I recently bought a RE SX 15" and had David make it a Dual 4 ohm model for me. The reason I did this is because I have an MTX 81000D and it is not 1 ohm stable (as is heehee). So I am able to give it up to 1225 watts rms at 12.5 volts.
I put the sub in a 5.5 cuft before dispacement (5.1 after) and it is tuned to 35 hz. The box is so big that it fits INTO my trunk but won't come out.
I tell you that around a ~35hz test tone, this thing is an SPL MONSTER. WinISD says that it will peak at 38.15hz in my enclosure. The SQ far exceeds any sub I personally have owned but I have heard a little better out of pure SQ style woofers.
It is rated at 1000rms, but I have heard that it can easily take 1300 with no problems. The efficiency rating was also very high for a 15" woofer ~91.
The best two songs I've heard so far on this sub are: Master P - Pass Me the Green and Three 6 Mafia - Late Nite Tip
Master P's song hit really low with authority which made me want to leave the car ASAP. Late Nite Tip has what seems like the perfect mix of SQ and SPL.
I paid $300 shipped & modded for this sub.
Space needed: 6/10
Frequency range: 8/10 (hits almost all freq's for a 15")