| 摘要 |
PURPOSE:To effectively damp the low frequency noise without requiring any special physical space by having the swelling on the opposing inner surfaces of a duct to form a resonating constriction of a length half of the wave length of the noise, and disposing resonating chambers on the fore and aft ends of said constriction which resonate at or near the noise frequency. CONSTITUTION:The duct 2 made of zinc-coated sheet metal has a rectangular section configuration, and a swelling plate 5 of the same material which is curved at the fore and aft ends is fitted to the inner sides of it over the entire height to form a swelling section 6. The length of the straight portion 8 of the swelling plate 5 excluding the curved sections 7 is half of the wave length of the targeted noise to be damped. Resonating chambers 4 are formed in the upper and lower levels in the fore and aft ends of the right and left hand side swelling sections 6 (eight locations altogether). Hollow spaces 11 are formed by partioning the space delimited by the duct outer sheet metal 9 and th swelling plate 5 over the entire height with inner walls 10, and a small hole 12 is opened to the resonating constriction 3 in the fore and aft parts of the straight section 8 of the swelling plate. |
