I only just started listening to Renaissance a few months ago. I've heard of them for a long time but never listened for some reason. I found this video and even though it's "lip synching" with the original recording, there are a couple of views of Jon Camp on a doubleneck! The part starting at 2:52 is cool - it looks like they are really playing and like @Bob_Ross said, it looks like he's attacking the bass! I think that might be part of the sound...
) on the intro to Can You Understand. He is getting it on.