PURPOSE: To optimally set an acoustic transfer function and to improve and maintain active muffling performance while keeping the execution of system identification at the irreducible minimum, by detecting the monitor sound level at the noise objective position in a duct and performing a system identification, when the average value of the detected level exceeds a reference value, assuming the muffling performance has been deteriorated by a characteristic variation.
CONSTITUTION: Using the monitored signals outputted from a monitor means 5, the filter coefficients of a muffling filter 10 are updated so as to reduce the sound pressure level in the vicinity of an observation point. An average value computing means 15 is provided to compute an average value of the monitored level detected by the means 5 per a prescribed time. When the average value of the monitored sound computed by the means 15 exceeds a reference value L, a system identification means is operated. When the monitored sound average value is less than the value L, a control means controls the system identification means so that the means stops its operation.
HIEI TAKEHIKO
ITO HIROYUKI
