mozartfan,
Although Joseph is emphasizing the "graphene" in the name, apparently it's really the re-design of the rest of the driver including motor etc that brought improvements, leading Joseph to also re design his crossover.
So it's quite plausible they sound different, and perhaps improved (even if it came from tweaking of the crossover). The Perspective Graphene model does measure different from the original - highs are a bit more flat.