i haven't read all of the posts...
but if you've built the insert EXACTLY like the plans, it means that if you set it as low as possible, only about 2" of the port would be unobstructed. i have mine tuned like that, loaded with a cheap 12" and it goes down to about 35hz in-home.
sealing the insert really makes a diffrence.
i was extremely upset after i've built my db-10, during tuning. the box sounded like crap. i sealed it up real good and locked it in place with 4 drywall screws on each side. the sound tightened and it got lower.
what i've noticed with db-10 is that the more rough edges you round, the smoother the box sounds.
i haven't had time or patience to play with the db-12. i like the db-10 a lot more.

[quote author=trashfire  link=1142126549/15#17 date=1142259190]Speaking of the insert, I'm looking at building a DB12 of my own here very soon.  I'm baffled (pun..) by the insert in the plans.  For the side view, which way is it facing, left or right?  I've stared at them for 15 minutes and studied the picture at the bottom but can't quite figure out the portion after the cutout behind the woofer.  The half wall of sorts is throwing me off.  Do the sides go all the way down or do you trim them short?  The picture isn't clear enough to zoom in on and get an idea of what I'm supposed to build.

If someone has a picture from their build of the butt end of the insert, I'd be most appreciative.  

Thanks [/quote]

they extend all the way down on 3 sides and the fourth side is removed to allow air to flow.

It definately requires a minute to look and figure out what is going on, but I had no problems putting it together.  I put together a cut sheet and intend to post it if anyone thinks it is relevant.  Just notes right now but I can easily type it up.

Ah right, good point.  Scratch that.

Yeah that would probably work.  I won't be much help until this weekend though.  I am working in Baltimore this week and the plans are in my shop in PA.

On it's way.  Thank you very much.

???