Field of the invention
[0001] The present invention relates to a composite sound-absorbing device and more particularly
relates to a composite sound-absorbing device with built-in resonant cavity.
Background of the invention
[0003] Although resonant sound-absorbing structure of perforated board, resonant sound-absorbing
structure of microperforated board and double layer microperforated sound-absorbing
structure are superior to porous sound-absorbing material in terms of sound absorption
characteristics, flow resistance, anti-moisture, anti-corrosion and hygiene, they
still cannot meet some practical needs of noise control engineering, especially when
dealing with low frequency noise within strictly limited space for sound absorption.
For as to common resonant sound-absorbing structure, the depth of cavity has to be
increased greatly to absorb more low frequency sound, which is almost impossible to
realize in practice. Applicant has searched G10K with a special emphasis on G10k 11/172
and found out "The Bundle Type Perforated board Resonant Sound-absorbing Device" with
patent number of
CN ZL00100641.X and "Muffler with Multi Insert Pipe Parallel Connected Structure" with patent number
of
CN ZL00264613.7.
[0004] The bundle type perforated board resonant sound-absorbing device features a bundle
type perforated board resonant sound-absorbing structure, which is consisted of a
perforated board, a bottom board and side board (forming a closed cavity) and a bundle
of tubes. The diameter of the tubes is equal to that of the pores on the perforated
board and the length of these tubes is not restrained by the cavity depth of the perforated
board resonant sound-absorbing device. The tubes can either be longer or shorter than
the cavity depth so as to tune resonance frequency and alter sound absorption coefficient.
This sound-absorbing structure is designed on the basis of the sound-absorbing principle
of coupling resonance to increase its sound absorption coefficient, acoustic impedance
and to enhance the sound-absorbing effect of low frequency sound. However this structure
absorbs only sound within low and medium frequency band, which band is not wide enough.
The length of those flexible tubes is critical in that if the tubes are not long enough,
the sound-absorbing performance would be greatly affected, i.e., greatly degrading
sound-absorbing effect. Therefore longer tubes have to be used to ensure good sound-absorbing
performance. Accordingly cavity has to be deeper correspondingly. However longer tubes
and deeper cavities are not beneficial to expand the application range of this structure.
It is further compounded by the fact that the tubes being wire like, this structure
cannot give full play the coupling resonance effect of tube cavity. Moreover, the
length of the tubes contributes less to the consumption of acoustic energy.
[0005] The muffler with multi insert pipe parallel connected structure described in ZL00264613.7
is designed for the intake system for internal combustion engine of automobiles and
that it includes an intake pipe and two or four resonant cavities arranged in parallel.
The resonant cavities are arranged in a casing. Each of the resonant cavities is connected
to a radial-direction pore axially arranged on the intake pipe, through conduct pipes.
The size of the radial-direction pore and the conduct pipes is designed to match with
the intake noise spectrum of the internal combustion engine. This muffler is not only
able to greatly reduce the intake noise but also increase the power of the internal
combustion engine. Moreover, it is compact in size.
[0006] Therefore, it has been a long-time effort internationally in the field of acoustics
and noise control engineering to invent a device, which can effectively absorb low
frequency sound and has a wide sound-absorbing frequency band to replace or improve
conventional sound-absorbing structure which is deficient in absorbing low frequency
sound. To this end, this invention proposes a composite sound-absorbing device with
built-in resonant cavity. This device is realized based on several principles, namely
by combining acoustic scattering inside the resonant cavity, sound elimination of
small pores and the coupling resonance of multiple resonant cavities, to increase
sound absorption coefficient and expand sound frequency band.
Summary of the Invention
[0007] The purpose of the present invention is to overcome the defect of the above sound-absorbing
structure used in current noise control engineering that it cannot absorb enough sound
with low and medium frequency by providing a composite sound-absorbing structure with
built-in resonant cavity.
[0008] According to the present invention, a composite sound-absorbing device with a built-in
resonant cavity, includes: a perforated board having a number of first pores thereon,
a back board and side boards, the perforated board, back board and side boards forming
a closed cavity, wherein: at least one or more of the resonant cavities being located
within the closed cavity; at least one or more of second pores being located on the
resonant cavities; and at least one of the second pores being connected with the closed
cavity; the resonant cavity having a volume of V=10mm
3—1×10
10mm
3, the thickness of the wall thereof being 0.05mm-10mm, the second pores having an
aperture of d'=0.05-100mm, with a perforation rate σ'=0.01%-30%.
[0009] In the composite sound-absorbing device of the present invention, the resonant cavity
is in a shape of sphere, ellipsoid or polyhedron. Furthermore, in the composite sound-absorbing
device of the present invention, the second pores are connected to the closed cavity
directly, or are connected to the closed cavity via tubes. Moreover, in the composite
sound-absorbing device of the present invention, when the number of the resonant cavities
is more than one, they are located within the closed cavity directly or fixed separately
within the closed cavity partitioned by a number of partition boards.
