A butterworth Q of 0.7071 for that driver is over 13 cubic feet so thats where the large box confusion may come in... Here is whats happening. the driver has a highish Q and low sensitivity, in order to make more bass you need to put it in a smaller box and bring out the "ring" In other words, make it boomy just a bit. technically it will have much better "SQ" in a larger box, but a lot less SPL... take your pick. Lots of people associate SQ with SPL and the two are really married contrary to popular belief. In a sealed box, you can get a way with drastic differences in volume without much consequence on frequency response. In 5 cubic feet the driver has about a 1dB ring and it looks quite nice. You'll get about 1.5db more SPL across the board from 30Hz and up from the larger box, but its a higher Q alignment. IMO, I would go with the small box as RE suggests. The larger boxes will make more SPL below 30Hz… not very critical in car audio. A bessel alignment is 35 cubic feet sealed for this driver! If you want a low Q out of this driver, you're **** with an IB in a house. Forget the ultra deep SPL and go for a little ring. (~5 cubes)
Ported.... we'll now you're dancing with the boomy alignments. Because the Fs is low and Q is high, most of the recommend alignments are ported very deep and none start below 16 cubic feet. Its extremely hard to put this driver in a ported box and get a linear alignment... don't even try!
Anything in a small or large box tuning high will just sound boomy, it doest matter. What you have to do is accept this and tune lower and then just use that ring (high Q) to even out the response naturally. Here is what looks good.
16 cubic feet tuned to 16Hz. Oddly enough in this case, you’re actually not losing much SPL (save for boomy peaks) anywhere tuning low, what’s happening is the high Q down around 16Hz, balances out with the natural 16 feet active driver alignment and you tend to get a very linear response with just a tad bit of boost peaking right at ~23Hz, and it continues throughout the entire pass band. The driver also had good throw, at least 3" worth so tuning low will be OK from a BL and Suspension standpoint.
If you tune higher, it pushes this peak up in the response and in SPL and there is no saving it no matter what size box you have. Basically you will lose SQ !
Here is what I would do.
16cubes at 16Hz OR
5 cubes sealed
Not much else looks good for SQ.
9 cubes at 30Hz… if you want SQ, this is going to be horrible! 11dB peak and everything will sound like its 35Hz (boomy)
You could also make the box smaller while keeping the tuning low (16Hz), this wont make anyhing peak, but you'lll just lose low end SPL and it may be OK if you need to save space because there is not much content below 25Hz in music. No matter what keep tuning below 20Hz if you want SQ. Its not because you need deep bass, its because otherwise it will become very boomy for the upper bass!
8 cubic feet at 20Hz would be my absooulte limit. You're looking at 4dB peak (ring) right at ~32Hz.. see, you would not have guess that tuning at 20Hz would produce a peak at 32Hz... without modeling softare, you can go very wrong with a tricky driver like this one.
