Acoustic replication in smart structures using active structural/acoustic control

There has been a great deal of research on the use of active vibration control with the goal of changing the vibration characteristics of structures. These vibration characteristics may result in undesirable acoustic fields that radiate from the structure. Traditional active noise control approaches center around canceling the offensive acoustic field using loudspeakers to set up opposing fields. A more recent approach is to use active vibration control techniques to directly modify the vibration characteristics and thus the acoustically radiative properties of the structure. A very effective way of achieving this structural/acoustic control is through the use of smart structures in which sensors and actuators are integrated into the structure itself. The subject of this thesis is to explore the potential for the use of active structural/acoustic control and smart structures in acoustic replication. In acoustic replication, an offensive acoustic response of an acoustically radiative smart structure is modified to match a desired acoustic response using active structural/acoustic control. The desired goal, in this case, is not necessarily suppression but to match the acoustic response of a similar structure that has desired acoustic properties. The model that is developed in detail is an elastic plate with piezoceramic sensors and actuators backed by a rigid, vented cavity. One specific application explored is the acoustic guitar. Detailed information on desired acoustic response of guitars is readily available in the literature, and experimental specimens are relatively easy to obtain. The way such an instrument vibrates in response to excitation of the strings determines the acoustic field that results. The feasibility of changing these vibrational characteristics using active structural/acoustic control is examined in detail including analytical and experimental results. The feasibility of applying acoustic replication to an aircraft cockpit is also examined including an experimental study on noise transmission reduction and an analytical study on acoustic signature modification.