US20060260870A1

US20060260870A1 - Sound absorber and sound absorbing device

Info

Publication number: US20060260870A1
Application number: US11/377,047
Authority: US
Inventors: Tetsutaroh Nakagawa; Shinya Nagata
Original assignee: Nagata Kosakusho Co Ltd
Current assignee: Nagata Kosakusho Co Ltd
Priority date: 2005-03-23
Filing date: 2006-03-15
Publication date: 2006-11-23
Also published as: JP4739785B2; JP2006267476A

Abstract

A sound absorber according to the present invention comprises: a tubular porous sheath with a non-circular cylindrical cross-section; a circular cylindrical soft fiber sound absorbent disposed inside the porous sheath in partial contact or non-contact with the porous sheath with the longitudinal direction thereof aligned with the longitudinal direction of the porous sheath; and a bar-like core with a non-circular cylindrical cross-section disposed inside the soft fiber sound absorbent in a partial contact or non-contact with the soft fiber sound absorbent with the longitudinal direction thereof aligned with the longitudinal direction of the soft fiber sound absorbent. A sound absorbing device according to the present invention comprises a plurality of the sound absorbers arranged side by side at specific intervals in two or more rows in a staggered configuration. Alternately, a plurality of sound absorbers having a generally isosceles trapezoidal cross-section are arranged in a row with the upper and lower bases of the isosceles trapezoidal cross-sectional shape thereof exposed to the outside alternately.

Description

CROSS REFERENCE OF RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2005-084833 (filed on Mar. 23, 2005) including the specification, claims, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention
The present invention relates to a sound absorber for use in a sound insulating wall for absorbing noise, and a sound absorbing device using the sound absorber.
2. Background Art
Various types of sound absorbers and sound absorbing devices are used to absorb noise generated by large machines or vehicles running on highways and railroad tracks. Conventionally, board-like sound absorbing panels composed of a thin film bag filled with a soft fiber sound absorbent and porous plates are widely used in sound absorbing devices. Recently, a circular cylindrical sound absorber having an improved sound absorbing ability and a sound absorbing device using the sound absorbers are disclosed in Patent Document 1. The Patent Document 1 discloses a circular cylindrical sound absorber composed of an aluminum porous sound absorbing plate formed into a circular cylindrical shape, a circular cylindrical soft fiber sound absorbent disposed in the circular cylindrical sound absorbing plate, and a round bar extending along the center axis of the circular cylindrical sound absorber. A see-through sound absorbing device is formed by the circular cylindrical sound absorbers arranged at spaced intervals and a transparent plate disposed behind them.
[Patent Document 1] JP-A-Hei 11-133979
However, the sound absorbing ability of the circular cylindrical sound absorber disclosed in the Patent Document 1 is still unsatisfactory. In the circular cylindrical sound absorber, the circular cylindrical aluminum porous sound absorbing plate, the cylindrical soft fiber sound absorbent disposed in the circular cylindrical sound absorbing plate via an air layer and the round bar extending along the center axis are all generally arranged around a common central axis. Therefore, sound waves as longitudinal waves of air emitted from a noise source pass perpendicularly through the circular cylindrical aluminum porous sound absorbing plate and are directed in one direction, and then enter the air layer with an interference effect and are transmitted therethrough. The sound waves directed in one direction enter the circular cylindrical soft fiber sound absorbent generally perpendicular to the outer surface thereof and pass through the sound absorbent. Then, the sound waves are reflected by the round bar along the center axis and returned into the sound absorbent. Since sound waves are transmitted to the center axis through the air layer with a uniform thickness along its entire circumference as described above, the attenuation effect caused by interference is small and sound waves only in a narrow frequency band can be attenuated effectively. This is obvious from the fact that there is a correlation between the thickness of air layer and the frequency of sound waves that can be attenuated. Further, although the sound waves having entered from a direction and passed through the soft fiber sound absorbent are reflected to the incident direction by the round bar along the center axis, some of the sound waves are reflected radially in the opposite directions to cause lowering of the sound absorbing effect.
The sound absorbing device in which the circular cylindrical sound absorbers and a transparent plate are combined has a problem in the see-through capability. That is, since the sound absorbing device is composed of the circular cylindrical sound absorbers arranged at specific intervals and a transparent plate disposed behind them, when the inside, that, is, the sound source side, of the transparent plate is darker than the outside, the transparent plate functions like a mirror which reflects the outside view and has almost no see-through capability. On top of that, it has been proven that when the sound absorbing device is illuminated from outside with a light source such as a flashlight, most of the illuminating light is reflected on the transparent plate and the reflected light is too bright to see the inside through it. Thus, when the noise absorbing device is installed around a large machine which generates large noise, it causes great inconvenience since visual inspection cannot be carried out from outside.
Additionally, since the transparent plate has a see-through capability but has no ventilating capability, that is, does not allow air to pass through it, its application in places where ventilation is required is limited. For example, when the sound absorbing device is installed around an office or residence, it causes discomfort since sufficient ventilation cannot be obtained. When the sound absorbing device is installed outdoors such as along a highway, it may adversely affect the natural environment since it blocks the flow of wind, for example.

