Thomas A. Funkhouser Ingrid Carlbom Gary Elko Gopal Sarma Pingali Mohan Sondhi Jim West A Beam Tracing Approach to Acoustic Modeling for Interactive Virtual Environments. 21-32 1998 SIGGRAPH http://doi.acm.org/10.1145/280814.280818 db/conf/siggraph/siggraph1998.html#FunkhouserCEPSW98