 43. Therefore, the sound wave of noise X emitted from the connection port 41 to the internal space 43 propagates through the air in the internal space 43 while colliding with the noise absorber 9. When the noise X is a noise in a high frequency band, the noise is absorbed by the noise absorber 9 and muffled or reduced.

  When the noise X is low frequency band noise having a long wavelength, the thickness of the noise absorbing material 9 may be smaller than the wavelength of the low frequency band noise. In this case, the noise level of the noise X in the low frequency band is not easily reduced by the noise absorber 9. However, in the noise reduction device 3, the speaker 5 is provided in the duct 4, and the control sound Y is output toward the internal space 43. The noise X1 that has reached the speaker 5 is offset with the control sound Y output from the speaker 5, and the noise level is reduced.

  The residual noise Z after interfering with the noise X1 and the control sound Y reaches the microphone 6 while being attenuated by the acoustic propagation characteristic β. The microphone 6 is disposed at a position where the sound wave becomes a uniform plane wave. Therefore, the microphone 6 converts the representative point of the residual noise Z1 released from the duct 4 to the atmosphere into an acoustic signal and transmits it to the control device 7.

  The control device 7 passes the acoustic signal received from the microphone 6 through the band pass filter 71. The band pass filter 71 extracts a signal in a predetermined frequency band from the acoustic signal and transmits the signal to the subtracter 74.

  The subtractor 74 receives the control signal transmitted from the antiphase filter 72 to the speaker 5 via the first propagation path filter 73. The subtracter 74 generates a second sound signal equivalent to the noise X <b> 2 that has reached the microphone 6, and transmits the second sound signal to the antiphase filter 72 and the second propagation path filter 75.

  The second propagation path filter 75 amplifies the second sound signal equivalent to the noise X2 reaching the microphone 6 by the acoustic propagation characteristic β, and generates a third sound signal equivalent to the noise X1 reaching the speaker 5, This is transmitted to the filter update calculator 76. The filter update calculator 76 calculates a filter coefficient based only on the third sound signal.

  The anti-phase filter 72 generates a control signal using the filter coefficient calculated by the filter update calculator 76 and transmits it to the speaker 5. The filter coefficient is calculated by the filter update calculator 76 based on the third sound signal equivalent to the noise X1 reaching the speaker 5. Therefore, the control signal output from the anti-phase filter 72 is supplemented with the acoustic propagation characteristic β, and a control delay due to the acoustic propagation characteristic β can be avoided. Therefore, the speaker 5 outputs the control sound Y that can sufficiently reduce the noise X1 reaching the speaker 5 into the duct 4. For this reason, the control device 7 uses the control sound Y even for noise that cannot be absorbed by the noise absorber 9 (for example, noise in a low frequency band or noise in which the noise level suddenly increases in the low frequency band). It can be silenced or reduced in the duct 4. In addition, the filter update calculator 76 is provided with a signal from the second propagation path filter 75 and has a smaller number of signals to be processed than when the signal is supplied from the microphone 6, so that the calculation time is shortened. Therefore, the time lag from when the microphone 6 collects the residual noise Z1 until the control sound Y corresponding to the residual noise Z1 is output from the speaker 5 is shortened, and the responsiveness is good.

  Subsequently, a test for verifying the effect of the noise reduction device 3 and the result thereof will be described. In the test, the noise reduction device 3 was attached to the generator so as to connect the connection port 41 to the muffler of the generator. Then, the noise level of the residual noise Z detected by the microphone 6 was measured for each frequency band. The test results are shown in FIG.

  As shown in Q1 of FIG. 10, the generator including the noise reduction device 3 generally reduces the noise level in a high frequency band of 700 Hz to 900 Hz as compared with the countermeasureless generator not including the noise reduction device 3. We were able to. For example, a generator using the noise reduction device 3 can reduce the noise level of noise generated at a frequency of about 780 Hz by 26.2 dBA as compared to a countermeasureless generator, as indicated by M1 in the figure. did it.

  Further, as shown in Q2 of FIG. 10, the generator provided with the noise reduction device 3 has a noise level lower than that of the countermeasureless generator without the noise reduction device 3 even in a low frequency band of 100 Hz to 300 Hz. It was possible to reduce.

  Furthermore, as shown in Q2 of FIG. 10, the generator provided with the noise reduction device 3 was able to reduce the noise level of noise that occurred suddenly in the low frequency band of 100 Hz to 300 Hz. For example, as shown by M2 in the figure, the generator using the noise reduction device 3 reduces the noise that suddenly increases the noise level when the frequency is about 180 Hz, by 12.5 dBA than the generator without countermeasures. I was able to.

  Furthermore, the generator using the noise reduction device 3 was able to reduce the overall value at the outlet of the opening 42 by 10.9 dBA compared to the generator without countermeasures. Therefore, the generator includes the noise reduction device 3 to reduce noise from the low frequency band to the high frequency band.

  As described above, according to the noise reduction device 3 of the present embodiment, the filter update calculator 76 does not receive an acoustic signal from the microphone 6 and uses only the third sound signal generated by the second propagation path filter 75. Since the filter coefficient is calculated, the calculation time in the filter update calculator 76 is short. That is, the response time from when the residual noise Z1 is detected by the microphone 6 until the control sound Y corresponding to the residual noise Z1 is output from the speaker 5 is shortened. Therefore, for example, even when the frequency of the noise X generated from the muffler of the construction machine 1 suddenly varies, the noise reduction device 3 can output the control sound Y suitable for the noise variation from the speaker 5 with high responsiveness. it can. Moreover, since the noise reduction device 3 has only one microphone 6 installed in the duct 4, it is only necessary to secure the distance between the microphone 6 and the speaker 5 by one microphone, and the duct 4 is shortened to reduce noise. The apparatus 3 can be made compact. Furthermore, since the number of microphones used is small, it is inexpensive.

