Two lightsabers in motion really does sound like a pair of Sousaphones! I don’t know how the original films created the sound effects for the fights, but a Sousaphone - an elegant instrument from a more civilized age - would have done just as well.
This video shows a scene from what I will guess is the band room of the marching band of Bennington High School in Bennington, Nebraska. The two duelists, one Jedi and one Sith, battle to determine who will claim the title of first chair.
- via Laughing Squid