Sound absorbing arrangement using a porous material

Abstract: A sound absorbing mechanism using a porous material has a sound absorbing plate (2) of a thin plate porous material made by partially heating for welding plastic particles and a supporting member (20) for supporting the sound absorbing plate (2) and forming a back air space (11). More than one pair of resonators (30) having a separated back air space (12) in the aforementioned back air space (11) are fixed to the sound absorbing plate (2), and the resonators (30) are disposed to be opposed to a sound insulator with the supporting member (20) between. Plural reflecting members (40) or increased sound absorbers may be disposed to be opposed to the surface of the sound absorbing plate (2) opposite to the surface equipped with the resonators (30), or a perforated protecting plate fixing the plural reflecting members or the increased sound absorbers thereon are may be equipped. The sound absorbing mechanism has a superior sound absorption characteristic from lower frequencies to higher frequencies.

Description: BACKGROUND OF THE INVENTION Field of the Invention: This invention relates to an improvement of a sound absorbing arrangement to be placed around a noise generating source or in a propagation path of a noise, and more particularly relates to a sound absorbing arrangement using a porous material. Description of the Prior Art: PRIOR ART 1. Fig. 13 is a sectional view showing the construction of a conventional sound absorbing arrangement using a hard porous material as a first prior (prior art 1), and the figure also has an explanatory diagram for showing a sound pressure distribution of a sound wave to be input into the sound absorbing plate thereof. In fig. 13 reference numeral 1 designates a sound insulator such as a wall; and numeral 2 designates a sound absorbing plate of a hard porous material made of plastic particles, a ceramic, foam metal or the like, for example. Reference numeral 11 designates a back air space of the sound absorbing plate 2; numeral 11a designates the thickness of the back air space 11; numeral 81 designates an input sound; reference character λ designates a wavelength of a sound wave having the highest sound pressure level among the input sounds 81. In the explanatory diagram showing a sound pressure distribution, mark + designates the operation of positive pressure on the sound absorbing plate 2; and mark - designates the operation of negative pressure on the sound absorbing plate 2. Arrows 85 and 86 designate directions of an input sound wave operating on the back air space 11 through the sound absorbing plate 2. Next, the operation thereof will be described. The input sound 81 passes through the sound absorbing plate 2 to be input into the back air space 11. The sound absorbing plate 2 has acoustic mass m and acoustic resistance r as the acoustic characteristics thereof, and the back air space 11 has acoustic capacity c as the acoustic characteristic thereof. The acoustic equivalent circuit according to the acoustic characteristics of the sound absorbing plate 2 and the back air space 11 can be expressed as a series resonance of r - m - c . According to this series resonance circuit, the resonance frequency thereof f 0 is expressed as the following formula. f 0 = ( 1 / 2 π ) x √ (1 / mc) When a sound wave having a frequency close to this resonance frequency f 0 is input into the sound absorbing plate 2, the input impedance observed from the sound source side becomes minimum. Accordingly, only the acoustic resistance r of the sound absorbing plate 2 should be considered. If the acoustic resistance r of the sound absorbing plate 2 is tuned to be a value close to the characteristic impedance ρ x a (ρ: density of air; a: sound velocity) of air, the sound absorption coefficient becomes 1.0 at the resonance frequency f 0 . Consequently, the sound wave having the frequency close to the resonance f 0 penetrates into the sound absorbing arrangement most efficiently. The penetrated sound wave forces the air existing in the back air space 11 and having an acoustic characteristic of acoustic capacity c to vibrate. The vibrated air goes in and out through gaps in the sound absorbing plate 2, and the sound wave is transformed into thermal energy by the acoustic resistance r of the gaps. That makes it possible to radiate energy. This means that the energy of the input sound wave was absorbed in the sound absorbing arrangement, namely sound absorption has been performed. In the aforementioned sound absorption arrangement, it is known that the efficiency of sound absorption is highest in the case where the input sound 81 is input into the sound absorption plate 2 perpendicularly. That is to say, in the case where a sound wave is input perpendicularly, the phase relation of the sound wave on the top surface of the sound absorbing plate 2 