[0010] Preferably, in the composite sound-absorbing device of the present invention, the
first or second pores are connected to one end of the tubes and the tubes are located
within the closed cavity for increasing acoustical impedance. Preferably, in the composite
sound-absorbing device of the invention, the other end of the tubes on the second
pores are connected to the closed cavity, the second pores on another resonant cavity
or the first pores on the perforated board.
[0011] Preferably, in the composite sound-absorbing device of the present invention, the
tubes are made of metal, glass, plastic or rubber; when the tubes are made of rubber,
they are connected to the first pores or second pores via binding, or they are connected
to the first pores via a first transition joint at the ends of the tubes, or they
are connected to the second pores via a second transition joint at the ends of the
tubes; when the tubes are made of metal, glass or plastic, they are connected to the
first pores or second pores via binding, welding, thread connection or injection,
or they are connected to the first pores via a first transition joint at the ends
of the tubes, or they are connected to the second pores via a second transition joint
at the ends of the tubes.
[0012] Preferably, in the composite sound absorptive device of the present invention, the
perforated board has a thickness of 0.5-10mm, the diameter of the first pores on the
perforated board d is 0.1-5mm, with a perforation rate of 0.1%-30%. Furthermore, the
first pores on the perforated board are arranged regularly in a shape of triangle
or square or irregularly. Moreover; the closed cavity has a depth D of 10-2000mm,
and is in a shape of cylinder composed by one side board or a polyhedron composed
by a plurality of side boards.
[0013] Preferably, in the composite sound-absorbing device of the present invention, the
back side of said perforated board is coated with a layer of porous sound-absorbing
material, the layer of porous sound-absorbing material being located within the closed
cavity, with a thickness of 0.1 mm-200mm.
[0014] In the above technical solutions, the perforated board can be iron board, steel board,
copper board, corrosion resistant board, aluminum board, plastic board, glass board,
PVC board, PE board or wood board.
[0015] In the above technical solutions, the resonant cavity can be made of metal, glass,
ceramics, rubber, plastic or fiber. The length L of the tubes is 1-5000mm. The diameter
of the tubes is 0.1-100mm.
[0016] The present composite sound-absorbing device with built-in resonant cavity comprises
a perforated board with a plurality of pores, a back board, side board(s) and multiple
resonant cavities. The resonant cavities are small cavities placed in a closed cavity.
The resonant cavities are used to scatter sound, connect with the closed cavity and
increase acoustic impedance. When a sound wave reaches the resonant cavities, the
air inside the cavity vibrates back and forth. Due to viscous damping, part of the
acoustic energy is converted into heat energy and is lost. By using the principle
of Helmholtz resonator, the pores on the wall of the resonant cavities increase acoustic
impedance of the perforated board, sufficiently consume the acoustic energy and so
enhance sound absorption.The fact that the resonant cavity being hollow increases
acoustic resistance of the present sound-absorbing device. At the same time, the resonant
cavities are connected with the closed cavity serially so as to realize multiple cavities'
coupled resonance, thereby expanding the frequency band of sound absorption consequently.
Furthermore, the size of each of the resonant cavities can be different from each
other and the size of each of the second pores can be different from each other in
order to tune the resonant frequency and alter sound absorption coefficient under
different frequencies. The present invention utilizes the resonant cavity to scatter
sound in the closed cavity and utilizes the second pores to increase acoustic impedance
and consume acoustic energy. In addition, the present invention modulates formant
and sound-absorbing frequency band based on the principle of multiple-cavity coupled
resonance. Therefore, the present invention increases acoustic impedance, improves
sound quality and the effect of sound absorption and expands sound-absorbing frequency
band.
[0017] Major technical features of the present invention include: the resonant cavity is
connected with the closed cavity via second pores to realize coupling resonance among
cavities and so expand sound-absorbing frequency band. In addition, there is no limitation
imposed on the number of the pores on the resonant cavity, thus increasing acoustic
impedance of the sound-absorbing device. The number of the pores and the diameter
of the pores can be adjusted as required to increase or reduce the acoustic impedance
and thus to increase sound absorption coefficient. The tubes connecting to the resonant
cavities increase the thickness of the pores on the resonant cavities, which is not
only to the benefit of increasing acoustic impedance but also realizes coupling resonance
by connecting the tubes with resonant cavities. Moreover, the present invention advantageously
can increase sound absorption coefficient, expand sound-absorbing frequency band and
cause the sound absorption frequency band to shift towards low frequency band, so
it is beneficial to absorb sound with low frequency. With the coupled resonance of
the resonant cavities and the closed cavity, it can be regarded that sound absorption
is carried out in a double-deck structure within the same and one cavity. In the meantime,
the capacity of the rear cavity is reduced. Therefore, the present invention is suitable
to the situations where space for sound absorption is strictly limited. Moreover,
in order to expand the frequency range of noise elimination of the present composite
sound-absorbing device, each of the resonant cavities can be different from each other
in size and shape, and each of the second pores can be different from each other in
size and shape, which is beneficial for the present invention to be used in different
sound elimination situations. The acoustic scattering on the surfaces of the resonant
cavities allows the sound wave to reach to every resonant cavity in the rear cavity
and pushes the air in the second pores to vibrate back and forth, thereby consuming
acoustic energy sufficiently and being beneficial to absorb sound by using the space
of the rear cavity.
