Complex sentence: It used four large rheostats housed in a large box, converted from 270 degrees rotation to 90 degrees and operated by a joystick which allowed the sound to be panned around the hall.
Split into simpler sentences: It used four large rheostats housed in a large box, converted from 270 degrees rotation to 90 degrees. The system was operated by a joystick, which allowed the sound to be panned around the hall.