Method and apparatus for reducing low to mid frequency interior noise

Abstract

A method and apparatus for reducing the low to mid frequency interior noise of a reinforced skin structure, such as the cabin of a jet aircraft, by reducing the vibration response of the structure to low to mid frequency disturbances is disclosed. Interior noise is reduced by forming the structure such that the skin panels bounded by reinforcing components have a higher fundamental frequency than the combined bending and tuning fork frequency of reinforcing components with spaced apart legs that support the skin; and, damping the bending, tuning fork and torsional vibration of the reinforcing components. Damping is accomplished by bridging the spaced apart legs of the reinforcing components with rigid elements, viscoelastically attached at either end to the legs. Preferably, the viscoelastic attachment is via flanges that extend outwardly from the legs. The entire length of the reinforcing components may be spanned by a single rigid element; or, a series of spaced apart rigid elements may span the reinforcing components. When spaced apart rigid elements are used, preferably, they are centered at the antinodal points of the reinforcing components, as determined by the frequency of the noise produced in the interior of the body by the vibration of an undamped reinforcing component. If the interior noise covers a spectrum, the antinodal points are determined by the frequency of the major contributor(s) to the interior noise.