The changes to the driver are supposed to improve reliability and consistency of sound. The impedance of the newer LCD3F is higher at 110 ohms than the old LCD3 which I think was around 50ohms? This is a good thing because it increases compatibility with headamps.
If you go back in the HF threads, you'll read about the "veiled LCD3" issues early on; and even up to a year ago, I've heard different sounding LCD3rev1 with some sounding better than others; and some really good sounding LCD3r1s regressing to the "veiled state" over time. Gurubai, the resident ortho master here surmised that it may have been tension on the diaphragm causing these changes.
The bad thing is sometimes the lottery works in your favor. I know a few people with better sounding LCD3r1s than others. For example, Jason's LCD3r1 is fantastic and better sounding than all of the LCD3Fs I've heard. (I've only heard two LCDFs, so take the small sample size into consideration).
One other aspect which Anaxilus mentioned: the LCD3F seems to have a hint of LCD-X's plasticky timbre quality. Just a hint of that. So we wonder if Audeze is now going with a consistent more reliable diaphragm material. But for most part, I feel Audeze has done something really impressive in getting a new driver design to mimic the LCD3r1 so well.
When it comes down to it, I'd rate the LCD3F the same as an "grade B" LCD3r1.
P.S. Everything above is pure speculation. We could be full of shit.
