1/25/17: I added another version-this one plays a cello ensemble cover of "Let's Get Down to Business" from Mulan while the timer counts down. My middle schoolers definitely felt pumped for rehearsal after listening to this!
Using tuning tracks I downloaded from orchestrateacher.net, I created two tuning-sequence videos that count down how much time they have left to get ready and then cycles through tuning drones. You can download the video by clicking the icon in the bottom right corner of the video player.
Video #1: Tuning Countdown Only (no class transition time)
Video #2: Class Transition + Tuning Countdown