big 3 and enclosure plans

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.

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.

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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.

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group_delay.jpg

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