DISCLOSURE OF THE INVENTION

It is, therefore, an object of the present invention to provide a sound absorber which can attenuate sound waves in a wide frequency band effectively using interference caused by an air layer and diffuse reflection caused by a sound wave reflector in addition to the sound absorbing ability of a material such as a sound absorbent, and to provide a sound absorbing device having a good sound absorbing ability and having a see-through capability and a ventilating capability.
A sound absorber according to the present invention comprises: a tubular porous sheath with a non-circular cylindrical cross-section; a circular cylindrical soft fiber sound absorbent disposed inside the porous sheath in partial contact or non-contact with the porous sheath with the longitudinal direction thereof aligned with the longitudinal direction of the porous sheath; and a bar-like core with a non-circular cylindrical cross-section disposed inside the soft fiber sound absorbent in a partial contact or non-contact with the soft fiber sound absorbent with the longitudinal direction thereof aligned with the longitudinal direction of the soft fiber sound absorbent.
Although the features of the present invention can be expressed as above in a broad sense, the constitution and content of the present invention, as well as the object and features thereof, will be apparent by reference to the following disclosure taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating an embodiment of a sound absorber of the present invention.
FIG. 2 is a side cross-sectional elevation of the embodiment shown in FIG. 1, taken along the longitudinal direction thereof.
FIG. 3 is a side view of the embodiment shown in FIG. 1.
FIG. 4 is a horizontal cross-sectional view illustrating an embodiment of a sound absorber of the present invention.
FIG. 5 is a top plan view of the embodiment shown in FIG. 4.
FIG. 6 is a cross-sectional view of the embodiment shown in FIG. 5, taken along the line C-C of FIG. 5.
FIG. 7 is a transverse cross-sectional view of a sound absorbing device in which sound absorbers are arranged in a row.
FIG. 8 is a cross-sectional view illustrating a sound absorber according to a first embodiment of the present invention.
FIG. 9 is a cross-sectional view illustrating a sound absorber according to a second embodiment of the present invention.
FIG. 10 is a cross-sectional view illustrating a sound absorber according to a third embodiment of the present invention.
FIG. 11 is a cross-sectional view illustrating a sound absorber according to a fourth embodiment of the present invention.
FIG. 12 is a cross-sectional view illustrating a sound absorber according to a fifth embodiment of the present invention.
FIG. 13 is a cross-sectional view illustrating a sound absorber according to a sixth embodiment of the present invention.
FIG. 14 is a cross-sectional view illustrating a sound absorber according to a seventh embodiment of the present invention.
FIG. 15 is a cross-sectional view illustrating a sound absorber according to an eighth embodiment of the present invention.
FIG. 16 is a cross-sectional view illustrating a sound absorber according to a ninth embodiment of the present invention.
FIG. 17 is a cross-sectional view illustrating a sound absorbing device according to a tenth embodiment of the present invention.
FIG. 18 is a cross-sectional view illustrating another sound absorbing device according to a twelfth embodiment of the present invention.
FIG. 19 is a cross-sectional view illustrating another sound absorbing device according to a thirteenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A technical means for solving the technical problem (which is hereinafter referred to as “first technical means”) is a sound absorber including: a tubular porous sheath with a non-circular cylindrical cross-section; a circular cylindrical soft fiber sound absorbent disposed inside the porous sheath in partial contact or non-contact with the porous sheath with the longitudinal direction thereof aligned with the longitudinal direction of the porous sheath; and a bar-like core with a non-circular cylindrical cross-section disposed inside the soft fiber sound absorbent in a partial contact or non-contact with the soft fiber sound absorbent with the longitudinal direction thereof aligned with the longitudinal direction of the soft fiber sound absorbent.
A technical means for solving the technical problem (which is hereinafter referred to as “second technical means”) is the sound absorber according to the first technical means, in which the core functions as a sound wave reflector for blocking passage of sound waves and as a support for ensuring mechanical strength.
A technical means for solving the technical problem (which is hereinafter referred to as “third technical means”) is the sound absorber according to the first or second technical means, further including outer caps for supporting longitudinal ends of the porous sheath, the soft fiber sound absorbent, and the core.
A technical means for solving the technical problem (which is hereinafter referred to as “fourth technical means”) is the sound absorber according to any one of the first to third technical means, in which the porous sheath has a generally polygonal cross-section. A technical means for solving the technical problem (which is hereinafter referred to as “fifth technical means”) is the sound absorber according to the fourth technical means, in which the porous sheath has a generally polygonal cross-section with sides having sawtooth-shaped projections and depressions.
A technical means for solving the technical problem (which is hereinafter referred to as “sixth technical means”) is the sound absorbers according to the fourth or fifth technical means, in which the porous sheathes has a generally rectangular cross-section.
