TAKE MY ADVICE
Get this through your head. WOOD IS *****NOT***** TO BE USED FOR WALL'S. ***ANY*** PERSON WHO SUGGEST WOOD ***NEEDS*** TO SPEAK WITH ACOUSTIC ENGINEERS AND STUDIO BUILDERS. YOU ****DON'T***** WANT A WALL MADE OF WOOD. WHAT YOU *DO* WANT IS A "LEAF" MADE OF DRYWALL (THIS IS THE SAME AS GYPSUM BOARD AND SHEET ROCK). A "LEAF" is ***two***pieces of "MASS". Both pieces should consist of Different materials (if possible) and thickness so they don't attenuate the same frequencies. Wood is NOT a good sound absorbant as it yields a VERY LOW STC rating. If you don't know what stc ratings are hit google and type: STC RATING.
My booth walls consist of 5/8 drywall and 1/2 drywall. The drywall is connected to the studs (i used wood studs instead of metal but you can use metal), I used 2.5 Thermafiber (a certain type of insulation that will *not* be found in home depot, yard birds or OSH) between the airspace (2.5 or 3 will improve the STC rating) and went back over that with another leaf of 5/8 dry wall and 1/2 drywall. If you decide to float the floor use NEOPRENE. BTW thermafiber is the ***best*** insulation you can use.
so basically it should look like this
5/8
1/2
studs
thermafiber
1/2
5/8
I don't know anything about filling walls with sand. I don't know of anyone who has filled their walls with sand. I don't even think that would pass the firecodes and how would you run an electrical box through that?
ONCE AGAIN STAY AWAY FROM WOOD AS YOUR WALLS.
:HGK:
PS GO OVER *ALL CORNERS* (INSIDE AND OUT) WITH CORNER BEADS.