I built a pair of h-frames several years ago that used Eminence Alpha 15a's and fed them a little over 250wpc with a Soundcraftsmen amp. In a 20x23 room playing on their own they sounded fantastic down to the high-30's, but didn't have much authority any lower than that and lost composure when SPL's started coming up above a casual listening level. When augmented with a pair of DIY sealed subwoofers using 12" Dayton Titanic drivers (positioned on the back wall and with DRC), the bottom of the first octave got filled in nicely and created a solid, robust, fast and musical low end. However, I didn't have any way to high pass the Alpha 15a's so they continued to be the limiting factor when I wanted to push the volume up.
The 15a's are long since gone, but I'm wanting to build X-Statiks...and later down the road NX-Oticas...and am wondering if I could recreate the OB sub/sealed sub scenario I had before, but instead use the 12" OB servo subs (one per side) with a goal of being able to play at higher output levels without any of the issues I had with the 15a's. Or, in a room the size of mine, will I need to go with two per side AND the DIY sealed subs if I want to achieve effortless and authoritative reproduction of low end down deep into the 20's at higher volume levels (say, up to the mid 90db range)?