is equal at any place on the top surface, and the whole of the sound absorbing plate 2 and the whole of the back air space 11 are unified consequently, so that the effective operation of resonance and sound absorption is performed. On the other hand, the case where the input sound 81 is input into the sound absorbing plate 2 not perpendicularly but at a certain input angle β will be considered as an ordinary case. As shown in Fig. 38, when a sound wave having a wavelength λ is input the sound absorbing plate 2 at an input angle β, a phase difference having a period of λ /cos (β) or sound pressure distribution is generated on the sound absorbing plate 2. A sound wave is basically absorbed by utilizing a resonance phenomenon. But, if a distribution of the strength of sound pressure is generated along a direction on a surface of the sound absorbing plate 2, pressures 85 and 86 having reverse directions to each other operate on the back air space 11, so that adjoining parts of the back air space 11 is acoustically oscillated reversely. Then, pressures are balanced in the back air space 11, and consequently it becomes difficult that air vibrations synchronized with the input sound waves are generated. That is to say, it becomes difficult that resonance phenomena are generated between the sound absorbing plate 2 and the back air space 11, so that sound absorption effect is extremely checked. PRIOR ART 2. Fig. 14 is a longitudinal sectional view showing a sound absorbing arrangement utilizing a sound absorbing material and a resonance phenomenon by combining them as a second prior art (prior art 2), which is shown, for example, in the Japanese Patent Gazette No. 76116/ 1992 (Tokko-Hei 4-76117). Fig. 15 is a sound absorption characteristic diagram of the sound absorbing arrangement shown in Fig. 14. In Fig. 14, reference numeral 91 designates a wall; numerals 92 and 93 designate air spaces; numeral 94 designates a nozzle; numeral 96 designates a porous plate; and numeral 97 designates a sound absorbing material. Next, the operation thereof will be described. the aforementioned sound absorbing arrangement of the prior art 2 is provided with a porous plate 96 apart from the wall 91 with the air space 92 between. The porous plate 96 has a large number of small openings or slits 94, which are provided with nozzles 95 connected to them. Across the porous plate 96, the sound absorbing material 97 which is made of a fibrous material or a material made of a large number of particles is set over the whole plane at the tips of the nozzles 95 with the air space 93 between. In this connection, the air space 92, the small openings or slits 94 and the nozzles 95 comprise sound absorbing arrangements utilizing a resonance phenomenon, and the sound absorbing material 97 and the air spaces 93 comprise sound absorbing arrangements utilizing sound absorbing materials. The aforementioned elements of the sound absorbing arrangements utilizing a resonance phenomenon are connected to each other through the air space 92, and the elements of the sound absorbing arrangements utilizing sound absorbing materials are connected to each other through the air space 93. The sound absorbing arrangement of the prior art 2 has a sound absorption characteristic of the curved line 3 shown with a solid line in Fig. 15. A sound absorption characteristic of a sound absorbing arrangement utilizing only a resonance phenomenon is shown with a dotted line (curved line 2) in Fig. 15, which sound absorbing arrangement has large sound reduction effects at lower frequencies. A sound absorption characteristic of a sound absorbing arrangement utilizing only sound absorbing materials is shown with a dashed line (curved line 1) in Fig. 15, which sound absorbing arrangement has large sound reduction effects at higher frequencies. PRIOR ART 3. Fig. 16 is a partially cutaway perspective view showing the construction of a conventional sound absorbing arrangement as a third prior art (prior art 3), which utilizes both the slits and a porous material and is shown, for example, at pp. 245 - 250 and pp. 351 - 356 of Kenchiku Onkyo Kogaku Hando Bukku (Architectural Acoustics Handbook) ed. by Nippon Onkyo Zairyo Kyokai (Japan Acoustical Material Association) (Gihodo, Tokyo, 1963). Fig. 17 is a sound absorption characteristic diagram of the sound absorbing arrangement shown in Fig. 16. In Fig. 16 reference numeral 91 designates a wall; numerals 92 and 93 designate air spaces; numeral 98 designates a porous material; and numeral 99 designates a slit plate. Next, the operation thereof will be described. The aforementioned sound absorbing arrangement of the prior art 3, which uses a structure utilizing slits and a porous material, raises the sound absorption characteristics of the porous material 98 and the air space 92 by means of the resonance phenomena of the slit plates 99 and the air