Well, on closer measurement this weekend, using my Rives disc that is recorded to take into account the problems with the RS SPL Meter, I find that my open baffles get down to 32.5hz with strong results (using a 15" Parts Express IB on the bottom w/seperate amp). But what I did find that was interesting is a big hole (-10 db or so) around 80 to 100hz. This may be related to crossover and/or phase, I'll have to look into that. I suppose it may also have to do with the spacing of the two drivers (the FR and the sub) on the baffle.