A technical means for solving the technical problem (which is hereinafter referred to as “seventh technical means”) is the sound absorbers according to the fourth or fifth technical means, in which the porous sheathes has a generally triangular cross-section.
A technical means for solving the technical problem (which is hereinafter referred to as “eighth technical means”) is the sound absorbers according to the fourth or fifth technical means, in which the porous sheathes has a generally isosceles trapezoidal cross-section.
A technical means for solving the technical problem (which is hereinafter referred to as “ninth technical means”) is the sound absorbers according to the fourth or fifth technical means, in which the porous sheathes has a star-shaped cross-section with at least five projections.
A technical means for solving the technical problem (which is hereinafter referred to as “tenth technical means”) is the sound absorber according to any one of the first to ninth technical means, in which the core has a generally polygonal cross-section.
A technical means for solving the technical problem (which is hereinafter referred to as “eleventh technical means”) is the sound absorbers according to the tenth technical means, in which the cores has a star-shaped cross-section with at least three projections arranged circumferentially.
A technical means for solving the technical problem (which is hereinafter referred to as “twelfth technical means”) is the sound absorbers according to the tenth technical means, in which the cores has a generally rectangular cross-section.
A technical means for solving the technical problem (which is hereinafter referred to as “thirteenth technical means”) is the sound absorbers according to the tenth technical means, in which the cores has a generally cross-shaped cross-section.
A technical means for solving the technical problem (which is hereinafter referred to as “fourteenth technical means”) is the sound absorbers according to the tenth technical means, in which the cores has a cross-section like that of a spline shaft with at least three rectangular tooth-like projections arranged circumferentially.
A technical means for solving the technical problem (which is hereinafter referred to as “fifteenth technical means”) is the sound absorbers according to the tenth technical means, in which the cores has a cross-section like that of a spline shaft with at least three trapezoidal tooth-like projections arranged circumferentially. A technical means employed in Claim 16 of the present invention (which are hereinafter referred to as “sixteenth technical means”) is the sound absorbers according to the fifteenth technical means, in which the trapezoidal tooth-like projections are wider at the top than at the base.
A technical means for solving the technical problem (which is hereinafter referred to as “seventeenth technical means”) is a sound absorbing device, including a plurality of sound absorbers according to any one of the first to sixteenth technical means arranged side by side at specific intervals in two or more rows in a staggered (or zigzag) configuration.
A technical means for solving the technical problem (which is hereinafter referred to as “eighteenth technical means”) is sound absorbing device, including a plurality of sound absorbers according to the eighth technical means arranged in a row with the upper and lower bases of the isosceles trapezoidal cross-sectional shape thereof exposed to the outside alternately and parallel to each other.
The technical means are described in detail below. The sound absorber according to the first technical means has a porous sheath, a soft fiber sound absorbent, and a core. These three are elongated tubular or bar-like members, and arranged in this order from outside to inside.
The porous sheath is a tubular member with a non-circular cylindrical cross-section and disposed in the outermost position. Therefore, the porous sheath preferably has mechanical strength, environmental resistance, waterproof property and so on in addition to a sound absorbing ability. Since the sound absorbing ability of the sheath depends on the material, thickness, conditions of the pores and so on thereof, these properties must be selected properly based on the desired attenuation rate of sound waves. The porous sheath can be formed by shaping a porous sound absorbing plate of a light metal such as aluminum.
The soft fiber sound absorbent is a circular cylindrical member and disposed inside the porous sheath in partial contact or non-contact with the porous sheath with the longitudinal direction thereof aligned with the longitudinal direction of the porous sheath. The material and thickness of the soft fiber sound absorbent are preferably selected depending on the desired attenuation rate. As the soft fiber sound absorbent, a molded product of glass wool or rock wool as conventionally used can be used. The method for covering the surfaces thereof for prevention of dispersal of fibers may be the same as a conventional method.
In order to prevent transmission of sound waves through solid matters, the sheath and the sound absorbent are preferably separated from each other. When there are structural restrictions, the sheath and the sound absorbent may be in point or line contact with each other or may be supported by a minimum solid support. A first air layer formed between the sheath and the sound absorbent has a function of causing sound waves to interfere with each other to attenuate them. Since the sound absorbent inside the air layer has a circular cylindrical cross-section and the sheath outside the air layer has a non-circular cylindrical cross-section, the thickness of the first air layer varies from one place to another. Therefore, the phases of the sound waves passing through the air layer are offset everywhere and an effective interference effect can be achieved.