[0018] The advantages of the invention lie in that, by arranging a plurality of resonant
cavities in the limited space of the rear cavity, the present invention makes full
use of the principles of acoustic scattering, pores' acoustic impedance consuming
acoustic energy and sound absorption by multi-cavity coupled resonance, as well as
the modulation features of the size of the cavities and the pores to formant and sound-absorbing
frequency band, thus increasing sound absorption coefficient, enhancing the absorption
of low and medium frequency noise and expanding sound-absorbing frequency band.
Description of the drawings
[0019]
Fig.1 schematically shows a composite sound-absorbing device with built-in resonant
cavities of the present invention, wherein each of the resonant cavities has a second
pore connecting directly with a closed cavity;
Fig. 2 schematically shows another embodiment of the composite sound-absorbing device
of the present invention, wherein each resonant cavity has 26 second pores connecting
with a closed cavity;
Fig. 3 schematically shows another embodiment of the composite sound-absorbing device
of the present invention, wherein each resonant cavity has four second pores, and
one of the second pores connects with one first pore on a perforated board via a tube,
while the other second pores connect with a closed cavity directly;
Fig. 4 is still another embodiment of the composite sound-absorbing device according
to the present invention, wherein each resonant cavity has three second pores, one
of which connects with a closed cavity via tubes;
Fig. 5 is still another embodiment of the composite sound-absorbing device according
to the present invention, wherein each resonant cavity has two second pores, and for
every two resonant cavities there are connected tubes therebetween, the other second
pores directly connects with a closed cavity;
Fig. 6 schematically shows an embodiment of the composite sound-absorbing device according
to the present invention, wherein a first transit joint and a second transit joint
are installed;
Fig. 7 is another embodiment of the composite sound-absorbing device according to
the present invention, wherein each of the resonant cavities has two second pores
with different diameters;
Fig. 8 is another embodiment of the composite sound-absorbing device according to
the present invention, wherein two resonant cavities with different volumes are arranged
in a closed cavity;
Fig. 9 is another embodiment of the composite sound-absorbing device according to
the present invention, wherein ellipsoid resonant cavities and cubic resonant cavities
are arranged in a closed cavity;
Fig. 10 schematically shows an embodiment of the composite sound-absorbing device
according to the present invention, wherein partition boards are installed;
Fig. 11 is still another embodiment of the composite sound-absorbing device of the
present invention, wherein first pores on a perforated board connect with tubes;
Fig. 12 is another embodiment of the composite sound-absorbing device of the present
invention, wherein the back side of the perforated board is covered with a layer of
porous sound-absorbing material;
Fig. 13 is a comparison chart showing the sound-absorbing performance of resonant
sound-absorbing device of the present invention and a perforated board (Cavity depth
is 50mm), by using a standing wave meter;
Fig. 14 is a comparison chart showing the sound-absorbing performance of different
composite sound-absorbing devices with different number of resonant cavities(cavity
depth is 100mm) according to the present invention, by using a standing wave meter;
and
Fig. 15 is a comparison chart showing low and medium frequency sound performance of
a composite sound-absorbing device with built-in resonant cavity, a perforated board
with tubes and a perforated board(cavity depth is 50mm), by using a standing wave
meter.
Detailed description of the embodiments
[0020] In the following, the present invention will be described in details with reference
to the accompanying drawings and embodiments.
Embodiment One
[0021] Referring to Fig. 1, the embodiment provides a composite sound-absorbing device with
built-in resonant cavity. The device comprises a closed cavity formed by a perforated
board 1, a back board 2 and side boards 3 all made up of stainless steel, wherein
the depth D of the closed cavity is 40mm. The perforated board 1 is a square board
with the length of the side being 80mm and the thickness being 5mm. On the perforated
board 1, first pores 6, with a diameter of 3mm, are formed. The perforation rate σ
of the first pores 6 is 28%. The first pores 6 are regularly arranged in the pattern
of a square on the perforated board 1. In the closed cavity, four resonant cavities
5 are formed, with each resonant cavity 5 being made of aluminum and having a shape
of sphere. The volume of the resonant cavity 5 is 1.4x 10
4mm
3 and the thickness of the wall of the resonant cavity 5 is 5mm. Moreover, on the wall
of the resonant cavity 5, a second pore 6', with a diameter of 2mm, is formed. The
perforation rate σ' of the second pore 6' is 0.06%. The resonant cavity 5 is arranged
in the closed cavity freely.
