Sound radiation is not only matter of comfort, but also of people's exposure noise limits. Public demand about the life quality is leading to produce laws and standards able to preserve people's health. The authors have been working for a long time in the field of Smart Structures, with the development of different hardware systems devoted to the characterization of implemented active devices and to their guidance. On the basis of what developed in the phase 1 of the research, a feed-forward controller has been developed, aimed at reducing the vibration field of, or the sound radiated by, generic elastic structures. Piezo-ceramic patches are used as actuators and accelerometers as sensors, so avoiding the use of microphones. In the specific case, a thin-walled beam has been referred to as representative of complex elements in general architectures and single tone excitations have been investigated. Key features of the controller: its capability in identifying the disturbance and following its frequency and amplitude variations; the frequency independence of the 90° phase shifter analog section. The application here presented deals with the band around 100 Hz, specifically interesting for human annoyance problems, a range where passive noise reduction systems are ineffective.