U.S. patent application number 10/545108 was filed with the patent office on 2006-05-11 for sound-absorbing structure using thin film.
Invention is credited to Toshimitsu Tanaka, Hiroki Ueda, Ichiro Yamagiwa, Zenzo Yamaguchi.
Application Number | 20060096183 10/545108 |
Document ID | / |
Family ID | 32905550 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060096183 |
Kind Code |
A1 |
Yamaguchi; Zenzo ; et
al. |
May 11, 2006 |
Sound-absorbing structure using thin film
Abstract
A sound-absorbing structure using thin film of the present
invention includes at least a first thin film (11) and a second
thin film (12), the first thin film (11) and the second thin film
(12) being layered over each other and one or both of the first
thin film (11) and the second thin film (12) having at least either
ridges or grooves (ridges (a) in the selected figure). As each of
the thin films (11) and (12), a metallic thin film or a resinous
thin film is employable. It is desirable that fine through holes
are formed in a large number in the thin films (11) and (12).
Inventors: |
Yamaguchi; Zenzo; (Hyogo,
JP) ; Yamagiwa; Ichiro; (Hyogo, JP) ; Tanaka;
Toshimitsu; (Hyogo, JP) ; Ueda; Hiroki;
(Hyogo, JP) |
Correspondence
Address: |
REED SMITH LLP
3110 FAIRVIEW PARK DRIVE, SUITE 1400
FALLS CHURCH
VA
22042
US
|
Family ID: |
32905550 |
Appl. No.: |
10/545108 |
Filed: |
January 23, 2004 |
PCT Filed: |
January 23, 2004 |
PCT NO: |
PCT/JP04/00593 |
371 Date: |
August 10, 2005 |
Current U.S.
Class: |
52/144 |
Current CPC
Class: |
B32B 3/30 20130101; G10K
11/172 20130101; B32B 2307/102 20130101; B32B 7/00 20130101; B32B
3/266 20130101; G10K 11/168 20130101 |
Class at
Publication: |
052/144 |
International
Class: |
E04B 1/82 20060101
E04B001/82 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2003 |
JP |
2003-046531 |
Claims
1. A sound-absorbing structure including at least a first thin film
and a second thin film, said first thin film and said second thin
film being layered over each other, and one or both of said first
thin film and said second thin film having at least either ridges
or grooves.
2. The sound-absorbing structure according to claim 1, wherein
through holes are formed in one or both of said first thin film and
said second thin film.
3. The sound-absorbing structure according to claim 2, wherein said
through holes are formed in both of said first thin film and said
second thin film, the through holes formed in said first thin film
being formed in positions not overlapping the through holes formed
in said second thin film.
4. The sound-absorbing structure according to claim 2, wherein said
through holes are fine holes and formed in a large number in said
thin films.
5. The sound-absorbing structure according to claim 1, wherein a
rear member is installed at a position opposite to a sound wave
incidence side with respect to said thin films.
6. The sound-absorbing structure according to claim 5, wherein an
air layer is formed between said thin films and said rear
member.
7. The sound-absorbing structure according to claim 5, wherein a
distance between said rear member and said thin films is
adjustable.
8. The sound-absorbing structure according to claim 1, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin films.
9. The sound-absorbing structure according to claim 8, wherein said
front member is formed with a large number of fine holes.
10. The sound-absorbing structure according to claim 1, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin films, a rear
member is installed at a position opposite to said front member
with respect to said thin films, and a space between said front
member and said rear member is divided into plural portions in the
surface direction of said thin films.
11. A sound-absorbing structure including at least a first thin
film and a second thin film, said first thin film and said second
thin film being layered over each other, and one or both of said
first thin film and said second thin film being folded so as to
have mutually contacting and overlapping portions.
12. The sound-absorbing structure according to claim 11, wherein
through holes are formed in one or both of said first thin film and
said second thin film.
13. The sound-absorbing structure according to claim 12, wherein
said through holes are formed in both of said first thin film and
said second thin film, the through holes formed in said first thin
film being formed in positions not overlapping the through holes
formed in said second thin film.
14. The sound-absorbing structure according to claim 12, wherein
said through holes are fine holes and formed in a large number in
said thin films.
