1467.3.4 Secondary Structure of Rooms........................................................... 178
7.3.4.1 Sound Reflections at Smooth Plane Surfaces............................................ 178
7.3.4.2 Sound Reflection at Smooth Curved Surfaces........................................... 179
7.3.4.3 Sound Reflections at Uneven Surfaces................................................. 180
7.3.4.4 Sound Absorbers.................................................................. 183
7.3.4.4.1 Sound Absorption Through Porous Materials.............................................. 184
7.3.4.4.2 Sound Absorption by Panel Resonances.................................................. 184
7.3.4.4.3 Helmholtz Resonators................................................................ 185
7.3.4.4.4 Sound Absorption by the Audience...................................................... 186
7.4 Variation of Room Acoustics by Construction or Electroacoustic Methods........................... 188
7.4.1 Variable Acoustics.................................................................... 188
7.4.1.1 Fundamentals of Variable Acoustics.................................................. 188
7.4.2 Electronic Architecture................................................................. 190
7.4.2.1 Use of Sound Delay Systems for Enhancing Spaciousness................................. 191
7.4.2.1.1 Ambiophony....................................................................... 191
7.4.2.1.2 ERES (Electronic Reflected Energy System).............................................. 191
7.4.2.2 Travel-Time-Based Reverberation-Time Enhancing Systems............................... 1 91
7.4.2.2.1 Assisted Resonance.................................................................. 192
7.4.2.2.2 Multi-Channel-Reverberation, MCR..................................................... 192
7.4.2.3 Modern Procedures for Enhancing Reverberation and Spaciousness.......................... 193
7.4.2.3.1 Acoustic Control System (ACS)........................................................ 193
7.4.2.3.2 Reverberation on Demand System, RODS................................................ 193
7.4.2.3.3 LARES............................................................................ 194
7.4.2.3.4 System for Improved Acoustic Performance (SIAP)........................................ 194
7.4.2.3.5 Active Field Control, AFC............................................................ 194
7.4.2.3.6 Virtual Room Acoustic System Constellation¥
7.4.2.3.7 CARMEN®........................................................................ 196
7.4.3 Conclusions and Outlook............................................................... 197
References................................................................................. 197