Woah this is cool. Another interesting simonw project based around sound through browsers. Lots of simple real world problems that can be tackled with this.

You can also solve this in O(logn) using a physical binary search:

1) Move half the boxes to another room.

2) Listen for a beep and determine which room the beep comes from.

3) Take the boxes in that room and split it in half again.

4) Repeat until one box is left.