15. The sound-absorbing structure according to claim 11, wherein a
rear member is installed at a position opposite to a sound wave
incidence side with respect to said thin films.
16. The sound-absorbing structure according to claim 15, wherein an
air layer is formed between said thin films and said rear
member.
17. A sound-absorbing structure according to claim 15, wherein a
distance between said rear member and said thin films is
adjustable.
18. The sound-absorbing structure according to claim 11, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin films.
19. The sound-absorbing structure according to claim 18, wherein
said front member is formed with a large number of fine holes.
20. The sound-absorbing structure according to claim 11, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin films, a rear
member is installed at a position opposite to said front member
with respect to said thin films, and a space between said front
member and said rear member is divided into plural portions in the
surface direction of said thin films.
21. A sound-absorbing structure including at least a first thin
film and a second thin film, said first thin film and said second
thin film being layered over each other, and through holes being
formed in one or both of said first thin film and said second thin
film.
22. The sound-absorbing structure according to claim 21, wherein
said through holes are formed in both of said first thin film and
said second thin film, the through holes formed in said first thin
film being formed in positions not overlapping the through holes
formed in said second thin film.
23. The sound-absorbing structure according to claim 21, wherein
said through holes are fine through holes and are formed in a large
number in said thin films.
24. The sound-absorbing structure according to claim 21, wherein a
rear member is installed at a position opposite to a sound wave
incidence side with respect to said thin films.
25. The sound-absorbing structure according to claim 24, wherein an
air layer is formed between said thin films and said rear
member.
26. The sound-absorbing structure according to claim 24, wherein a
distance between said rear member and said thin films is
adjustable.
27. The sound-absorbing structure according to claim 21, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin films.
28. The sound-absorbing structure according to claim 27, wherein
said front member is formed with a large number of fine holes.
29. The sound-absorbing structure according to claim 21, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin films, a rear
member is installed at a position opposite to said front member
with respect to said thin films, and a space between said front
member and said rear member is divided into plural portions in the
surface direction of said thin films.
30. A sound-absorbing structure including at least one thin film
folded so as to have mutually contacting and overlapping
portions.
31. The sound-absorbing structure according to claim 30, wherein
through holes are formed in said thin film.
32. The sound-absorbing structure according to claim 30, wherein a
rear member is installed at a position opposite to a sound wave
incidence side with respect to said thin film.
33. A sound-absorbing structure according to claim 32, wherein an
air layer is formed between said thin film and said rear
member.
34. The sound-absorbing structure according to claim 32, wherein a
distance between said rear member and said thin film is
adjustable.
35. The sound-absorbing structure according to claim 30, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin film.
36. The sound-absorbing structure according to claim 35, wherein
said front member is formed with a large number of fine holes.
37. The sound-absorbing structure according to claim 30, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin film, a rear
member is installed at a position opposite to said front member
with respect to said thin film, and a space between said front
member and said rear member is divided into plural portions in the
surface direction of said thin film.
38. A sound-absorbing structure including at least a first thin
film and a second thin film, said first thin film and said second
thin film being layered over each other, and an air-permeable front
member being installed at a position on a sound wave incidence side
with respect to said thin films.
39. The sound-absorbing structure according to claim 38, wherein
said front member is formed with a large number of fine holes.
40. The sound-absorbing structure according to claim 38, wherein a
rear member is installed at a position opposite to a sound wave
incidence side with respect to said thin films.
41. The sound-absorbing structure according to claim 38, wherein a
front member having air permeability is installed at a position on
a sound wave incidence side with respect to said thin films, a rear
member is installed at a position opposite to said front member
with respect to said thin films, and a space between said front
member and said rear member is divided into plural portions in the
surface direction of said thin films.
Description
TECHINICAL FIELD
[0001] The present invention relates to a technique of a
sound-absorbing structure using a thin film.
BACKGROUND ART
[0002] Sound-absorbing techniques have heretofore been known
publicly.
[0003] For example, those disclosed in Patent Document 1 (Japanese
Patent Laid Open No. 2002-59510) and Patent Document 2 (Japanese
Patent Laid Open No. 2000-34937) are known. Patent Documents 1 and
2 are each concerned with a sound-absorbing structure using a
sound-absorbing material which is a combination of a porous
sound-absorbing material such as glass wool and a material
excellent in weather resistance, water resistance and heat
resistance.
