@proceedings {2642, title = {A physically motivated room reverberation enhancement system that is stable in any (dissipative) room: An application of sound portholes}, journal = {NOISE-CON 2010 in conjunction ith the 159th Meeting of the Acoustical Society of America}, year = {2010}, month = {04/2010}, address = {Baltimore, MD}, abstract = {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. To avoid feedback
instabilities, we apply passivity techniques from control theory to design a stable room
reverberation enhancement system from the ground up. In particular, we employ sound
portholes, which are special transducers that operate concurrently as microphones and
loudspeakers.\  With these sound portholes, the feedback controller implements a passive
connection to virtual acoustic spaces, which are realized using digital waveguide networks.\ 
Because the feedback controller models a passive system, it is theoretically stable in any
(dissipative) acoustic environment and for arbitrarily large loop gains. 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. 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.
}, url = {https://ccrma.stanford.edu/~eberdahl/Papers/NOISECON2010Reverb.pdf}, author = {Edgar Berdahl and Gunter Niemeyer and Julius O. Smith} }