Ok... let me give you some background:

I had two JL Audio 12w7 subwoofers in my TT with the FocalUtopia front and rear components. The JL's took up way too much space so I pulled them out to redesign my setup with something much smaller (thinner, less airspace commitment). Well I had not found a subwoofer that fit my taste so I figured I would wait for next year's line-up and see if any of the companies brought some better slimline shallowmount subs to the market. In the mean time, I decided to upgrade my rear midrange focals with some 6½" CDT ES6+ Midbass woofers for rear channel midbass. This would accomplish two things. It would satisfy my midbass needs much better than a focal 6½" and it would also provide enough bass-tone until I could choose a subwoofer. Here's a picture of the CDT Mid-Bass speakers I purchased:


Cone view


As you can see... these things are HUGE. After installing these speakers in the rear panels of my TT, I realized that they are so deep that the back of the driver grounds out on the car's frame. Additionally, not only does the back touch the frame... but the cone hits the rear backseat panel every time the bass hits. Obviously this is no good. The speaker is so deep that it hits on the front and rear of the driver.
So now I am trying to figure out how this speaker is suppoed to be mounted. the sheet that came with this speaker actually has enclosure dimensions on it. Is this midrange speaker ACTUALLY intended to be mounted in a box?!
This evening I reinstalled the Focals in the rear and tomorrow's project is to build a box for these two 6½" mids. -sigh- It's a damn good thing these speakers sound incredible or I would just take them back. However, they DO sound incredible.... they have the bass output of a 6x9 or an 8" sub and still maintain the midrange tones with that bass.
*Update* I finally decided on a subwoofer. I originally was looking for an Illusion Audio Cd10i but for the life of me I just cannot find a way to buy them. Their site shows everything except how/where to purchase the product. I decided to go with a Sound Splinter Ignition 10" instead.

Does anyone have any idea how to build a "vented" enclosure for a 6½" woofer? Airspace requirement is .5cf. It's .3cf for a sealed enclosure.

If someone has a link to an enclosure calculator... please help me out. This is a little out of my realm of expertise.

 

Considering that you had 2 12w7's I dont think that you are too serious about SQ, but if you want a small box that sounds good, check out JL W5 thin line subs. They are less than 3 inches deep and only need less than .75 cf per woofer. Apperently, they sound inbetween a w3 and a w6 according to my JL rep. Unfortunately, they arent out yet but were supposed to ship this year.
And for the record I have a D-900 screen h701 processor, 3 JLslash amps, and Alpine F17c components all around including the center channel just to let you know where im coming from.