Embodiment Two
[0022] Referring to Fig.2, the present embodiment provides a composite sound-absorbing device
with built-in resonant cavity according to the present invention. The device comprises
a closed cavity formed by a perforated board 1, a back board 2 and side boards 3 all
made of stainless steel, wherein the depth D of the closed cavity is 50mm. The perforated
board 1 is a round board, with a diameter of 100mm and a thickness of 0.7mm. On the
perforated board 1, first pores 6, with a diameter of 1.7mm, are formed. The perforation
rate σ of the first pores 6 is 4.6%. The first pores 6 are arranged regularly in the
pattern of a square on the perforated board 1. In the closed cavity, four resonant
cavities are formed, with each resonant cavity being made of plastic. The volume of
the resonant cavity 5 is 3.35×10
4mm
3 and the thickness of the wall of the resonant cavity 5 is 0.4mm. Furthermore, there
are 26 second pores 6' on the wall of the resonant cavity 5, evenly distributed on
the circumferences of three mutually perpendicular hemispheres. (There are 16 second
pores 6' on each hemispherical circumference, with 4 second pores 6' overlapping on
every two hemispherical circumferences), the diameter d' of the second pores 6' being
0.5mm and the perforation rate σ' being 0.1 %. The resonant cavities 5 are arranged
in the closed cavity freely.
[0023] An experiment was conducted to test low and medium frequency sound muffling mechanism
of the composite sound-absorbing device with built-in resonant cavity by using a standing
wave meter. In the experiment, the low and medium frequency sound absorption coefficient
of a perforated board, a perforated board whose cavity is provided with sphere without
pores and a composite sound-absorbing device with built-in resonant cavity are measured
to verify that multiple cavities coupling is beneficial to increase sound absorption
coefficient. Other parameters of resonant sound-absorbing structures employed in the
experiment are listed as follows:
Parameters of the perforated board: the pores are arranged in the pattern of a square,
with the diameter of the pores being 1.7mm, the center to center spacing of the pores
being 7mm, the thickness of the perforated board being 0.7mm and the depth of the
closed cavity being 50mm.
Parameters of the perforated board whose cavity is provided with sphere without pores:
the pores are arranged in the pattern of a square, with the diameter of the pores
being 1.7mm, the center to center spacing of the pores being 7mm, the thickness of
the perforated board being 0.7mm. Four plastic hollow spheres without pores are placed
in the closed cavity, with the thickness of the wall of the sphere being 0.4mm and
the volume V of the sphere being 3.35×104mm3. The spheres are arranged in the closed cavity freely, with the depth of the closed
cavity being 50mm.
[0024] Fig. 13 shows that the sound absorption coefficient of the perforated board and the
perforated board with built-in spheres without pores is similar to each other, with
the highest sound absorption coefficient being no greater than 0.35 at the frequency
band of 1000Hz and 1250Hz, i.e., the sound-absorbing effect of these two devices is
not desirable. As to the composite sound-absorbing device with built-in resonant cavity,
its formant reaches 0.928 at the frequency of 630Hz and reaches above 0.5 at the frequency
band of 500Hz and 1250Hz(i.e., the band width is 750Hz). From the above, it is apparent
that the sound-absorbing effect of the composite sound-absorbing device with built-in
resonant cavity is superior to the other two.
Embodiment Three
[0025] Referring to Fig. 2, the embodiment provides a composite sound-absorbing device with
built-in resonant cavity. The device comprises a closed cavity formed by a perforated
board 1, a back board 2 and side boards 3 all made up of stainless steel, with the
depth D of the closed cavity being 100mm. The perforated board 1 is a round board,
with a diameter of 100mm and thickness of 0.7mm. On the perforated board 1, first
pores6, with a diameter of 1.7mm are formed. The perforation rate of the first pores
6 is 4.6%. The first pores 6 are arranged regularly in a pattern of square on the
perforated board 1. Separately, nine, seven, four and one resonant cavity 5, made
of plastic and having a shape of sphere and a volume V of 3.35×10
4mm
3 and the thickness of the wall of the resonant cavity 5 being 0.4mm, is arranged in
the closed cavity. Furthermore, there are 26 second pores 6' on the wall of the resonant
cavity 5, evenly distributed on the circumferences of three mutually perpendicular
hemispheres (There are 16 second pores 6' on each hemispherical circumference, with
4 second pores 6' overlapping for every two hemispherical circumferences) . The second
pores 6' have a diameter d' of 0.5mm and the perforation rate σ' of the second pores
6' is 0.1%. The resonant cavities 5 are arranged in the closed cavity freely.
[0026] I n the experiment, four composite sound-absorbing devices with built-in resonant
cavity according to the present invention are separately provided with nine, seven,
four and one resonant cavity inside the closed cavity. The experiment tests the low
and medium frequency sound muffling mechanism by using a standing wave meter to verify
the impact of the number of resonant cavities on sound absorption coefficient and
the frequency band of sound absorption. The other parameters of the resonant sound-absorbing
structures employed in the experiment are listed as follows:
Parameters of the perforated board: the pores, with a diameter of 1.7mm, are arranged
in a pattern of square, with the center to center spacing of the pores being 7mm,
the thickness of the board being 0.7mm and the depth of the closed cavity being 100mm.
