| 摘要 |
PURPOSE:To permit the attenuation of sound in a low frequency area, by a method wherein the opposing two surfaces of a ventilating passage are constituted of a sound absorbing layer consisting of a perforated sheets and a sound absorbing material and the other opposing two surfaces of the same are constituted of only the lining of the sound absorbing material while the ventilating passage from the outlet and inlet port of a muffler to a resonance unit is choked with an acute angle. CONSTITUTION:The opposing two surfaces of a ventilating passage 4 are provided with a sound absorbing layer consisting of a perforated sheet 5 and a sound absorbing material 6 and an air layer 8 having partitioning sheets on the outside thereof to constitute a resonance unit. Further, the angle theta of the resonance unit, from the outlet and inlet ports of a muffler to the ventilating passage, is determined so as to be 60 deg.<=theta<=90 deg.. The other opposing two surfaces are not provided with the air layer and are provided with only the lining of the sound absorbing material 6. Metallic sheet or the like is used for the perforated sheet while inorganic or organic fibers, such as glass wool, rock wool or the like, is used for the sound absorbing material. Further, at least one piece of splitter is provided in the ventilating passage 4. According to this constitution, attenuation of sound in low frequency area as well as the reduction of weight of the title muffler may be achieved.
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