JP2017210845A - Noise reduction device, compaction plate, compaction device and noise reduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compaction device to reduce noise of compaction work.SOLUTION: A noise reduction device 400 comprises: a rectangular elastic plate 420; a rectangular metal plate 440, which is disposed on one face of the elastic plate 420 and has multiple open holes 442; a fixture 460, which fixes the elastic plate 420 and the metal plate 440 to undersurface of the compaction plate of a plate compactor that is cited as one example of a compaction device in a state where the elastic plate 420 is positioned on upper side. Multiple open holes are formed on the elastic plate 420 so as to continue to the open holes 442 of the metal plate 440. Multiple open holes may be displaced from the open holes 442 of the metal plate 440 if necessary.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a noise reduction device, a compaction plate, a compaction device, and a noise reduction method that reduce noise during compaction work using a plate compactor, a rammer, and the like.

  In road paving work, plate compactors are widely used to compact roadbeds and asphalt mixture layers. Further, as a use other than compaction, a plate compactor is used in order to efficiently infiltrate cement milk in the construction of semi-flexible pavement in which cement milk is infiltrated into the voids of the open-graded asphalt mixture. However, when using a plate compactor on a hardened asphalt mixture layer, the plate compactor's compaction plate and the asphalt mixture layer come into contact with each other, generating a loud vibration noise (noise), which causes noise complaints in urban areas and residential areas. End up. The noise is generated not only in the plate compactor but also in a compacting operation using a rammer which is an example of a compacting device.

  As a countermeasure against this noise, as described in Japanese Patent Application Laid-Open No. 8-53809 (Patent Document 1), vibration suppression such as foamed urethane resin or epoxy resin is provided in a sealed space located on the upper surface of the compaction plate (consolidation plate). Techniques for filling materials have been proposed.

JP-A-8-53809

  However, the vibration noise when the compaction plate (consolidation plate) comes into contact with the hardened asphalt mixture layer cannot be suppressed simply by filling the sealed space located on the upper surface of the compaction plate (consolidation plate) with damping material. It was difficult to reduce the noise during the rolling operation (consolidation operation).

  Therefore, an object of the present invention is to provide a noise reduction device, a compaction plate, a compaction device, and a noise reduction method that can reduce the noise of compaction work using a plate compactor, a rammer, and the like.

  For this reason, the noise reduction device has an elastic plate, a metal plate disposed on one surface of the elastic plate, a plurality of through holes formed therein, an elastic plate and a metal plate, with the elastic plate positioned at the upper level. And a fixture for fixing to the lower surface of the compaction plate of the compaction device. The compacting device includes the noise reduction device on the lower surface of the compaction plate.

  Furthermore, in the noise reduction method, a metal plate having a plurality of through holes is attached to the lower surface of the compaction plate of the compaction device, and a sound is attenuated by the through holes of the metal plate. Reduce noise.

  According to the present invention, it is possible to reduce noise during compaction work using a plate compactor, a rammer, or the like.

It is a side view which shows an example of a plate compactor. It is a front view which shows an example of a plate compactor. It is a front view which shows 1st Embodiment of a noise reduction apparatus. It is a side view which shows an example of the plate compactor which attached the noise reduction apparatus which concerns on 1st Embodiment. It is a front view which shows an example of the plate compactor which attached the noise reduction apparatus which concerns on 1st Embodiment. It is the elements on larger scale which show the detail of the fixation structure of the noise reduction apparatus in 1st Embodiment. It is a top view which shows the modification of the elastic board which concerns on 1st Embodiment. It is the elements on larger scale which show an example of the lamination | stacking state of the elastic board and metal plate in 1st Embodiment. It is a front view which shows 2nd Embodiment of a noise reduction apparatus. It is the elements on larger scale which show an example of the lamination | stacking state of the elastic body and metal plate in 2nd Embodiment. It is a front view which shows an example of the plate compactor which attached the noise reduction apparatus which concerns on 2nd Embodiment. It is a front view which shows the 1st modification of a fixing tool. It is a top view which shows the 2nd modification of a fixing tool. It is a front view which shows the 2nd modification of a fixing tool. It is explanatory drawing of the method of measuring noise.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.
1 and 2 show an example of a plate compactor 100. FIG. Here, although the plate compactor 100 is mentioned as an example of a compaction apparatus, a rammer etc. may be sufficient.

