Could you please explain this? Reason I ask is because I've seen quite a few builds with people using using sealed subs and getting flat responses well into single digits. I realize all rooms are different, which is why I'm not opposed to adding more subs to increase output. But I'm thinking 4 Q's (or 2 of the SP4's as you suggested) might be a good start. I guess I'll sort of revise my previous comments. Flat to single digits is "possible".....but with the inherent roll off characteristics of a sealed enclosure and displacement limitations it's not as simple as tossing subs in a sealed enclosure, sticking them in your room and calling it good. It would likely require some substantial EQ work and probably some luck with the room gain. I'm not familiar with the SMS-1 to know what it does, so I honestly don't know what EQ power you have available to you. But the main problem with trying to dig that deep sealed (aside from the inherent frequency response of the enclosure) is that sealed enclosures rely entirely on displacement for generating output. For every one octave decrease in frequency you need to quadruple displacement to maintain the same SPL. So if you are at 110db at 30hz, you would need quadruple displacement to have the same SPL at 15hz, then quadruple it again to have the same SPL at 7.5hz. So between 30hz and 8hz you would need a 16x increase in displacement to maintain the same SPL. This ofcourse doesn't consider the effects of room gain, which will help some. But my guess would be that the people getting flat to single digits with sealed enclosures end up having to reduce the output of the system at higher frequencies to keep the frequency response itself flat that low in frequency.......or they have a significant amount of room gain. Not to mention the drivers are probably operating at (or possibly over) Xmax at those very low frequencies, which increases distortion. Obviously you aren't going to hear the 2nd harmonic with a sub 15hz frequency, but possibly the 3rd, 4th and 5th harmonics are going to start reaching into the audible frequency spectrum which may color the sound if the distortion is severe enough. On the other hand with a LLT you are minimizing excursion at those very low frequencies which reduces driver generated distortion. I'll readily admit HT isn't my forte, I'm just extending basic audio principles over to that realm. My opinion would be an LLT would be a more efficient and better performing means to the end you are trying to achieve.