A summary of general considerations in active vibration isolation obtained from our experience in developing a testbed system is given. Application of this perspective is illustrated by a description of the testing facility and the results achieved to date. These include broadband active vibration isolation of 20 dB over a decade wide frequency band on the nearly full-scale testbed. Significant features of the testing facility are a s m a l l diesel engine mounted on a representatively complex structural foundation, the correspondingly complex open-loop transfer h c t i o n of the system, and the use of a hybrid analog/digital controller, to partition the compensation filter frequency coverage.

The use of a single actuator tuned to an optimum impedance to control the sound power radiated from a turbulent boundary layer (TBL) excited aircraft panel into the aircraft interior is examined. An approach to calculating the optimum impedance is defined and the limitations on the reduction in radiated power by a single actuator tuned to that impedance are examined. It is shown that there are too many degrees of freedom in the TBL and in the radiation modes of the panel to allow a single actuator to control the radiated power. However, if the panel modes are lightly damped and well separated in frequency, significant reductions are possible. The implementation of a controller that presents a desired impedance to a structure is demonstrated in a laboratory experiment, in which the structure is a mass. The performance of such a controller on an aircraft panel is shown to be effective, if the actuator impedance is similar to but not the same as the desired impedance, provided the panel resonances are well separated in frequency and lightly damped.

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