[0027] From Fig. 14, it is known that, the sound absorption coefficient of the resonant
sound-absorbing device with one resonant cavity is no greater than 0.4 at the formant
of 630Hz, and reaches about 0.6 at the frequency of 2000Hz; the sound absorption coefficient
of the resonant sound-absorbing device with four resonant cavities is above 0.8 at
the formant of 630Hz, and is greater than 0.5 at the frequency band of 500Hz and 800Hz,
and is 0.8 at the frequency of 2000Hz; the sound absorption coefficient of the resonant
sound-absorbing device with seven resonant cavities is above 0.95 at the formant of
800Hz, and is greater than 0.5 at the frequency band of 400Hz and 800Hz, and is about
0.85 at the frequency of 2000Hz; the sound absorption coefficient of the resonant
sound-absorbing device with nine resonant cavities is above 0.9 at the formants of
500Hz and 800Hz respectively, and is greater than 0.5 at the frequency band of 400Hz
and 1000Hz, and is about 0.8 at the frequency of 2000Hz. As can be seen, as the number
of the resonant cavity provided in the closed cavity increases, the frequency band
is expanded and the formant of the major sound-absorbing frequency band becomes bigger
gradually and the number thereof increases from one to two, whose features are similar
to the sound-absorbing structure of double-layer microperforated board; in addition,
the sound absorption coefficient at the frequency of 2000Hz increases as the number
of resonant cavities grows.
Embodiment Four
[0028] Referring to Fig. 3, the embodiment provides a composite sound-absorbing device with
built-in resonant cavity. The device comprises a closed cavity formed by a perforated
board 1, a back board 2 and side boards 3 all made up of stainless steel, with the
depth D of the closed cavity being 200mm, 500mm, 1000mm or 2000mm. The perforated
board 1 is a square board, with the length of the side being 1000mm and the thickness
thereof being 2mm. On the perforated board 1, first pores 6, with a diameter of 2mm,
are formed. The perforation rate of the first pores 6 is 0.031%. The first pores 6
are arranged regularly in a pattern of square on the perforated board 1. In the closed
cavity, 100 resonant cavities 5, made of glass and in a shape of sphere and having
a volume of 2.7x 10
5mm
3 and having a wall thickness of 10mm, are arranged. Four second pores 6', with a diameter
d' of 2mm, are provided on the wall of the resonant cavity 5, evenly distributed on
the circumference of a hemisphere. The perforation rate σ' of the second pores 6'
is 0.06%. Three of the four second pores 6' on each of the resonant cavities 5 are
connected with the closed cavity. The other second pore 6' is connected with a tube
4, whose other end is connected with a first pore 6 on the perforated board 1. The
tube 4 may be made of metal, rubber or glass, with a length I of 10mm, 50mm or 100mm
and a diameter of 2mm. The tubes 4 may be connected to the perforated board 1 by splicing,
threaded connection or injection mold.
Embodiment Five
[0029] Referring to Fig. 4, a composite sound-absorbing device with a built-in resonant
cavity is provided. The device comprises a closed cavity formed by a perforated board
1, a back board 2 and side board 3. The perforated board 1 may be made of glass, PVC,
PE or wood. The back board 2 and the side boards 3 are made of glass, with the depth
D of the closed cavity being 100mm. The perforated board 1 is a square board with
a side length of 200mm and a thickness of 3mm. On the perforated board 1, first pores
6, with a diameter of 1mm, are provided. The perforation rate of the first pores 6
is 0.6% and the first pores 6 are arranged in a pattern of hexagon on the perforated
board 1. In the closed cavity, 16 resonant cavities 5, which are rubber sphere-shaped
cavity, are arranged, with the volume of the resonant cavities 5 being 3.35×10
4mm
3and the thickness of the wall of the resonant cavities 5 being 0.8mm. On the wall
of the resonant cavities 5, three second pores 6' are provided, evenly distributed
on the circumference of a hemisphere. The diameter d' of the second pores 6' is 1
mm and the perforation rate σ' of the second pores 6' is 0.047%. Furthermore, the
second pores 6' of each resonant cavity 5 are connected with tubes 4 whose other ends
are connected with the closed cavity. The tubes 4 are made of rubber and have a length
I of 60mm and a diameter of 1 mm. The resonant cavities 5 are connected with the tubes
4 by splicing or injection molding. The resonant cavities 5 are arranged in the closed
cavity freely.
Embodiment Six
[0030] Referring to Fig. 5, a composite sound-absorbing device with built-in resonant cavity
is provided. The device comprises a closed cavity formed by a perforated board 1 made
of copper, a back board 2 made of stainless steel and side boards 3 made of stainless
steel, with the depth D of the closed cavity being 40mm. The perforated board 1 is
a square board with a side length of 80mm and a thickness of 1mm. On the perforated
board 1, first pores 6, with a diameter of 3mm, are provided. The perforation rate
σ of the first pores 6 is 28%. The first pores 6 are arranged regularly in a pattern
of square on the perforated board 1. In the closed cavity, four resonant cavities
5 made of copper and having a shape of sphere are provided, whose volume is 1.4×10
4mm
3 and whose wall has a thickness of 5mm. On the wall of the resonant cavities 5, two
second pores 6', with a diameter d' of 5mm, are provided. The second pores 6' are
evenly distributed on the circumference of a hemisphere. The perforation rate of the
second pores 6' σ' is 1.4%. Every two resonant cavities 5 form a group and are connected
with two second pores 6' on two resonant cavities through tubes 4 and the other second
pores 6' are connected with the closed cavity, as shown in Fig. 5. The tubes 4 are
made of steel and have a length of 5mm and a diameter of 5mm. The tubes 4 and the
perforated board 1 are connected by splicing, threaded connection or injection molding
and the resonant cavities are connected with the tube 4 by welding or threaded connection.
