Your own choice of music in a restaurant, your preferred language in a cinema, and a personal tour in a museum. All are possible if you can control the sound in almost any place.
We find them at the beach, in every sound and light show, the miracle of wi-fi and now in the fabric of space-time itself. But what exactly is a wave?
Sound waves can do useful things and move physical objects, so a sonic screwdriver isn't out of the question.