spaces 93. As shown in Fig. 17, the raised sound absorption characteristics are particularly effective at lower frequencies around 200 to 500 Hz due to the resonance phenomena at the slit parts. Since the sound absorbing arrangement of the prior art 1 is constructed as mentioned above, the resonance frequency f 0 is determined in accordance with the thickness 11a of the back air space 11 if the sound absorbing plate 2 is specified. The sound absorption coefficient becomes maximum at the resonance frequency f 0 , and the sound absorption characteristic has large values in a narrow frequency f 0 as a 1/3 octave band center frequency. Since some sound pressure distributions are generated in some directions on the sound absorbing plate 2 when sound waves are input the sound absorbing plate 2 at angles other than a right angle, the prior art 2 has a problem that the interference of input sound waves is generated at some frequencies according to phase differences to bring about the reduction of the sound absorption coefficient. Since the sound absorbing arrangement of the prior art 2 is constructed as mentioned above so that a sound absorbing arrangement utilizing a resonance phenomenon to be generated by elements connected to each other and a sound absorbing arrangement utilizing sound absorbing materials connected to each other are combined to absorb sound waves, the prior art 2 has problems that some sound pressure distributions are generated in some directions on the sound absorbing material 97 when sound waves are input into the sound absorbing material 97 at angles other than a right angle similarly in the prior art 1, so that the interference of input sound waves is generated at some frequencies according to phase differences to bring about the reduction of the sound absorption coefficients at lower frequencies as shown in, for example, Fig. 15. The sound absorbing arrangement of the prior 3, which utilizes slits and a porous material, has a problem that the sound absorption coefficients at lower frequencies around 200 Hz to 500 Hz are large due to sound resonance phenomena at the slits but the sound absorption coefficients at higher frequencies more than 500 Hz are small. Further, EP-A-46559 and EP-A-246464 each disclose a sound absorbing arrangement using a porous material to be placed on a sound insulator such as a wall, which comprises a sound absorbing plate made of a thin plate of a porous material and a supporting member the sound absorbing plate above the sound insulator. The supporting member forms plural adjacent back air spaces by subdividing the space between the sound absorbing plate and the sound insulator. SUMMARY OF THE INVENTION It is an object of the present invention to provide a sound absorbing arrangement and a sound absorbing means using a porous material which has a superior sound absorption characteristic from lower frequencies to higher frequencies by disposing plural sound absorbers composed of a thin plate of a porous material and a hollow member in front of a sound absorbing plate. This object is solved by a sound absorbing arrangement according claim 1 and as sound absorbing means according to claim 4. Advantageous improvements of the arrangement are provided in claim 2. The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purpose of illustration only and are not intended as a definition of the limits.of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a longitudinal sectional view showing the construction of a sound absorbing arrangement using a porous material according to the embodiment 1 of the present invention; Fig. 2 is a longitudinal sectional view showing the construction of a sound absorbing arrangement using a porous material according to the embodiment 1 of the present invention; Fig. 3 is a longitudinal sectional view showing the construction of a sound absorbing arrangement using a porous material according to the embodiment 1 of the present invention; Fig. 4 is a longitudinal sectional view showing the construction of an increased sound absorber of a sound absorbing arrangement using a porous material according to the embodiment 2 of the present invention; Fig. 5 is a longitudinal sectional view showing the construction of an increased sound absorber of a sound absorbing arrangement using a porous material according to the embodiment 2 of the present invention; Fig. 6 is a longitudinal sectional view showing the construction of an increased sound absorber of a sound absorbing arrangement using a porous material according to the embodiment 2 of the present invention; Fig. 7 is a perspective view showing the construction of a sound absorbing arrangement using a porous material according to the embodiment 3 of the present invention; Fig. 8 is a longitudinal sectional view showing the construction of a sound absorbing arrangement using a porous material according to