Noise Transmission Characteristics of Damped Plexiglas Windows

Most general aviation aircraft utilize single layer plexiglas material for the windshield and side windows.Adding noise control treatments to transparent panels is a challenging problem. In this paper, damped plexi-glas windows are evaluated for replacement of conventional windows in general aviation aircraft to reduce thestructure-borne and airborne noise transmitted into the interior. In contrast to conventional solid windows,the damped plexiglas window panels are fabricated using two or three layers of plexiglas with transparent vis-coelastic damping material sandwiched between the layers. Results from acoustic tests conducted in the NASALangley Structural Acoustic Loads and Transmission (SALT) facility are used to compare different designs ofthe damped plexiglas panels with solid windows of the same nominal thickness. Comparisons of the solid anddamped plexiglas panels show reductions in the radiated sound power of up to 8 dB at low frequency resonancesand as large as 4.5 dB over a 4000 Hz bandwidth. The weight of the viscoelastic treatment was approximately1 % of the panel mass. Preliminary FEM/BEM modeling shows good agreement with experimental results forradiated sound power.