Approach to interior noise control. I - Damped trim panels

Abstract

The attenuation mechanisms for interior trim panel systems are reviewed, emphasizing the significance of structure-borne transmission through the trim attachments. The significant factors for high-frequency performance include number of attachments per unit area, panel critical frequency, and panel damping. The need for sufficient damping below and maximal damping above the trim panel critical frequency is described. Described are two experimental flight demonstrations that emphasize the role of trim panel damping. One program involves the new interior system design for a large business jet. Utilization of portions of the weight budget in the form of structural damping treatments permitted a +40% weight savings in acoustical materials with no significant increase in cabin noise levels. Significant reductions in noise levels were achieved in the cockpit, galley, and lavatory. A second program involved a commercial twin-engine jet, with a design objective of significant reduction in noise with minimal weight increase. A reduction of 5 dBA and 5 dB in the speech interference level in the cabin average noise was achieved with only a 0.7% increase in the maximum gross takeoff weight. Only simple add-on skin, trim, and bulkhead damping treatments were used.