  The plate compactor 100 includes an engine base 120, an engine 140, a fuel tank 160, a compaction plate 180, a vibration generator 200, a driving pulley 220, a belt 240, a driven pulley 260, a handle 280, and a belt. And a cover 300.

  The engine base 120 is made of, for example, a box-shaped metal plate having an open bottom surface, and the engine 140 is detachably fixed to the top surface of the engine base 120 with an anti-vibration rubber interposed therebetween. Here, the box shape is not limited to a rectangular parallelepiped surrounded by six rectangles, and the adjacent surfaces are all vertical, but may be such that it can be recognized as a rectangular parallelepiped. The engine 140 is a four-stroke engine considering the environment, and includes a carburetor, a muffler, an air cleaner, and the like (not shown). Further, a fuel tank 160 is attached above the engine 140 via a stay (not shown).

  A rear portion of the metal compaction plate 180 is detachably fixed to the lower portion of the engine base 120 with an anti-vibration rubber (not shown) interposed therebetween. The compaction plate 180 has a compaction plate body 182 and a mounting bracket 184. The compaction plate body 182 has a shape in which both ends in the front-rear direction rise obliquely outward and both ends in the left-right direction (width direction) rise vertically. The mounting bracket 184 has a channel shape (a U-shape) in which the lower surface is opened, following the shape of the upper surface of the compaction plate body 182, and in the state along the front-rear direction of the compaction plate body 182, The upper and lower ends are fixed to the upper surface of the compaction plate body 182 by welding or the like. Here, the mounting bracket 184 can be filled with a vibration control material such as foamed urethane resin or epoxy resin.

  In addition, a vibration generator 200 that vibrates by rotating an eccentric load (unbalance weight) is detachably fixed to the front portion of the mounting bracket 184 of the compaction plate 180. Here, since the vibration generating device 200 is positioned in front of the compaction plate 180, the plate compactor 100 can be moved forward by the vibration.

  The rotational driving force of the engine 140 is transmitted to the vibration generator 200 via the driving pulley 220, the belt 240, and the driven pulley 260. Specifically, the drive pulley 220 is fixed to the output shaft (crankshaft) of the engine 140, the driven pulley 260 is fixed to the input shaft of the vibration generator 200, and the drive pulley 220 and the driven pulley 260 are interposed between them. The belt 240 is wound. An adjustment mechanism that adjusts the tension of the belt 240 can also be provided.

  A lower end portion of a U-shaped handle 280 held by a worker who performs a compacting operation is fixed to the rear portion of the engine base 120. Here, the U shape is not limited to a shape in which adjacent sides form a right angle, but may be a level that can be recognized as a U shape in appearance. In addition, a belt cover 300 that covers the periphery of the drive pulley 220, the belt 240, and the driven pulley 260 is fixed to the engine base 120 in order to ensure the safety of workers and the like.

  In the compacting operation using the plate compactor 100, when the engine 140 is started, the rotational driving force is transmitted to the vibration generator 200 via the driving pulley 220, the belt 240, and the driven pulley 260, and the eccentric load is increased. Rotates and vibrates up and down. This vibration causes the compaction plate 180 to vibrate in the vertical direction, thereby compacting the roadbed, the asphalt mixture layer, and the like. At this time, since the vibration generating device 200 is installed at a position away from the center of gravity, the plate compactor 100 is moved forward by the vibration of the vibration generating device 200 even if an operator or the like does not push the plate compactor 100 forward. Self-propelled.

  Next, an example of a noise reduction device that is detachably attached to the compaction plate 180 of the plate compactor 100 and that reduces noise generated when the compaction plate 180 comes into contact with a roadbed or the like will be described.

