In episode 7, I cover some cost effective methods I use to help control cabinet vibrations and midrange coloration. For cabinet vibrations, there are several methods you can use to help reduce them. Bracing strengthens the cabinet walls to keep the from flexing and vibrating. What you should focus on is making sure you break up large panel walls with a brace. Corner battens are not effective in doing this. You need to make sure the brace connects from the middle area of one wall to an opposite wall.
Constrained layer damping, or CLD, two functions in reducing vibrations. First, it adds mass to the cabinet walls, requiring more energy to be applied to the cabinet to make it vibrate. Second, it has a flexible layer that is applied to the stiff cabinet side, and a stiff layer, usually some type of aluminum, on the outside. The combinations of the three layers creates an environment that resists sheer forces that are created when the cabinet wall tries to flex from vibrations.
Acoustic absorption material comes in many forms. I tend to prefer the denim insulation type (I'm using Duck brand UltraTouch) because it has a high absorption coefficient over a wide range, is fairly cheap, and doesn't cause itching or irritation like fiberglass insulation can. A driver radiates sound from both sides of its cone. Absorption material is used in the cabinet to absorb the back wave of a driver so it doesn't interfer with the output in the forward direction. Without it, the rear wave can reflect off the wall behind the driver and come back through the cone with a delay, causing coloration of the output. In a ported cabinet, you don't want to use too much or you will actually reduce the output of the port, which uses the rear wave of the driver. I typically line most of the walls in my ported cabinet, making sure there is an unobstructed path to the port. In a sealed cabinet or midrange enclosure in a 3-way, I would heavily stuff the cabinet to reduce the rear wave as much as possible.