A physically motivated room reverberation enhancement system that is stable in any (passive) room.
Edgar J. Berdahl, Günter Niemeyer, Julius O. Smith · The Journal of the Acoustical Society of America · 2010
Prior active room reverberation enhancement systems have typically employed microphones, artificial reverberator filters, and loudspeakers to change the reverberant properties of a room. However, acoustic feedback from the loudspeakers to the microphones has had the potential to drive such systems unstable. In contrast, techniques from feedback control can be used to design a stable room reverberation enhancement system from the ground up. A feedback controller implements a passive connection between virtual acoustic spaces, which are realized using digital waveguide networks, and special transducers, which operate concurrently as microphones and loudspeakers. Because the feedback controller models a passive system, it is theoretically stable for arbitrarily large loop gains in any (passive) acoustic environment. As a consequence, the system does not suffer from “ringing tones” at high-loop gains in the same way as prior systems have suffered. Furthermore, the system does not need to be re-calibrated if the properties of the room change or even if moved to a whole new room. Finally, this method for designing room reverberation enhancement systems may generally result in more realistic reverberant sound because it implements the acoustical features of a system that could exist naturally in the physical world.