FIG. 3 shows a first embodiment of the noise reduction device.
The noise reduction device 400 includes an elastic plate 420, a metal plate 440 disposed on one surface of the elastic plate 420, a fixing tool 460 that detachably fixes the elastic plate 420 and the metal plate 440 to the lower surface of the compaction plate 180, Have

  The elastic plate 420 is, for example, a plate-like member having a rectangular shape in plan view, in which rubber, a resin having elasticity (for example, polyurethane, silicon), or a rubber chip is bonded with a resin, and at least the compaction plate body 182. It has a size that covers a flat portion (grounding surface) located on the lower surface of the. The metal plate 440 is a plate-like member that is made of a metal such as iron, steel, stainless steel, aluminum alloy and has a rectangular shape in plan view, and has a size that covers at least one surface of the elastic plate 420. ing. In addition, a plurality of through holes 442 are formed on the plate surface of the metal plate 440 so as to penetrate in the thickness direction. The through holes 442 have, for example, the same cross section such as a circle, a square, a rectangle, a triangle, a polygon, and the distribution state per unit area is the same (that is, a uniform distribution) with respect to the plate surface of the metal plate 440. State). Here, the through-holes 442 of the metal plate 440 are arranged at a predetermined interval in each of two orthogonal directions of the metal plate 440. Note that the through holes 442 of the metal plate 440 can be arranged in a staggered manner in which holes in adjacent rows are shifted by a half pitch.

  When the through hole 442 of the metal plate 440 has a circular cross section, the diameter is desirably 1 mm or more and 40 mm or less. When the diameter of the through-hole 442 is less than 1 mm, it is difficult to remove foreign matter that clogs the through-hole 442 by compaction work. When the diameter of the through-hole 442 is larger than 40 mm, the sound attenuation effect that causes noise is reduced. It becomes difficult to demonstrate. In addition, when the through-hole 442 of the metal plate 440 is other than a circular cross section, it is desirable that the minimum interval is 1 mm or more and 40 mm or less. The pitch of the through holes 442 formed in the metal plate 440 is desirably at least 1.1 times the diameter of the through holes 442 so that the strength of the metal plate 440 is not affected.

  The fixture 460 includes a rectangular plate-like member 462, a screw member 464 having a male screw formed on the outer peripheral surface, an angle member 466 having a cross-sectional angle shape (L-shape), and a screw member 464. And two nuts 468 to be mated.

  The plate-like member 462 is made of the same metal as the metal plate 440, and is fixed to the metal plate 440 through, for example, welding so as to rise upward at right angles from both ends in the left-right direction of the metal plate 440. . The plate member 462 can be integrally formed when the metal plate 440 is manufactured. The screw member 464 is an outer surface of the plate-like member 462, that is, an outer surface located on the left and right outer sides of the metal plate 440, and at least two positions separated by a predetermined distance along the front-rear direction of the metal plate 440. For example, the metal plate 440 is fixed so as to extend vertically upward from the plate surface via welding or the like. The screw member 464 can be fixed here via a bracket or the like fixed to the outer surface of the plate-like member 462.

  The angle member 466 is made of, for example, a metal such as iron, steel, stainless steel, or aluminum alloy, and has a total length that can be attached to and detached from the left and right ends of the compaction plate body 182 in the compaction plate 180. Further, an insertion hole (not shown) through which the shaft portion of the screw member 464 fixed to the plate-like member 462 is inserted is formed on one surface of the angle member 466. The insertion hole of the angle member 466 is detachably fixed to the screw member 464 so that the relative position with respect to the axial direction of the screw member 464 can be adjusted by two nuts 468.

  In order to prevent the metal plate-like member 462 and the metal compaction plate 180 from coming into direct contact with the inner surface of the plate-like member 462 of the fixture 460, for example, rubber, elastic resin ( For example, an elastic plate 480 having a rectangular shape in which polyurethane, silicon) or a rubber chip is bonded with a resin may be provided. By doing so, the plate-like member 462 and the compaction plate 180 are not in direct contact with each other, and for example, abnormal noise generated by contact between metal plates can be suppressed.

  In addition, when it is not necessary to detachably fix the noise reduction device 400 to the compaction plate 180 of the plate compactor 100, the compaction plate main body 182 is used as the fixture 460 using, for example, an adhesive. The elastic plate 420 and the metal plate 440 can be fixed to the lower surface of the plate. In this case, the metal plate 440 only needs to have the same shape as that of the elastic plate 420 in a plan view, and no abnormal sound is generated due to the contact of the metal plate. Therefore, the elastic plate 480 can be omitted.

