2 Axis 12's in 2.8cf3 on 6k would be best.

 

Would a smaller port increase SPL versus a larger port?

Meaning the smaller port would have more air velocity, and therefore make the low notes feel more fierce opposed to the larger port that would have slower moving air?

 

maybe since you have 8 of the smaller ones, the velocity would be rougly the same.

 

I only have a slot port.

I meant, narrow port, short length.
Versus,
Wide port, long length.

 

How is your BTL not loud enough? Do you have vids? If you can't go past 3 cubes than you don't have many options. Can you put the box through the rear seat? Don't use a 15 unless it's in 4-5cf3.

 

I can get vids, what do you want a video of?

I just noticed that when I went from a smaller box @ 32Hz with less port area, to a larger box 28-30Hz with more port area, that it doesn't feel as intense (IE, mirrors move less), but it sounds alot deeper. Was wondering if I could maybe build another box that's large, tuned low with less port area and I would get the best of both.

Old box, 2.25 @ 32Hz, 35sqin of port.
New box, 2.9 @ 28-30Hz, 45sqin of port.
All before displacement.

 

2 DD 9510's on that amp in 3 cubes (48 sq.in. port area) @ 35hz pointing forewards and sealed off, I think would be better.