[Owen Bartley]

I think there are a lot of variables that you just can't account for. Maybe the displacement of the driver is a little more or less than stated, maybe your bracing displaces more or less, or the port. Maybe there's some cabinet flex, a bit too much or too little stuffing. Maybe the design software is off by a 3rd decimal place somewhere, or is subject to rounding inconsistencies. Maybe th atmospheric pressure where you are is different than where the software and drivers were developed, and that accounts for a small difference. I think if you're that close, you've done a pretty great job, and probably the only guys who are hitting their exact tune without a little luck are the manufacturers who can use some trial and error to dial things in before mass manufacturing.

In any case, you've got yourself an amazing sub, soon to have a twin(!), and I think you did a great job to come very close to your calculated tuning frequency.