Yes what they stated. The tube looks like this one shown below. You place a plug in the middle of the tube. The plug can be glued in, or crimped in. Even some screws put in to help keep the plug in place. The on both sides of the plug, you drill a series of three sets of holes. If you add up all of the holes diameters, then the holes total size is larger than the tube inside diameter. But since the hot gasses cool and shrink in volume the second and third set of holes become progressively less.

Anyway here are some pics of how I did it for a smaller muffler. One can scale it up or down in size as needed.

Oos sorry I forgot to add the pictures.