i just finished my DB12 and have a JLw3 in it. I was wondering where the insert sounded best when you tuned them. i know they will vary. but it's hard for me to tell where it sounds best. for mine it seems to be 2 or 3 inches below the top if the upside down v opening. but it seems that wouldn't take full advantage of the port opening cause half of it is blocked. is this about where yours sounded best? thanks  i will post some pics.

I have have an old Mach5 12" in the DB and I have the insert about 2" from the bottom. its in the trunk of a 93 civic. Its low solid and fast.
It was initially for my HT but MDF is not allowed in the house now so it went into my Sons civic. Way too nice of a build for the trunk of a car but oh well.
He has a single pair of Polk in the front ( boxing day sale) A garage sale pioneer ( 5 bucks)
a 350 Watt ok sub amp ( someone gave me).
$200 total cost, most of in in the DB. It rules and will move your hair and the bass tends to stay in the car. His friends have some nice cars and nice systems but guess what they like to ride around in . The overall SQ is outstanding and good luck getting close with a thousand $

last time I went for a ride with him, his friend asked if he could just run the bass and turn the full range off.
weird kids

I like the mach but it took a long time to loosen up. Can't say enough about the 12 DB. not fond of the 10 and I have built several just to see if it was my fault. Only had to build one DB12. built three 10's with several sub drivers and really never happy with any of them. Tried everything over about 5 years with them.

well, i just foolishly tore out my db12 about a year ago to make room in the back of my honda accord for baby strollers and such...

WHAT A HUGE MISTAKE, so i ripped up the box to get my 2 isobaric loaded 12's, i was gonna make a WO with the 12s for my living room...the WO box is just sitting in the garage collecting dust

anyway, I loaded my db with 2 12" cerwin vegas...the older better ones of course...the insert was just an inch or so above the top portion of the port...it was AMAZING!! although it wasnt as punchy as 10's with reproducing the kick drum sound...it still was incredible.

so my recommendation to you is to load 2 woofers...thats gonna increase your accuracy tremendously!

since then, I just decided to take 2 10" infinity 10.1 perfects and build a double db10. I just finished it Thursday...its scarry how low a frequency these 10's can go, almost like the 12's...here are some pics:

in the car