Experimental study of the active sound transmission reduction through a double panel test section

The present study addresses the reduction of the sound transmission through a double panel test section by means of an active noise and vibration cont rol system. This stiffened double panel can be seen as a section of an airc raft fuselage, whereas the active control system has to reduce the noise le vel inside the passengers' cabin generated by the incident sound waves from the propellers. Experiments prove that control loudspeakers and error micr ophones in the cavity between both panels yield higher reductions in the ra diated sound power than control shakers and error accelerometers on the rad iating panel. This conclusion remains valid when the receiving and the radi ating panel are mechanically connected by means of four vibration isolators , and when the cavity is filled with thermal insulation blankets. It also a ppears that, in case of an active cavity noise control system, there exists an almost linear relation between the reduction of the acoustic potential energy in the cavity and the reduction of the radiated sound power. The opt imised control system performs much better than a control system with senso rs and actuators in arbitrarily chosen positions. The experimental results of this study are interpreted in the light of results obtained by other res earchers on similar test cases.