Active control of transmission loss in lightly damped panels

The transmission of non-deterministic, broadband noise across a panel is considered. An active feedback control solution that improves the transmission loss in lightly damped panels is presented. The additional transmission loss is achieved using accelerometer feedback and point force actuators to reduce the panel vibration at those frequencies that contribute significantly to the radiated noise. The multivariable controller is designed in the frequency domain through a sequential loop closure process. An experimental method for determining appropriate panel locations for the sensors and actuators is developed. Beneficial panel dynamics are utilized during the controller design process through the use of non-minimum phase zeros and unstable poles in the controller. The controller design methodology is also verified experimentally. The test facility consists of a panel that is coupled to an enclosure containing the noise source. Reductions in the transmitted sound pressure level of 14 dB are achieved at the frequencies corresponding to panel vibration modes which efficiently radiate sound. An overall reduction in transmitted noise of 3.2 dB is achieved over the 10-300 Hz frequency range despite the presence of an acoustic mode within the test enclosure.