Last year I was wandering Menard's and came across a damaged sheet of 1" MDF. I bought it and decided to build some speaker boxes from it. I had some old speakers left over from a car audio project for a car that I no longer owned. I ended up buying some 1/2" MDF for partitioning inner chambers as well. These suckers weigh about 80 lbs each.
I used 6.5" Blaupunkt speaker with built-in tweeters. Below is a 12" Sony subwoofer. The speakers actually have three sealed chambers in them. The bottom chamber has the 12" subwoofers with 12" passive radiators on the back. The top-front chamber has the 6.5" speakers with 6.5" passive radiators. The top-back chamber houses the crossover and the hole for the wire clips. I painted them with flat black chalk paint (figured it would show imperfections less).
They sound AWESOME. I'm so happy I'm considering buidling a custom center channel now with some leftover single speakers that I have laying around....