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In many active noise control applications, it is necessary that acoustic actuators be mounted in small enclosures due to volume constraints and in order to remain unobtrusive. However, the air spring of the enclosure is detrimental to the low-frequency performance of the actuator. For launch vehicle noise control applications, mass and volume constraints are very limiting, but the low-frequency performance of the actuator is critical. This work presents a novel approach that uses a nonlinear buckling suspension system and partial evacuation of the air within the enclosure to yield a compact, sealed acoustic driver that exhibits a very low natural frequency. Linear models of the device are presented and numerical simulations are given to illustrate the advantages of this design concept. An experimental prototype was built and measurements indicate that this design can significantly improve the low-frequency response of compact acoustic actuators.

Launch acoustic and vibration loads have the potential to damage sensitive payloads within a payload fairing, often requiring more structural mass to withstand these loads than would otherwise be necessary to survive launch. Experiments demonstrating several vibro‐acoustic mitigation technologies developed by AFRL/VS and its contractors flew on the Vibro‐Acoustic Launch Protection Experiment 2 (VALPE‐2) aboard a Terrier‐Improved Orion sounding rocket from Wallops Island Flight Facility in August 2003. Flight data collected in November 2002 from a nearly identical launch (VALPE‐1) was used to characterize the fairing environment for comparison. Preparations for the flight experiments are discussed along with the performance of the various experiments in flight. The several experiments include an Adaptive Vibro‐Acoustic Device (AVAD) to mitigate acoustic loads, an active/passive hybrid vibration isolation system using voice‐coil actuation and a ShockRing passive component, a voice‐coil regenerative electronics vibration isolation system to absorb a portion of the vibration energy during launch and use it to power an active isolation system during a staging event, and a ChamberCore composite fairing with implications for passive acoustic performance.