Acoustic optimization within structural dynamics involves automatic changes of structural design variables such as geometric dimensions, shell thickness, material parameters, fiber density and orientation angles, and others to obtain minimum noise or a specified sound quality in specified regions inside or outside the structure. The objective of the present paper is to compare numerical optimization results with experimental ones. The analysed structure is geometrically simple; a closed cylinder. The objective function is the sound intensity at specified points outside the structure. The variable used is the shell thickness. The structural dynamic behaviour is analysed with the finite element method and the acoustic analysis is performed with the boundary element method.