With reference to FIG. 1, an active sound control system comprises a loudspeaker LS having an input qs and operable to generate sound waves for interference with unwanted sound so as to produce a region close to the user of the system in which the perceived sound is substantially reduced. A monitoring microphone ro is positioned closer to the loudspeaker LS than to the region of sound reduction. Loudspeaker control means for controlling the input qs to the loudspeaker LS operate to energise the loudspeaker such that the sound waves emitted by the loudspeaker substantially cancel the unwanted sound waves in said region. The loudspeaker control means includes a signal processing means (FIG. 3) arranged to simulate a microphone output that would be obtained if that microphone, instead of being positioned closer to the loudspeaker LS than the user, were to be positioned in a notional position ra relatively close to the user. The resulting simulated or virtual microphone output is then used to control the signal fed to the loudspeaker input qs.