The core has a non-circular cylindrical or non-circular cross-section and disposed inside the soft fiber sound absorbent in a partial contact or non-contact with the soft fiber sound absorbent with the longitudinal direction thereof aligned with the longitudinal direction of the soft fiber sound absorbent. The surface shape of the core is important since the core has a function of a sound wave reflector for reflecting the incident sound waves. The core may be of a tubular shape with a hollow therein or a bar-like shape without a hollow. Since the core has a non-circular cylindrical or non-circular cross-section, irregular or diffuse reflection can be achieved. Therefore, the use of a material with high rigidity, such as a metal, for the core is preferred from the viewpoint of the reflection of sound waves.
The sound absorber and the core are preferably separated from each other and supported through minimum contact, and a second air layer is formed between the sound absorber and the core as in the case with the sheath and the absorbent. Since the thickness of the second air layer also varies from one place to another, an effective interference effect can be achieved.
The features and effects of the sound absorber constructed as above according to the first technical means are next described. Sound waves from an unidentified direction are attenuated when passing through the tubular porous sheath with a non-circular cylindrical cross-section, enters the first air layer perpendicularly from the inner surface of the porous sheath, and are transmitted through the first air layer. Since the thickness of the first air layer is not uniform, the sound waves interfere strongly with each other to attenuate each other significantly. This happens in a wide frequency band effectively. Then, the sound waves pass through the cylindrical soft sound absorbent toward the center axis with attenuation, enters the second air layer, and are transmitted through the second air layer. The sound waves interfere strongly with each other to attenuate each other significantly also in the second air layer.
Then, the sound waves are reflected diffusely on the surfaces of the core with a non-circular cylindrical or non-circular cross-section. The diffusely reflected sound waves are attenuated again when transmitted back through the same propagation path and interfere with incident sound waves before reflection. The attenuation effect caused by interference produces a synergistic effect as described above, and the sound waves are significantly attenuated.
Applications, embodiments, and supplemental explanation of the sound absorber are given below. As a second technical means, the core preferably functions as a sound wave reflector for blocking passage of sound waves and as a support for ensuring mechanical strength. Since the sound absorber of the present invention has an elongated external shape, a core with high mechanical strength is preferably used so that it can also serve as a support which can prevent the sound absorber from being curved or bent at a mid-point thereof. Therefore, the core is preferably made of a metal material as a sound wave reflector and as a support.
As a third technical means, the sound absorber preferably has outer caps at both longitudinal ends thereof. The outer caps are made of strong plates, and the outer peripheries of the plates are bent to surround the outer ends of the outermost porous sheath. Projections conforming to the cross-sectional shapes of the sheath, the soft fiber sound absorbent and the core may be formed on the inner surface of each outer cap so that the members can be supported with the distances therebetween maintained. The first and second air layers are thereby formed reliably. When the outer caps are provided, the sound absorber has a waterproof property and can be used outdoors.
Fitting pieces may be attached to the outer surfaces or peripheries of the outer caps. The outermost porous sheath is porous and has low mechanical strength. Therefore, it is not preferred to apply external force to it during installation. In constructing the sound absorbing device, each sound absorber is installed such that the outer caps can support the weight of the sound absorber. The sound absorbers may be fixed by clamping the outer caps without using fitting pieces.
The tubular porous sheath with a non-circular cylindrical cross section is next described in detail. According to the fourth technical means, the porous sheath has a generally polygonal cross-sectional shape. Accordingly, the first air layer is generally polygonal in external cross-section and circular in internal cross-section. Since the thickness of the first air layer varies from one place to another, the phases of the sound waves passing through the first air layer are offset and an effective interference effect can be achieved. In addition, in the sound absorber according to the fifth technical means, the porous sheath has a generally polygonal cross-section with sides having sawtooth-shaped projections and depressions. The thickness of the first air layer varies little by little from one place to another because of the multiplicity of small sawtooth-shaped projections and depressions, a better interference effect can be achieved.
As the sixth to ninth technical means, illustrative examples of the cross-sectional shape of the porous sheath are shown. The cross-sectional shapes are a generally rectangular shape, a generally triangular shape, a generally isosceles trapezoidal shape, and a star-like shape with at least five projections, respectively. The cross-sectional shape can be properly selected based on the type or characteristics of the noise source or the installation position, production difficulties and production costs of the sound absorbers, and so on. The features and effects of the sixth to ninth technical means are the same as those of the first technical means.
