| 摘要 |
PROBLEM TO BE SOLVED: To solve the following problems with the conventional sound absorbing boards; there are two kinds of the sound absorbing board made of concrete and the sound absorbing board stuck with a sound absorbing material on its front surface has poor long-term durability, such as exfoliation of the front surface sound absorbing material; the sound insulating board merely insulates the sounds and reflects the sounds to eventually diffuse the sounds and while there is a metallic board as the sound insulating board, such metallic sound insulating board has a drawback of a poor sound insulating effect because of its small thickness. SOLUTION: The sound absorbing material and an air layer consisting of a gap are arranged within a precast board. The sounds inputted from sound introducing holes drilled on a sound source side board are changed from acoustic energy to thermal energy by friction in the inside, by which the sounds are attenuated. The sound absorbing material and the air layer consisting of the gap constitute a resonance absorption mechanism and provide the precast sound absorbing board which attenuates the sounds and exhibits a sound absorbing effect. The direct deterioration by sunshine, wind and rain is averted and the improvement in the durability is made possible by incorporating the sound absorbing material into the precast board.
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