I have an 18" Atomic APX and am about to build the box. Atomic reccommends 6 cubes at 32hz. with 5000rms. Im doing a wall thats about 10 cubes at 32hz. With the extra cubes how much power should I run to it?

I would only put 2,500 on it just to be safe. How much port area do you plan on using?

Lookin like 147.5 on the port area. Thats from 12.8^3 gross and that brings it down to about 10.3 ^3 - sub and bracing. The problem is I really have 26.95^3 to fill. I guess I can do a 2nd sub but I dont really want to. Can I just make a stupid monstrous ported box for my 1 18 and just not give it too much power? Or is that not going to work?

well, you would normally lower power requirements when a larger box is built and this is strictly due to mechanical reasons.

If the mechanical limit didn't come into effect, then you could still run 5000w... well u still can depending on what this install is for.

If this is for daily driving ONLY, then i would recommend(if u already have the amp), then i would wire the sub in series and be done with it.

If this is for both music and comp, i would extend all runs of terminal wire out of the box so u can wire in parallel or series whenever u need to.

If using for comp, make interchangeable port and keep internal volume as large as possible, tune port very close if not actually at your peak note to restrict mechanical movement.

If you do not already have an amp and it's only for music, then drop power like said above or add another sub.

Its for daily! So can I just do a 20^3 box for my 1 18 and lower my power? I do not have an amp yet

u can but it's gonna almost be like runnin free air... that and a HUGE group delay... almost everything that would come out of that box would sound "muddy" as if all the bass notes were soft and blended with each other.

I would seriously make it smaller or buy another one.