I poked around to see if I could find this specific question already, but no. My thought is this, I've got 6 Electro-voice SP12-B's (12" full range, highish Qt, very efficent). I'm using a pair on OB right now, really nice sound! Highly recommend this vintage speaker. Now we all know that below a particular freqency (in my case it seems to be about 200hz), the bass falls off at 6db per octave (right?). So if I add a 2nd speaker to the OB, and low pass to it (1st order) to start rolling on at 200hz, am I covered to another octave? And so on... 3 on a side would get me down even further, each coming on to support the sagging bass of the one above it. The only reason I'm wondering is because I have the additional speakers, and it seems like a neat way to maintain a simple crossover, and avoid an augmetted bass driver.