  Moreover, according to the noise reduction device 3 of the present embodiment, noise from the low frequency band to the high frequency band can be reduced with a simple configuration in which the noise absorbing material 9 is simply provided on the inner wall of the duct 4 used in the ANC. .

  Further, in the noise reduction device 3 of the present embodiment, the microphone 6 is disposed at a position where the sound wave becomes a uniform plane wave in a cross section in a direction orthogonal to the axial direction of the duct 4. In such a noise reduction device 3, the microphone 6 converts the representative point of the residual noise released from the duct 4 into the atmosphere into an acoustic signal, so that it is possible to guarantee the mute on the same plane.

  Thus, since the noise reduction device 3 reduces the noise X in the low frequency band to the high frequency band generated from the construction machine 1, the construction machine 1 can be used even at night. By using the construction machine 1 at night, it is possible to shorten the construction period of civil engineering work and construction work.

  In addition, the noise reduction device 3 follows changes in temperature, wind speed, etc. by the ANC performed by the control device 7 even when the construction machine 1 operates at night when the temperature is lower than daytime or at night when wind is strong. Thus, the control sound Y can be automatically varied to reduce or mute the noise X generated by the construction machine 1. Therefore, at the construction site, the burden of deciding the setup for using the construction machine 1 in consideration of the environment that the air temperature, wind speed, etc. give to noise is reduced.

  In addition, the noise reduction device 3 analyzes the acoustic signal detected by the microphone 6 and corrects the filter coefficient of the anti-phase filter 72 by the control device 7 including the second propagation path filter 75 and the filter update calculator 76. To do. Therefore, the filter update computing unit 76 performs the computation only with the acoustic signal extracted by the second propagation path filter 75, so that the filter coefficient is corrected, and the control sound Y suitable for silencing or reducing the noise is obtained with high responsiveness. Can be output.

  Furthermore, since the noise reduction device 3 can retrofit the duct 4 to the main body 2 of the construction machine 1, the user of the construction machine 1 does not need to re-buy or modify the construction machine 1. By simply attaching the noise reduction device 3 to the main body 2, noise countermeasures can be applied to the existing construction machine 1 at low cost.

  In addition, this invention is not limited to the said embodiment, Various application is possible.

  For example, the duct body 12 may be divided by partitioning the duct body 12 with a partition plate 13 as in the duct 11 shown in FIG. It is known that the frequency of noise is determined by the opening area of the duct. Therefore, by dividing the duct body 12 by the partition plate 13, the opening area of the duct 11 can be adjusted so that a predetermined frequency band suitable for noise reduction is obtained. According to this, the effect of reducing noise can be enhanced by the ANC function of the control device 7. The duct 11 is not limited to two divisions and may be three or more divisions.

  The duct may be configured by combining a plurality of independent ducts in addition to the division by the partition plate. In this case, the work of adjusting the opening area of the duct 4 at the site becomes easy.

  For example, the duct 4 is not limited to a rectangular shape, but may be a round tube shape, a polygonal shape, or the like. Moreover, you may form the duct 4 with resin other than a metal.

  For example, the duct 4 may be welded to the main body 2 besides being attached with a fixing member, a magnet, or the like.

  For example, in the above embodiment, the duct 4 is disposed on the upper surface of the main body 2 of the construction machine 1, but the duct 4 may be disposed on the side surface of the main body 2. Further, the speaker 5 and the microphone 6 are not limited to the upper surface of the duct 4 and may be disposed on the side surfaces.

  For example, the noise reduction device 3 may be installed in the construction machine 1 so as to connect the connection port 41 of the duct 4 to a noise outlet other than the muffler (for example, an exhaust port provided in the construction machine 1). .

  For example, the control device 7 may omit the band pass filter 71 and connect the subtractor 74 to the microphone 6.

  For example, the filter update computing unit 76 outputs the third sound signal output from the second propagation path filter 75 and the signal output from the bandpass filter 71 (the acoustic signal output from the microphone 6 when the bandpass filter 71 is not provided). ) May be received.

DESCRIPTION OF SYMBOLS 1 Construction machine 3 Noise reduction apparatus 4 Duct 5 Speaker 6 Microphone 7 Control apparatus 9 Noise absorption material 41 Connection port 42 Opening part 71 Band pass filter 72 Reversed phase filter 73 1st propagation path filter 74 Subtractor 75 2nd propagation path filter 76 Filter update calculator β Acoustic propagation characteristics

Claims (4)

In a noise reduction device that reduces noise generated from noise sources of construction machinery,
A duct having a predetermined length and having a first communication port communicating with the noise source and a second communication port communicating with the atmosphere;
A noise absorber provided on the inner wall of the duct;
A speaker disposed between the first communication port and the second communication port and outputting a control sound;
A microphone that is disposed between the speaker and the second communication port and converts residual noise after the noise and the control sound interfere with each other into an acoustic signal;
A control device that is connected to the microphone and the speaker, receives the acoustic signal from the microphone, generates a control signal for controlling the control sound by making the acoustic signal in reverse phase, and transmits the control signal to the speaker And having
Noise reduction device characterized by The noise reduction device according to claim 1,
The noise reduction device according to claim 1, wherein the microphone is disposed at a position where the sound wave becomes a uniform plane wave in a cross section in a direction orthogonal to the axial direction of the duct. In the noise reduction device according to claim 1 or 2,
The noise reduction device, wherein the duct is divided.   A construction machine comprising the noise reduction device according to any one of claims 1 to 3.

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