  Then, the noise reduction device 400 can be attached to and detached from the compaction plate main body 182 of the compaction plate 180 via the fixture 460 with the elastic plate 420 positioned at the upper position, as shown in FIGS. Secure to. Specifically, the two nuts 468 of the fixture 460 are loosened, and the elastic plate 420 of the noise reduction device 400 is in contact with the lower surface of the compaction plate body 182 as shown in FIG. Tighten the nut 468 to be tightened. Then, the lower end portion of the angle member 466 comes into contact with the upper surface of the compaction plate main body 182, and the plate-like member 462 of the fixture 460 is moved upward as the nut 468 is tightened. Then, in a state where the elastic plate 420 is sandwiched and fixed between the compaction plate main body 182 and the metal plate 440 of the noise reduction device 400, the nut 468 positioned below is moved in the direction of the angle member 466, so that the fixed state is obtained. Can be locked.

  When such a plate compactor 100 is used to compact a roadbed, an asphalt mixture layer, or the like, the lower surface of the metal plate 440 of the noise reduction device 400 comes into contact with the roadbed or the like, and noise due to this contact is generated. However, since a plurality of through holes 442 are formed on the plate surface of the metal plate 440, when noise passes through the through holes 442, for example, the amplitude is attenuated and noise can be reduced. Moreover, since the compaction board main body 182 does not contact the metal plate 440 of the noise reduction apparatus 400 directly, the noise which generate | occur | produces when metal plates contact can be suppressed. Furthermore, since the metal plate 440 contacts the roadbed or the like, the plate compactor 100 is not prevented from traveling forward.

  Here, on the plate surface of the elastic plate 420 of the noise reduction device 400, as shown in FIG. 7, a through hole 422 continuous with the through hole 442 of the metal plate 440, that is, the same position as the through hole 442 of the metal plate 440. A plurality of through-holes 422 can also be formed. The through hole 422 of the elastic plate 420 has the same cross section such as a circle, a square, a rectangle, a triangle, and a polygon. When the through hole 422 of the elastic plate 420 has a circular cross section, the diameter is desirably 1 mm or more and 40 mm or less. When the diameter of the through hole 422 is less than 1 mm, it is difficult to remove foreign matter that clogs the through hole 422 by the compacting operation. When the diameter of the through hole 422 is larger than 40 mm, the sound attenuation effect that causes noise is reduced. It becomes difficult to demonstrate. When the through hole 422 of the elastic plate 420 has a shape other than a circular cross section, it is desirable that the minimum interval is 1 mm or more and 40 mm or less. In this way, the through hole 422 of the elastic plate 420 and the through hole 442 of the metal plate 440 are continuous, so that the total length of the hole for attenuating the amplitude of noise becomes long, and the effect of the attenuation can be effectively achieved. it can. In the case where the through hole 422 is formed in the elastic plate 420, the cross-sectional area such as the diameter can be appropriately set in consideration of the strength required for the elastic plate 420.

  Further, as shown in FIG. 8, the through hole 422 of the elastic plate 420 and the through hole 442 of the metal plate 440 are, for example, half pitch in the front-rear direction within the limit of communication between the upper opening and the lower opening in the stacked state. The noise attenuation characteristics can be changed by shifting each other. In this case, for example, the elastic plate 420 and the metal plate 440 are permanently fixed with an adhesive or the like so that the relative position between the elastic plate 420 and the metal plate 440 does not change due to vibration caused by compaction work or the like. Also good. When the noise attenuation characteristics are changed, for example, noise having a frequency that causes noise complaints can be intensively attenuated. Here, the through hole 422 of the elastic plate 420 and the through hole 442 of the metal plate 440 can be shifted not only in the front-rear direction but also in an arbitrary direction, and the shift width is not limited to a half pitch, It can be arbitrarily set within the limit of communication with the lower opening. The through hole 422 of the elastic plate 420 may change its cross-sectional area in the thickness direction such as a conical shape or a stepped columnar shape, for example, in order to tune the noise attenuation characteristics.

  FIG. 9 shows a second embodiment of the noise reduction device. In the following description, only parts different from the first embodiment will be described in order to avoid redundant description. For the parts common to the first embodiment, refer to the description of the first embodiment.

