This talk deals with active noise control applied to a one-dimensional acoustic propagation system. The aim here is to keep over time a zero noise level at a given point. Based on symmetry property, we are able to design a feedback boundary control allowing this fact. Moreover, this control only depends on past observations made at an other point in the spatial domain. Finally, using D'Alembert formula, an explicit formula of the control can be computed. Even if the focus is made on the wave equation, this approach can be easily extended to more general operators.