Installing angled wall over pre-existing wall

The pre existing wall is 20 ft long, likely 2x4, and contains a window. This is the side that faces my neighbors, and I plan on recording rock bands so I need more isolation. I am planning on building a wall down the entire length at a slight angle, the flared out side would start near the window the wall would end at the back corner by the wood wall. I planning on building a 2x6 staggered stud wall with double drywall with green glue in between the sheets. I am unsure of how to block this window off, and also unsure of what the stuff in this open space between the old and new wall. Look at the picks and tell me what you think. Thanks, Ryan

Aloha and welcome to the forum, There is a post here somewhere regarding building a "window plug." Try the search function - may prove fruitful :wink: Also, try reading through some of the stickies in the construction forum for a few ideas to get the creative juices flowing. Hope this helps, Aloha 8)