U.S. patent application number 11/795154 was filed with the patent office on 2008-06-05 for double-wall structure.
Invention is credited to Toshimitsu Tanaka, Kazuki Tsugihashi, Hiroki Ueda.
Application Number | 20080128200 11/795154 |
Document ID | / |
Family ID | 36740184 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080128200 |
Kind Code |
A1 |
Tsugihashi; Kazuki ; et
al. |
June 5, 2008 |
Double-Wall Structure
Abstract
A double-wall structure (1), comprising plate-like bodies (2)
and (3) disposed oppositely to each other to form an inner room (4)
therebetween, peripheral members (5) disposed so that the inner
room (4) can be completely or approximately closed, and perforated
plates (13) with a large number of holes (8) disposed between the
plate-like bodies facing each other. The double-wall structure is
characterized in that an air layer (A) is interposed between the
perforated plates and the peripheral members. Thus, since the
double-wall structure can suppress the deterioration of a sound
reduction index for sound with specific frequencies, it can stably
develop sound insulation performance for sound with the various
frequencies.
Inventors: |
Tsugihashi; Kazuki; (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: |
36740184 |
Appl. No.: |
11/795154 |
Filed: |
December 13, 2005 |
PCT Filed: |
December 13, 2005 |
PCT NO: |
PCT/JP05/22826 |
371 Date: |
July 12, 2007 |
Current U.S.
Class: |
181/284 |
Current CPC
Class: |
B60R 13/0815 20130101;
G10K 11/172 20130101; B60J 5/0418 20130101; B60R 13/08
20130101 |
Class at
Publication: |
181/284 |
International
Class: |
E04B 1/82 20060101
E04B001/82 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 27, 2005 |
JP |
2005-019017 |
Claims
1. A double-wall structure comprising: a pair of plate-like members
disposed in opposition to each other to form an air space
therebetween; a circumferential member disposed in such a manner
that the said air space is closed completely or substantially; and
a perforated plate disposed between the said opposed plate-like
members in a direction intersecting the plate-like members, the
said perforated plate having a multitude of holes, wherein a layer
of air is interposed between the said perforated plate and the said
circumferential member.
2. A double-wall structure according to claim 1, wherein the said
perforated plate is disposed at an incline to the said
circumferential member.
3. A double-wall structure according to claim 1, wherein the said
perforated plate is provided in a plural number and a layer of air
is interposed between the plural perforated plates.
4. A double-wall structure according to claim 2, wherein the said
perforated plate is provided in a plural number and a layer of air
is interposed between the plural perforated plates.
5. A double-wall structure according to claim 2, wherein the said
perforated plate is disposed so that an end thereof is in contact
with the said circumferential member, and in the vicinity of the
contacted end a hole is formed in the said circumferential
member.
6. A double-wall structure according to claim 1, further comprising
a partition member for partitioning the space between the said
perforated plate and the said circumferential member.
7. A double-wall structure according to claim 6, wherein a
multitude of holes are formed in the said partition member.
8. A double-wall structure according to claim 6, wherein at least
one of a thickness of the said perforated plate, a thickness of the
said partition member, a diameter or a ratio of the said holes
formed in the said perforated plate or the said partition member,
and a thickness of the layer of air interposed between the said
perforated plate and the said circumferential member, is made
different between the spaces partitioned by the said partition
member.
9. A double-wall structure according to claim 1, wherein a
vibration damping/isolating member is disposed between the said
perforated plate and at least one of the said opposed plate-like
members.
10. A double-wall structure according to any of claim 1, wherein a
foil- or film-like member comprised of a single foil or film, or
superimposed foils or films is disposed in place of the said
perforated plate.
11. A double-wall structure according to claim 10, wherein a
multitude of holes are formed in the said foil- or film-like
member(s).
12. A double-wall structure comprising: a pair of plate-like
members disposed in opposition to each other to form an air space
therebetween; a circumferential member disposed in such a manner
that the said air space is closed completely or substantially; and
a porous member disposed in the vicinity of the said
circumferential member.
13. A double-wall structure according to claim 4, wherein the said
perforated plate is disposed so that an end thereof is in contact
with the said circumferential member, and in the vicinity of the
contacted end a hole is formed in the said circumferential
member.
14. A double-wall structure according to claim 7, wherein at least
one of a thickness of the said perforated plate, a thickness of the
said partition member, a diameter or a ratio of the said holes
formed in the said perforated plate or the said partition member,
and a thickness of the layer of air interposed between the said
perforated plate and the said circumferential member, is made
different between the spaces partitioned by the said partition
member.
