AN EXPERIMENTAL INVESTIGATION INTO THE ACTIVE CONTROL OF SOUND-TRANSMISSION THROUGH STIFF LIGHT COMPOSITE PANELS

A possible means of controlling the transmission of noise into the cab in of a propeller driven aircraft is the replacement of part of the in ternal trim with stiff, light composite panels and the use of vibratio n actuators acting as secondary force inputs between these panels and the fuselage. Experiments are described that use a freely mounted alum inum honeycomb composite panel and a clamped steel plate with secondar y forces acting between the steel plate and the composite panel. The d ouble partition was mounted between two reverberation chambers. A sing le frequency primary source is placed in the source chamber and the Mu ltiple Error LMS algorithm is used to minimize the sum of the squared pressures at 24 microphones in the receiving chamber by adjusting the outputs of three force actuators attached to the honeycomb panel. The results for frequencies between 80 Hz and 100 Hz are presented and dis cussed. Further experiments are also described where the single alumin um honeycomb panel is replaced by four small aluminum honeycomb panels with secondary forces acting between each panel and the steel plate. Results are presented and briefly discussed for the 80 Hz to 100 Hz fr equency range and also the harmonically related ranges of 160 Hz to 20 0 Hz and 240 Hz to 300 Hz.