I've spent the past few weekends working on DIY room acoustics. The first part I knocked out was bass traps. This method was influenced by many of the knowledgeable room acoustic professionals I've learned from online, most notably Ethan Winer.
I chose to use Roxul Safe N' Sound because it is very effective and seems less messy than other insulation alternatives. You can purchase Roxul Safe N' Sound at Lowes, but most stores only carry the 16" width batts. However, you can order 24" from their website, and if you buy 3 or more packages you get free shipping to your local Lowes store.
I wanted to build mine in such a way that the insulation would fill the whole corner, but they could be stacked up without building anything into the walls. After some trial and error, this is the most cost effective and efficient way I came up with for what I wanted. I shot some video while building one of them and put together this tutorial.
Remember to investigate your room for any obstacles or obstructions, and to measure the distance from your floor to ceiling. I recommend going with 8 layers of Roxul per section, and possibly one section with fewer layers on each corner to accommodate your ceiling height.
~ Music Credits ~
Song 1: Jazzhar - Friends
Song 2: Alec's Band - Young Adult Friction
Song 3: Daniel Veesey - Beethoven's Sonata No. 13 in E Flat Major
Song 4: Revolution Void - Line of Flight