the embodiment 3 of the present invention; Fig. 9 is a sound absorption characteristic diagram of a sound absorbing arrangement using a porous material according to the embodiment 3 of the present invention in conformity with the method for measurement of sound absorption coefficients in a reverberation room; Fig. 10 is a characteristic diagram showing an effect of a sound absorbing arrangement using a porous material according to the embodiment 3 of the present invention; Fig. 11 is a longitudinal sectional view showing the construction of a sound absorbing panel using a porous material according to the embodiment 4 of the present invention; Fig. 12 is a longitudinal sectional view showing the construction of a sound absorbing arrangement using a porous material according to the embodiment 5 of the present invention; Fig. 13 is a longitudinal sectional view showing the construction of a conventional sound absorbing arrangement using a porous material, including an explanatory diagram showing a sound pressure distribution of a sound wave to be input into the sound absorbing plate thereof; Fig. 14 is a longitudinal sectional view showing the construction of a conventional sound absorbing arrangement utilizing a sound absorbing material and a resonance phenomenon by combining them; Fig. 15 is a sound absorption characteristic diagram of the conventional sound absorbing arrangement utilizing a sound absorbing material and a resonance phenomenon by combining them; Fig. 16 is a partially cutaway perspective view showing the construction of a conventional sound absorbing arrangement utilizing both slits and a porous material; and Fig. 17 is a sound absorption characteristic diagram of the conventional sound absorbing arrangement utilizing both slits and a porous material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. EMBODIMENT 1 Figs. 1, 2 and 3 are longitudinal sectional views showing the construction of a sound absorbing arrangement using a porous material according to a first embodiment (embodiment 1) of the present invention. In Figs. 1, 2 and 3, reference numeral 1 designates a sound insulator such as a wall. Reference numerals 3a and 3b designate sound absorbing plates using a thin plate porous material similar to the sound absorbing plate 2 of the embodiment 1. The materials of the sound absorbing plates 3a and 3b are plastic particles, a ceramic, foam metal or the like. Reference numeral 11 designates a back air space of the sound absorbing plate 3a; and numeral 11a designates the thickness of the back air space 11. Reference numeral 14 designates a back air space of the sound absorbing plates 3b; numeral 14a designates the thickness of the perpendicular direction of the back air spaces 14; and numeral 14b designates the thickness of the horizontal direction of the back air spaces 14. Reference numeral 32 designates plural increased sound absorbers composed of a sound absorbing plate 3b and a hollow member 32a and disposed in front of the sound absorbing plate 3a so as to be opposed to the sound absorbing plate 3a with a space. Reference numeral 81 designates an input sound into the back air space 11; numeral 81a designates a re-input sound into the back air space 11 which re-input sound 81a is the input sound 81 having been reflected by the sound absorbing plate 3a and an increased sound absorber 32; and numeral 81c designates a re-input sound into a back air space 14 which re-input sound 81c is the input sound 81 having been reflected by the sound absorbing plate 3a. Reference numeral 84 designates an input sound into a back air space 14. Next, the operation thereof will be described. The resonance frequency f 0 of the input sound 81 is determined in accordance frequency f 0 of the input sound 84 is also determined in accordance wit the thickness 14a or 14b of the back air spaces 14. Sound absorption coefficients respectively become maximum at the resonance frequencies f 0 of them. Since each sound absorbing arrangement is independent of each other, the total sound absorption characteristic is the sum of the respective sound absorption characteristics. Many sounds do not pass through the sound absorbing plate 3a but are reflected on the surface thereof in the case where the sound absorbing coefficient thereof is small. Accordingly, when the increased sound absorbers 32 are disposed so as to be opposed to the sound absorbing plate 3a, the reflected sound becomes the re-input sound 81c or the re-input sound 81a which is the re-input sound 81c reflected by an increased sound absorber 32 again and is input into the sound absorbing plate 3a to be absorbed. Because sounds having a shorter wavelength become re-input sounds 81a and 81c more efficiently, sound absorption coefficients at frequencies higher than the resonance frequency f 0 are increased, and thereby sound absorption coefficients can be improved from