This is an ideal project for a science fair etc. – it’s not too difficult to construct, yet makes a playful interactive exhibit.
The idea is to have a lot of proximity sensors – each triggering a different sound sample. No touch needed – no complex light-beams etc – everything is just sitting on the one table.
The distance someone needs be from the table for a note is triggered is customisable.
It has an custom optimized ultrasonic code for sampling multiple detectors at once – it is highly responsive and does not block for seconds like the standard libraries tend to do when objects are far away.