The tubular core with a non-circular cylindrical cross-section or the bar-like core with a non-circular cross-section is next described in detail. Since the core has a function of a sound wave reflector and a function of defining the second air layer, its cross-sectional outer shape is the key. According to the tenth technical means, the core has a generally polygonal cross-sectional shape. Accordingly, the second air layer is generally polygonal in internal cross-section and circular in external cross-section. Since the thickness of the second air layer varies from one place to another, the phases of the sound waves passing through the second air layer are offset and an effective interference effect can be achieved. Also, the core has a non-circular cross-section, it causes diffuse reflection, not uniform radial reflection.
As the eleventh to fifteenth technical means, illustrative examples of the cross-sectional shape of the core are shown. The cross-sectional shapes are a star-like shape with at least three projections arranged circumferentially, a generally rectangular shape, a generally cross-like shape, a shape like that of a spline shaft with at least three rectangular tooth-like projections arranged circumferentially, and a shape like that of a spline shaft with at least three trapezoidal tooth-like projections arranged circumferentially, respectively. According to the sixteenth technical means, the trapezoidal tooth-like projections are wider at the top than at the base. The cross-sectional shape of the core can diversify and complicate the propagation path through which the reflected sound waves travel and makes the interference effect more effective. The features and effects of the eleventh to fifteenth technical means are the same as those of the first technical means.
The sound absorbing device according to the seventeenth technical means is next described. In the sound absorbing device of the present invention, the sound absorbers according to any one of the first to sixteenth technical means are arranged side by side at specific intervals in at least two rows in a staggered configuration. As the direction of the side-by-side arrangement, both horizontal and vertical can be taken. To arrange the sound absorbers side by side in a staggered configuration, fixing plates, for example, can be used. More specifically, when two fixing plates with mounting holes at specific intervals are erected, spaced in the longitudinal direction of the sound absorbers, the sound absorbers can be fixed by fitting the outer caps thereof into the mounting holes. The sound absorbers without the outer caps may be used. That is, a sound absorbing device can be constructed by placing the sound absorbers between two fixing plates with projections like those of the outer caps on their opposite inner sides and tightening screws extending through the fixing plates from outside of the fixing plates to fix the cores of the sound absorbers.
When the sound absorbers are arranged in two, front and rear, rows in a staggered configuration, the distance between the sound absorbers in each row is smaller than double the width of the sound absorbers. Then, since sound waves traveling straight from a noise source facing the sound absorbing device collide with the sound absorbers in either the front or rear row, in other words, there is no propagation path through which the sound waves can leak out without attenuation, a reliable sound absorbing effect can be achieved. When the sound absorbers are arranged in three or more rows, the sound absorbers are preferably arranged in such a manner as to block straight propagation paths of sound waves. Even if the sound absorber are arranged in such a manner that straight propagation paths remains and some of the sound waves can leak out, the sound absorbing device is effective since most of the sound waves are attenuated by the sound absorbers.
With the sound absorbing device with the staggered arrangement as above, the noise source cannot be seen when viewed from outside front but can be seen through a gap between the sound absorbers arranged in a staggered configuration when viewed from an oblique direction. Although the sound absorbing device of the present invention is inferior in see-through capability to a conventional sound absorbing device with a single row arrangement, a sufficient see-through capability required for visual inspection of the inside can be achieved by adjusting the distance between the sound absorbers arranged in a staggered configuration. In addition, air can freely pass through the sound absorbing device, good ventilation can be achieved.
In the sound absorbing device according to the eighteenth technical means, the sound absorbers having a tubular porous sheath with a generally isosceles trapezoidal cross-section according to the eighth technical means are arranged side by side in a row at specific intervals with their upper and lower bases of the isosceles trapezoidal cross-sectional shape exposed to the outside alternately. In the arrangement in which the isosceles trapezoidal cross-sectional shapes are alternately inverted, even if sound waves pass through a gap between the upper base of a sound absorber and the lower base of an adjacent sound absorber, the sound waves collide with upper base side parts of the legs of the trapezoid. The straight propagation paths of the sound waves are thereby blocked and the sound waves are prevented from leaking out. However, the noise source cannot be seen when viewed from front. However, since a gap parallel to an oblique direction is formed between the legs of the adjacent isosceles trapezoids opposed to each other, visual observation can be carried out from an oblique direction and a see-through capability can be ensured. In addition, a ventilation capability can be achieved.