[0004] According to the sound-absorbing structures disclosed in
Patent Documents 1 and 2, it has been possible to supplement the
weather resistance, water resistance and heat resistance of glass
wool but not to a satisfactory extent; besides, the problem of
recyclability has not been solved. Further, in case of utilizing a
resonance type sound-absorbing structure, a plate vibration type
sound-absorbing structure or the like, which are other
sound-absorbing structures than those using the porous
sound-absorbing material typified by glass wool, since a sound
absorbing mechanism corresponds to energy dissipation based on
resonance phenomenon, a sound absorbing band is narrow and a sound
absorbing capacity is inferior to that of the porous
sound-absorbing material such as glass wool.
DISCLOSURE OF THE INVENTION
[0005] In a first aspect of the present invention, there is
provided a sound-absorbing structure including at least a first
thin film and a second thin film, the first thin film and the
second thin film being layered over each other and one or both of
the first thin film and the second thin film having at least either
ridges or grooves.
[0006] The thin films vibrate upon incidence of a sound wave on the
sound-absorbing structure of the present invention and their
overlapping portions contact and are rubbed against each other. As
a result, there occurs energy dissipation of the sound wave and a
high sound absorption coefficient is attained in a wide band.
[0007] Besides, recycling is easy because a metallic thin film such
as aluminum foil or a resinous thin film such as a polyvinyl
chloride film is employable as each of the thin films.
[0008] In a second aspect of the present invention there is
provided a sound absorbing structure including at least a first
thin film and a second thin film, the first thin film and the
second thin film being layered over each other and one or both of
the first thin film and the second thin film being folded so as to
have mutually contacting and overlapping portions.
[0009] Upon incidence of a sound wave on the sound-absorbing
structure of the present invention, the first and second thin films
vibrate, contact (including their overlapping portions) and are
rubbed against each other. As a result, there occurs energy
dissipation of the sound wave and a high sound absorption
coefficient is attained in a wide band.
[0010] Besides, recycling is easy because a metallic thin film such
as aluminum foil or a resinous thin film such as a polyvinyl
chloride film is employable as each of the thin films.
[0011] In a third aspect of the present invention, there is
provided a sound-absorbing structure including at least a first
thin film and a second thin film, the first thin film and the
second thin film being layered over each other, and through holes
being formed in one or both of the first thin film and the second
thin film.
[0012] Upon incidence of a sound wave on the sound-absorbing
structure of the present invention, the thin films vibrate and
their overlapping portions contact and are rubbed against each
other. As a result, there occurs energy dissipation of the sound
wave and a high sound absorption coefficient is attained in a wide
band. Moreover, a higher sound absorbing effect can be attained
because a damping effect is added when the sound wave passes
through the through holes.
[0013] Further, recycling is easy because a metallic thin film such
as aluminum foil or a resinous thin film such as a polyvinyl
chloride film is employable as each of the thin films.
[0014] In a fourth aspect of the present invention, there is
provided a sound-absorbing structure including at least one thin
film folded so as to have mutually contacting and overlapping
portions.
[0015] Upon incidence of a sound wave on the sound-absorbing
structure of the present invention, the thin film vibrates and
their overlapping portions contact and are rubbed against each
other. As a result, there occurs energy dissipation of the sound
wave and a high sound absorption coefficient is attained in a wide
band.
[0016] Besides, recycling is easy since a metallic thin film such
as aluminum foil or a resinous thin film such as a polyvinyl
chloride film is employable as the thin film.
[0017] Further, it is possible to reduce the cost because a sound
absorbing effect is obtained even with use of a single thin
film.
[0018] In a fifth aspect of the present invention, there is
provided a sound-absorbing structure including at least a first
thin film and a second thin film, the first thin film and the
second thin film being layered over each other, and an
air-permeable front member being installed at a position on the
sound wave incidence side with respect to the thin films.
