When the front and side panels are securely glued it's a good time to install the damping material. For these speakers I used some R13 fiberglass insulation from Home Depot. It comes in 16" wide rolls, and you will need to cut across the insulation at about 19" (the 19" provides a snug fit). The insulation is paper backed and about 4" thick - you should peel off the paper backing, then divide the 4" thickness into two 2" thicknesses. It pulls apart easily. Apply some glue to the side braces and back of the enclosure to hold it securely in place, and install it.