This suppressor design is meant to be attached to the chamber from the improved cannon as it uses the same interface. Thats what is great about the improved design, you can make any number of barrel/chamber combinations. I'll explain the physics of a supressor after I tell you how to build it.
A piece of PVC for the barrel, 3 feet in length, 2in diameter
A male threaded adapter, 2in
2 2-3in reducers
A piece of PVC for the "outer barrel", 2 feet in length, 3in diameter
A shitty towel, that is 1ftx2ft
A dril and .5in drill bit
A dremel tool with grinding bit, you'll understand what you need, but a dremel tool of some sort is the best thing, though you could do it with a file.
1. Glue one end of the male threaded adapter to the barrel.
2. Bevel the edge on the 2in side of both the reducers, this is so that they will slide down the barrel. Don't do its so they slide easily, make it so that they move but you have to give a good push.
3. Push one of the reducers onto the barrel, about a foot from the bottom (where the male threaded piece is).
4. Drill two lines of holes down the barrel, opposite each other. These should be about an inch to 2 inches apart.
5. Put the towel around the holes, so that it covers all/most of them. Put a couple pieces of duct tape on it, Nashua 398 is the shit.
6. Put the outer barrel around the towel, but make sure the towel stays in place. It takes a little bit of working. Shove this PVC into the reducer that is in place. Shove the other reducer onto the barrel and pushe them both to make sure they are tight.
7. I would highly suggest that you bevel the barrel.
8. This barrel is loaded and fired like any other but, because the supressor, in its essence, absorbs some of the gas you need to have a good, tight load to get a good shot. Try getting a big potato and slicing it so that the ends are flat, then shove it STRAIGH down into the beveled barrel.