the best mode for carrying out the present invention is described with reference to FIG. 1 to FIG. 19. FIG. 1 is a cross-sectional view illustrating a sound absorber 100 employing the first to fourth, sixth, tenth and eleventh technical means. The sound absorber 100 has a tubular porous sheath 1 having a generally rectangular cross-section with a side length of L, a circular cylindrical soft fiber sound absorbent 2 disposed inside the porous sheath 1, and a tubular core 4 having a star-shaped cross-section with at least three projections arranged circumferentially and disposed inside the soft fiber sound absorbent 2. The spaces between the projections of the core 4 form a second air layer 6. FIG. 2 is a side cross-sectional elevation of the sound absorber 100, taken in the longitudinal direction thereof. Plate-like outer caps 3 are provided on both ends of the sound absorber 100. The outer peripheries of the outer caps 3 are bent inward toward each other to form bent portions 31. The bent portions 31 surround and support the outer ends of the porous sheath 1. A projection 32 is formed on the inside of each outer cap 3. The protrusions 32 of the outer caps 3 are inserted between the sheath 1 and the sound absorbent 2 to ensure a gap as a first air layer 7 therebetween. FIG. 3 is a side view of the sound absorber 100 as viewed from a side of FIG. 2. Screws 5 extend through the outer caps 3 from outside to fix the core 4.
As shown in FIG. 1, sound waves S1 emitted from unidentified directions and having reached the surfaces of the porous sheath 1 enter the first air layer 7 as sound waves S2 directed generally perpendicular to the surfaces of the porous sheath 1 and are transmitted through the first air layer 7. Since the thickness of the first air layer 7 is not uniform, the sound waves interfere strongly with each other to attenuate each other significantly. This happens to sound in a wide frequency band effectively. Then, the sound waves pass through the soft fiber sound absorbent 2 with attenuation and are transmitted into the second air layer 6. The sound waves interfere strongly with each other to attenuate each other significantly also in the second air layer 6. In addition, the sound waves are reflected diffusely on the surfaces of the core 4 and attenuated again when transmitted back through the same propagation path. While being attenuated, the sound waves interfere with incident sound waves before reflection in every place. The attenuation effect caused by interference produces a synergistic effect as described above and the sound waves are significantly attenuated.
FIG. 4 is a horizontal cross-sectional view illustrating a sound absorbing device 200 using the sound absorbers 100 and employing the seventeenth technical means. The sound absorbing device 200 has sound absorbers 100A and 100B arranged side by side in two, front and rear, rows in a staggered configuration. The distance D between the sound absorbers 100A and 100B in each row is slightly smaller than double the width L of the sound absorbers 100. Therefore, as seen from a position facing the sound absorbing device 200, the sound absorbers 100B in the rear row can be seen through the gaps between the sound absorbers 100A in the front row but the area behind the sound absorbers 100B cannot be seen. FIG. 5 is a plan view illustrating the top face of the sound absorbing device 200, and FIG. 6 is a cross-sectional view taken along the line C-C of FIG. 5. As shown in the drawings, the sound absorbing device 200 has fixing plates 8 at both longitudinal ends of the sound absorbers 100, and screws 5 extending through the fixing plates 8 fix the cores 4 of the sound absorbers 100A and 100B.
As shown in FIG. 4, sound waves emitted from a noise source N shown in a lower part of the drawing enter the sound absorbing device 200 facing the noise source N generally perpendicular to the sound absorbing device 200. Some sound waves S10 are attenuated when they collide with the sound absorbers 100A in the front row, and the other sound waves S11 having passed through the gaps between the sound absorbers 100A are attenuated when they collide with the sound absorbers 100B in the rear row. There is no sound wave which does not collide with the sound absorbers 100A or 100B and travel straight without being attenuated. FIG. 7 is a horizontal cross-sectional view illustrating a sound absorbing device 300 in which the sound absorbers 100 are arranged in a row. Since the sound absorbers 100 are arranged in a row at spaced intervals, some sound waves S30 travel straight and leak out. The sound absorbing device 200 of the present invention which allows no sound wave to travel straight has a high sound absorbing ability.
In addition, the noise source N can be observed from outside through the gaps between the sound absorbers 100 arranged in a staggered configuration when seen from an oblique direction V1 as shown in FIG. 4. Although the sound absorbing device 200 of the present invention is inferior in see-through capability to the sound absorbing device 300 with single row arrangement, a see-through capability necessary for visual inspection or a discovery of a failure of the equipment installed inside can be ensured by properly adjusting the distances between the sound absorbers 100 arranged in a staggered configuration. In addition, the gaps between the sound absorbers 100 arranged in a staggered configuration ensures ventilation.

