Ok then, let's talk a little...
@ Mike Butler: There are many good DIY tops out there, whereas the Fitzmaurice tops are for people who don't know better. Physics don't work the way these DR-tops are designed. Ask other professional cab designers about it. Mids don't bend, for example. Multiple, non-angled HF drivers or even Piezos aren't professional. Nothing on his site can work as a true line array. His performance claims and comparisons are outrageous (at best!).
I have not built a DR-cab (I design cabs myself, and I know they won't work as I want cabs to work), but I heard them. They can't compete with real designs, no matter if professionally manufactured or DIY.
@ Matt Loretitsch: NOBODY said that measurement is silly, but PROS know that RTA measurements are basically worthless. They tell us as good as nothing. If you want to measure a system or a cab the right way, you need at least a waterfall spectogram, an impulse response, distortion measurement over frequency AND power and some more things. A frequency plot tells us actually NOTHING about how we will perceive the sound. It can be completely flat and sound like crap, and it can go pretty wild and sound really good (especially indoors, because the RTA doesn't know anything about the first wave law or Haas).
@ Dave Rickard: It's performance, also performance vs. size. See above, why. The worst thing would be the mids performance. From second sources (one of them is here) I know that Mr. Fitzmaurice himself KNOWS that the only way of getting mids to be heard is by masking the mids with the HF drivers output (trick the ear in believing to hear the mids).
@ DAVID_L_PERRY: It's not folded, it's bent. It's not a matter of believing. I know this simply can not work as intended. Every speaker designer or everyone a bit into acoustics knows... It is trickery, not the real deal. But even if it was folded, that wouldn't help much. Mids NEED horns as straight as possible.
@ Antone Atmarama Bajor: Right on!
@ peter.golde: I would be REALLY REALLY surprised if transient response would be really good on these (measured!). Don't confuse transient response with massive clean lowmid output (what his designs can surely do!). It's a mistake you wouldn't be the first committing it.
@ all: I think the DR design can work very well on upper bass and lowmids (up to say 250Hz). That's where folds/bents too far away from the horn throat start to be problematic. Make them bigger, add some cone mids and less but better HF drivers and go for it. I don't see how the original design could really work like intended (or let's say as advertised) with only two ways. There is a reason why EAW, EV, JBL and so on go threeway in the top on the big systems (to which BFM compares his DRs).
NEVER underestimate the human hearings ability to 'clean up' a mess of sound. I tested it a lot. In some designs with mid drivers working from 800 - 2kHz most people didn't even notice when the mid driver was turned off (WITHOUT changing the crossover so the range would be covered by other drivers. There was a big fat GAP!)until there was an AB comparison.
Again, I wish I could get over to UK and USA to demonstrate the difference between DRs and real tops. I wouldn't say that the DR cabs aren't a step up from ultra-cheap china boxes or JBL TR-cabs (and everything in the like), but they can't even compete to good middle-class equipment.
BTW: By admitting that the LAB sub needs tops with beefy lowmids, because it plays only to 80 to 100Hz, you already proved me right (can I say that this way?).... Of course you can still measure energy from the LAB at least to 250Hz, but nobody wants to HEAR this energy.....