A while back I started a thread about a pretty large pair of sonosubs I will be building. I'm going to start by only building one. 28" diameter, 70" tall, the new 18" avalanche driver that ascendant audio will be coming out with (I'll have to redo my calculations), 450 watts, tuned to 14hz, with a very thin layer of batting inside, and then just when I thought I was sure about the ports I'm second guessing myself again. I originally was going to go with 2, 6" ports, close to 3' in length, spaced 5.5" from the sides with 5" between each other. I was going to go this way because I thought I would have to use pvc pipe. But when I started looking around to find sonotube, I found there is a place very close to me that sells it in diameters from 6" to 56". So now I am thinking about using a single 10" port, about 44.25" in length. This dramatically reduces port velocity from what used to be about a 23m/s peak to about a 14.8m/s peak at the highest point. The material for the 10" port will also take up less internal volume than the 2, 6" ports. Are there any down sides to going with such a big port? The end caps will be made from 3 layers of 3/4" mdf, two inside, one outside. I'm thinking of using some of the extra circles that will be cut out for the driver space on the bottom layers as more supports for the 10" port on the inside of the top cap. What I mean by that is that instead of only giving a 44.25" long port 2.25" to be caulked to the top cap, I can give it 4.5" at the expense of loosing a few cubic inches of internal volume. I'll finish that off with a 12" parts express steel mesh speaker grill. Any other potential down sides to doing this? I've noticed that many people have problems when cutting the mdf for the end caps, and I don't have a router, so I am taking my mdf to a woodshop to have all the pieces cut for me by a cnc router. I would think that would eliminate most of the problems right there. I am going to take the leftover 4" piece of sonotube with me to make measurements and make sure the caps fit while I am there. For the legs, I notice that most people use 3 to keep it balanced easier. I was thinking of using 4 to give this heavy sub more support. Also, most people use legs only about 6" long, I'm thinking of going 12" to give the driver a lot of breathing room. For baseplate I'm thinking of using 2 layers of 1/2" plywood that I already have. I'll be using small rubber pads on the bottom of the base plate and then use a couple layers of rigid foam insulation under that to isolate the sub from my floor. Any forseeable problems? In terms of assembly, I will be using t nuts for the driver with a ring of weatherstrip, wood glue and screws to connect layers of the caps, silicone caulk for sealing the caps in place along with a few small nails around the sides of the sonotube, weatherstrip around the grill mounting, spray adhesive for the batting on the inside and around the port, and silicone caulk and a few small nails for attaching the port to the top cap. Finally, with the binding posts, the bottom cap will be too thick to go through, so I'm thinking of going through the lower side of the sonotube, just above where the end cap reaches inside. I'm going to space them a couple inches apart and go around the inside and outside contact points with hot glue to ensure the sub stays air tight. Aside from those questions, does anybody else have any suggestions or tips that might save me some headaches during the building of these subs? Any and all comments are appreciated. This will be my first time building a subwoofer.