The resonant cavities 5 are arranged in the closed cavity freely.
Embodiment Seven
[0031] Referring to Fig. 3 and Fig. 6, a composite sound-absorbing device with built-in
resonant cavity is provided. The device comprises a closed cavity formed by a perforated
board 1 made of plastic, a back board 2 made of stainless steel and side boards 3
made of stainless steel, with a depth D of 200mm. The perforated board 1 is a square
board with a side length of 1000mm and has a thickness of 2mm. On the perforated board
1, first pores 6, with a diameter of 2mm, are provided. The perforation rate of the
first pores is 0.031 %. The first pores 6 are arranged regularly in a pattern of square
on the perforated board 1. In the closed cavity, one hundred resonant cavities 5,
which is in a shape of sphere and made of plastic and having a volume V of 2.7×10
5mm
3, are arranged. The thickness of the wall of the resonant cavities 5 is 10mm. On the
wall of each of the resonant cavities 5, two second pores 6', with a diameter d' of
2mm, are provided. The second pores 6' are evenly distributed on the circumference
of a hemisphere. The perforation rate σ' of the second pores 6' is 0.03%. One second
pore 6' of each resonant cavity 5 is connected with the closed cavity and the other
second pore 6' is connected with a tube 4 whose other end is connected with a first
pore 6 on the perforated board 1. The tubes 4 are made of rubber and have a length
of 100mm and a diameter of 2mm. The perforated board 1 is connected with the tubes
4 by using a first transit joint 7 and the resonant cavities 5 are connected with
the tubes by using a second transit joint 7'.
Embodiment Eight
[0032] Referring to Fig.7, a composite sound-absorbing device with built-in resonant cavity
is provided. The device comprises a closed cavity formed by a perforated board 1 made
of plastic, a back board 2 made of stainless steel and side boards 3 made of stainless
steel, with a depth D of 200mm. The perforated board 1 is a square board with a side
length of 1000mm and a thickness of 2mm. On the perforated board 1, first pores 6,
with a diameter of 2mm, are provided. The perforation rate of the first pores 6 is
0.031%. The first pores 6 are arranged regularly in a pattern of square on the perforated
board 1. In the closed cavity, one hundred resonant cavities 5, which are in a shape
of sphere and made of plastic and have a volume V of 2.7×10
5mm
3, are arranged. The thickness of the wall of the resonant cavities 5 is 2mm. On the
wall of each of the resonant cavities 5, two second pores 6', one of which has a diameter
d' of 3mm and the other has a diameter d' of 1 mm, are not evenly distributed on the
circumference of a hemisphere. The perforation rate σ' of the second pores 6' is 0.039%.
The resonant cavities 5 are arranged in the closed cavity freely.
Embodiment Nine
[0033] Referring to Fig. 8, a composite sound-absorbing device with built-in resonant cavity
is provided. The device comprises a closed cavity formed by a perforated board 1 made
of copper, a back board 2 made of stainless steel and side boards 3 made of stainless
steel, with the depth D of the closed cavity being 40mm. The perforated board 1 is
a square board with a side length of 80mm and a thickness of 1mm. On the perforated
board 1, first pores 6, with a diameter of 3mm, are provided. The perforation rate
of the first pores 6 is 28%. The first pores 6 are arranged regularly in a pattern
of square on the perforated board 1. In the closed cavity, four resonant cavities
5, which are in a shape of sphere and made of plastic, are arranged. On the wall of
each of the resonant cavities 5, three second pores 6' are provided, which are evenly
distributed on the circumference of a hemisphere. The thickness of the wall of the
resonant cavities 5 is 1 mm. Two resonant cavities 5 have a volume of 3.3×10
4mm
3 and the diameter of the second pores 6' thereon is 2mm and the perforation rate of
the second pores 6' thereon is 0.19%, and the other two resonant cavities 5 have a
volume of 8.3×10
3mm
3 and the diameter of the second pores 6' thereon is 1 mm and the perforation rate
of the second pores 6' thereon is 0.12%. The resonant cavities 5 are arranged in the
closed cavity freely.
Embodiment Ten
[0034] Referring to Fig. 8, a composite sound-absorbing device with built-in resonant cavity
is provided. The device comprises a closed cavity, formed by a perforated board 1
made of copper, a back board 2 made of stainless steel and side boards 3 made of stainless
steel, with the depth D of the closed cavity being 40mm. The perforated board 1 is
a square board with a side length of 80mm and a thickness of 1mm. On the perforated
board 1, first pores 6, with a diameter of 3mm, are provided. The perforation rate
of the first pores 6 is 28%. The first pores 6 are arranged regularly in a pattern
of square on the perforated board 1. In the closed cavity, four resonant cavities
5 made of plastic are arranged, wherein the thickness of the wall thereof is 0.5mm.
