WingNut, thanks for stopping by here darlin.... Glad to hear your adding extra units to your room... and its working out so well... I had a feeling you wouldn't be able to get by with just 2.
I have roughly the same size room, and decided to go sealed as well...
I decided on DIY sealed 18's though.... Starting with 2 to see how it plays out, and I still have a couple of 15's to add If I still need more...
crosiev;
That would not be a good combination buddy... porting introduces group delay, which by itself is forgivable, but combine delayed (ported) and non delayed (sealed) bass it's highly likely you're going to end up with less clarity than if you had chosen just one box model.
Subwoofers create sound waves with peaks and nulls. If the subs are identical they will reinforce each other making for much louder bass. When they are not identical the peaks and nulls will not match up. The way the peaks and nulls are misaligned, they will tend to degrade the SQ of the bass.