If you really want to use that driver I can help you out. It is a beast but the 18 is NOT an easy driver to use and if you are going to pay that much for an Uber driver you want to make sure you get maximum performance from it. A pair of cheaper drivers like RLP's or Mal-X's will most likely outperform it, but they will require twice the enclosure volume to do it.
First things first, you should forget about using PR's with it. There are no PR's made that can cope with the displacement that will be required when that driver starts moving in a massive way, unless you want to use 4 18" pr's. That's right 4 .
And say that you did use 4 PR's, well this then ends up getting the box so large to tune the PR's low like you would want to with this driver, that you might as well go ported. This brings in a whole other problem, which is that you really need a 10" port, or even larger on this driver. It will easily overload and compress an 8" port at high volumes. Mine is using a 10" based high flow port design and I still get some serious compression if it is really pushed near the tuning (pretty rare really but hey you do want to get every bit of performance you paid for right?). I wouldn't tune it any higher than 15hz and ideally around 10-12hz. Even in a 25cu ft box a 10" port is around 60" or longer to tune that low. This is why I ended up using a power port design. Even tuned to 11hz in a box that large it is in no danger of over excursion until 9.5hz and over 2500w.
Also you will need a big power amp to put on it as it will easily handle an EP2500. If going with a resonant system I recommend the Crown CE4000 which is what I use. It is just about right to where the amp and driver both run out of gas at the same time. If you went sealed I'd recommend a QSC PLX3402 or 3602, because the Crown rolls off below 10hz and the QSC's are flat till 5hz. Sealed is a much easier implementation with this driver and it will not disappoint in about 8cu ft with a real 3KW behind it. This is the way I'll be going with my other 4 XXX's.
The good news is that if it's done right it can come close to matching the performance of a pair of other high performance 18's in the HT range (<30hz) in a ported system half the size. If you use it sealed it is pretty much the same story. While other drivers are running out of excursion and compressing or damaging themselves trying to produce the really low stuff it will just happily belt it out. This is bandwidth uniformity. It won't compress the deepest bass until much higher levels than most drivers.
Sorry about being so long winded. I spent MONTHS formulating the ported design I went with and how to get the best performance out of that driver while it sat there unused. :coocoo: