Do a google search for "detuned cabinets". These things use 1 port per speaker, with the port area equalling the speaker area. A couple of sites have dimension specs for the cabinets, construction techniques, etc. I use two for my bass, one with 2x10", one with 1x18". Made 'em out of 3/4 plywood and 2x2s. They sound really good. You might think, "Why don't you just fill the other two holes with speakers and get twice the sound?" The sites explain the physics of the concept, so my uneducated self won't try to.All I know is that my 2x10 is louder, and sounds better, than commercially available 4x10 cabinets that I've tried. You can see some pics and hear music samples at my band's myspace page:
www.myspace.com/thetransmissions.
As for construction tips, mine is: measure twice, cut once...