  In the noise reduction apparatus 400 according to the second embodiment, instead of one elastic plate 420, a stack of a plurality of (three in the present embodiment) elastic plates 420 having a thin plate shape is used. On the plate surface of each elastic plate 420, a plurality of through-holes 422 are formed at the same position as the through-holes 422 of one elastic plate 420 in the thickness direction. As shown in FIG. 10, the through hole 422 of each elastic plate 420 is in a state where the elastic plate 420 is laminated on the metal plate 440, and the through hole 422 (upper opening) of the elastic plate 420 positioned at the uppermost position and the metal plate. The metal plate 440 and the elastic plate 420 are displaced from each other on the plate surface within the limit of communication with the through-hole 442 (lower opening) of 440. In this case, in order to prevent the relative positions of the elastic plates 420 and the metal plate 440 from changing due to vibration of the compaction operation, for example, the adjacent surfaces are permanently fixed with an adhesive and the peripheral portion is cut. Then, it may be formed into a rectangular shape in plan view. Here, the displacement direction and displacement width of each elastic plate 420 with respect to the metal plate 440 can be arbitrarily set within the above limits. Then, as shown in FIG. 11, the noise reduction device 400 is detachably fixed to the compaction plate 180 of the plate compactor 100 via a fixing tool 460.

  In this way, since the noise attenuation hole formed by the through hole 442 of the metal plate 440 and the through hole 422 of each elastic plate 420 changes in the middle and the cross-sectional area, the noise attenuation characteristics can be varied. Can be changed. Since the attenuation characteristics of noise can be changed in various ways, for example, noise at a specific frequency can be efficiently reduced. Since other operations and effects are the same as those in the first embodiment, description thereof will be omitted. If necessary, refer to the description of the first embodiment.

  As shown in FIG. 12, as the fixture 460, an insertion hole is formed in the plate surface of the plate-like member 462, and the shaft portion of the screw member 464 is inserted therethrough, and an angle member 466 is inserted into one end portion of the screw member 464. May be fixed. In this manner, the angle member 466 can be moved in the left-right direction of the compaction plate 180 of the plate compactor 100 by tightening or loosening the nut 468, and the angle member 466 is compacted by one surface of the angle member 466 and the plate-like member 462. The compaction plate body 182 of the plate 180 can be sandwiched and fixed.

  As shown in FIGS. 13 and 14, the fixture 460 includes a rectangular first member 462, a rectangular second member 464, a rib member 466 for ensuring strength, a screw It can also have a member 468 and two nuts 470.

  The long side of the first member 462 is fixed so as to extend obliquely outward from both ends of the metal plate 440 in the front-rear direction along the bottom surface shape of the compaction plate body 182 of the compaction plate 180. Has been. The second member 464 forms a right angle with the plate surface of the obliquely extending portion of the compaction plate main body 182 at the tip portion of the first member 462, that is, the end portion located at both ends in the front-rear direction. For example, it is fixed by welding or the like. The plate surface of the second member 464 is formed with an insertion hole 464A that faces an obliquely extending portion of the compaction plate main body 182 at at least two positions spaced apart in the left-right direction. The rib member 466 has a shape that connects both ends of the metal plate 440, the first member 462, and the second member 464 in the left-right direction, and is fixed to the rib member 466 by welding, for example. Therefore, the fixing tool 460 has two plate members orthogonal to each other, and has a strength to firmly fix the noise reduction device 400 to the compaction plate 180.

  The screw member 468 has a rod shape in which a male screw is formed on the outer peripheral surface, and a slit 468A that sandwiches a portion extending obliquely of the compaction plate main body 182 is formed at the tip thereof. The shaft portion of the screw member 468 is inserted into the insertion hole 464A of the second member 464. Further, the two nuts 470 are screwed into positions where the second member 464 is sandwiched with respect to the shaft portion of the screw member 468.

  In such a fixture 460, when the nut 470 located below the second member 464 is tightened, the screw member 468 slides in the direction of the compaction plate body 182, and the slit 468A formed at the tip thereof is the compaction plate. The end of the main body 182 is sandwiched. Further, by further tightening the nut 470, the compaction plate body 182 can be sandwiched between the tip portions of the pair of screw members 468, and the noise reduction device 400 can be fixed to the compaction plate 180. The nut 470 positioned above the second member 464 can exert a function as a so-called lock nut by tightening the nut 470.

  In addition, since the plate compactor 100 provided by each company differs in the size and shape of the compaction plate 180 in the front-rear direction, the fixture 360 of the noise reduction device 400 includes both end portions of the compaction plate 180 in the left-right direction. It is desirable to fix.

