Glass and fingers work together underwater like a violin bow and string, making them a natural choice for a world in which music evolved in the oceans
The Rotacorta was inspired by a traditional Byzantine hurdy-gurdy, but more musically flexible and with more expressive dimensions. It has six stainless steel strings which can each be either a drone string or sound only when fingered.
Using tactile fingering instead of keys and tangents enables both pitch bending and arbitrary chording. And adjustable bridges allow for subtle changes in intonation.
Making music underwater was even more challenging than I’d anticipated. But as usual, the difficulties only become apparent during the process.
I knew that the mass of the water would absorb and dampen vibrations. And that sound travels about four times faster underwater, making the sound waves four times longer. That would make most resonators impractically large for these human-scale aquariums.
But there were also many new material challenges. The first was corrosion. These instruments had to be made of materials that could survive underwater. No wood; no ferrous metals. And they could not be from materials at far ends of the galvanic series, or together they would create corrosive electric cells when placed underwater.
And all of the materials must be completely non-toxic to humans, as the players and instruments would certainly be commingling on a molecular level. This ruled out many metal alloys, lubricants, adhesives, and leaded glass.
Friction was different underwater. Smooth bearings ground roughly and rough violin bows slipped silently across strings.
But the acoustic challenges — coupling and impedance, were the most confounding. The vibrations of adjacent glass bowls or stainless steel strings would couple and interfere with their neighbors in unpredictable ways pulling everything out of tune. Physical oscillators that ring separately in air were intimately intertwined underwater.
And the oscillators were coupled with even the water itself. Unlike in the air, underwater oscillators could only move freely in modes in which the whole mass of water itself could vibrate. And those vibrations were determined by not just the dimensions of each aquarium, but also the water temperature and its the mixture of gasses absorbed in the water. That may be been controllable in a NASA-like environment. But once you put a human in the tank, all bets are off.
Many thanks to the irreplaceable Matt Nolan, who helped to modify and fine-tune the instruments on-site in Aarhus, Denmark.