[0019] It is possible to protect the thin films which are apt to be
damaged and hence possible to enhance durability and prolong a
service life of the sound-absorbing structure. Since the front
member is air-permeable, it does not shut off an incident sound
wave and hence does not obstruct the sound absorbing effect.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1(a) is a perspective view of a sound-absorbing
structure according to a first embodiment of the present
invention;
[0021] FIG. 1(b) is an enlarged sectional view of the
sound-absorbing structure of the first embodiment;
[0022] FIG. 2(a) is an explanatory diagram showing an effect of the
sound-absorbing structure of the first embodiment;
[0023] FIG. 2(b) is an explanatory diagram showing the effect of
the sound-absorbing structure of the first embodiment;
[0024] FIG. 3 is an enlarged sectional view of a sound-absorbing
structure according to a second embodiment of the present
invention;
[0025] FIG. 4 is an enlarged sectional view of a sound-absorbing
structure according to a third embodiment of the present
invention;
[0026] FIG. 5 is an explanatory diagram showing a sound wave
passing route in the sound-absorbing structure of the third
embodiment;
[0027] FIG. 6 is an enlarged sectional view of a sound-absorbing
structure according to a fourth embodiment of the present
invention;
[0028] FIG. 7 is an enlarged sectional view of a sound-absorbing
structure according to a fifth embodiment of the present
invention;
[0029] FIG. 8 is an enlarged sectional view of a sound-absorbing
structure according to a sixth embodiment of the present
invention;
[0030] FIG. 9 is an enlarged sectional view of a sound-absorbing
structure according to a seventh embodiment of the present
invention;
[0031] FIG. 10(a) is an enlarged sectional view of a
sound-absorbing structure according to an eighth embodiment of the
present invention;
[0032] FIG. 10(b) is an enlarged sectional view of the
sound-absorbing structure of the eighth embodiment;
[0033] FIG. 11 is an enlarged sectional view of a sound-absorbing
structure according to a ninth embodiment of the present
invention;
[0034] FIG. 12 is a diagram showing a modification of the first
embodiment with three or more thin films being layered over one
another;
[0035] FIG. 13(a) is a diagram showing a modification of the sixth
embodiment with three of more thin films being layered over one
another;
[0036] FIG. 13(b) is a diagram showing another modification of the
sixth embodiment with three or more thin films being layered over
one another;
[0037] FIG. 14 is a diagram showing a modification of the eighth
embodiment with three or more thin films being layered over one
another;
[0038] FIG. 15 is an explanatory diagram of an apparatus used in
verification experiments for the sound-absorbing structures
according to the present invention;
[0039] FIG. 16 is a graph showing results of verification
experiments using aluminum foil as a thin film; and
[0040] FIG. 17 is a graph making comparison between a sound
absorbing effect obtained by using aluminum foil formed with
through holes and a sound absorbing effect obtained using aluminum
foil not formed with through holes.
BEST MODE FOR CARRYING OUT THE INVENTION
FIRST EMBODIMENT
[0041] In a sound-absorbing structure according to a first
embodiment of the present invention, as shown in a perspective view
of FIG. 1(a), a first thin film 11 and a second thin film 12 are
layered over each other. As each of the thin films 11 and 12, there
may be used, for example, a metallic thin film such as aluminum
foil or a resinous thin film such as a polyvinyl chloride film, but
no limitation is made thereto.
[0042] As shown in an enlarged sectional view of FIG. 1(b), though
not concretely shown in the perspective view of FIG. 1(a), each of
the two thin films 11 and 12 has a large number of ridges (a) which
face one side in the layered direction of the thin films.
[0043] FIG. 2 shows an effect of this embodiment. Upon incidence of
a sound wave as shown in FIG. 2(a), the thin films 11 and 12
vibrate and their overlapping portions contact and are rubbed
against each other as shown in FIG. 2(b), with the result that
there occurs energy dissipation of the sound wave and absorption of
sound is effected. In FIGS. 2(a) and 2(b), the ridges (a) are not
shown for the convenience of explanation.
[0044] This embodiment adopts a mechanism that the two thin films
11 and 12 vibrate upon the incidence of the sound wave, contact and
are rubbed against each other to dissipate energy of the sound
wave. Thus, an excellent sound absorbing capacity can be exhibited
in a wide band as compared with a configuration wherein the energy
is dissipated using a resonance phenomenon.
