(Previous searches: Galton whistles, flute making and many variations thereof.)
The story is set in Europe in the middle ages, so something of the period would be awesome, but the story is flexible enough for a certain amount of handwaving to get the instrument I need.
My story requires a wind instrument that can play music both within and beyond human hearing. Does such an instrument exist? If not, would it be possible to modify or custom build some sort of flute or recorder that could do it? What would be the physical characteristics of the instrument? (I'm guessing longer and thinner than a regular flute.) Would it require special skill to play it? I know that if you blow hard enough into a regular flute or recorder, the sound will go up an octave. Perhaps a "Galton flute" could only be correctly played by somebody with immense lung-power? (This would actually be a major benefit, story-wise.)
Thank you in advance.