Correlated active attenuation system with error and correction signal input

DETAILED DESCRIPTION Prior Art FIG.
1 shows an active acoustic attenuation system in accordance with incorporated U.
S.
Pat.
Nos.
4,677,676 and 4,677,677 at FIG.
5, and like reference numerals are used from said patents where appropriate to facilitate understanding.
For further background, reference is also made to "Development of the Filter-U Algorithm for Active Noise Control", L.
J.
Eriksson, Journal of Acoustic Society of America, 89(1), January, 1991, pages 257-265.
The system includes a propagation path or environment such as within or defined by a duct or plant 4.
The system has an input 6 for receiving an input acoustic wave, e.
g.
input noise, and an output 8 for radiating or outputting an output acoustic wave, e.
g.
output noise.
An input transducer such as input microphone 10 senses the input acoustic wave.
An output transducer such as canceling loudspeaker 14 introduces a canceling acoustic wave to attenuate the input acoustic wave and yield an attenuated output acoustic wave.
An error transducer such as error microphone 16 senses the output acoustic wave and provides an error signal at 44.
Adaptive filter model M at 40 adaptively models the acoustic path from input transducer 10 to output transducer 14.
Model M has a model input 42 from input transducer 10, an error input 44 from error transducer 16, and a model output 46 outputting a correction signal to output transducer 14 to introduce the canceling acoustic wave.
As noted in incorporated U.
S.
Pat.
Nos.
4,677,676 and 4,677,677, model M is an adaptive recursive filter having a transfer function with both poles and zeros.
Model M is provided by a recursive least mean square, RLMS, filter having a first algorithm filter provided by least mean square, LMS, filter A at 12, FIG.
2, and a second algorithm filter provided by LMS filter B at 22.
Adaptive model M uses filters A and B to adaptively model both the acoustic path from input transducer 10 to output transducer 14 and the feedback path from output transducer 14 to input transducer 10