JP2018081267A - Noise reduction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve noise reduction efficiency over conventional devices.SOLUTION: A noise reduction device comprises a microphone for detecting a volume of noise emitted from a noise emission port, a speaker for emitting an opposite phase sound having a phase opposite to the phase of the noise, and an acoustic signal generator for outputting an acoustic signal indicating the opposite phase sound of a volume corresponding to the volume The noise reduction device reduces noise emitted from the noise emission port by using the opposite phase sound. The noise reduction device comprises an acoustic duct to which the speaker is attached and which accommodates the noise emission port, and the speaker emits the opposite phase sound into the acoustic duct.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a noise reduction device.

  In Patent Document 1 below, a pair of speakers are provided in the vicinity of an engine muffler of a construction machine, an engine sound measurement microphone is installed at the output destination of the engine muffler, and a sound having a phase opposite to that from the engine muffler is output. An engine noise silencer that reduces the noise of a construction machine by outputting from a pair of speakers is disclosed. As clearly shown in FIG. 3 of Patent Document 1, this engine noise silencer intersects the noise emitted from the engine muffler with a predetermined angle by arranging a pair of speakers on the side of the engine muffler. As described above, the opposite phase sounds emitted from the pair of speakers are caused to interfere with each other.

JP 2010-24876 A

  However, since the noise of the engine muffler propagates radially into the air, and the sound of the reverse phase of the speaker also propagates radially into the air, the sound of the reverse phase that interferes with the noise is emitted from the speaker. It is limited to a part of the sound of opposite phase. That is, in the above prior art, only a part of the reverse phase sound emitted from the speaker contributes to the noise reduction, and thus there is a problem that the noise reduction efficiency due to the reverse phase sound is low.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to improve noise reduction efficiency as compared with the prior art.

  In order to achieve the above object, in the present invention, as a first solution means for a noise reduction device, a microphone for detecting the volume of noise emitted from a noise emission port, and a phase opposite to the phase of noise are provided. A speaker that emits sound, and an acoustic signal generator that outputs to the speaker an acoustic signal indicating the anti-phase sound having a volume corresponding to the sound volume, and is emitted from the noise emission port using the anti-phase sound. A noise reduction device for reducing noise, comprising: an acoustic duct to which the speaker is attached and accommodating the noise emission port; wherein the speaker emits the anti-phase sound into the acoustic duct; adopt.

  In the present invention, as the second solving means relating to the noise reduction apparatus, a means is adopted in which, in the first solving means, the noise discharge port is an exhaust gas exhaust port in a construction machine.

  In the present invention, as a third solving means relating to the noise reduction device, in the second solving means, the acoustic duct is provided with an outside air intake port in the vicinity of the speaker, and the exhaust gas is used as a driving gas. A means is adopted in which outside air is taken into the acoustic duct from the outside air inlet by the ejector effect.

  In the present invention, as a fourth solving means related to the noise reduction device, in any one of the first to third solving means, a guide duct that sets a discharge direction of the noise at the noise discharge port is further provided. Adopt means.

  In the present invention, as a fifth solving means relating to the noise reduction device, in the first to fourth solving means, the noise reduction device can be retrofitted to a noise generating source. adopt.

  According to the present invention, since the speaker emits the antiphase sound into the acoustic duct that houses the noise emission port, the antiphase sound interferes with the noise in the acoustic duct. Therefore, according to the present invention, it is possible to improve the ratio of the antiphase sound that contributes to the noise reduction as compared with the prior art, and thus the noise reduction efficiency can be improved as compared with the conventional art.

1 is an overall perspective view of a noise reduction device according to an embodiment of the present invention. It is a top view of the noise reduction apparatus which concerns on one Embodiment of this invention. It is AA sectional drawing (a) in FIG. 2, and the arrow line view (b) from the B direction in FIG. It is a bottom view of the noise reduction device concerning one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The noise reduction device R according to the present embodiment is a device that is mounted on a construction machine that is a noise generation source, and that reduces exhaust sound (noise) emitted from an exhaust port C1a (noise release port) of the engine. That is, the noise reduction device R is installed on a substantially horizontal engine cover C in a construction machine as a retrofit, and exhaust gas discharged from an exhaust port C1a of an exhaust pipe C1 protruding in a substantially vertical posture from the engine cover C. Reduces exhaust noise.

  Such a noise reduction device R includes an acoustic duct 1, a casing 2, four support legs 3, a guide duct 4, a microphone 5, an acoustic signal generator 6, and a speaker 7, as shown in the drawings. The acoustic duct 1 is a cylindrical member placed horizontally on the engine cover C. A speaker 7 is attached to the rear end surface of the acoustic duct 1 and a guide duct 4 is accommodated therein. That is, the acoustic duct 1 is a duct port 1a whose rear end surface is a mounting surface of the speaker 7 and whose front end surface is released. Such a rear end surface and the duct port 1a (front end surface) are parallel surfaces parallel to each other.

