With the interior skeleton largely in place it is time to turn my attention to putting some skin on these bones–the inside bones anyway.
So to begin, first we have to ensure that there is a layer of dampening material between each layer of the structure. In this case I’m using an underlayment foam. It is relatively inexpensive, easy to come by (the flooring isle), and effective in covering a large surface area. This is partly to dampen the wall surface and partly to help create another layer to seal one side from the other. It isn’t much of a barrier to sound, but it does help.
Beginning with the roll foam: