iso booth / joist sound proofing

[28seven]

i just built an iso booth (pictured below) it is a double 2x4 wall. the door is cut in on a 45 which was one bitch to make a door frame for .... buy any way thats done and it is currently pretty sound proof, but the joist and door surround still havent been touched in the ways of sound proofing what do you guys suggest ... any thing will be apreciated

thanks
chris

(i dont know if that attachment will work if not u can see the picture at www.28seven.com/isobooth.jpg , also my studio site is 28seven.com if you want to see that)