Description
FIELD OF ART
[0001] The present invention relates to a double-wall
structure.
BACKGROUND ART
[0002] It has heretofore been proposed to use a double-wall
structure as automobile parts such as doors, hood and a trunk lid.
For example, a conventional double-wall structure is a hollow
box-like structure (bag structure) wherein an air space is formed
between plate-like members opposed to each other at a predetermined
distance, the air space being closed with side plates. In this
conventional double-wall structure, however, when a sound wave of
noise containing a sound component of a specific frequency is
incident from below on the double-wall structure, there occurs
resonance (mainly resonance in a direction parallel to the plate
members) in the air space against the sound component. This causes
an increase in amplitude of the upper plate-like member as a
radiation plane and the resulting increase of a radiation sound
deteriorates the sound insulating performance. Further, the
conventional double-wall structure in question is characteristic in
that in the state of resonance the sound pressure becomes high
particularly in the vicinity of the side plates.
DISCLOSURE OF THE INVENTION
[0003] It is an object of the present invention to provide a
double-wall structure capable of suppressing the deterioration of a
sound transmission loss against a sound of a specific frequency and
capable of displaying sound insulating performance stably against
sounds of various frequencies.
[0004] The double-wall structure according to the present invention
has the following basic configurations and effects.
[0005] In a first aspect of the present invention there is provided
a double-wall structure having an air space formed between opposed
plate-like members, the air space being closed completely or
substantially, wherein a perforated plate having a large number of
holes is disposed between the opposed plate-like members and a
layer of air is interposed between the perforated plate and a
circumferential member of the double-wall structure.
[0006] A sound absorbing mechanism is formed by the space between
the perforated plate and the circumferential member.
With the sound absorbing mechanism, it is possible to effectively
diminish a sound pressure near the circumferential members and
suppress the resonance of the whole of the air space. Consequently,
the sound pressure of the air space decreases and so does the
vibration generating force on the radiation plane side, so that the
vibration of the radiation plane decreases and it is possible to
improve the sound transmission loss. Moreover, by adjusting the
hole diameter, plate thickness and the ratio of holes in the
perforated plate, as well as the thickness of the layer of air, it
is also possible to obtain a configuration capable of suppressing
an arbitrary frequency particularly effectively.
[0007] In the above double-wall structure, the perforated plate may
be disposed so as to be inclined with respect to the
circumferential member.
[0008] According to this configuration, it is possible to suppress
resonance in every direction within the air space and hence
possible to provide a double-wall structure superior in sound
insulating performance.
[0009] In the above double-wall structure it is preferable that the
perforated plate be provided in a plural number and that a layer of
air be interposed between the plural perforated plates.
[0010] According to this configuration, the resonance in the air
space can be suppressed to a greater extent by two layers of air
and hence it is possible to provide a double-wall structure
superior in sound insulating performance.
[0011] In the above double-wall structure, the perforated plate,
may be disposed so that an end thereof is in contact with the
circumferential member, and in the vicinity of the contacted end a
hole may be formed in the circumferential member. Even in the
presence of such a hole the air space of the double-wall structure
is substantially kept closed.
[0012] Consequently, foreign matters such as dust and water getting
into the air space can be discharged easily through the aforesaid
hole.
[0013] It is preferable for the double-wall structure to have a
partition member for partitioning the space formed between the
perforated plate and the circumferential member.
[0014] With such a partition member, the sound insulating
performance of the double-wall structure is improved.
[0015] In the above double-wall structure it is preferable that a
large number of holes be formed in the partition member.
[0016] According to this configuration, the sound insulating
performance of the double-wall structure is further improved.
[0017] In connection with the perforated plate used in the
double-wall structure, at least one of its thickness, the hole
diameter, the ratio of holes, and the thickness of the layer of
air, may be made different between the spaces partitioned by the
partition member. In the case where the thickness of the layer of
air is not uniform in each of the partitioned spaces, a
representative thickness (e.g., an average thickness) of the layer
of air may be different between the spaces partitioned by the
partition member. In the case where holes are formed in the
partition member, at least one of the thickness of the member, the
hole diameter and the ratio of the holes may be made different
between the spaces partitioned by the partition member.
[0018] According to this configuration, the sound absorbing
structure composed of the perforated plate and the circumferential
member can display sound absorbing performance at a desired
frequency and it is possible to provide a double-wall structure
having particularly good sound insulating performance.