[0045] Besides, since a metallic thin film such as aluminum foil or
a resinous thin film such as a polyvinyl chloride film is
employable as each of the thin films 11 and 12, recycling of the
sound-absorbing structure is easy in comparison with the
conventional material difficult to be recycled such as glass wool
which has so far been compelled to be disposed of as shredder dust
or the like.
SECOND EMBODIMENT
[0046] FIG. 3 shows a sound-absorbing structure according to a
second embodiment of the present invention, which is the same as
the first embodiment in that two thin films 21 and 22 are layered
over each other.
[0047] In this second embodiment, however, the two thin films 21
and 22 are each folded so as to have mutually contacting and
overlapping portions (b) instead of forming such ridges (a) as
described above.
[0048] In this second embodiment, the two thin films 21 and 22 also
vibrate upon incidence of a sound wave and both films (including
their folded portions (b)) contact and are rubbed against each
other, whereby energy of the sound wave can be dissipated and a
high sound absorption coefficient can be attained in a wide
band.
THIRD EMBODIMENT
[0049] FIG. 4 shows a sound-absorbing structure according to a
third embodiment of the present invention, which is the same as the
previous embodiments in that two thin films 31 and 32 are layered
over each other.
[0050] However, each of the two thin films 31 and 32 is formed with
fine through holes (c) extending in the film thickness direction
through the film.
[0051] When seen in the layered direction of both thin films 31 and
32, the through holes (c) in the first thin film 31 are formed in
positions not overlapping the through holes (c) formed in the
second thin film 32. That is, the through holes (c) of one thin
film (31 or 32) are formed in positions not overlapping the through
holes (c) of the other thin film (32 or 31).
[0052] According to the configuration of this third embodiment, a
more excellent sound deadening effect can be obtained not only
because there is obtained the same effect as in the previous first
and second embodiments, i.e., excellent sound deadening effect in a
wide band resulting from vibration and mutual rubbing of the thin
films 31 and 32, but also because the sound wave is further damped
during passage thereof through the through holes (c).
[0053] Moreover, since through holes (c) used in this embodiment
are fine holes, the above damping effect is further improved, that
is, there is attained a remarkable improvement of the sound
deadening effect.
[0054] Further, according to the configuration of this third
embodiment, since the through holes (c) of the thin films 31 and 32
are formed in positions such that the through holes of one thin
film do not overlap the through holes of the other thin film, the
sound wave, as shown in FIG. 5, passes from the incidence side
through the through holes (c) of the first thin film 31, then
passes between the two thin films 31 and 32 and goes out through
the through holes (c) of the second thin film 32.
[0055] That is, the sound wave propagates along inner surfaces of
the two thin films 31 and 32 as in FIG. 5, so that a damping action
induced during passage of the sound wave through the through holes
(c) and a viscous damping action induced during propagation of the
sound wave along the surfaces of both thin films 31 and 32 are
combined to let a still higher sound deadening effect be
exhibited.
[0056] The through holes (c) may also be formed in the thin films
used in the previous first and second embodiments or in the
following fourth embodiment, whereby the sound deadening effect can
be further improved.
FOURTH EMBODIMENT
[0057] FIG. 6 shows a sound-absorbing structure according to a
fourth embodiment of the present invention. This sound-absorbing
structure is constituted by using a single thin film 41.
[0058] The thin film 41 is folded so as to have mutually contacting
and overlapping portions (b). Therefore, when the overlapping
portions (b) contact and are rubbed against each other, energy of
the sound wave can be dissipated and it is possible to attain a
high sound absorption coefficient in a wide band.
[0059] Since the sound-absorbing structure of this embodiment can
be attained by using only one thin film 41, there is an advantage
that a manufacturing cost can be reduced.
FIFTH EMBODIMENT
[0060] FIG. 7 shows a sound-absorbing structure according to a
fifth embodiment of the present invention. In this sound-absorbing
structure, which uses the thin films 31 and 32 in the third
embodiment, a rear member 50 is installed on the side opposite to
the sound wave incidence side with respect to the thin films 31 and
32.
[0061] According to this embodiment, a sound deadening effect can
be further improved not only because the effect of the third
embodiment can be equally attained, but also because a sound wave
can be damped by utilizing a resonance phenomenon of the sound wave
which occurs between the thin films 31, 32 and the rear member
50.
