What would be the best htz to tune to for 2 dc audio level 4 xl 18

 

I just modeled it at 5.5cf3 and it looks decent between 28hz and 30hz

if it was me I would tune it low with lots of port area
5.5cf3 plus displacements .......... 92sq inches of port 49.11" long
this gives a port velocity of 6.59%

don't skimp on the port area ....
the enclosure will be large but it will be worth it

 

is that for 1 or two subs

 

that was for one