Box type for two 18s getting windy?

[SlammedRides]

*EDIT* As stingray72 pointed out, for a windy setup, two 18s isn't really the play over four 15s, and as such, I'll be doing more research on 15s instead. I'd still like input about the type of box to use for four 15s for moving air, but you can ignore the comments about 18s. Thanks! 

 

*ORIGINAL*

   Hey all, looking for some input. I have a 1991 Isuzu spacecab walled with 4 15"s and I'm looking to switch to two 18"s and tune them low - around 28hz or 30hz. I've never made a box before, so I reached out to some builders in my area and was quoted $1,500 in labor for a wall or a grand starting for a box for the two 18"s and that was not including materials. I'm not one to cheap out, but $1,500 seemed like a price point where I'd be willing to learn and do it myself. My truck has roughly (no exact numbers because I've got a wall in there now and it's been there for almost 20 years) 52*34*22 inches available for a box. Any advice as to what type of box and where to learn about building it? I've got the time to do it right. Subs I'm looking at are Skar ZVX 18 (5.25ft³ airspace) or FI NEO 3.5 (5ft³-8ft³). Thanks for being great here on these forums 💯

[stingray72]

You have 706 square inches of cone area with the four 15's and two 18's would only be 508 square inches and your measurements with a double baffle gives you 16.70 cubic feet of space.  You would be better buying new 15's with good xmax capabilities to get the windy outcome.

[SlammedRides]

You've got a really good point. I've been looking at so many things I overlooked cone area. Back to the drawing board 😂 thanks