sub box math, am i doing it right?

my goal is to gain more low end frequency as right now I can kinda hear it but not at any volume. its like its empty sound if that makes since. secondly I'd like to be able to see my sub as right now it fires into the seat. I want this sub to blow my tool boxes around., just crazy amounts of bass to the SPL side of things with out loosing to much quality. this is why I bought a BL as opposed to a Q. I am open to installing 2 18 BL's so long as it takes up no more than 1/2 of the back seat for storage. Another question, I am thinking of removing the backseat of the truck and installing quarter inch plate to set the speaker on top of. Will this aid in the transfer of bass or does it not matter? 1 advantage of this either way is that it will give me about another 4 inches back and three inches down to install a larger box.

I ran your sub in WinISD and in 7.9 cuft vented at 31Hz you get a peak at 69Hz and the F3 is at 38Hz. The woofer has an Fs at 33Hz so it's never going to produce a lot of SPL at the lowest frequencies, it is more designed as a high SPL sub and works best between 70 and 100Hz. The Fi web site says it is rated for 1500 watts so I really can't recommend using more than that. By the way, to get good numbers in WinISD, try setting the power input at 500 watts or less. If you really want high output in the first octave of 20-40Hz, you'll likely need a different woofer. But the Fi is a really well-made machine and will give you great output in the most musical subwoofer range.Support the12volt.com

i was having such a hard time getting the specs into win isd, how did you end up getting yours to work? maybe i was trying to adhear to the fi's website specs to much? *shrug* here is what i came up with for a box, its port length is 18.5" at 7.92 cubic ft, tuned to 36.46. people seem to think that fi can take much more than 1500 so im going to upgrade to a 2500W amp and take it up untill i find its max and pull it back a bit, we shall see. when i ordered teh sub i got all the cooling and spider extras. the sub port would be pretty much at ear level, is that an issue? i am building this box as squar as i can get it so i can just rotate it to try different angles, top, bottom, front, and rear firing. modle of new box idea

larger image, i accidently pasted in the small one... i gotta read these rules and figure out why i cant edit at some point >.< large picture

Port at ear level? The port sound might dominate and you'll perceive the system much more like a one-note bandpass. I'd mount it with the port on the bottom. Also, with an enclosure that large I hope you have good bracing plans?Support the12volt.com

my thoughts were some angled pieces of .75 on the edges and such. ive read some people place cross members across from wide to side and build a basket to hold the sub magnet. do you think that is necessary for this one?

BRACE IT!!! Yes, ANY flex in the cabinet wall translates to output loss. The less flex you have, the more accurate your response will be, AND you'll get more output. You're thinking that "It's a vented cabinet, the walls can't flex as much as a sealed cabinet..." You're dead wrong there! The internal pressure gradients inside a vented cabinet can be as much as TWO TO FOUR TIMES AS MUCH as a sealed cabinet! A vented cabinet relies FAR more on proper bracing than does an equivalently aligned sealed box... Additionally, EVERY box calculator assumes a theoretical "lossless" wall. If you have vibrations, you have loss. If you're wondering what Dave considers the right amount of bracing is, check this out... You cannot overbrace a cabinet. Period.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

ncc74656 wrote: my thoughts were some angled pieces of .75 on the edges and such. ive read some people place cross members across from wide to side and build a basket to hold the sub magnet. do you think that is necessary for this one?

Oh yes, it is more than necessary, Please see Mr. Haemphyst's post above. :)Support the12volt.com

so if i add much more bracing than i had intended i will need to increase the box size to make up for the loss in cubic feet. from there i could also use double walled thickness so id have 1.5" on all sides. that sound good?

doubling the thickness of the box all around is nice to have but you would be better served by running strong pieces of wood between opposite walls to keep them from flexing. a double wall can still flex although it is very hard to make them flex. as far as my experience goes with big woofers and low tuning, bigger is usually better, this includes the port too. big slot port allows for the huge air flow you typically see in any "hair trick" video. the problem with big ports is that they need to be huge and long to keep a low tuning which in turn takes up valuable airspace and requires a much bigger box. it will help your port to round the edges to have slightly better air flow but over all not necessary inside the box.