U.S. patent application number 11/377047 was filed with the patent office on 2006-11-23 for sound absorber and sound absorbing device.
This patent application is currently assigned to NAGATA KOSAKUSHO CO., LTD.. Invention is credited to Shinya Nagata, Tetsutaroh Nakagawa.
Application Number | 20060260870 11/377047 |
Document ID | / |
Family ID | 37203544 |
Filed Date | 2006-11-23 |
United States Patent
Application |
20060260870 |
Kind Code |
A1 |
Nakagawa; Tetsutaroh ; et
al. |
November 23, 2006 |
Sound absorber and sound absorbing device
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.
Inventors: |
Nakagawa; Tetsutaroh;
(Anjo-shi, JP) ; Nagata; Shinya; (Chiryu-shi,
JP) |
Correspondence
Address: |
HOGAN & HARTSON L.L.P.
1999 AVENUE OF THE STARS
SUITE 1400
LOS ANGELES
CA
90067
US
|
Assignee: |
NAGATA KOSAKUSHO CO., LTD.
|
Family ID: |
37203544 |
Appl. No.: |
11/377047 |
Filed: |
March 15, 2006 |
Current U.S.
Class: |
181/295 |
Current CPC
Class: |
E04B 9/34 20130101; E04B
1/8209 20130101; G10K 11/16 20130101; E01F 8/0082 20130101 |
Class at
Publication: |
181/295 |
International
Class: |
E04B 1/82 20060101
E04B001/82 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2005 |
JP |
2005-084833 |
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.
Description
CROSS REFERENCE OF RELATED APPLICATIONS
[0001] 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
[0002] 1. Field of Invention
[0003] 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.
[0004] 2. Background Art
[0005] 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.
[0006] [Patent Document 1] JP-A-Hei 11-133979
[0007] 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.
[0008] 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.
[0009] 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
[0010] 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.
[0011] 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.
[0012] 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
[0013] FIG. 1 is a cross-sectional view illustrating an embodiment
of a sound absorber of the present invention.
[0014] FIG. 2 is a side cross-sectional elevation of the embodiment
shown in FIG. 1, taken along the longitudinal direction
thereof.
[0015] FIG. 3 is a side view of the embodiment shown in FIG. 1.
[0016] FIG. 4 is a horizontal cross-sectional view illustrating an
embodiment of a sound absorber of the present invention.
[0017] FIG. 5 is a top plan view of the embodiment shown in FIG.
4.
[0018] FIG. 6 is a cross-sectional view of the embodiment shown in
FIG. 5, taken along the line C-C of FIG. 5.
[0019] FIG. 7 is a transverse cross-sectional view of a sound
absorbing device in which sound absorbers are arranged in a
row.
[0020] FIG. 8 is a cross-sectional view illustrating a sound
absorber according to a first embodiment of the present
invention.
[0021] FIG. 9 is a cross-sectional view illustrating a sound
absorber according to a second embodiment of the present
invention.
[0022] FIG. 10 is a cross-sectional view illustrating a sound
absorber according to a third embodiment of the present
invention.
[0023] FIG. 11 is a cross-sectional view illustrating a sound
absorber according to a fourth embodiment of the present
invention.
[0024] FIG. 12 is a cross-sectional view illustrating a sound
absorber according to a fifth embodiment of the present
invention.
[0025] FIG. 13 is a cross-sectional view illustrating a sound
absorber according to a sixth embodiment of the present
invention.
[0026] FIG. 14 is a cross-sectional view illustrating a sound
absorber according to a seventh embodiment of the present
invention.
[0027] FIG. 15 is a cross-sectional view illustrating a sound
absorber according to an eighth embodiment of the present
invention.
[0028] FIG. 16 is a cross-sectional view illustrating a sound
absorber according to a ninth embodiment of the present
invention.
[0029] FIG. 17 is a cross-sectional view illustrating a sound
absorbing device according to a tenth embodiment of the present
invention.
[0030] FIG. 18 is a cross-sectional view illustrating another sound
absorbing device according to a twelfth embodiment of the present
invention.
[0031] 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
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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
[0072] 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
[0073] 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
[0074] 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
[0075] 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
[0076] 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
[0077] 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
[0078] 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
[0079] 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
[0080] 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
[0081] 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
[0082] 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
[0083] 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.
[0084] 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.
[0085] 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.
[0086] 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.
[0087] 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.
[0088] 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.
[0089] 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.
* * * * *