Smart panel with multiple decentralized units for the control of sound transmission. Part III: control system implementation

This is the third of three companion papers that summarize the theoretical and experimental work carried out to develop a prototype smart panel with 16 decentralized vibration control units for the reduction of sound transmission/radiation. In this paper the control effectiveness of the smart panel has been assessed experimentally by measuring, in a anechoic chamber, the reduction of its total sound power radiation when it is mounted on a Perspex box with very thick and rigid side walls. The panel has been excited either by the acoustic field produced by a loudspeaker placed in the Perspex box or directly by a point force generated with a shaker. The vibration averaged over the panel surface has also been measured with a laser vibrometer. Laser measurements have also been taken at some specific frequencies, in such a way as to highlight the spatial vibration of the panel with the 16 decentralized control units. The various tests carried out have shown that the 16 control units can produce good reductions of the radiated sound power and averaged vibratory field over the panel surface, particularly when the panel is excited by the shaker. Indeed, when the panel is excited by the shaker, reductions of the sound radiation were measured in all the third octave bands in the frequency range 0-5 kHz and it was found that there were at least seven bands with reductions between 5 and 8 dB. Also, the averaged vibration field over the panel surface was found to be completely damped down in a frequency range between 0 and I kHz with reductions of about 10 dB in correspondence to all resonance frequencies. (C) 2003 Elsevier Ltd. All rights reserved.