Soundproof wall

Abstract: A soundproof wall comprising a wall structure (10) having a rising portion (1) and a sound absorbing member (2) or hollow structure (4) attached to either the inner or outer side, or to both, of the rising wall portion. The soundproof wall is highly effective in sound absorption and can advantageously be manufactured with reduced costs.

Description: The present invention relates to a soundproof wall intended for use as erected along railways and highways, around houses, schools, factories, airport buildings, etc. and in similar places from or to which undesired sound or noise should desirably be attenuated or shut off. To insulate or attenuate undesired sound or noise, it has so far been proposed to use a porous concrete panel, a panel made of aluminium or similar metal, and a wall formed from an assembly of boxes made of aluminium or FRP and which have glass wool or the like packed therein. Recently, such boxes have been made of ceramic. A soundproof wall made only of a porous concrete panel does not effectively absorb or attenuate sound, does not have sufficient shock resistance and has reduced strength when wetted in rain. A box made of aluminium, FRP or ceramic having glass wool or the like packed therein is effective in absorption but expensive when many pieces are assembled to form a soundproof wall. Attention is also drawn to the disclosures of EP-A-0160358, W0-A-93/12298, and CH-A-590366. JP-05-061488 discloses a soundproof wall having a wall structure and vertical passages for sound. The present invention aims at providing a soundproof wall highly effective in sound absorption or attenuation and advantageous in view of manufacturing costs. According to the invention, there is provided a soundproof wall comprising a wall structure having a rising main wall portion and a non-sealed hollow structure comprising a series of tubular or hollow members disposed side by side on the surface of a sound source side, of the rising main wall portion, characterized in that said tubular or hollow members forming said hollow structure are provided horizontally. The hollow structure of the soundproof wall according to the present invention can be easily attached with bolts to the surface of an existing concrete wall erected along a railway, for example, absorbs sound highly effectively and can be manufactured with a reduced cost. The invention will be further described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a sectional view of a first embodiment of the present invention in which a hollow structure of the soundproof wall is shown; FIG. 2 is a perspective view of a second embodiment of the present invention in which a second variant of the hollow structure constructed by tubular members different in length and diameter from one another, is attached to a rising wall portion; FIG. 3 is a perspective view of a third variant of the hollow structure; FIG. 4 is a sectional view of a third embodiment of the present invention in which the hollow structure shown in FIG. 3 is attached to the rising portion of a wall structure having an overhanging portion; FIG. 5 is a sectional view of a fourth embodiment in which a combination of a hollow structure shown in FIG. 1 and a sound absorbing member, is used on the upper portion of a rising wall portion; FIG. 6 is a sectional view of a wall structure other than a simple rising wall structure; FIG. 7 is a sectional view of a further wall structure; and FIG. 8 is a sectional view of a yet further wall structure. FIG. 1 is a sectional view of the first embodiment 4 of a hollow structure of the soundproof wall according to the present invention, having a single layer including a series of identical tubular members 41 horizontally joined side by side to each other. The horizontal arrangement of the tubular or hollow members of the present invention may be used in combination with similar members which are arranged in a vertical manner. Although the tubular members 41 shown in FIG. 1 have a cylindrical shape, they may be polygonal shaped. Each hollow-structure tubular member 41 is made of a material selected from among metals such as aluminium, synthetic resins such as FRP, and ceramics. The hollow structure 4 can be used not only on a wall structure 10 having a rising wall portion 1 but also on one having an overhanging portion. Furthermore, it can also be used on a wall structure 10 as shown in FIGS. 6 to 8. FIG. 6 shows a wall structure 10 formed concave at the base of the rising wall portion 1 thereof. FIGS. 7 and 8 show further wall structures 10, respectively, formed thicker at the base of the rising wall portion. In addition, a second variant of the hollow structure 4 may be formed in a second embodiment of the invention from a combination of tubular members 41 different in diameter and length as shown in FIG. 2. FIG. 3 is a perspective view of a third variant of the hollow structure 4. The hollow structure 4 is constructed of a series of tubular members 41 each partially cut longitudinally