Audioholics will be doing a review of the 4000 subs, I don't know which and to what extant exactly at this point. I know that if I do any reviews, they won't be until the spring, since it is too cold to test anything during winter on my end.
If you want to see what a dual sub can do against some other model, just take the measurements for a single unit and add 6 dB on all of the max output measurements, both burst and long-term testing. If you want to see what a triple sub configuration does, just add 9.5 dB. If you want to see a quad sub setup can do vs a single, just add 12 dB. For a five sub setup, add 14 dB.
Dual ULS-15 mk2s would be a very good system. Quad ULS-15 mks would be a beast. Adding 12 dB onto its CEA-2010 numbers makes for a monster system. Looking at something that could equal that, I checked data-bass for its top sealed subs. A quad ULS-15 mk2 system performs on par with a JTR Captivator S2 in deep bass, and exceeds it a bit in mid bass. It also costs about the same. Quad ULS-15 mk2s outperforms the Funk 21.0SW. It outperforms the Rockford Fosgate 19" $2.5k super driver on Ricci's 20 kW amp. It can even match the Stereo Integrity HS24 in a giant cab at all frequencies except from 16 Hz to 31 Hz, where the HS24 does have a significant advantage (not surprising since that range centers around that system's resonance).