  In addition, as shown in FIG. 3A, the acoustic duct 1 is formed with an outside air inlet 1 b in the vicinity of the speaker 7. As shown in FIGS. 3A and 4, the outside air intake 1 b is a circular opening provided between the guide duct 4 and the speaker 7 in the lower part of the acoustic duct 1. More specifically, as shown in FIG. 4, the outside air intake 1 b is provided at a position where the axis L of the acoustic duct 1 passes through the center when viewed from below.

  The casing 2 is a horizontal cylindrical member similar to the acoustic duct 1 and is integrally connected to the rear end of the acoustic duct 1 so as to be coaxial with the axis L of the acoustic duct 1 and the acoustic duct 1. The casing 2 functions as an enclosure for accommodating the speaker 7 as shown in the figure.

  The four support legs 3 are two pairs of support members for supporting the acoustic duct 1 and the casing 2, which are an integrated object, on the engine cover C, and the pair is an axis of the acoustic duct 1 on the outer peripheral surface of the acoustic duct 1. The other pair is provided at the approximate center in the axis L direction of the casing 2 on the outer peripheral surface of the casing 2. That is, one end of the two pairs of support legs 3 is fixed to the outer peripheral surface of the acoustic duct 1 and the casing 2 by welding and the other end is fixed to the engine cover C with screws, so that the acoustic duct 1 and the casing 2 are placed horizontally. To support.

  The guide duct 4 is a curved tubular member that is curved in an arc shape so that the rear end surface 4a and the front end surface 4b are orthogonal to each other, and the axis at the rear end surface 4a is substantially vertical, and the axis at the front end surface 4b is approximately. It is being fixed to the acoustic duct 1 so that it may become a horizontal direction. That is, the guide duct 4 is attached to the acoustic duct 1 so that the axis of the front end surface 4 b is coaxial with the axis L of the acoustic duct 1.

  In such a guide duct 4, the exhaust pipe C1 is inserted at the rear end, and exhaust gas and exhaust sound discharged from the exhaust port C1a of the exhaust pipe C1, which is a noise discharge port, are transmitted from the front end surface 4b to the axis of the acoustic duct 1. Release to the front side in the L direction. That is, the guide duct 4 changes the flow direction and the propagation direction of the exhaust gas and the exhaust sound emitted from the exhaust port C1a, so that the discharge direction of the exhaust gas and the exhaust sound is substantially horizontal and the front side of the exhaust port C1a. It is a guide member set to.

  Further, the front end surface 4b of the guide duct 4 emits exhaust gas and exhaust sound in a substantially horizontal direction. The front end surface 4b of the guide duct 4 is parallel to the duct port 1a (front end surface) of the acoustic duct 1 and recedes toward the mounting surface (rear end surface) side of the speaker 7 by a predetermined dimension from the duct port 1a. More specifically, as shown in FIG. 4, the guide duct 4 is provided at a position where the axis L of the acoustic duct 1 passes through the center when viewed from below.

  The microphone 5 is provided in the vicinity of the duct port 1a on the acoustic duct 1 as shown in the figure, detects an exhaust sound (noise) released from the duct port 1a into the air, and an acoustic signal ( An exhaust sound signal) is output to the acoustic signal generator 6. The microphone 5 includes, for example, a diaphragm that vibrates by sound waves, a voice coil attached to the diaphragm, and a permanent magnet that is magnetically coupled to the voice coil. The electromotive force generated at both ends is output as the acoustic signal (exhaust sound signal). As shown in FIG. 4, such a microphone 5 is provided at a position where the axis L of the acoustic duct 1 passes through the center when viewed from below.

  Based on the exhaust sound signal, the acoustic signal generator 6 generates an acoustic signal (exhaust sound reduction signal) indicating a sound having a phase opposite to that of the exhaust sound (an antiphase sound). The acoustic signal generator 6 includes, for example, an inverting amplifier circuit that inverts and amplifies the exhaust sound signal and a power amplifier circuit that amplifies the output of the inverting amplifier circuit, and uses the output of the power amplifier circuit as an exhaust sound reduction signal. Output. That is, the exhaust sound reduction signal is a signal having a signal phase obtained by inverting the phase of the exhaust sound signal and having an amplitude corresponding to the volume (sound pressure) of the exhaust sound. The acoustic signal generator 6 outputs such an exhaust sound reduction signal to the speaker 7.