[0019] In the above double-wall structure it is preferable that a
vibration damping/isolating member be disposed between the
perforated plate and at least one of the opposed plate-like
members.
[0020] According to this configuration it is possible to further
improve the sound insulating performance of the double-wall
structure.
[0021] In the above double-wall structure, a foil- or film-like
member comprised of a single foil or film, or superimposed foils or
films may be disposed in place of the perforated plate.
[0022] Also in this case, as in the above case, by a sound
absorbing mechanism formed by the space (layer of air) between the
foil- or film-like member and the circumferential member, it is
possible to diminish the sound pressure near the circumferential
member and hence possible to suppress resonance of the whole of the
air space. Consequently, the sound pressure of the air space
decreases and so does the vibration generating power on the
radiation plane side, so that the vibration of the radiation plane
decreases and it is possible to improve the sound transmission
loss. As a result, it is possible to afford a structure superior in
sound insulating performance.
[0023] In the above double-wall structure it is preferable that a
large number of holes be formed in the foil- or film-like
member.
[0024] According to this configuration it is possible to further
improve the sound insulating performance of the double-wall
structure.
[0025] In a second aspect of the present invention there is
provided a double-wall structure having an air space formed between
opposed plate-like members, the air space being closed completely
or substantially, wherein a porous member is disposed near a
circumferential member of the double-wall structure.
[0026] According to this configuration, the sound pressure near the
circumferential member can be diminished by the porous member and
it is possible to suppress resonance of the whole of the air space.
Consequently, the sound pressure of the air space decreases and so
does the vibration generating power on the radiation plane side, so
that the vibration of the radiation plane diminishes. Further,
coupled with the sound absorbing effect of the porous member
itself, it is possible to improve the sound transmission loss. As a
result, it is possible to afford a structure superior in sound
insulating performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic perspective view of embodiment 1-1 of
the double-wall structure of the present invention.
[0028] FIG. 2 is a schematic diagram of the embodiment 1-1.
[0029] FIG. 3 is a schematic diagram of embodiment 1-2.
[0030] FIG. 4 is a schematic diagram of embodiment 1-3.
[0031] FIG. 5 is a schematic diagram of embodiment 1-4-1.
[0032] FIG. 6 is a schematic diagram of embodiment 1-4-2.
[0033] FIG. 7 is a schematic diagram of embodiment 2-1.
[0034] FIG. 8 is a schematic diagram of embodiment 2-2-1.
[0035] FIG. 9 is a schematic diagram of embodiment 2-2-2.
[0036] FIG. 10 is a schematic diagram of embodiment 2-3-1.
[0037] FIG. 11 is a schematic diagram of embodiment 2-3-2.
[0038] FIG. 12 is a schematic diagram of embodiment 2-4.
[0039] FIG. 13 is a schematic sectional diagram of embodiment
3-1-1.
[0040] FIG. 14 is a schematic sectional diagram of embodiment
3-1-2.
[0041] FIG. 15 is a schematic diagram of embodiment 4-1.
[0042] FIG. 16 is a schematic diagram of embodiment 5-1.
[0043] FIG. 17 is a graph showing a sound transmission suppressing
effect of the embodiments 1-1 to 1-3 in comparison with that of a
conventional example.
[0044] FIG. 18 is a graph showing a sound transmission suppressing
effect of the embodiments 2-1, 2-2-1, 2-3-1 and 2-3-2 in comparison
with that of a conventional example.
[0045] FIG. 19 is a graph showing a sound transmission suppressing
effect of the embodiments 4-1 and 5-1 in comparison with that of a
conventional example.
BEST MODE FOR CARRYING OUT THE INVENTION
[0046] Embodiments of the present invention will be described
hereinunder with reference to FIGS. 1 to 16.
First Embodiment
See FIGS. 1 to 6
[0047] A double-wall structure of embodiment 1-1 shown
schematically in FIGS. 1 and 2 assumes a door as a part of a
passenger car. This double-wall structure, indicated at 1, has
plate-like members 2 and 3 disposed in parallel with each other and
opposed to each other at a predetermined distance. The plate-like
members 2 and 3 are each formed in a rectangular shape which is a
little longer in one direction and an air space 4 is formed between
the two opposed plate-like members 2 and 3. Four side plates
(circumferential members) 5 are disposed so as to connect edges of
the plate-like members 2 and 3 with one another, whereby the air
space 4 is closed substantially. In other words, with the
plate-like members 2, 3 as double walls and the side plates 5, the
double-wall structure of this embodiment is constituted as a bag
structure which encloses the air space 4.
