It is a slow day at work, so I started working up some math on a 2nd sub for my theater.

My first sub is a SVS 20-39PCi as seen the OLD photo at the bottom of this with my now almost 14 year old daughter who was almost 6 at the time of the photo.

Anyway, after geting some assistance elsewhere on the idea of "replicating" the SVS so that I have 2 closely matched subs in the theater, I was given the following design based off of cubic feet, the driver, amp, etc.

Use either a cement form (Sonotube) and make a "sonosub" that looks identical (cost would run about $50 for the tube and endcap material, not including some sort of covering, port grate, etc) or a rectangular sub cabinet out of .75" MDF which would cost me $35 for a sheet of MDF and I could have the home improvement store make some of the big cuts to save time.

So I am leaning towards the rectangle sub enclosure because it will be easier to get the material, and also easier to mount the amp since it isn't going onto a curved surface (plus a few other reasons).

NOW to the question. With the rectangular sub build, the bottom plate would be either tacked on to the end with a piece that is 16.75" x 16.75" with an interior box opening of 15.25" x 15.25" (I could also put the end cap "inside" the opening using just a 15.25" x 15.25" piece and make the whole thing a little taller to compensate for the volume lost).
Would an effective opening of 15.25" x 15.25" be enough material for a 12" woofer to mount to?

Again, this was a design that a couple of other DIY sub builders at AVS agreed would work (it was one of their plans), but it just dawned on me that I wonder if that is enough material...

The SVS is 16" in diameter and once taking out the .50" on the thickness of the tube, that comes out to about a 15" diameter circle for a bottom plate. So it SEEMS like it should be OK.

The woofer I am using is the popular Dayton Audio RSS315HF-4 and it lists the dimensions as: Overall diameter: 12-3/8", Cutout diameter: 11-1/8", Depth: 5-3/8".

I am not in a rush on this, but am just trying to gear up for my winter projects (I still need to get the crown molding and LED rope lights up in the theater, plus the star ceiling before I work on this). Thanks for any help, guideance, or reassurance.

2-M60s, VP180, 8-M3s, SVS 20-39PCi, DIY Sub, 8-Shakers, JVC RS45, Anthem MRX-1120