  The speaker 7 is a sounding body that vibrates a circular diaphragm by driving an electromagnet with an exhaust sound reduction signal. The speaker 7 is provided on the rear end surface of the acoustic duct 1 so that the center of the diaphragm coincides with the axis L of the acoustic duct 1, and the antiphase sound is guided forward in the direction of the axis L of the acoustic duct 1, that is, the guide. It emits in the same direction as the emission direction of the exhaust sound emitted from the duct port 1a (tip surface) of the duct 4. That is, such a speaker 7 is provided on the side opposite to the front end surface 4b of the guide duct 4 in the exhaust sound emission direction, and emits a reverse phase sound in the same direction as the exhaust sound emission direction.

Next, the operation of the noise reduction device R configured as described above will be described in detail.
In this noise reduction device R, the exhaust gas discharged from the exhaust port C1a of the exhaust pipe C1 of the construction machine and the exhaust sound thereof are guided forward by the guide duct 4 from the front end surface 4b of the guide duct 4. Released. Here, since the front end surface 4 b of the guide duct 4 is located at a position retracted backward from the duct port 1 a of the acoustic duct 1, the exhaust sound is emitted into the acoustic duct 1.

  The exhaust sound propagates through the acoustic duct 1 and is emitted from the duct port 1a to the outside of the acoustic duct 1. The exhaust sound is captured by the microphone 5 and converted into an exhaust sound signal, which is input to the acoustic signal generator 6 as the exhaust sound signal. The acoustic signal generator 6 generates an exhaust sound reduction signal indicating an opposite phase sound having an opposite phase to the exhaust sound based on the exhaust sound signal and outputs the signal to the speaker 7. Then, the speaker 7 emits a reverse phase sound into the acoustic duct 1 based on the exhaust sound reduction signal.

  As a result, in the acoustic duct 1, the sound volume (sound pressure) of the exhaust sound is attenuated due to the interference of the opposite phase sound with the exhaust sound in the exhaust sound. Here, the exhaust sound reduction signal is optimally set by the acoustic signal generator 6 so that the attenuation amount of the volume (sound pressure) of the exhaust sound is maximized. Therefore, the volume (sound pressure) of the exhaust sound emitted from the acoustic duct 1 to the outside is minimized.

  Here, the speaker 7 of the noise reduction device R is provided on the side opposite to the front end surface 4b of the guide duct 4 in the exhaust sound emission direction, and the exhaust sound at the front end surface 4b of the guide duct 4 in the acoustic duct 1 is provided. Since the antiphase sound is emitted in substantially the same direction as the emission direction, most of the acoustic energy of the antiphase sound contributes to the reduction (attenuation) of the exhaust sound.

  Therefore, according to the noise reduction device R, the exhaust noise (noise) reduction efficiency can be improved as compared with the conventional technique in which the sound in the opposite phase intersects the exhaust sound (noise). Further, according to the noise reduction device R, since the anti-phase sound is interfered with the exhaust sound in the acoustic duct 1, the exhaust sound (noise) is reduced as compared with the conventional technique that does not include components similar to the acoustic duct 1. Efficiency can be improved.

  On the other hand, in this noise reduction device R, the exhaust gas of the construction machine is released forward from the front end surface 4b of the guide duct 4, and this exhaust gas becomes the driving gas, and the fluid ejector effect is generated in the acoustic duct 1. . That is, due to the ejector effect, outside air is taken into the acoustic duct 1 from the outside air intake port 1 b of the acoustic duct 1. This outside air passes through the vicinity of the diaphragm of the speaker 7 and flows out from the duct port 1a of the acoustic duct 1 to the outside. According to the noise reduction device R, the speaker 7 can be effectively cooled by such a flow of outside air.

  Furthermore, in this noise reduction device R, the other ends of the four support legs 3 are fixed to the engine cover C with screws, so that they can be retrofitted to the construction machine.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above embodiment, the noise reduction device R for reducing the exhaust sound (noise) discharged from the exhaust port C1a of the construction machine has been described, but the present invention is not limited to the above embodiment. The present invention can also be applied to various noise reduction targets other than exhaust noise, that is, noise generation sources.

(2) In the present embodiment, the noise reduction device R is installed on the engine cover C of the construction machine, but the present invention is not limited to the above embodiment. The noise reduction device R may be installed at a place other than on the engine cover C as long as the acoustic duct 1 as a part of the configuration is installed so as to accommodate the noise emission port.

(3) In this embodiment, although the acoustic duct 1 is installed horizontally with respect to the engine cover C of the construction machine which is an installation surface, this invention is not limited to the said embodiment. The acoustic duct 1 may be installed obliquely upward with respect to the installation surface. By adopting the above configuration, the exhaust sound, which is noise, is emitted obliquely upward from the acoustic duct 1. Therefore, the exhaust sound can be emitted upward from a building having a height approximately equal to that of the construction machine, and the exhaust sound felt by residents around the place where the construction machine is used can be reduced. .

