My first sealed box for my 2 Q15's was 4.4ft^3. It sounded perfect. Now I have 4 Q15's sealed in 8.6ft^3 (after displacement). It is a little less then half the doulbed volume of the dual sub box. I assumed that my roll off would be nearly identical to my first box, or my tuning would be slightly higher, but it is actually opposite. It peaks at 35hz +/- but rolls off quickly above 40hz, as if the box is too big. Could it be possibe that the specs need to be adjusted do to box size or the amount of subs used? Maybe because it is all a single chamber?

Because if this, I am considering doing a box that is about 10ft^3 with 4-5 4" round ports tuned to 34hz. That would technicaly give each sub 2.5ft^3. I am attempting to gain a few more db's without going to an all out SPL setup with SQ subs and without having to put a permenant wall, which I would need to do if I went to 12ft^3 like the actual specs require.

What do you guys think?

It's because they are all in a single chamber...

If you divided them you'd get your response curve back...

Ok, so I'm kinda of right then....I can put all four in a 9-10cube box single chamber and port it and I should be fine.