I had it done when it was first announced (I think I have the second pair he did, guessing from the S/N). Well, it's hard to compare w/o both versions side by side, especially after some time elapsed. The upgraded speaker is really damn amazing, I can say that! I actually prefer it to his newer stuff, which I drove out there to audition. After the upgrade the 4's bass is definitely tighter and far more crisp; more realistic for common things like kick drums. The base 4 (at least early ones) had incredible bass extension but were a bit soft on bass transient impacts. That's totally fixed; the bass is as close to perfect as I've heard anywhere. There might be a touch less extreme LF extension afterwards, but it's very hard to say (ample bass down so low few recordings have much info that low). Mid/highs are incredible, and of course the bass is simply awesome. I've yet to find anything I like as much as the upgraded 4's for even 4x more $, even after all this time. I wish they were smaller, ofc, but then that's part of how they do the full range so well while still being relatively efficient and natural sounding. If you're considering his new ones go hear them first. If you like the sound of the 4, as I do, the upgrade is great. Now if only I could get my damn cat to stop pulling the stuffing out thru the bass port...and eating it.
