Perhaps a completely stupid question, but is there a limiting factor for the size of the horn slot? I'm doing a bit of thinking outside of the box, and wondering if it might be possible to re-orient the horn to the long side of the box, leaving the port where it is. Granted, the box construction gets "interesting", but it's a bit of thought experiment.
Could the fact that the Full Marty is a relatively simple ported box be the reason why the Kraken seemingly worked so well in it. It would also explain why the Kraken would be a lousy fit for the Dev.
Putting the vent on the back wall assuming the cabinet lays on the side and having that vent exit what is typically the bottom of the cabinet? I have considered doing that. I am sitting back waiting for data before I push too much more out in the way of designs. If you go on DB and look at the review of the X21 you can see how much a vent can compress output. The answer is a lot. That problem only gets worse with woofers like the NSW that can really drive hard into a BR chamber. That review was with a 21DS115 which is a good woofer, but the NSW is more capable.Oh, I just checked GSG's website. They're listing the NSW6021 for $749
BR is not the most complex alignment which could help the Kraken. The standard and lossy inductance was showing roll off fairly early in the response. Ideally if the Kraken gets a DB review Josh will post the semi inductance figures which are going to be a lot more accurate. If Le was down to 4.0mH the roll off is pushed back and it models well in a high order cabinet, like a Devastator. Without a review pushing the Kraken through its paces it has question marks and does not simulate in a well behaved manner. I was a kid on Christmas day when I opened up the webpage, until I read the Le value in the spec sheet. I ran the sims and it did not behave the way a high performance 21" should. That is unusual for Dayton.
Do not go off the posted pricing for the NSW, GSG does offer discounts. Shipping is starting to go up with fuel prices, so it might not be as good as it was.