Technology for controlling sound field by electro-acoustic means is often called Active Field Control, AFC, which is used to improve auditory impressions such as liveness, loudness, and spaciousness in auditoria. The AFC system, which has been developed at Yamaha, utilizes feedback control techniques to re-create natural reverberation based on the existing acoustics of the room. Time varying control, including EMR (Electric Microphone Rotator) and fluc-FIR (fluctuating FIR), is implemented in the AFC system to improve stability, preventing the coloration caused by a feedback loop in the system. In this paper, these technologies are summarized, together with an introduction to the recent representative venues using AFC. A system plan using core devices named AFC1, which has been developed at Yamaha and released recently in the US, is also presented.
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