[0048] In this embodiment, finely perforated rectangular plates 13
are disposed so as to partition the air space 4. Each of the finely
perforated plates 13 is formed with a large number of fine through
holes (fine holes 8). In this embodiment 1-1 four finely perforated
plates 13 are disposed in a rectangular shape to partition the air
space 4 of the double-wall structure 1 into two spaces which are a
central space and a circumferential space close to the side plates
5. In other words, the finely perforated plates 13 are disposed in
parallel with the side plates 5 respectively while leaving a
predetermined spacing with respect to the four side plates 5 and a
layer of air A having a thickness corresponding to the above
predetermined spacing is interposed between the finely perforated
plates 13 and the side plates 5. As the material of the finely
perforated plates 13 there may be used, for example, iron,
aluminum, resin, fiber-reinforced composite material, or paper.
[0049] In connection with the above configuration, a description
will now be given about the case where the plate-like member 2 is
vibrated under sound pressure by noise from below in FIG. 1. If the
noise contains a sound component of a specific frequency, resonance
tends to occur in the longitudinal or transverse direction of the
air space 4 as a result of vibration of the plate-like member 2. In
this resonance mode, the sound pressure becomes high particularly
in the vicinity of the side plates 5. However, the high sound
pressure near the side plates 5 is reduced effectively by a sound
absorbing mechanism which is constituted by the finely perforated
plates 13, the side plates 5 and the layer of air A present
therebetween. Consequently, a resonance mode becomes difficult to
be formed and resonance is suppressed. As a result, the vibration
generating power of the upper plate-like member 3 as the radiation
plane is deteriorated, so that the amplitude of the radiation plane
is decreased and it is possible to diminish a drop of the sound
transmission loss.
[0050] According to the configuration of embodiment 1-2 (FIG. 3),
finely perforated plates 13 are installed near one of the four side
plates 5 in the double-wall structure 1. The finely perforated
plates 13 are disposed at an incline to the side plate 5 so as to
be in a generally V shape in FIG. 3. As a result, layers of air A
of a triangular shape are formed between the finely perforated
plates 13 and the side plate 5. In this configuration, the layers
of air A are located at corners where the sound pressure is high
particularly in resonance mode, whereby the sound pressure at the
corners can be reduced to a satisfactory extent. Besides, since the
finely perforated plates 13 are disposed at an incline to the side
plates 5, it is possible to suppress resonance in every direction
within the air space 4 and hence possible to improve the sound
insulating performance of the double-wall structure 1.
[0051] According to the configuration of embodiment 1-3 (FIG. 4),
additional finely perforated plates 13 are used in the
configuration of embodiment 1-2 (FIG. 3) and plural finely
perforated plates 13 are disposed in parallel so that a gap is
formed in the thickness direction between both finely perforated
plates 13 facing each other. As a result, a layer of air B is
interposed between both finely perforated plates 13 facing each
other. That is, in this embodiment 1-3, there are formed two layers
of air. One is the layer of air A formed between a finely
perforated plate 13 and a side plate 5 and the other is the layer
of air B formed between a pair of finely perforated plates 13
facing each other.
Consequently, the resonance suppressing effect can be made more
outstanding.
[0052] According to the configuration of embodiment 1-4-1 (FIG. 5),
a hole 10 is formed in the side plate 5 at a position near ends of
the finely perforated plates 13, in addition to the configuration
(FIG. 3) of embodiment 1-2 wherein the finely perforated plates 13
are disposed at an incline. Foreign matters such as dust and water
getting into the air space 4 can be discharged easily through the
hole 10. The hole 10 is formed in the side plate 5 at a position
not confronting the layer of air A and therefore the sound
absorbing function of the layer of air A is not obstructed. In the
construction of embodiment 1-4-1 (FIG. 5), the hole 10 is formed in
the side plate 5 in a state in which ends of the finely perforated
plates 13 are put in contact with the side plate 5. However, it is
not always necessary that the ends of the finely perforated plates
13 be brought into contact with the side plate 5. That is, even in
a configuration wherein the ends of the finely perforated plates 13
are spaced apart from the side plate 5, if the hole 10 is formed in
the side plate 5 at a position not confronting the finely
perforated plates 13, both the sound absorbing function of the
layer of air A and the discharge of foreign matters such as dust
and water getting into the air space 4 can be made compatible with
each other. There may be adopted such a configuration as embodiment
1-4-2 (FIG. 6) wherein finely perforated plates 13 are disposed in
a generally W shape and two holes 10 are formed. Thus, the shape of
inclination of the finely perforated plates 13 and the number of
holes 10 are not limited.
