Optimization of the Active Control of Turboprop Cabin Noise

In this paper, a modified cost function is proposed in order to achieve the maximum noise attenuation using a set of secondary sources for a harmonically excited sound field. The modified cost function drives the error signal to the optimally attenuated sound field instead of minimizing the squared pressure. Moreover, changing the value to which the error signals must be driven allows change of the control strategy from global to local. The modified cost function requires the knowledge of the attenuated sound field, which is a condition that is well suited to narrowband noises, as is the case of turboprops. A numerical example of the application of the cost function is carried out using a finite element model/boundary element model of a real turboprop, with the goal of minimizing the interior sound field in the cabin to about 17m(3). A maximum averaged attenuation of 7dB at blade-passage frequencies is achieved using six secondary sources and six error sensors. Besides, when the same control system is tuned to achieve local control around the head of a seated crew member, 11dB of attenuation is achieved.