They will be used for HT, they were designed ported for low bass extension which will NOT be used,since they will be crossed at 80hz with Subs,.. so i might as well designe them sealed to get benifits, the sealed variant will have more accurate, phase coherent bass.The vented original design is only 24 liters net, you're not going to be able to fit the drivers, mid tunnel, braces etc in a cab much smaller. Why modify a great design?
If you don't want them ported, exclude the port.
This is one of the rare designs where all box dimensions have an affect on sound, due to the presence of a mid tunnel that's dependent on depth. You can't reduce height - no room - and width is critical when BSC is applied. The tunnel takes out your last degree of freedon, this side of dense fill, eg. bricks.
That said, Unibox predicts you'll be in a very good spot at 24L - fill will take you from box Q of 0.74 (empty) to 0.66 (heavy fill), allowing you to tune your bass response around the optimally flat Q of 0.707.
The downside is that 10W at 40Hz will push the driver past Xmax... at 30W it's 70Hz. This most certainly will work in your HT with normal 80Hz cross to subwoofer. I don't see much more to ask for...
I dont have Excel2000 on my home computer ,only at work ,but i took a picture ,you cant see the F3 but it is at 52hz for a (20L) sealed box . If i remember correctly (24L) F3 was around 51hz !If your results are at odds with someone else's, post them and let us take a look. It's not hard to mis-enter T/S parameters... just did that today, in fact. Having built RS180-base vented MTMs, I don't think I'm far off, but I used 8 ohm versions so data entry errors for the 4 ohm are possible in my analysis, too.
Yes that is excactly what i get !"Print Screen" and "Paste" are your friend...
Using the same spec sheet data, I get the same as you, to within the least significant digit. I get 52.97Hz as an F3. 24L is 51.5Hz. This is well beyond "close enough."