Gobos For Drums

I am wondering if the gobos found in http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5928 would be appropriate for reducing the reflections from my half granite room. If this idea would be good for this i would like to build about 5-10 of them over the summer. My room is nearly impossible to treat in the corners. only 1 of them could be properly treated. I need this treatment to reduce the slapback from my granite walls being intercepted in my overheads for my drums. The dimensions of my room are 20x14x8. the twenty foot long wall on one side has a ten foot window and on the other has a 18 foot granite wall. The granite wall is from floor to ceiling. My floors are carpet. I notice during my rehearsals with my band i do get a little bass build up so i would shove these in the very small corners during rehearsals to reduce the boom. Another use i wanted to use was reducing the reflections for mixing too. I plan to move my computer and speakers into the room with the drums to mix since the room they are in now is small and cramped with my three desks and other computers. I was wondering if these could make a better listening quality like a miniature properly treated room. I am fourteen years old and plan to get a job this summer. My budget for building these would be around 300-500 dollars. I have attached some simple sketups of what the room looks like.

Hi there, I've been using the gobos I built in your linked thread for a while now. I like them very much for tracking. There are a few things to keep in mind. First, Gobos are NOT bass traps. Gobos are designed to block sound, whereas bass traps depend on sound passing through them in order to work properly (here I'm speaking of common velocity absorbers, ie, absorptive material straddling corners or superchunks, etc). The gobos work well as first-reflection point absorbers, and I often use them as such while mixing. I also use them on the rear wall. But, I do highly recommend using them in conjunction with bass traps, rather than instead of. If your wall/wall corners are (largely) inaccessible, what about the wall/ceiling corners, or even the wall/floor corners?

ohhh ok i was confused if they acted as bass traps or not. ok well i guess i could make them along with some bass traps. i have three ceiling wall corners and maybe one or two wall corners. i just have this huge granite wall, beautiful to luck at but a horror for sound, that constricts my corner use along with the room being directly attached (no doors or windows) to the next room.