Active acoustic attenuation system with differential filtering

Abstract From the Canadian patent

An adaptive active acoustic attenuation system is provided with extended frequency range to attenuate undesired noise which was previously filtered out to avoid instability of the adaptive model. The input signal from the input microphone to the model and the error signal from the error microphone to the model are differentially bandpass filtered to provide a narrower frequency range error signal. In one embodiment, the model operates in its stable region to provide accurate well behaved correction signals to the cancelling loudspeaker, while still receiving a low frequency input ncise signal from the input microphone including frequencies below such range. Minimum attenuation frequency has …