Here's a quick and easy retrofit job I just finished on an old HSU sub that I have owned for over a decade. The old sub was still working fine right to the very end, but I wanted to try a servo sub.
Last year I fitted in a 12" non-servo Rythmik driver into the vented sono tube, use it for a while, but was afraid I might over drive it. So this time decided to go 15" sealed.
First I fitted a 1x2 brace across the sub, for a center point to cut out a larger hole. BTW, my jasper jig was too small for the larger holes, so I cheaped out and picked up a Circle/Edge Guide from Lowes...can't recommend this attachment tool, was very sloppy (1/16" play) and cheap. Almost disposable.
Since I was fitting all the new flanges and spacers inside the original cabinet, I cut all the pieces in halves. I added 1/16" to the speaker cut out measurements, then after the saw cuts, they were "close enough". By adding two layers of 3/4" mdf to the topside, along with the 3/4" mounting flange pieces, the sono tube is now right at 3 cubic feet (accounting for driver area). Used 2" deck screws where I couldn't get clamps to hold the glued pieces together.
Brian of Rythmik even supplied some 1" polyfil and driver gasket with the DS1500 kit, and was plenty for what I needed. Used 3m spray glue to stick the polyfil to the walls. Since the servo amp was to be mounted in a separate enclosure, I used two of the Cardas Patented binding posts (my favs), mounted on a small piece of 1/2" mdf, for the driver and sensing coil connections. I was able to reuse the original HSU spiked legs, since they were the required 2 1/2" long. I used #10 x 1 3/4" allen head bolts, lock and flat washers to secure the driver to the installed T-nuts, less chance of pokin the driver surround with a screwdriver.
For the amp enclosure, I picked up an electrical box from a local supplier, and then added some aluminum angle and flat bar to "make it work". Installed Cardas posts, same as on sub. Turned out fine, but in hindsight, it would of been easier (and cheaper) to build the box out of MDF. I am using 12/4 bi-wiring speaker cabling between the amp and sub.
Just got it going tonight, and am very impressed. No measurements yet, but I had to pull out the Masters and Commanders DVD...awesome! Thanks to Brian Ding of Rythmik, he was as helpful as possible. I recommend the Rythmik kits to anyone (like me) who is a diy newbie.