Here, an embodiment for the purpose of explaining the noise reduction effect of the noise reduction device 400 will be described.
As a precondition, a noise reduction device 400 in which three elastic plates 420 and a metal plate 440 are laminated is fixed to the lower surface of the compaction plate 180 of the plate compactor 100. Each elastic plate 420 is made of a rubber plate having a thickness of 5 mm, and through holes 422 having a diameter of 7 mm are formed at intervals of 14 mm. The metal plate 440 is made of steel having a thickness of 3 mm, and similarly to the elastic plate 420, through holes 422 having a diameter of 7 mm are formed at intervals of 14 mm. The through hole 422 of each elastic plate 420 and the through hole 442 of the metal plate 440 are a through hole 422 (upper opening) of the upper elastic plate 420 and a through hole 442 (lower opening) of the lower metal plate 440. Are within 3 mm of each other within the limit of communication. The fixing tool 460 fixes the noise reduction device 400 to the lower surface of the compaction plate 180 using both left and right ends of the compaction plate 180.

  As Comparative Example 1, a general plate compactor is used. Further, as Comparative Example 2, a silent plate compactor in which a sealed space located on the upper surface of the compaction plate is filled with a resin damping material as in Patent Document 1 is used.

  Then, as shown in FIG. 15, three test sections 500, 520, and 540 of 1 m × 1 m are set in an open-graded asphalt mixture layer having a maximum particle diameter of 13 mm using a masking tape. The sound level meter 600 is fixed to the tip of the tripod 620, and the sound level meter 600 is installed at a position 4m from the center of each test section 500, 520 and 540 and 1.2m from the road surface. Similarly to the construction of the semi-flexible pavement, a predetermined amount of cement milk is applied to the open-graded asphalt mixture layer, and the cement milk is mixed with the asphalt mixture layer using the plate compactors of Examples, Comparative Examples 1 and 2. The noise of the compaction work that penetrated into the surface was measured.

As a result, the following measurement results were obtained.

  Referring to the measurement results, in the example, the maximum noise value was reduced by about 13% compared to Comparative Examples 1 and 2. Moreover, in the Example, the width of the frequent value of noise became small with respect to Comparative Examples 1 and 2. Therefore, it is considered that noise generated during the compacting operation by the plate compactor 100 is reduced, and noise complaints are reduced.

100 plate compactor (compacting device)
180 Compaction plate 182 Compaction plate body 400 Noise reduction device 420 Elastic plate 422 Through hole 440 Metal plate 442 Through hole 460 Fixing tool

Claims (10)

An elastic plate,
A metal plate having a plurality of through holes formed on one surface of the elastic plate;
A fixture for fixing the elastic plate and the metal plate to the lower surface of the compaction plate of the compaction device in a state where the elastic plate is positioned at the upper position;
A noise reduction device comprising: The elastic plate is formed with a plurality of through holes continuous with the through holes of the metal plate.
The noise reduction device according to claim 1. The through hole of the elastic plate changes its cross-sectional area in the thickness direction of the elastic plate.
The noise reduction device according to claim 2. The elastic plate is composed of a plurality of elastic plates having a thin plate shape,
The through hole of the metal plate and the through hole of the elastic plate are shifted from each other on the plate surfaces of the metal plate and the elastic plate within the limit of communication between the upper opening and the lower opening in the stacked state.
The noise reduction device according to claim 2 or claim 3, wherein The fixing device detachably fixes the elastic plate and the metal plate to the compaction plate.
The noise reduction device according to any one of claims 1 to 4, wherein the noise reduction device is provided. The noise reduction device according to any one of claims 1 to 5 is fixed to the lower surface of the compaction plate.
A compaction device characterized by that. A metal compaction plate body in which a plurality of through holes are formed;
An elastic plate disposed on the upper surface of the compaction plate body;
A compaction board characterized by comprising: The elastic plate is formed with a plurality of through holes that are continuous with the through holes of the compaction plate body.
The compaction board according to claim 7 characterized by things. A metal plate having a plurality of through holes is attached to the lower surface of the compaction plate of the compacting device, and a noise is attenuated by the through holes of the metal plate to reduce noise.
The noise reduction method characterized by the above-mentioned. The elastic plate is composed of a plurality of elastic plates having a thin plate shape,
By shifting the through hole of the metal plate and the through hole of the elastic plate from each other on the plate surface of the metal plate and the elastic plate within the limit of communication between the upper opening and the lower opening in the stacked state, Change the attenuation characteristics of
The noise reduction method according to claim 9.