We produced this video in response to a request a to produce a video demonstrating how to Tie Bagpipe Drone Cords. The distance between the drones should be such that they sit comfortably on your shoulder. A space of about 6" to 7" has been found to be the most suitable spacing between the drones. Spacing of the drones can also affect the way a listener perceives the sound of your drones. The correct spacing will result in a solid, full and balanced sound emanating from your bagpipes.
Andrew Lenz has an excellent article on his website called Andrew's Tips: Tying/Making Bagpipe Drone Cords. It is a good complement to this video and worth reading.