I just threw LAB 12's data into liniarteams calculator. An optium 4th order BP design gives 49 liters for back, 35 liters for front ( giving a total internal volume at about 3 cu.ft.), tuned at 41 Hz. -3 dB would be ~25 and 70 Hz. I use a BP of almost similar size, and I'm very satisfied with it - mine 'only' have a 10" Peerless unit, but is more than enough for my needs. I haven't ever even come close to playing it at the loudest...