Source placement for equalization in small enclosures

The results of a theoretical study of sound equalization in enclosures at low frequencies are presented. The sound field is controlled by sources distributed in the enclosure so that a certain region has a desired complex pressure corresponding to that of a traveling plane wave. The task is the detection of the optimum positions for a number of sources in order to minimize the energy of the error over the region of control. According to the direction of propagation, the sources should be placed so as to couple with the modes that will benefit the reproduction of the plane wave (the "desired" modes) but not with those that will deteriorate it (the "undesired" modes). Simulation results in rectangular rooms and in a car cavity show the benefits of source placement in terms of reduced overall error and increased spatial robustness in the equalization process. Additional benefits, which can be derived by proper placement of the listening zone, are also discussed.