First Embodiment

FIG. 8 is a cross-sectional view illustrating a sound absorber 101 of a first embodiment according to the fifth technical means. The sound absorber 101 has a first air layer 71 defined by a tubular porous sheath 11 having a generally rectangular cross-section with sides having sawtooth-shaped projections and depressions.

Second Embodiment

FIG. 9 is a cross-sectional view illustrating a sound absorber 102 of a second embodiment according to the seventh technical means. The sound absorber 101 has a first air layer 72 defined by a tubular porous sheath 12 having a generally triangular cross-section. As shown in FIG. 9, sound waves S1 emitted from unidentified directions and having reached the surfaces of the porous sheath 12 enter the first air layer 72 as sound waves S2 directed generally perpendicular to the surfaces of the porous sheath 12 and are transmitted into the air layer 72.

Third Embodiment

FIG. 10 is a cross-sectional view illustrating a sound absorber 103 according to the eighth technical means. The sound absorber 103 has a first air layer 73 defined by a tubular porous sheath 13 having a generally isosceles trapezoidal cross-section. The height H of the isosceles trapezoid may be generally the same as the length L of one side of the generally rectangular cross-section of the first technical means shown in FIG. 1. As shown in FIG. 10, sound waves S1 emitted from unidentified directions and having reached the surfaces of the porous sheath 13 enter the first air layer 73 as sound waves S2 directed generally perpendicular to the surfaces of the porous sheath 13 and are transmitted into the air layer 73.

Fourth Embodiment

FIG. 11 is a cross-sectional view illustrating a sound absorber 104 according to the ninth technical means. The sound absorber 104 has a first air layer 74 defined by a tubular porous sheath 14 having a star-shaped cross-section with at least five projections.

Fifth Embodiment

FIG. 12 is a cross-sectional view illustrating a sound absorber 105 according to the twelfth technical means. The sound absorber 105 has a second air layer 61 defined by a tubular core 41 having a generally rectangular cross-section.

Sixth Embodiment

FIG. 13 is a cross-sectional view illustrating a sound absorber 106 according to the thirteenth technical means. The sound absorber 106 has a second air layer 62 defined by a tubular core 42 having a generally cross-shaped cross-section.

Seventh Embodiment

FIG. 14 is a cross-sectional view illustrating a sound absorber 107 according to the fourteenth technical means. The sound absorber 107 has a second air layer 63 defined by a tubular core 43 having a cross-section like that of a spline shaft with at least three rectangular tooth-like projections arranged circumferentially.

Eighth Embodiment

FIG. 15 is a cross-sectional view illustrating a sound absorber 108 according to the fifteenth technical means. The sound absorber 108 has a second air layer 64 defined by a tubular core 44 having a cross-section like that of a spline shaft with at least three trapezoidal tooth-like projections arranged circumferentially.

Ninth Embodiment

FIG. 16 is a cross-sectional view illustrating a sound absorber 109 according to the sixteenth technical means. The sound absorber 109 has a second air layer 65 defined by a tubular core 45 having a cross-section like that of a spline shaft with at least three trapezoidal tooth-like projections which are wider at the top than at the base and arranged circumferentially. Since the second air layer 65 has wide inner spaces with narrow entrances, the sound waves having entered the second air layer 65 are repeatedly reflected and interfere strongly with each other to attenuate each other significantly.

Tenth Embodiment

FIG. 17 is a cross-sectional view illustrating another sound absorbing device 201 using the sound absorbers 101 of the first embodiment and employing the seventeenth technical means. The constitution, features and effects of the sound absorbing device 201 are the same as those of the sound absorbing device 200.

Eleventh Embodiment

FIG. 18 is a cross-sectional view illustrating another sound absorbing device 204 using the sound absorbers 104 of the fourth embodiment and employing the seventeenth technical means. The constitution, features and effects of the sound absorbing device 204 are the same as those of the sound absorbing device 200.