On the wall of each of the resonant cavities 5, one second pore 6' is provided. Among
the four resonant cavities 5, two are ellipsoid having a volume of 3.3x 10
4mm
3 and the diameter of the second pores 6' on them is 2mm and the perforation rate of
the second pores 6' is 0.063%, the other two are cubic having a volume of 6.4×10
4mm
3 and the diameter of the second pores 6' on them is 2mm and the perforation rate of
the second pores 6' is 0.03%. The resonant cavities 5 are arranged in the closed cavity
freely.
Embodiment Eleven
[0035] Referring to Fig. 10, a composite sound-absorbing device with built-in resonant cavity
is provided. The device comprises a closed cavity formed by a perforated board 1,
a back board 2 and side boards 3 all made up of stainless steel, with the depth D
of the closed cavity being 40mm. The perforated board 1 is a square board with a side
length of 80mm and a thickness of 5mm. On the perforated board 1, first pores 6, with
a diameter of 3mm, are provided. The perforation rate of the first pores 6 is 28%.
The first pores 6 are arranged regularly in a pattern of square on the perforated
board 1. In the closed cavity, four resonant cavities 5 made of plastic are provided,
wherein the resonant cavities 5 are in shape of a sphere with a volume of 942mm
3 and the thickness of the wall of the resonant cavities 5 is 1 mm. On the wall of
each of the resonant cavities 5, one second pore 6', with a diameter of 2mm, is provided.
The perforation rate σ' of the second pores 6' is 0.7%. Furthermore, partition boards
are installed inside the closed cavity, thereby separately fixing the four resonant
cavities 5.
Embodiment Twelve
[0036] Referring to Fig.11, a composite sound-absorbing device with built-in resonant cavity
is provided. The device comprises a closed cavity formed by a perforated board 1,
a back board 2 and side boards 3 all made up of stainless steel, with the depth D
of the closed cavity being 50mm. The perforated board 1 is a round board with a diameter
of 100mm and a thickness of 0.7mm. On the perforated board 1, first pores 6, with
a diameter of 1.1mm, are provided. The perforation rate of the first pores 6 is 1.9%.
The first pores 6 are arranged regularly in a pattern of square on the perforated
board 1. In the closed cavity, four resonant cavities 5 made of plastic are provided,
wherein the resonant cavities 5 are in shape of a sphere having a volume of 3.35×10
4mm
3 and the thickness of the wall thereof is 0.4mm. Moreover, there are twenty-six second
pores 6', with a diameter of 0.5mm,.on the wall of the resonant cavities 5, evenly
distributed on the circumferences of three mutually perpendicular hemispheres (There
are 16 second pores on each hemispherical circumference, with 4 second pores overlapping
for every two circumferences). The perforation rate σ' of the second pores 6' is 0.1
%. The resonant cavities 5 are arranged freely in the closed cavity. Each of the first
pores 6 on the perforated board 1 is connected with a stainless steel tube 4, which
is 8.5mm long and has a diameter of 1.1 mm. The tubes 4 are welded on the first pores
6 of the perforated board 1.
[0037] A comparison experiment is conducted to verify the sound muffling mechanism of low
and medium frequency sound of the composite sound-absorbing device according to the
present invention and the perforated board with tubes by using a standing wave meter.
In the experiment, the low and medium sound absorption coefficient of the perforated
board, the perforated board with tubes and the composite sound-absorbing device with
built-in cavities are measured respectively to determine the effect of resonant cavities
provided in the perforated board sound-absorbing structure. The other parameters of
the resonant sound-absorbing structure are listed as follows:
Parameters of the perforated board: the pores are arranged in a pattern of square,
with the diameter of the pores being 1.7mm, the center to center spacing of the pores
being 7mm, the thickness of the wall of the perforated board being 0.7mm and the depth
of the cavity being 50mm.
Parameters of the perforated board with tubes: the pores are arranged in a pattern
of square, with the diameter of the pores being 1.1mm, the center to center spacing
of the pores being 7mm, the thickness of the wall of the perforated board being 0.7mm,
the length of the tubes being 8.5mm and the diameter of the tubes being 1.1 mm. The
tubes are welded on the pores on the perforated board. The depth of the cavity is
50mm.
[0038] As shown in Fig. 15, in comparison with the perforated board, the main resonance
frequency band of the perforated board sound-absorbing structure with tubes and the
composite sound-absorbing device according to the present invention tend to move towards
low frequency and their average sound absorption coefficient is greater. In comparison
with the perforated board sound-absorbing structure with tubes, the sound-absorbing
formant of the composite sound-absorbing device according to the present invention
is much higher and its frequency band is wider.
