Looks like one of these - Link
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Looks like one of these - Link
Your theory about 'not compressing the air so much' is wrong.
That combination would still have acted as a Helmholtz resonator, just completely out of tune with the rest of the components, unless you were extremely lucky!
But yes, ported cabintets are good all-rounders, offering good efficiency and relatively light-weight construction. (As compared to a horn or bandpass.)
They are good subs
WinISD is only a tool to help you.... there are 10000 things that will effect how a driver & speaker cabinet work together / or not.
b&c have some great yet simple designs on there website which are free :) They have also done most the work for you as there are cut sheets available to download and there tell you what driver(s) do & don't work.
Tim
I prefer to use Bass Box Pro. Much better program in my personal opinion.
If you really want to go in depth check this out : http://www.voidaudio.com/news/news_item.asp?NewsID=38