I am building a freestanding 4x6 vocal booth. I purchased blue prints that were for a 4x4 booth but that only called for one plywood wall. Other information I have read said that it is important to have a frame and two plywood boards. Which one is the best idea? What is the best material to go between the plywood that would assist with sound proofing the booth? It was recommended by home depot to purchase deadening board and place that in between the plywood to help with the sound proofing. Has anyone heard of this or used it? Also what how do you make it so that there is air circulating in the booth without sound coming in?