[0062] Moreover, by installing the rear member 50 through a space
with respect to the thin films 31 and 32, the sound wave of a
frequency corresponding to the thickness of the air layer present
between the rear member 50 and the thin films 31, 32 can be damped
particularly strongly. Consequently, it becomes possible to adopt a
mode of use such that a distance L between the rear member 50 and
the thin films 31 and 32 is adjusted to strongly damp the sound
wave of or near a desired frequency.
[0063] Although the thin films 31 and 32 used in the third
embodiment are used in this fifth embodiment, the thin films used
in the first, second or fourth embodiment may be used instead.
Likewise, flat thin films free of ridges, grooves or holes, and
unfolded thin films are also employable. This is also the case with
the following sixth and subsequent embodiments.
SIXTH EMBODIMENT
[0064] A sound-absorbing structure according to a sixth embodiment
of the present invention is shown in FIG. 8. In this
sound-absorbing structure, the configuration of the previous fifth
embodiment is provided with a front member 60 as a protecting
member disposed on the sound wave incidence side of the thin films
31 and 32.
[0065] The front member 60 possesses air permeability and is
installed on the sound wave incidence side of the sound-absorbing
structure shown in FIG. 4 in order to protect the thin films 31 and
32 together with the rear member 50. As examples of the
air-permeable front member, there are a perforated plate and an
expanded metal, but no limitation is made thereto.
[0066] According to this sound-absorbing structure, it is possible
to enhance durability of the sound-absorbing structure and prolong
a service life thereof. Moreover, since the front member 60 is
air-permeable, it does not shut off an incident sound wave and
hence does not obstruct the sound absorbing effect.
SEVENTH EMBODIMENT
[0067] FIG. 9 shows a sound-absorbing structure according to a
seventh embodiment of the present invention, in which the front
member 60 used in the previous sixth embodiment is replaced by a
member (porous member) 70 formed with a large number of fine
holes.
[0068] The porous member 70 not only can protect the thin films 31
and 32 like the front member 60 used in the previous sixth
embodiment, but also brings about a sound wave damping effect
during passage of a sound wave through the porous member 70 and can
thereby further improve the sound absorbing capacity.
EIGHTH EMBODIMENT
[0069] FIG. 10 shows sound-absorbing structures according to an
eighth embodiment of the present invention. In this eighth
embodiment, a space between the porous member 70 and the rear
member 50 in the seventh embodiment is divided in the surface
direction of the thin films 31 and 32.
[0070] More specifically, in this eighth embodiment, the space
between the porous member 70 and the rear member 50 is partitioned
in the surface direction of the thin films 31 and 32 by plural
partition members 80 to form plural cells 81. The partition members
80 may be installed perpendicularly to the thin films 31 and 32 as
in FIG. 9(a) or may be inclined with respect to the direction
perpendicular to the thin films 31 and 32 as in FIG. 9(b).
[0071] According to such divided structures, there are formed
resonance type sound-absorbing structures, whereby the sound
absorbing effect is particularly improved in a low frequency
range.
NINTH EMBODIMENT
[0072] FIG. 11 shows a sound-absorbing structure according to a
ninth embodiment of the present invention. In this ninth
embodiment, the thin films 31, 32, rear member 50 and porous member
70 used in the eighth embodiment are separated along the partition
members 80 into individual cells 81.
[0073] By thus dividing the sound-absorbing structure into
individual cells 81 as small pieces, portability of the same
structure is improved. Besides, various combinations are available
according to required places and shapes, whereby a mode of
application can be widened.
[0074] Although the number of thin films used in the above
embodiments is two, a sound-absorbing structure including a
suitable combination of three or more thin films can also exhibit
equal or even higher sound absorbing capacity. For example, there
are sound-absorbing structures each including a combination of
plural thin films such as a sound-absorbing structure including the
thin films 11 and 12 shown in FIG. 1 with another thin film (any of
the thin films described in the above embodiments, a thin film
having neither ridges or grooves nor holes, an unfolded thin film)
or the like, a sound-absorbing structure including another thin
film sandwiched in between the thin films 21 and 22 shown in FIG.
3, and a sound-absorbing structure including the thin films 31 and
32 shown in FIG. 4 with the thin films 11 and 12 shown in FIG.