lower frequencies to higher frequencies as compared wit those of the prior art 1. Because re-input sounds have a propagation path longer than those of input sounds, their phases are shifted. Consequently, resonance phenomena are reinforced at some frequencies, which brings about the increase of sound absorption coefficients. Some sounds of the input sounds into the increased sound absorbers 32 are pulled into the spaces between the increased sound absorbers 32 owing to the phenomena such as diffraction. Because the impedance of them is matched and their input angles become close to be perpendicular, they are absorbed efficiently. According to the results of some experiments, sound absorption coefficients are most improved in case of the construction shown in Fig. 1 among the constructions shown in Figs. 1 to 3. EMBODIMENT 2 Figs. 4, 5 and 6 are longitudinal sectional views showing the constructions of increased sound absorbers 32 of sound absorbing arrangements using a porous material according to a second embodiment (embodiment 2) of the present invention respectively. In Figs. 4, 5 and 6, reference numerals 3b, 3c, 3d and 3e designate sound absorbing plates using a thin plate porous material. The materials of the sound absorbing plates 3b, 3c, 3d and 3e are plastic particles, a ceramic, foam metal or the like. Reference numerals 14, 15, 16 and 17 designate back air spaces of the sound absorbing plates 3b, 3c, 3d and 3e. Because this embodiment separates the sound absorbing plates 3b, 3c, 3d and 3e and their back air spaces 14, 15, 16 and 17 respectively, plural resonance frequencies f 0 can be set, and thereby the frequencies having the local maximum sound absorption coefficient can be dispersed. Consequently, the distribution of a sound absorption coefficients having a furthermore wider frequency band can be obtained. EMBODIMENT 3 Fig. 7 is a perspective view showing the construction of a sound absorbing arrangement using a porous material according to a third embodiment (embodiment 3) of the present invention; Fig. 8 is a longitudinal sectional view showing the sound absorbing arrangement using a porous material shown in Fig. 8; Fig. 9 is a sound absorption characteristic diagram in conformity with the method for measurement of sound absorption coefficients in a reverberation room; and Fig. 10 is a characteristic diagram showing the ratios of the sound absorption coefficients in the case where the sound absorbing arrangement shown in Figs. 7 and 8 is equipped with the increased sound absorbers 32 to the sound absorption coefficients in the case where the sound absorbing mechanism is not equipped with the increased sound absorbers 32. In Figs. 7 and 8, reference numeral 1 designates a sound insulator such as a wall. Reference numerals 3a and 3b designate sound absorbing plates using a hard thin plate porous material. The materials of the sound absorbing plates 3a and 3b are plastic particles, a ceramic, foam metal or the like. Reference numerals 11 and 12 designate back air spaces of the sound absorbing plate 3a; and numerals 11a and 12a designate the thicknesses of the back air spaces 11 and 12 respectively. Reference numeral 14 designates the back air spaces of the sound absorbing plates 3b; and numeral 14a designates the thickness of the perpendicular direction of the back air spaces 14. Reference numerals 20a and 20b designate latticed supporting members for supporting the sound absorbing plate 3a so as to be opposed to the sound insulator 1 above the sound insulator 1 with the space of the thickness 11a of the back air spaces 11. Reference numeral 30 designates resonators equipped to the sound insulator 1 side of the sound absorbing plate 3a with the space of the thickness 12a of the back air spaces 12; and numeral 30a designates hollow members for forming the resonators 30. The resonators 30 are disposed so as to be parallel to the supporting members 20a and perpendicular to the supporting members 20b. Reference numeral 32 designates plural increased sound absorbers composed of a sound absorbing plate 3b and a back air space 14 and disposed so as to be opposed to the top surface of the sound absorbing plate 3a. Reference numeral 81b designates a re-input sound into a back air space 12 which re-input sound 81b is the input sound 81 having been reflected by the sound absorbing plate 3a and an increased sound absorber 32; numeral 82 designates an input sound into a back air space 12; and numeral 82b designates a re-input sound into a back air space 11 which re-input sound 82b is the input sound 82 having been reflected by the sound absorbing plate 3a and an increased sound absorber 32. Reference numeral 84 designates an input sound into a back air space 14. Next, the operation thereof will be described. Since the back air spaces 11 are separated by the supporting members 20a and 20b and the back air spaces 