Second Embodiment
See FIGS. 7 to 12
[0053] According to the configuration of embodiment 2-1 (FIG. 7),
which is a modification of embodiment 1-1 (FIGS. 1 and 2), plural
plate-like partition members 9 are provided so as to provide
connections between side plates 5 and finely perforated plates 13.
With the partition members 9, the layer of air A interposed between
the side plates 5 and the finely perforated plates 13 is
partitioned in both longitudinal and transverse directions of the
double-wall structure 1. It is preferable that the partition
members 9 be disposed at positions where a resonance phenomenon
occurring in the extending direction of the layer of air between
the finely perforated plates 13 and the side plates 5 is difficult
to occur at a desired frequency. More specifically, the partition
members 9 are disposed at a spacing not coinciding with an integer
multiple of a half of the wavelength for the frequency intended to
improve the sound insulating performance. As a result, it is
possible to enhance the sound absorbing performance of sound
absorbing mechanism constituted by the layer of air A between the
finely perforated plates 13 and the side plates 5. In this
configuration, in order to enhance the sound absorbing performance
at a desired frequency, the hole diameter of the fine hole 8 or the
ratio of holes, or the thickness of each finely perforated plate
13, may be made different among the spaces partitioned by the
partition members 9. The partition members 9 are not always
required to be plate-like members. For example, the partition
members 9 may each be constituted by a reinforcing foaming agent
formed in a lump shape.
[0054] The configuration of embodiment 2-2-1 (FIG. 8) corresponds
to a combination of embodiment 1-2 (FIG. 3) and embodiment 2-1
(FIG. 7). In this configuration, the thickness (average thickness)
of the layer of air A formed between the finely perforated plates
13 and the side plates 5 is made different among the spaces
enclosed with the partition members 9. As in embodiment 2-2-2 (FIG.
9), like the foregoing embodiment 1-4-1, a hole 10 may be formed in
a side plate 5.
[0055] The configuration of embodiment 2-3-1 (FIG. 10) corresponds
to a combination of embodiment 1-3 (FIG. 4) and embodiment 2-2-1
(FIG. 8). Partition plates 9 are installed so as to partition each
of two layers of air A and B.
[0056] According to the configuration of embodiment 2-3-2 (FIG.
11), which is a modification of embodiment 2-1 (FIG. 7), a
plurality of finely perforated plates 13 are disposed in the
thickness direction and a layer of air B is interposed
therebetween.
[0057] According to the configuration of embodiment 2-4 (FIG. 12),
a large number of fine holes 8 are formed in partition plates 9 of
embodiment 2-1 (FIG. 7).
Third Embodiment
See FIGS. 13 and 14
[0058] FIG. 13 is a sectional view of a double-wall structure 1
according to embodiment 3-1-1. As shown in FIG. 13, there is a case
where a finely perforated plate 13 cannot contact the plate-like
member 2 on the vibration generating side and the plate-like member
3 on the opposite side in a completely airtight manner and certain
slits are formed. The absence of such slits is preferred, so in
this embodiment a vibration damping/isolating member 16 formed of,
for example, rubber or urethane is installed in each of the
portions corresponding to the slits. As a result, it is possible to
enhance the sound absorbing performance of sound absorbing
mechanism. As shown in embodiment 3-1-2 (FIG. 14), the vibration
damping/isolating member 16 may be disposed between the finely
perforated plate 13 and only one of the two plate-like members 2
and 3. If the above slits are fine slits, the vibration
damping/isolating member 16 may be omitted and it is possible to
let the slits themselves exhibit a sound absorption function.
Fourth Embodiment
See FIG. 15
[0059] In embodiment 4-1 (FIG. 15), the finely perforated plates 13
used in embodiment 2-2-1 (FIG. 8) are each substituted for a
superimposed foil- or film-like members 14. In this embodiment 4-1,
a large number of fine holes 8 are formed in the foil- or film-like
members 14 in order to improve the sound absorbing performance,
provided the fine holes 8 may be omitted. A single such foil- or
film-like member may be used without using such foils- or films in
a superimposed form.