Twelfth Embodiment

FIG. 19 is a cross-sectional view illustrating another sound absorbing device 203 using the sound absorbers 103 of the third embodiment and employing the eighteenth technical means. The sound absorbing device 203 has sound absorbers 103A and 103B with a generally isosceles trapezoidal cross-section arranged in a row with their upper and lower bases exposed to the outside alternately and parallel to each other. In the sound absorbing device 203, most sound waves S20 of the sound waves emitted from the noise source N are attenuated when they collide with the upper bases of the sound absorbers 103A or the lower bases of adjacent sound absorbers 103B. Although some sound waves S21 pass through the gaps between the sound absorbers 103A and 103B, they collide with upper base side parts of the legs of the trapezoidal sound absorbers 103A and are attenuated. Since gaps parallel to an oblique direction V1 are formed between opposed legs of adjacent sound absorbers 103A and 103B, the noise source N can be observed from outside and a see-through capability can be ensured. Even though the sound absorbers 103 are arranged in a row in the sound absorbing device 203, the straight propagation paths can be closed and a see-through capability can be ensured.
The sound absorber according to the present invention comprises: a tubular porous sheath with a non-circular cylindrical cross-section; a circular cylindrical soft fiber sound absorbent disposed inside the porous sheath in partial contact or non-contact with the porous sheath with the longitudinal direction thereof aligned with the longitudinal direction of the porous sheath, and a bar-like core with a non-circular cylindrical cross-section disposed inside the soft fiber sound absorbent in a partial contact or non-contact with the soft fiber sound absorbent with the longitudinal direction thereof aligned with the longitudinal direction of the soft fiber sound absorbent.
As a result, sound waves in a wide frequency band can be attenuated effectively by synergistic effects of the interference caused by the first and second air layers and the diffuse reflection caused by the core in addition to the sound absorbing abilities of the sheath and the sound absorbent.
The sound absorbing device according to the present invention is constructed by arranging a plurality of the sound absorbers side by side at specific intervals in two or more rows in a staggered configuration. Alternately, the sound absorbing device according to the present invention is constructed by arranging a plurality of sound absorbers having a tubular porous sheath with a generally isosceles trapezoidal cross-section in a row with the upper and lower bases of the isosceles trapezoidal cross-sectional shape thereof exposed to the outside alternately and parallel to each other.
As a result, sound waves traveling straight from a noise source cannot leak out without attenuation and attenuated significantly by the sound absorbents. The inside of the sound absorbing device can be observed through the gaps between the sound absorbers although the sound absorbing device does not have a transparent plate, and ventilation can be achieved freely. That is, a see-through capability and a ventilation capability can be achieved.
The sound absorber and sound absorbing device of the present invention can be used in various places whether indoors or outdoors. For example, the sound absorbing device of the present invention is applicable to a large machine which generates noise and heat. Then, a great sound absorbing effect can be achieved. In addition, visual inspection of the equipment can be carried out from outside, and the heat can be dissipated by ventilation. The sound absorbing device of the present invention is also applicable to sound insulating walls along highways. Since the sound absorbing device does not block the flow of wind, there is no risk of adverse effect to the natural environment.
Description has been made of the preferred embodiments of the present invention. The terminology employed herein is for the purpose of illustration but not of limitation. It should be understood that many changes and modification can be made within the scope of the appended claims without departing from the scope and spirit of the present invention.

Claims

1. A sound absorber, comprising:

a tubular porous sheath with a non-circular cylindrical cross-section;

a circular cylindrical soft fiber sound absorbent disposed inside the porous sheath in partial contact or non-contact with the porous sheath with the longitudinal direction thereof aligned with the longitudinal direction of the porous sheath; and

a tubular core with a non-circular cylindrical cross-section or a bar-like core with a non-circular cross-section disposed inside the soft fiber sound absorbent in a partial contact or non-contact with the soft fiber sound absorbent with the longitudinal direction thereof aligned with the longitudinal direction of the soft fiber sound absorbent.

2. The sound absorber of claim 1, wherein the core functions as a sound wave reflector for blocking passage of sound waves and as a support for ensuring mechanical strength.

3. The sound absorber of claim 1, further comprising outer caps for supporting longitudinal ends of the porous sheath, the soft fiber sound absorbent, and the core.

4. The sound absorber of claim 1, wherein the porous sheath has a generally polygonal cross-section.

5. The sound absorber of claim 4, wherein the porous sheath has a generally polygonal cross-section with sides having sawtooth-shaped projections and depressions.

6. The sound absorber of claim 4, wherein the porous sheath has a generally rectangular cross-section.

7. The sound absorber of claim 4, wherein the porous sheath has a generally triangular cross-section.

8. The sound absorber of claim 4, wherein the porous sheath has a generally isosceles trapezoidal cross-section.

9. The sound absorber of claim 4, wherein the porous sheath has a star-shaped cross-section with at least five projections.

10. The sound absorber of claim 1, wherein the core has a generally polygonal cross-section.

11. The sound absorber of claim 10, wherein the core has a star-shaped cross-section with at least three projections arranged circumferentially.

12. The sound absorber of claim 10, wherein the core has a generally rectangular cross-section.

13. The sound absorber of claim 10, wherein the core has a generally cross-shaped cross-section.

14. The sound absorber of claim 10, wherein the core has a cross-section like that of a spline shaft with at least three rectangular tooth-like projections arranged circumferentially.

15. The sound absorber of claim 10, wherein the core has a cross-section like that of a spline shaft with at least three trapezoidal tooth-like projections arranged circumferentially.

16. The sound absorber of claim 15, wherein the trapezoidal tooth-like projections are wider at the top than at the base.

17. A sound absorbing device, comprising a plurality of sound absorbers according to claim 1 arranged side by side at specific intervals in two or more rows in a staggered configuration.

18. A sound absorbing device, comprising a plurality of sound absorbers according to claim 8 arranged in a row with the upper and lower bases of the isosceles trapezoidal cross-sectional shape thereof exposed to the outside alternately and parallel to each other.

19. A sound absorbing device, comprising a plurality of sound absorbers according to claim 4 arranged side by side at specific intervals in two or more rows in a staggered configuration.

20. A sound absorbing device, comprising a plurality of sound absorbers according to claim 10 arranged side by side at specific intervals in two or more rows in a staggered configuration.