12 are separated by the hollow members 30a and the supporting members 20b respectively, each back air space 11 and each back air space 12 respectively operate independently as described in the embodiment 1, and thereby it becomes easy to generate resonance phenomena, which brings about the improvement of the sound absorption performance thereof. Since the interference of sound waves due to phase differences is thus little, the present sound absorbing arrangement has larger sound absorption coefficients as compared with those of the prior arts 1 and 2. The resonance frequency f 0 of the input sound 81 is determined mainly in accordance with the thickness 11a of the back air spaces 11. The resonance frequency f 0 of the input sound 84 is also determined mainly in accordance with the thickness 14a of the back air spaces 14. Sound absorption coefficients respectively become maximum at the resonance frequencies f 0 of them. Since each sound absorbing arrangement is independent of each other, the total sound absorption characteristic is the sum of the respective sound absorption characteristics. Furthermore, many sounds do not pass through the sound absorbing plate 3a but are reflected on the surface thereof in the case where the sound absorbing coefficient thereof is small. Accordingly, when the increased sound absorbers 32 are placed so as to be opposed to the sound absorbing plate 3a, the reflected sounds are reflected by the increased sound absorbers 42 again and are input into the sound absorbing plate 3a as the re-input sounds 81b and 82b to be absorbed by it. Because sounds having a shorter wavelength become re-input sounds 81b and 82b more efficiently, sound absorption coefficients at frequencies higher than the resonance frequency f 0 are increased, and thereby sound absorption coefficients can be improved from lower frequencies to higher frequencies as compared with those of the prior arts 1 to 3. Because the re-input sounds have a propagation path longer than those of the input sounds, their phases are shifted. Consequently, resonance phenomena are reinforced at some frequencies, which brings about the increase of sound absorption coefficients. Some sounds of the input sounds into the increased sound absorbers 32 are pulled into the spaces between the increased sound absorbers 32 owing to the phenomena such as diffraction. Because the impedance of them is matched and their input angles become close to be perpendicular, they are absorbed efficiently. The sound absorbing arrangement uses a thin plate porous material as the sound absorbing plates 3a and 3b, which porous material is made by partially heating and welding plastic particles made from polypropylene resin, polyvinyl chloride resin, ABS resin, polycarbonate resin or the like, and is fully disclosed in Japanese Published Unexanined Patent Application of No. 289333 / 1990 (Tokkai-Hei 2-289333) titled " Takoshitsu Kozotai (Porous Material) ". The sound absorbing plate 3a having the thickness of about 3.5 mm is fixed so that the thickness 11a of the back air spaces 11 becomes about 35 mm, and the hollow members 30a are fixed to the sound absorbing plate 3a so that the thickness 12a of the back air spaces 12 becomes about 9 mm for forming the resonators 30. The sound absorbing plates 3b having a thickness of about 3.5 mm are fixed so that the thicknesses 14a of the back air spaces 14 becomes about 10 mm. And then, the increased sound absorbers 32 thus constructed and sized to have the width of about 33 mm and the height of about 15 mm are disposed with a space of about 15 mm from the sound absorbing plate 3a so as to be perpendicular to the resonators 30. The sound absorption characteristic of the sound absorbing arrangement thus constructed is improved in sound absorption coefficients at frequencies higher than about 1.25 kilo-Hz and is totally improved at a wider frequency band as compared to the sound absorption characteristic in case of having no increased sound absorbers as shown in Figs. 28 and 29. Since the sound absorbing plate 3a is supported by the supporting members 20a and 20b, the strength of the sound absorbing plate 3a is increased. According to the results of some experiments, sound absorption coefficients are furthermore improved at the thickness 12a of the back air space 12 being about 15 mm. In Figs. 7 and 8, the embodiment 12 has latticed supporting members 20a and 20b, but the present invention comprises the use of the supporting members 20a alone or the supporting members 20b alone. By such usage, the effects similar to those of the present embodiment can be expected. Similar effects also can be expected in the case where the increased sound absorbers 32 are disposed to be parallel to the resonators 30. EMBODIMENT 4 Fig. 11 is a longitudinal sectional view showing the construction of a sound absorbing panel using a porous material according