| 摘要 |
PROBLEM TO BE SOLVED: To realize the stable silencing effect by identifying a secondary sound path in accordance with the change of a temperature T in an exhaust duct 1. SOLUTION: The secondary sound path C exists between an output part of an adaptive filter 3 to an error microphone 7 through an adder 6, a speaker 5 and a part on the downstream of the exhaust duct 1. In this active muffler, the silencing effect of high accuracy can be obtained only by allowing the secondary sound path C and a transfer function Se of a FIR filter 8 for compensating the secondary sound path C to be approximately equivalent to each other, that is, by identifying the secondary sound path C with the FIR filter 8. As it is known that the secondary sound path C depends on the temperature T in the exhaust duct 1, a temperature detector 12 is mounted in the exhaust duct. LMS operation parts 4, 10 are controlled by a control part 13 to identify the secondary sound path C when the fluctuation|ΔT|of the temperature T obtained on the basis of the detection by the temperature detector 12 is increased.
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