Michael Rubin

“Star Wars introduced a new way for using the five screen speakers [in theaters]. By pushing left and right sound channels to the farthest out speakers the pair just inside those was made available. Lucas' mixers then placed low frequency effects in those speakers, and named it the 'baby boom' channel. Human ears can hear frequencies up to around 20,000 hertz, and down to around 20 Hertz for very low sounds. Below that you don't *hear* the sound, but if the 'volume' is 'loud' enough, you can *feel* the sound. Super-low frequencies affect us emotionally, usually inducing something like fear. We feel them during earthquakes. Lucasfilm put sound effects in the baby boom channel for audiences to feel--for instance, in the opening shot of Star Wars where the little diplomatic ship is running from the Imperial Cruiser. It's no wonder this is one of the most memorable and ominous shots in cinematic history. It was not only cool looking, but cool *sounding*”
― Michael Rubin, Droidmaker: George Lucas and the Digital Revolution