ported and sealed enclosure

I know what you are thinking, another newb trying to invent his own type of enclosure.  But I am not actually planning on doing this, it is more for information sake.

I was debating with someone else why a ported enclosure along with a sealed enclosure would not work well.  We were arguing whether if you had, say 3 subs.  Two of the subs were in a sealed enclosure while the other was in a ported enclosure.  I said that this was not a good idea because you would likely have cancellation, among other things.  He said that it would give you good output while having low-end extension.

Basically, I really think this is a bad idea but I didn't know what would actually happen if you did this.  Does anyone know what the end result would be?  I need info to be able to argue back and make my point.

P.S. - The subs are the same model for all 3.

Here are some points to make in favor of your argument, killa (and I'm reasoning that by arguing which is "better", you are referrring to final sound quality):

• A sub will work best in one type of enclosure over the other.  If it specs out best for vented, use vented.  If the parameters favor sealed, use sealed.
• Some subs are borderline and can be used in either type of enclosure, although one of the topologies will sound best to the particular person who is going to own and listen to it.  Each type will have a particularly different sound even when all subs are the same model.
• Never use two or more different models of subs.  That's covered in Subs 101.  That would be much worse yet.
• Two types of enclosures in the system will, instead of providing "the best of both worlds", only work to muddy the quality of the final output.  There is inherently a difference in dropoff steepness between the two topologies, which, for one, will deteriorate the low end output when played together.  There will also be a difference in delay at the low frequencies.  The sealed sub will "hit", or attack, at a slightly different time than the vented sub will.  Although either way, if used alone, is fine...the combination of both will help to create a confused attack.  That is called "muddy".  Thus, phase issues cannot be completely solved unless he's a genius with a lot of expensive equipment...maybe.
• Attempts to move the enclosures around in the vehicle to try to solve one problem will only serve to magnify another acoustic anomaly.  That's one reason why using all subs of same model and enclosure type, and facing the same direction, allows for best overall accuracy (with the rest of the system) when experimenting with placement and direction.
• And finally, this very old and worn out  "best of both worlds" argument is proffered only by rookies.  Your opponent in this debate certainly wouldn't want to fall into that category, would he?  ;)