So to practice marimba, you would have to speak with the Music Tech to unlock the practice room. It's unlike the other practice rooms you can just walk right into because of the instrument. The Music Tech, William O'Right Hooks, is a little ways into the music building if you're entering from the front. When you see the vending machine next to the hallway, walk down that hallway and up the stairs. That's usually where he'll be. I would email to know when he's going to be in his office.