Performance of an active control system near a reflecting surface

This paper deals with the evaluation of power radiated by two monopoles located near a refl ective surface, especially in the case when one monopole-strength is actively controlled for the minimisation of total radiated power. The radiated power and the optimal input for the controlled monopole are derived analytically. It is found that the power output of an active noise control system consisting of two point sources and located near a refl ective surface is dependent upon the system orientation angle. Based on the mechanism that the refl ecting surface can convert a dipole vertical to the surface into a longitudinal quadrupole, we demonstrate that the introduction of a rigid surface to the active noise control system could further enhance the total power reduction.