I asked a similar question a few weeks back. there is'nt any diff in output meaning it's not going to sound louder or anything. However, someone else posted that you could actually hear the mechanical noise of the motor.
it has the same effect on sealed enclosures as it would with ported enclosures. just not to the same degree. the volume is going to change because you no longer have the basket and motor structure to account for inside the box. all of that is now on the exterior. so if you construct your box with inverting the subs in mind, then the subs will sound the same as they would if the box was constructed taking into account the displacement of the driver. it's still a matter of interior volume (as the link states).
volume as in the amount of 3-dimensional space occupied by an object. not the magnitude of sound.
if you fill the bath tub to the top and somehow manage to hover on top of the water, then it is likely not to spill over. but if you decide to sit in the water, it will spill over onto the floor because you did not take into account the displacement of your body. the same goes for the "body" of the sub. that's about as simple as i can make it.
I like Joe's answer better, I won't hear any audible difference. I have a very simple dual 12" box. Simple as can be for that matter. The ONLY question I have about this, is where do I put the subs terminal wires...Basically, how do I run them from outside to inside...