Static structures (e.g. – buildings) – With exposed configuration having acoustical function – Absorbing material behind foraminous facing sheet
Reexamination Certificate
2000-04-24
2003-05-27
Friedman, Carl D. (Department: 3635)
Static structures (e.g., buildings)
With exposed configuration having acoustical function
Absorbing material behind foraminous facing sheet
C052S144000, C181S208000, C181S286000, C181S288000, C181S290000
Reexamination Certificate
active
06568135
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sound absorbing structure excellent in durability, weather resistance and recycling easiness.
2. Description of the Related Art
Sound-proof walls for preventing noise are provided for an expressway and a railroad. In general, the sound-proof wall is constituted by sound absorbing panels each having a panel-shape structure which accommodates inorganic fibers, such as glass wool or rock wool.
The sound absorbing panel constituted by the inorganic fibers suffers from the following problems:
(1) Glass wool and the like have a problem of unsatisfactory water draining performance. When moisture content is absorbed, the sound absorbing performance deteriorates. Therefore, complicated maintenance of the performance must be performed.
(2) Glass wool and the like encounter “fatigue” owing to use for a long time. Thus, the sound absorbing performance and the strength deteriorate.
(3) When the period of durability has elapsed, recycling requires a great cost. In general, a waste disposal process of the glass wool or the like must be performed as the industrial waste. In the foregoing case, recycling of rock wool does not require a high cost which is required for the glass wool. However, the cost is not satisfactorily low.
(4) When the glass wool or the like is exposed to air flows, flying and flotation of the fibers easily occurs. Thus, the sound absorbing performance deteriorates.
(5) In an environment, such as a location for manufacturing foods or chemicals, which requires a high degree of cleanness, flying and flotation of fibers cause a problem to arise. Therefore, the foregoing material cannot easily be employed.
(6) When the foregoing material is handled, there arises problems of aspiration and prickling of the fibers.
(7) The inorganic fibers deteriorate and become brittle owing to exposure to ultraviolet rays for a long time. Therefore, a countermeasure against the foregoing problem must be taken when the inorganic fibers is used outdoors.
(8) To solve the problems (1) and (4) to (7), a means for covering the inorganic fiber material with PVF films or the like is employed. In this case, there arises a problem in that the sound absorbing performance deteriorates and the films are broken.
Since a large quantity of the sound absorbing panels are used especially in a an expressway and railroad, the foregoing problem (3) is a critical problem which must be solved also from a viewpoint of the environment protection.
As a sound absorbing material which does not raise the problems experienced with the inorganic fibers, for example, a structure formed into a plate-like shape is known which is obtained by pressurizing and compressing aluminum fibers. Also a sound absorbing member is known which is obtained by foaming sintered aluminum particles or an aluminum material.
The sound absorbing member made of the foregoing metal material encounters a problem of inferior sound absorbing performance to that of the sound absorbing member made of the inorganic fibers, such as glass wool or the rock wool.
The foregoing sound absorbing members absorb sound by converting a part of acoustic energy into heat energy caused from friction of molecules in the air against the fibers and the particles when the molecules in the air pass through the gaps of the fibers or the particles.
The effect of absorbing sound using the foregoing sound absorbing member can be improved such that further bass range sound can be absorbed when the thickness of the rear air layer is enlarged. In usual, the size (in particular, the thickness) of the sound absorbing panel is, however, limited. Therefore, satisfactory sound absorbing performance cannot easily be realized in a frequency range not higher than 500 Hz. In particular, the sound absorbing member of a type constituted by the metal material demonstrates a propensity to have the foregoing characteristic.
As one of means for absorbing sound, a method is known which uses the following resonant structure. That is, the method uses the Helmholtz resonant structure as the basic principle thereof. As distinct from the sound absorbing member represented by fibers, frictional loss of movement of air occurring when the resonant structure called a Helmholtz resonator causes loss of the acoustic energy in the vicinity of the resonant frequency range to be produced. Thus, sound absorbing effect can be obtained.
As a representative sound absorbing structure using the Helmholtz resonator as the principle thereof, a structure is exemplified in which the surface of the wall is constituted by plates each having a multiplicity of openings or slits. Moreover, an air layer is formed in the rear portion of the sound absorbing structure. In this specification, a structure using the Helmholtz resonance as the basic principle for absorbing sound is hereinafter called a resonant sound absorbing structure.
A usual resonant sound absorbing structure encounters a problem in that the sound absorbing performance can be obtained only in a range in the vicinity of a specific resonant frequency. However, the foregoing structure has a characteristic that sound absorption is permitted in a bass range which cannot easily be realized when the sound absorbing member is employed.
In Japanese Examined Utility Model Publication Hei. 5-2646, a structure has been disclosed which includes sound absorbing members each incorporating aluminum fibers to serve as the sound absorbing materials, wherein the sound absorbing members are disposed in a state where air layers are formed such that the sound absorbing members are disposed apart from one another. Thus, sound absorption owing to the sound absorbing members and sound absorption owing to the resonant structure (resonant spaces) constituted by the gaps of the sound absorbing members and the rear air layers can simultaneously be performed.
The foregoing structure incorporating the aluminum fibers is able to solve the problems experienced with the structure incorporating the inorganic fiber sound absorbing member. Moreover, the sound absorbing performance in the bass range is attempted to be improved by also employing the resonant sound absorbing structure. The disclosed structure, however, has a problem in that a complicated structure is required and installation of the structure cannot be easily performed.
In general, the sound absorbing member constituted by forming aluminum fibers into a plate-like shape suffers from unsatisfactory strength. Therefore, a large size structure cannot be realized. Hence it follows that a satisfactorily large sound absorbing member cannot be obtained by the disclosed structure. Thus, there arises a problem in that a multiplicity of sound absorbing members must be joined and, therefore, the cost required to install the structure becomes high.
Moreover, the sound absorbing members must individually be disposed at positions apart from one another for predetermined distances. In addition, the air layers must be formed in a state where the sound absorbing members have been disposed. As a result, the overall structure is enlarged and complicated excessively. It leads to a fact that the cost required to install the structure becomes high.
The foregoing structure does not permit a sufficiently long length of the neck in each gap (the dimension in the direction of the depth of the inlet/outlet portion of the resonant structure). Therefore, when a resonant sound absorbing structure which is effective up to a furthermore bass range is required, the capacity of the resonant space must be enlarged. Hence it follows that the overall structure is enlarged excessively. Thus, the portion for which the sound absorbing structure can be provided is limited. When the space for installing the sound absorption structure required for a road or a railway is usually limited. Therefore, thick air layers cannot easily be provided. As a result, the foregoing structure cannot be easily put into practical use.
Therefore, development of a sound absorbing structure having a small thi
Fujimoto Takuya
Fujiwara Kyoji
Hattori Yukio
Migita Shinji
Okuzono Shinichi
Friedman Carl D.
Horton Yvonne M.
Nichias Corporation
Nixon & Vanderhye P.C.
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