Thanks for the replies, guys.
I guess I really have a lot to learn about modeling. The tutorial I only used ported boxes as an example and seemed to indicate that I should play around with box size, tuning frequency, port diameter, and port length in order to flatten the frequency response of the sub as much as possible, or at least that is how I interpreted the instructions. And I found that it was fairly easy to juggle those parameters in order to achieve results that looked pretty flat on the transfer function magnitude graph.
But with sealed boxes, the only variable is box size since there is no port to affect frequency response otherwise. When I looked at the transfer function magnitude graph of the 2 drivers I own, I noticed that the sub starts to roll of around 200 hz, and F3 is around 65 hz. F10 is 28 hz, and at 20 hz the sub is down to -14 db. After playing around with ported enclosures, this looked pretty bad to me, but after the explanation from both of you, LTD02 and nograveconcern, I understand how the sealed design can be made to be flatter in room. Not considering room gain, I can improve the response significantly by adding a parametric EQ at 20 hz with 12 db gain and a Q of 1.5. 12 db is a pretty drastic increase in gain, though, and I assume that it would cause other complications, like running out of power, but I don' t know due to lack of experience and knowledge. Chances are that with the room gain I would not need such a high boost at 20 hz either.
Is there any general rule of thumb or common policy used when adding DSP to sealed boxes?
Thanks again for your patience as I go through this learning process.