1.
[0075] For example, in FIG. 12 is shown a structure wherein n
sheets (n.gtoreq.3) of the thin films used in the first embodiment
of FIG. 1 are layered over one another, and in FIG. 13(a) is shown
a structure wherein n sheets (n.gtoreq.3) of the thin films used in
the sixth embodiment of FIG. 8 are layered over one another.
Further, in FIG. 13(b) is shown a structure wherein stacks each
comprising plural sheets of the thin films used in the sixth
embodiment of FIG. 8 are formed in n layers (n.gtoreq.2) while
forming an air layer between adjacent layers. Further, in FIG. 14
is shown a structure wherein n sheets (n.gtoreq.3) of the thin
films used in the eighth embodiment of FIG. 10 are stacked or a
structure wherein stacks each comprising plural thin films are
formed in m layers (m.gtoreq.2) with an air layer between adjacent
layers.
[0076] The thin films used in the above embodiments may be
different materials.
[Verification Experiment]
[0077] Next, with respect to the sound-absorbing structures
described above, verification experiments were conducted using
aluminum foil as a thin film and a rigid wall (a wall completely
reflecting a sound wave) as a rear member. FIG. 15 shows an
apparatus used in the experiment.
[0078] In the experiment apparatus shown in FIG. 15, a rigid wall
101 (corresponding to the rear member 50) is installed behind a
double aluminum foil 100 through an air layer, and a sound wave is
applied from a speaker 102 to a surface of the aluminum foil 100
located on the opposite side to the rigid wall 101. Sound pressure
is measured by sound pressure measuring devices 111 and 112 at two
points ahead of the double aluminum foil 100 to determine a
reflected wave against an incident wave on the double aluminum foil
100. In this way, it is possible to measure a sound absorption
coefficient of the double aluminum foil 100.
[0079] FIG. 16 shows results of an experiment which has been
conducted using a perforated double aluminum foil 100
(corresponding to the fifth embodiment). More specifically,
aluminum foils having a large number of holes (corresponding to the
through holes (c), dia. 1 mm, the ratio of the holes: 1%) were
superimposed each other while avoiding overlapping of holes and a
sound absorption coefficient was measured using the experiment
apparatus shown in FIG. 15.
[0080] As a comparative example, an experiment was conducted in the
same manner as above with use of glass wool as a sound-absorbing
material, and sound absorption coefficients obtained are also shown
in FIG. 16.
[0081] As is seen from FIG. 16, in both of the case where a
distance L between the double aluminum foil 100 and the rigid wall
101 is 10 mm and the case where the distance L is 40 mm, excellent
sound absorption coefficients (about 0.8 or more) are obtained over
wide frequency bands. A band which can exhibit an excellent sound
absorption coefficient is different between L=10 mm and L=40 mm.
This means that when only sound waves in a specific frequency band
are to be effectively absorbed according to a certain purpose of
use, it can also be done by such a simple method as suitably
setting the distance L between the double aluminum foil 100 and the
rigid wall 101.
[0082] It has been confirmed by this experiment that particularly
in a low frequency range, the sound-absorbing structures according
to the present invention are higher in sound absorption coefficient
than glass wool having substantially the same degree of
thickness.
[0083] FIG. 17 shows results of an experiment conducted using a
double aluminum foil 100 free of holes with results of an
experiment conducted using a double aluminum foil 100 formed with
holes. L was set to 10 mm.
[0084] As shown in FIG. 17, it is seen that an excellent sound
absorbing effect is exhibited substantially throughout the whole
frequency range of 500 to 3000 Hz in case of the double aluminum
foil 100 formed with holes as compared with the same foil free of
holes. This is presumed to be not only because aluminum foils are
rubbed against each other to dissipate the energy of the sound wave
as shown in FIG. 2 but also because (1) the energy dissipating
effect during passage of the sound wave through the holes and (2)
the viscous damping effect during passage of the sound wave through
the holes and further through a THE gap between layered aluminum
foils are added, as shown in FIG. 5, thus affording the above
excellent results.
[0085] The present invention is described in the above preferred
embodiments, but is not limited thereto. It will be understood that
various other embodiments not departing from the spirit and scope
of the present invention can be adopted.
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