All good questions...You can download a few design options by clicking "project ideas" on the woofer page at the PE website, or you can just copy the Titanic MKIII cabinet dimensions and build it yourself. If you're really keen, you could hit the PE forum and ask for some advice...there's lots of people who ask this same question for other woofers, and people would be glad to help you choose dimensions.

I would think for your room the 12" would be more than enough, but for the price, fun factor, and extra performance, you could go all the way with the 15"...the difference is about 10 dB max volume output, double the power, and the ability to go below 20 Hz vs. about 22 Hz in room. The 15" goes below 20 Hz and is tight and accurate. Check the DIY forums, I think Sealed did a review on the 15" a few months back here.

There's alot of guys who've built that and compare it to $2000-$3000 servo models and the latest and greatest popular internet retailers prime models....even if it falls short a bit, the price is right. As I said, my PW-2200 is outperformed , enough to warrant selling it and replacing it with the 12" MKIII. The 15" would be a massive upgrade, so that's what I'm doing.

Here's my take...if you build the 12" and love it, but still feel like you need a bit more, you could end up driving yourself crazy wishing you went with the 15". If you build the 15" and still aren't happy, you just have unrealistic expectations for DIY sub in this price range.

I can't say the MKIII's are the best woofers or best kit out there because I haven't heard them all, but in the last 14 months I have yet to find anything that's received as much praise from the knowledgeable DIY community and non DIY-ers who took the plunge (myself included). I know there's lots of popular kits out there, but these seem to stand out. The next step up in kits will cost considerably more. The option exists to design your own cabinet and elect to use a port (or not) and just use the woofer and plate amp, but the Kit's design is tested and proven. Dayton makes awesome drivers for the money, great value and solid performance. Good reputation among DIY-ers too, which means you can probably sell the sub, or the parts used if you ever get ambitious and want something more.

The only downside is the 15" will require more space and money...she ain't small.
When were you thinking of starting it?