  In theory, active control could be used to reduce the unwanted noise
reflections from surfaces such as a submarine hull or the walls of an anechoic
room. In the recent years, a real-time algorithm has been developed to this
effect at the Laboratoire de M\'ecanique et d'Acoustique: the noise scattered
by the surface is estimated through linear filtering of acoustic pressure
signals provided by ordinary microphones and an adaptive feedforward algorithm
minimizes the resulting error signals. The paper summarizes the theory
underlying the control algorithm, which stems from the integral representation
of the scattered pressure, and presents the successive experiments which have
been conducted with it: control of terminal reflections in a duct, control of
the noise scattered by a parallelepiped in an anechoic room, estimation of the
noise reflections on the walls of a small room. It appears that an accurate
identification of the linear filters that account for the surface scattering
leads to an effective estimation and control of the scattered noise. Facilities
allowing such an accurate estimation of the scattered noise are suggested for a
future anechoic room where active devices would deal with the wall reflections
in the 20-100Hz frequency range.