Embodiment Thirteen
[0039] Referring to Fig. 12, a composite sound-absorbing device with built-in resonant cavity
is provided. The device comprises a closed cavity formed by a perforated board 1,
a back board 2 and side boards 3 all made up of stainless steel, with the depth D
of the closed cavity being 300mm. The perforated board 1 is a round stainless steel
board and the diameter of the board is 100mm, with a thickness of 0.8mm. On the perforated
board 1, first pores 6, with a diameter of 1.1mm, are provided. The perforation rate
of the first pores 6 is 1.9%. The first pores 6 are arranged regularly in a pattern
of square on the perforated board 1. In the closed cavity, four resonant cavities
5, made of plastic and being in a shape of sphere and having a volume of 3.35×10
4mm
3, are arranged. The thickness of the wall of the resonant cavities 5 is 0.4mm. Six
second pores 6' are arranged on the wall of the resonant cavities 5, evenly distributed
on the circumferences of three mutually perpendicular hemispheres. The diameter of
the second pores 6' is 0.5mm and the perforation rate σ' of the second pores 6' is
0.023%. The resonant cavities 5 are arranged in the closed cavity freely. Furthermore,
the back side of the perforated board 1 is covered with a layer of porous sound-absorbing
material, the thickness of the layer being 0.5mm, 5mm, 30mm, 100mm or 200mm and the
porous sound-absorbing material being glass wool, foamed aluminum, foamed plastic,
slag wool or cotton fiber.
[0040] To conclude, the composite sound-absorbing device with built-in resonant cavity according
to the present invention makes full use of the acoustic scattering on the surface
of the resonant cavity, acoustic impedance of the second pores on the resonant cavity
and the modulation to the sound-absorbing formant and sound-absorbing frequency band
by resonant cavities' coupling and etc., to absorb sound, wherein its sound-absorbing
frequency band is wider, sound absorption coefficient is bigger and so the absorption
effect of low and medium frequency noise is improved, when compared with conventional
perforated board resonant sound-absorbing structure. Moreover, the present device
is compact, economical and practical. It is clear from the above comparison experiments
that the sound-absorbing effect of the present device is obviously superior to the
perforated board resonant sound-absorbing device and as the number of the resonant
cavities increases, the sound frequency band becomes wider and the formant of major
sound-absorbing frequency becomes higher and gradually evolves into two formants,
which is similar to the double layer microperforated board sound-absorbing structure.
The number of resonant cavities and the pores on the resonant cavities is crucial
to the present device, and if the number of the resonant cavities is not enough, the
sound-absorbing effect would be greatly reduced.
[0041] It should be noted that the present invention is not necessarily limited to the foregoing
embodiments, which can be further modified in various ways within the scope of the
invention as defined in the appended claim.
1. A composite sound-absorbing device with built-in resonant cavity, including:
a perforated board having a number of first pores thereon, a back board and side boards,
said perforated board, back board and side boards forming a closed cavity, wherein:
at least one or more of said resonant cavities being located within said closed cavity;
at least one or more of second pores being located on said resonant cavities; and
at least one of said second pores being connected with said closed cavity;
said resonant cavity having a volume of V=10mm3—1×1010mm3, the thickness of the wall thereof being 0.05mm-10mm; said second pores having an
aperture of d'=0.05-100mm, with a perforation rate σ'=0.01 %-30%.
2. The composite sound-absorbing device of claim 1, wherein the number of said resonant
cavities is more than one, which are arranged within said closed cavity directly or
fixed separately within said closed cavity partitioned by a number of partition boards.
3. The composite sound-absorbing device of claim 1, wherein said resonant cavity is in
shape of sphere, ellipsoid or polyhedron.
4. The composite sound-absorbing device of claim 1, wherein said second pores are connected
to said closed cavity directly.
5. The composite sound-absorbing device of claim 1, wherein said second pores are connected
to said closed cavity via tubes.
6. The composite sound-absorbing device of claim 1, wherein said first or second pores
are connected to one end of said tubes and said tubes are located within said closed
cavity for increasing acoustical impedance.
7. The composite sound-absorbing device of claim 6, wherein the other ends of said tubes
on said second pores are connected to said closed cavity, said second pores on another
resonant cavity or said first pores on said perforated board.
8. The composite sound-absorbing device of claim 6, wherein said tubes are made of metal,
glass, plastic or rubber, with a length of 1-5000mm and diameter of 0.1-100mm;
when said tubes are made of rubber, they are connected to said first pores or second
pores via binding, or they are connected to said first pores via a first transition
joint at the ends of said tubes, or they are connected to said second pores via a
second transition joint at the ends of said tubes;
when said tubes are made of metal, glass or plastic, they are connected to said first
pores or second pores via binding, welding, thread connection or injection, or they
are connected to said first pores via a first transition joint at the ends of said
tubes, or they are connected to said second pores via a second transition joint at
the ends of said tubes.
9. The composite sound absorptive device of claim 1, wherein said perforated board has
a thickness of 0.5-10mm, the diameter of said first pores on said perforated board
d being 0.1-5mm, with a perforation rate σ of 0.1%-30%; said closed cavity having
a depth of D=10-2000mm, and said closed cavity having a shape of cylinder composed
by one side board or polyhedron composed by a plurality of side boards;
said first pores on said perforated board are arranged in a shape of regular triangle
or square or are arranged irregularly.
10. The composite sound-absorbing device of claim 1, wherein the back side of said perforated
board is coated with a layer of porous sound-absorbing material, said layer of porous
sound-absorbing material being located within said closed cavity, with a thickness
of 0.1mm-200mm.