Fifth Embodiment
See FIG. 16
[0060] In the configuration of embodiment 5-1 (FIG. 16), two porous
members 15,15 are disposed near side plates 5 in the double-wall
structure 1. As the material of the porous members 15 there may be
used not only glass wool or felt but also, for example, PET fiber,
polyurethane or open-cell foamed material. In this embodiment 5-1
the porous members 5 are formed in a triangular shape and are
disposed at two corners on one side of the air space 4 so as to
contact the side plates 5. The shape and layout of the porous
members 15 are not limited those described above. In this
configuration, sound is absorbed particularly at positions (near
the side plates 5, especially at and near the corners of the air
space 4) where the sound pressure is high in resonance, whereby the
sound pressure in resonance of the entire air space 4 can be
reduced and it is possible to improve the sound transmission
loss.
[0061] The following experiment was conducted to check the
effectiveness of the above embodiments. First, the double-wall
structures 1 having the configurations of embodiments 1-1 to 1-3,
2-1, 2-2-1, 2-3-1, 2-3-2, 4-1 and 5-1 were each positioned between
a sound source chamber and a sound receiving chamber in a
reverberant chamber comprising both such chambers. Then, on the
basis of JIS A 1416 (ISO 140-3, 140-1), a certain noise was
generated from one side of the double-wall structures 1 and sound
pressures were measured on both sides of the double-wall structures
1 with use of noise meters to determine a sound transmission
loss.
[0062] Experiment Results (see FIGS. 17 to 19)
[0063] The results of the experiment are shown in FIGS. 17 to 19.
In the graphs of these figures there are also shown the results of
an experiment conducted for a conventional structure. As shown in
the graph of FIG. 17 it is seen that in the configurations of
embodiments 1-1 to 1-3, in comparison with the conventional
example, the formation of a resonance mode is suppressed by the
finely perforated plates 13, whereby the sound transmission loss is
improved and so is the sound insulating performance. It is seen
that also in the configurations (FIG. 18) of embodiments 2-1,
2-2-1, 2-3-1 and 2-3-2 and the configurations (FIG. 19) of
embodiments 4-1 and 5-1 the sound transmission loss is improved and
so is the sound insulating performance by the resonance mode
suppressing function of the finely perforated plates 13 and the
porous members 15.
[0064] Although preferred embodiments of the present invention have
been described above, the technical scope of the present invention
is not limited to the above embodiments, but the invention may be
practiced in various modified forms.
[0065] For example, the double-wall structure of the present
invention is applicable not only to the doors of a passenger car
but also to, for example, the hood and trunk lid. As to the shape
of the plate-like members 2 and 3, it goes without saying that no
limitation is made to the rectangular shape described above, but
that various changes may be made in accordance with the shape of a
part required.
[0066] The direction and degree of the sound pressure mode which
causes resonance differ depending on various circumstances such as
the shape of the double-wall structure 1 and a positional relation
thereof to a noise source. Therefore, the direction, thickness and
the number of the finely perforated plates 13, as well as the
number, diameter, shape and ratio of the fine holes 8, may be
determined suitably taking the above circumstances into account.
That is, where and how many the finely perforated plates 13 and the
porous members 15 are to be provided may be determined optimally in
consideration of a resonance mode within the air space 4 of the
double-wall structure 1 caused by a presumed noise. The fine holes
8 formed in the finely perforated plates 13, partition members 9
and foil- or film-like members 14 in the above plural embodiments
may be increased in diameter into holes of a size not regarded as
"fine" holes. In case of applying the double-wall structure 1 to
the doors of a passenger car, it is presumed that various devices
and reinforcing members are disposed in the air space 4, therefore,
the finely perforated plates 13 and the porous members 15 may be
disposed at sidestepped positions.
[0067] It is optional whether the finely perforated plates 13 and
the porous members 15 are to be disposed for all or a part of the
side plates 5. For example, in the case of the finely perforated
plates 13 used in embodiment 1-2 (FIG. 3), the layer of air A is
interposed between them and only one of the four side plates 5, the
finely perforated plates 13 may be disposed so as to surround the
whole circumference of the air space 4.
[0068] Although in the above plural embodiments the finely
perforated plates 13 and the partition plates 9 are installed
perpendicularly to the plate-like members 2 and 3, no limitation is
made thereto. The finely perforated plates 13 and the partition
members 9 may be installed at an incline to the plate-like members
2 and 3.
[0069] As to the application of the above embodiments, no
limitation is made to the case where the embodiments are applied
each independently, but plural such embodiments may be applied in
combination.
* * * * *