Active control of noise in a three-dimensional enclosure using indirect adaptive control

Noise control in the interior of a rotorcraft is of significant importance due to the presence of noise levels of the order 100 dB and above concentrated around discrete peaks in a wide frequency range of about 50 Hz-5500 Hz. Hence, in related noise reduction (NR) efforts, one is required to attenuate sound fields with many dominant tones. Noise control efforts initially focused on controlling harmonic disturbances which were recently extended to include disturbances with multiple frequency components. The analytical models included those developed using state-space techniques and were implemented using feedforward and feedback control principles. In this study, numerical investigations into active noise control in a three dimensional enclosure are carried out using a state-space model. The identification of the structural-acoustic system is carried out using stochastic realization algorithms based on experimental input-output data. A digital controller based on LQG control techniques is developed and numerically implemented for disturbances with multiple frequency components.