I built a box to go under the back seat of an ext. cab f150. The box has 2 pioneer 10's in it now running on 300w rms a piece. I'm wanting to build another box for 2 more 10's that kinda looks like a center console for the middle of the rear bench seat and get another amp just like the one I have so I'll have 4 10's all on 300w rms. The box I already have has about .55 cu feet per sub and is sealed. When I build the other box it will also be sealed but my question is does the airspace need to be close to the same as the other box? Thanks for any help.