Concepts of Active Noise Aircraft Cockpits Reduction Employed in High Noise Level

Abstract

During the past two decades, reducing exposure to high-level noise in aircraft cockpits by methods of active noise control (ANC) has aroused the interest of researchers. Also, some commercial applications were initiated by leading manufacturers. For this purpose, fundamentally different approaches were used. While active noise compensation reduces the noise level by generating an interfering antinoise, structural vibration control aims to limit sound emittance through active damping of the aircraft structure vibrations. These approaches are linked with very different financial and technical boundary conditions, which implied distinct degrees of success. The ANC approaches used in cockpit noise reduction will be summarised, and their success or failure reasons will be analysed. Thereafter, the focus will be set on the industrially more successful way of protecting pilots from high noise levels, which is the use of active headsets. The development and the current state of commercial products will be presented, and the requirements of future trends will be derived. These requirements consist in extending the band width of noise reduction and making the control adaptive to changing conditions. Finally, the development of a prototype of a new generation of ANC headsets is presented. The prototype combines standard feedback with adaptive feedforward control techniques and processes the control algorithms by an integrated DSP platform.