big 3 and enclosure plans

the battery in my car rests under the back seat. no i didnt put it there it came like that from the factory. the battery positive is split, one wire goes to a fuse box right next to the battery, the other wire goes to another fuse box under the hood. the fuse box under the hood has the alt pos wire connected to it. so am i correct in assuming that is the wire i should upgrade or should i upgrade both wires to each fuse box? i already have the batt neg to chassis replaced with 0 guage as well as the engine ground to chassis (and by the way the engine ground to chassis was not a flat braided uninsulated wire...for anyone who is working on a 2000 pontiac bonneville).


ive also got another question. ive got in my possession a jl audio 12w7-3. the specs say build a box that is 1.75 cu.ft. with a port that is 24 inches long 14 inches high and 1.75 inches wide. 1.75 cu ft.!?!?! does this seem a little small? i went ahead and designed a box that will fit in the trunk that is exactly 1.74 cu ft. after the port and driver displacement is considered but that .01 difference shouldnt be that significant should it? also instead of adding internal bracing to the enclosure could i just make the walls 1.5 inches thick (.75 inch mdf, 2 layers = 1.5 inches)and still get good results?   thoughts, suggestions???

Doubling all the walls will make a sturdy and very heavy box.  .01 cu ft is impossible to measure in this type of situation, so don't consider it detrimental to your plan.  And I would upgrade all the wiring.

You're going to get a +4db bump at 50 Hz with that vent design (tuning at 36+ Hz)...and a very steep rolloff.  Are you sure you want to go vented with this sub?  That box at the gross size you have it now would be great as a sealed alignment.  Qtc would be at about  .74 and sound very musical.  But I guess you chose the vented alignment because you want it to be extra loud?  There will likely be some port noise that will contribute to that, as well.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

i do prefer a ported box because they give that extra "oomph", but in this case i would rather it sound good rather than being extremely loud.   the only time i got to listen to a w7 was in the sound room and i believe they had the sub in a ported box, but im not sure. so, you are suggesting a sealed enclosure at 1.75 cu. ft.? back to the drawing board! :-) and since it will be sealed i could give it more power to make up for the efficiency loss... thanks stevdart for the input!!

Give it a shot in that box.  1.75 cu ft is fine but I was figuring on the extra dimensions you had to add for the port, which made it a bit bigger (I used 1.85 cu ft to model it).  You've got a lot of play with that driver.  WinISD shows me an enormous difference in sound quality between sealed and vented.

jl_w7_sealed_vs_vented.jpg

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

man, thanks a lot for those models! i don't have a pc at home, just the one here at work, so i cant model the sub myself. i really appreciate the pic! if its not too much to ask, is there a ported box that you could model that would give me good sound quality and dB? i am just looking at all the options i have because i want this woofer to shine!

First question is always, "How much space can you dedicate to the sub?"

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

I've got enough space for a 4.5 cu ft. box

I looked at several scenarios with that woofer.  Biggest problem in going vented is the time delay of port vs. driver, especially in larger enclosures with low tuning ( in the 20's).  That led to a smaller enclosure with tuning in the 30's as the only vented alternative, IMO.  The best vented model looks to be 2.5 cu ft net with a slotted port of 36 square inches and a rather lengthy 38 inches long, but you can build that into the box with one turn and it will help with bracing.

With an EBP of 52, this woofer wants a sealed box.  Venting it necessitates that the port is long, and to keep port noise out of the picture altogether you need to have a large port opening similar to what I modeled using a 3 X 12 slot.  Also, I used 700 watts as power reference for this model.

No overexcursion exists until it gets to 20 Hz, so you shouldn't have to worry about a subsonic filter if you decide to use vented.  Group delay is acceptable (as far as vented enclosures go) with the model I described above.

SPL at 40 Hz should be considerably higher with the vented box, although sound quality suffers due to the group delay.  This driver looks like a nice SQ model in a 2.3 cu ft sealed box, giving it a modeled Qtc of .703.  I believe, if it were me, I'd build the easy sealed enclosure, install and tune the system, and give it a test ride.  Only if I felt it was lacking in SPL would I build the alternative vented box.  But if you have the time and resources building both might be a good experiment to consider.

cone_excursion.jpg

group_delay.jpg

spl.jpg

transfer_function.jpg

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Thanks a billion stevdart! i cant explain how much this helps.