Abstract:

The results of an experimental investigation into using multiple tunable vibration absorbers to minimize sound radiation from vibrating plates will be presented. The vibration absorbers consist of lumped mass-spring systems whose characteristics (i.e., resonance frequency) can be electronically varied. A multiple channel, gradient search algorithm, implemented on a DSP, is used to adapt the characteristics of each of the absorbers (i.e., detune them) so as to minimize the radiated sound at selected multiple positions in the farfield. Experimental results for the detuned case are presented and compared to those obtained by tuning the resonance frequency of the vibration absorbers to the disturbance frequency. Preliminary results indicate that attenuation of sound radiated from the plate can be significantly improved by detuning the vibration absorbers away from the disturbance frequency via a gradient search. Thus, an adaptive-passive approach to minimizing sound radiation has been demonstrated to obtain good attenuation with very little electrical power requirement while adapting. This result is in contrast to active structural acoustic control which typically requires a signicant control power. [Work supported by NASA LaRC and ONR.]