to a fourth embodiment (embodiment 4) of the present invention. In Fig. 11, reference numeral 1a designates a sound insulating plate also serving as a housing of the sound absorbing panel. Reference numeral 4 designates a protecting plate made of a punching metal or the like, which protecting plate 4 has at least one opening and is fixed to the insulating plate 1a so as to cover the opened part of the sound insulating plate 1a. Reference numeral 21a designates a supporting member for disposing the increased sound absorbers 32. The subject matter realized in the embodiment 12 brings about effects similar to those of the embodiment 12 even if it is applied to the form of a sound absorbing panel as shown in this embodiment. EMBODIMENT 5 Fig. 12 is a longitudinal sectional view showing the construction of a sound absorbing arrangement using a porous material according to a fifth embodiment (embodiment 5) of the present invention: In Fig. 12, reference numeral 1 designates a sound insulator such as a wall. Reference numerals 3a and 3b designate sound absorbing plates using a thin plate porous material. The materials of the sound absorbing plates 3a and 3b are plastic particles, a ceramic, foam metal or the like. Reference numeral 4 designates a protecting plate made of a punching metal or the like, which protecting plate 4 has at least one opening and is disposed so as to be opposed to the top surface of the sound absorbing plate 3a. Reference numeral 11 designates the back air space of the sound absorbing plate 3a; and numeral 11a designates the thickness of the back air space 11. Reference numeral 14 designates back air spaces of the sound absorbing plates 3b; and numeral 14a designates the thickness of the perpendicular direction of the back air space 14. Reference numeral 32 designates plural increased sound absorbers fixed to the protecting plate 4 and composed of a sound absorbing plate 3b and a back air space 14 and furthermore disposed so as to be opposed to the top surface of the sound absorbing plate 3a. Reference numeral 81 designates an input sound into the back air space 11; and numeral 81c designates a re-input sound into a back air space 14 which re-input sound 81c is the input sound 81 having been reflected by the sound absorbing plate 3a. Since the sound absorbing arrangement using a porous material of the embodiment 15 is thus constructed, it can improve sound absorption coefficients at lower frequencies to higher frequencies similarly in the embodiment 10. And it can prevent the damage of the sound absorbing plate 3a by means of the protecting plate 4. Furthermore, since the increased sound absorbers 32 are fixed to the protecting plate 4 in advance, they serve also as reinforcements to the protecting plate 4 and the efficiency of fitting operation of the protecting plate 4 at fitting sites is high. The sound absorbing plate 3b can be expected to have similar effects in case of being fixed perpendicularly to the protecting plate 4 as shown in Fig. 3.

Claims: A sound absorbing arrangement using a porous material to be placed on a sound insulator (1), such as a wall, comprising a sound absorbing plate (3a) made of a thin plate of a porous material and disposed above said sound insulator (1) with a back air space (11) between, further comprising plural sound absorbers (32), which are separate from each other, characterised in that each separate sound absorber is composed of a thin plate (3b) of a porous material and a concave member (32a), said separate sound absorbers (32) being disposed in front of said sound absorbing plate (3a) with a space from the sound absorbing plate (3a). The sound absorbing arrangement according to claim 1, characterized by further comprising a protecting plate (4) disposed in front of said plural sound absorbers (32) for fixing the sound absorbers (32), the protecting plate (4) having an opening. The sound absorbing arrangement according to claim 1, characterized in that said sound absorbing plate (2, 3a) is made of plastic particles bound by partially surface melting. A sound absorbing means comprising a sound insulator (1) such as a wall characterized in that a sound absorbing arrangement according to one of claims 1 to 3 is placed on the sound insulator (1).

Inventors: IMAI TOSHIHISA, KURASHINA MASAYUKI, OOTSUTA KATSUHISA, TANI SHUICHI, TSUKAMOTO KOUJI, IMAI, TOSHIHISA, KURASHINA, MASAYUKI, OOTSUTA, KATSUHISA, TANI, SHUICHI, TSUKAMOTO , KOUJI, Imai, Toshihisa c/o Mitsubishi Electric, Kurashina, Masayuki, c/o Mitsubishi Denki K.K., Ootsuta, Katsuhisa, c/o Mitsubishi Denki K.K., Tani, Shuichi c/o Mitsubishi Denki K.K., Tsukamoto , Kouji c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI ELECTRIC HOME APPL, MITSUBISHI DENKI KABUSHIKI KAISHA, MITSUBISHI ELECTRIC HOME APPLIANCE CO., LTD
Application year: 1995
Main classification: G10K11
IPC codes: G10K11, E01F8, E04B1