Here is my build thread for the Maelstrom 21. I'll try to provide enough quality pics during my build for you.
I'm using Kevin's Maelstrom 21"er with the passive radiator design. I normally don't like building a passive radiator sub with a Qts over .4, but it is so close, I won't have a problem.
Here's the deal....23" x 23" x 60"; 13 cubes and 15.5 hz box tuning. With the typical passive radiator design there is more of a roll off but at this already low box tuning, I'll have more than plenty of bass. I needed the height to match my main speaker's height and get the cabinet volume I need. Better WAF here.
I just picked up the pallet of materials from my mill. My construction material is 1.25" mdf. It looked like I had ten bags of concrete in my truck going down the road. In the roll of plastic, I've got two sheets of Pionite black slate laminate to match all of my other speakers.
Cabinet resonance with this thick material; I don't think so. Moving it? Now that's another challenge.
Just got back from Houston with the materials so here is the first build pic: