1. A method for monitoring an acoustic target in a target location in a space monitored by N microphones, the method comprising: providing a number D equal to or greater than 2 and smaller than N to a processor; providing a number of L locations in the space, wherein each location in the L locations is treated by a processor as an interference source; and determining by the processor a set of D microphones from the set of N microphones, the determining including: minimizing a maximum interference gain relative to the target location and the L interference locations over at least 2 different frequencies expressed in microphone weights for all N microphones; and performing a convex optimization of the microphone weights for all N microphones over an l 1 penalty to determine a set of D microphone weights not equal to zero for each of the at least 2 frequencies.