I know you can use HTML5 DeviceOrientation for angle and the "swip" for relative positioning. But how did you get the physical size of the screen of each device?
One solution would be create a companion app that determines the physical screen size, then makes that available to your network via web sockets.
There our a few steps I left out here but it's possible.
The app could be optional - if its installed that device will have fully automatic configuration. If it's not installed, you just fall back to your user prompt.
I wonder how it sounds to play sound across devices. Streaming and clock syncing can happen beforehand, just the playback has to be very sync to an absolute timing.
Maybe one can do something crude sound propagation synthesis by playing with timing, sound runtime, gps and a crowd. If you synthesize the sound the app even stays very small. You could e.g. make an ocean wave roll through the audience (when every device knows where it is and knows the exact time of when the wave will hit that position).
Same could work with devices as pixels, but I don't find it that interesting.
They split the room into 3 sections, and then controlled each section to play it's own tune.