PURPOSE:To prevent exhaust gas from entering a waveguide as much as possible. CONSTITUTION:The active duct sound elimination device, which eliminates a source sound propagated in a duct by superposing a canceling sound on the source sound, is equipped with an expanded chamber 12 provided halfway in the duct 11, the waveguide 13 which is open to the expanded chamber 12, and a canceling sound generating means 14 which is connected to the waveguide 13, and, an intake and an outlet for the gas, which communicate with the expanded chamber 12 of the duct 11 are linked by a pipe 16 and the peripheral surface of the pipe 16 on the opposite side to the waveguide 13 is open to the expanded chamber 12.
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