Drubin, for me the C3's are a little rounder, warmer and perhaps more forgiving. The C1's seem, comparatively, like they are more like an unbelievable studio or mastering monitor. Precise, unforgiving, detailed, etc. The C3's are no less precise or detailed, but are softer to the ear. More of a musical caress. And, I think, better detail in the bass......I am also a sucker for the Esotar tweeter of that era (T 330D).