1. Introduction
Generating acoustically bright and dark zones [1] and multiple sound zones are important and challenging acoustic communication techniques. They are useful not only for personal sound systems [2]–[8] but also for multilingual guide services and other virtual reality applications. Many methods have been proposed that control both the acoustic contrast and the energy between two spaces [1], [3] [6], [9] [14] and reproduce multiple sound fields [8], [15] [19] using multiple loudspeakers. For realizing personal audio systems and multiple sound zones, these approaches are more effective than beamforming methods [2], [20] [22], which maximize the energy to the target direction with the given input source power.