(4) Although the guide duct 4 is provided in the noise reduction device R in the above embodiment, the present invention is not limited to the above embodiment. You may delete the guide duct 4 as needed. For example, when the noise reduction device is attached to an exhaust pipe whose tip is bent in the horizontal direction, the speaker 7 is disposed on the side opposite to the noise emission port in the exhaust sound (noise) emission direction without providing the guide duct 4. Is possible. That is, it is possible to delete the guide duct 4 according to the shape of the exhaust pipe.

(5) In the present embodiment, the outside air inlet 1b is provided at a position where the axis L of the acoustic duct 1 passes through the center when the noise reduction device R is viewed from below. The present invention is not limited to the above embodiment. The outside air inlet 1b may be provided on the side surface of the acoustic duct 1 as long as it is in the vicinity of the speaker 7 in the noise emission direction. Furthermore, the outside air intake port 1b may be provided with a pipe extending vertically upward from the outside air intake port 1b, and the outside air may be taken in from a place away from the engine room of the construction machine. By adopting the above configuration, outside air that is not heated by the engine room can be taken in from the outside air inlet 1b, and the speaker 7 can be cooled more effectively.

(6) In the present embodiment, the acoustic duct 1 and the casing 2 are cylindrical members, but the present invention is not limited to the above embodiment. The acoustic duct 1 may have a frustoconical shape whose diameter increases or decreases from the rear end side of the acoustic duct 1 toward the duct port 1a (front end surface) side in the noise emission direction. In contrast to the acoustic duct 1, the casing 2 may have a truncated cone shape whose diameter decreases or expands from the front end side to the rear end side in the noise emission direction. Furthermore, the acoustic duct 1 and the casing 2 may be square tubes having a square cross section perpendicular to the noise emission direction. In this case, the diaphragm of the speaker 7 may be square.

(7) In the present embodiment, the casing 2 is integrally connected to the rear end of the acoustic duct 1 coaxially with the acoustic duct 1, but the present invention is not limited to the above-described embodiment. As long as the casing 2 is provided behind the acoustic duct 1, it may not be installed coaxially with the acoustic duct 1. By having the said structure, it becomes possible to install the noise reduction apparatus R also in the installation surface which cannot be installed by connecting the acoustic duct 1 and the casing 2 integrally coaxially.

(8) In the present embodiment, the front end surface 4b of the guide duct 4 is configured to recede toward the mounting surface (rear end surface) side of the speaker 7 by a predetermined dimension from the duct port 1a. The form is not limited. The front end surface 4b of the guide duct 4 may coincide with the duct port 1a (front end surface) in the noise emission direction.

(9) In the present embodiment, the noise reduction device R is configured to be screwed onto the engine cover C via the support legs 3, but the present invention is not limited to the above embodiment. A turntable may be provided between the engine cover C and the support leg 3, and the noise reduction device R may be rotatably installed on the engine cover C. By having the said structure, exhaust sound can be discharge | released from the acoustic duct 1 in a desired direction.

C Engine cover C1 Exhaust pipe C1a Exhaust port (noise emission port)
L axis R Noise reduction device 1 Acoustic duct 1a Tip surface (duct port)
DESCRIPTION OF SYMBOLS 1b Outside air intake 2 Casing 3 Support leg 4 Guide duct 4a Rear end surface 4b Front end surface 5 Microphone 6 Acoustic signal generator 7 Speaker

Claims (5)

A microphone for detecting the volume of the noise emitted from the noise emission port; a speaker that emits a reverse phase sound having a phase opposite to the phase of the noise; and an acoustic signal indicating the reverse phase sound having a volume corresponding to the volume. An acoustic signal generator that outputs to a speaker, and a noise reduction device that reduces noise emitted from the noise emission port using the antiphase sound,
An acoustic duct that is mounted with the speaker and accommodates the noise outlet;
The noise reduction device, wherein the speaker emits the antiphase sound into the acoustic duct.   The noise reduction device according to claim 1, wherein the noise discharge port is an exhaust port for exhaust gas in a construction machine. The acoustic duct is provided with an outside air inlet near the speaker,
The noise reduction device according to claim 2, wherein outside air is taken into the acoustic duct from the outside air inlet by an ejector effect using the exhaust gas as a driving gas.   The noise reduction device according to claim 1, further comprising a guide duct that sets a discharge direction of the noise at the noise discharge port. The noise reduction device according to any one of claims 1 to 4, wherein the noise reduction device can be retrofitted to a noise generation source having the noise discharge port.

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