thereof (to a trough-like structure having a C-shaped section as shown), joined side by side to each other. Such a hollow structure 4 may be used in combination with that shown in FIG. 1. Also the hollow structure 4 may be constructed by a combination of such trough-like members 41 different in size in respect of the longitudinal opening, depth and orientation thereof. FIG. 4 is a sectional view of a third embodiment of the present invention in which the hollow structure 4 as shown in FIG. 3 is attached to the inner side of a rising wall portion 1 of a wall structure 10 having also an overhanging portion 3. Sound measurement was done at a position of 1 m distant from the rising wall portion 1 on which the hollow structure 4 was attached to the upper half thereof, the measuring position being located opposite to the sound source side and at the same level as the bottom end of the rising wall portion 1. The measured acoustic pressure was 6 to 7 dB lower than that measured with no hollow structure 4 attached on the rising wall portion 1 and overhanging portion 3. FIG. 5 is a sectional view showing a combination of the hollow structure 4 shown in FIG. 1 and a sound absorbing member 2. The hollow structure 4 is installed to the inner side of the rising wall portion 1 and the sound absorbing member 2 is installed to the hollow structure 4. The combination of the hollow structure 4 and sound absorbing member 2 can also be used as attached to a wall structure 10 having an overhanging portion 3, or to a desired side of a wall structure 10 as shown in FIGS. 6 to 8. Also in the embodiment shown in FIG. 5, only the hollow structure 4 or sound absorbing member 2 may be attached to the surface other than where the combination of the hollow structure 4 and sound absorbing member 2 is used. The sound absorbing member 2 may be composed of a flat box made of aluminium, FRP, ceramic or the like, and a fiber such as glass wool packed inside the box. The box may have small holes formed in the outer surface thereof. Also, the box may have formed therein at every corner thereof fixing holes through which a fastener such as bolt or the like is introduced to fix the sound absorbing member 2 to the rising wall portion 1 of the wall structure 10. The fiber packed in the box of the sound absorbing member 2 should preferably be a fiber block of 0.04 to 0.15 g/cm 3 in mean apparent density, formed by compacting from a short fiber of 30 or less deniers at the center of fiber diameter distribution. This combination of the short fibers of 30 or less deniers with an apparent density falling in a predetermined range permits to increase the ventilation resistance in the fiber block, thereby providing an improved sound absorption. Assume here that a fiber of 30 or more deniers is used for this purpose. The fiber block formed from the fiber will have a lower density even with a same apparent density so that the ventilation resistance will be lower, resulting in a poor sound absorption. On the contrary, if it is tried to improve the sound absorption by forming such fiber block higher only in the apparent density, the fiber block will be too hard and more likely to reflect incident sound. Namely, the sound absorption will be poorer. To avoid the above, the upper limit of the fiber-block apparent density should be set to 0.15 g/cm 3 as in the above. On the other hand, a fiber block made of a short fiber of 30 or less deniers will have no larger ventilation resistance if its apparent density is 0.04 g/cm 3 or less. No sufficient sound absorption can be expected of a sound absorbing member thus made. The short fiber may be any one selected from synthetic fibers such as polyester, polypropylene, nylon, Vinylon, etc. as well as natural fibers such as wool, cotton, hemp, etc. For production of a fiber block used in the sound absorbing member 2, a bituminous or similar material is processed by a melt spinning or similar method to be fibrous and mixing the fiber thus produced in an amount of 10 or more percent by weight into the above-mentioned short fiber. A fiber block formed from this mixture will insulate or absorb sound very effectively. Of course, a fiber block formed, by packing, from only one of the above-mentioned synthetic or natural fibers, also provides an equivalent sound insulation and absorption. The above-mentioned similar material to the bituminous material contains 30 or more % by weight of a bituminous material of which the brittleness and temperature dependence are improved through modification thereof by addition of a resin, rubber or thermoplastic elastomer. The reason why the fiber block, made of a short fiber to which the bituminous fiber made from a bituminous or similar material, insulates and absorbs sound highly effectively is that the butiminous material has an excellent damping property which will be imparted to the fiber block if the bituminous material is added to the latter. The fiber block can also be formed by setting in a mold a short-fiber aggregate containing a binder and preformed to a flat shape (preformed fiber block), and compressing it while it is being heated. Such a preformed fiber block may be a polyester fiber clenched with a binder such as polyethylene fiber, low melt-point polyester fiber or bituminous fiber. The fiber block can be produced by using any of the above-mentioned methods. For a more uniform filling and smaller density distribution of the fiber block, however, a method should preferably be adopted in which discrete fiber pieces resulted from splitting of a fiber are blown into a mold along with a gas (air), and only the gas is discharged through a multi-hole network while only the short fiber is filled into the mold to form a fiber block. By this fiber filling by transfer with air, it is possible to fill the fiber in a desired shape and produce a fiber block which is generally uniform, soft and porous. As mentioned above, a binder is used to form and clench the material filled in the mold. The binder used for this purpose may be selected from a variety of materials including a reaction-sensitive phenol resin which will be melted when heated, a reaction-sensitive urethane adhesive will react with blown-in steam, etc. However, a fibrous binder can be suitably used. The fibrous binder may be any one selected from a low melt-point polyester fiber which will be melted when heated or applied with steam and a polyethylene or polypropylene fiber which will be melted when heated or in steam and be solidified when cooled. Preferably, the fiber is composed of low and high melt-point components. Moreover, the fiber should advantageously be a composite one in which the low melt-point component exists outside the high melt-point one to serve as the fiber surface, in view of the durability and acoustic property of the preformed fiber block or so'und absorbing member. More particularly, by molding the composite fiber as heated to a temperature higher than the melt point of the low melt-point component and lower than that of the high melt-point component, the binder can bind the preformed fiber block by the low melt-point component melted while the binder keeps a complete fibrous state, thereby assuring a high durability and acoustic property of the sound absorbing member. Also, the binder may be any other material which is fibrous like the bituminous fiber and is meltable when heated or otherwise. To mold a porous layer having a fibrous binder mixed therein, it is preferred to adjust the temperature of a mold to lower than the melt point of the binder and melt the binder with a hot blast or steam blow at a higher temperature than the melt point. In this case, addition of a means of enabling a selection between the hot and cold blasts will lead to a further improvement of the molding cycle, and the blow of a hot blast will uniformly melt and solidify the entire porous layer to the deepest point thereof. Thus, a soft and lightweight fiber block having a desired shape can be produced by blowing a short fiber as the material together with the fibrous binder into a mold and then a hot blast into the mold to melt the binder which in turn will bind the short fiber. The fiber block thus produced is superior in dimensional precision and soundproof performance. As has been described in the foregoing, the sound absorbing means according to the present invention can be easily attached to an existing wall structure with fasteners such as bolts or the like. It absorbs sound with an extremely high effectiveness and can advantageously be manufactured with reduced costs. Also, many tubular or hollow members horizontally joined side by side to each other to form a hollow structure provide an improved sound absorption, and such a hollow structure can be manufactured with a low cost. The hollow structure thus manufactured is very lightweight, so it can be easily handled. The combination of the hollow structure with the sound absorbing member provides a further improved sound absorption or attenuation.

Claims: A soundproof wall comprising a wall structure (10) having a rising main wall portion (1) and a non-sealed hollow structure (4) comprising a series of tubular or hollow members (41) disposed side by side on the surface of a sound source side of the rising main wall portion (1), characterized in that said tubular or hollow members (41) forming said hollow structure (4) are provided horizontally. A soundproof wall as claimed in claim 1, characterized in that the hollow or tubular members (41) are different in length from each other. A soundproof wall as claimed in any one of Claims 1 or 2, characterized in that the said members (41) of the hollow structure (4) are open tubular members each having a C-like cross-section which can be formed by halving a tube longitudinally and which are joined to each other.

Inventors: IIDA KAZUYOSHI, MIZUNO KEIICHIRO, MURASE MASANORI, IIDA, KAZUYOSHI, MIZUNO, KEIICHIRO, MURASE, MASANORI
Applicants: BRIDGESTONE CORP, BRIDGESTONE CORPORATION
Application year: 1995
Main classification: E01F8
IPC codes: E01F8