Pitch Controlled Aeolian Harp

Memebers: Camren Chraplak, Lyle Edwards, and Noah Newton

Course: Making Music with Machines, A Term, 2024

Aeolian Harps are a unique musical machine with an even more unique sound. It is a stringed instrument that has a resonating body, similar to a guitar without the neck. The big difference is that the strings aren’t actuated by a musician striking the string in some way, but by air. As air passes over the strings of the harp, it creates what’s known as the ‘Kármán vortex street’ effect.

This effect makes the pitches produced by the instrument only create harmonic frequencies, which creates creepy and ethereal sounds. A big limitation of these machines, however, is that they rely on natural wind speeds to produce sounds, making the instrument hard to control by a musician. To bridge this gap, we created an Aeolian Harp that can control its wind speed to vary the pitches produced. To do this, we used a DC motor connected to a MOSFET. This would enable a microcontroller, such as an Arduino Uno, to control the speed of the motor. This speed would then be controlled by a potentiometer. This would allow the user to use a physical knob to control the motor speed from predetermined speeds in the code.

To further experiment with the harp, we also added the ability for the base of the harp to oscillate back and forth on the Z-Axis. This would adjust the angle at which the wind generated would blow against the string. This was done through turning a servo motor between two pre-established angles. This enables the harp to be experimented in ways that previous harps haven’t seen. Another feature we added to our harp is the ability to switch between cooperative mode and MIDI control mode. There is a button on the system that when pressed, changes the current mode of either cooperative or MIDI to the other mode. Through MIDI mode, the pitch of the harp can be controlled by altering the speed of the DC motor and the motor can be turned off by setting the note to be a pitch of 0. Likewise, the oscillation period of the servo can be adjusted by setting the pitch to 1 and the velocity between 1 and 127.

In our Aeolian Harp implementation, we unfortunately didn’t get a fully integrated system working. The prime reason for this is that the selected motor and propeller weren’t powerful enough or consistent enough for our harp to be sounded in the setup. We did, however, get the individual components working together. We were able to control the pitch through the potentiometer, have the servo oscillate, switch between co-op mode and MIDI mode, and made an Aeolian Harp that can produce sound, given the correct conditions. If we were able to get the harp to sound from a better motor and propeller, we would have been able to make a fully functional system that could act autonomously or cooperatively.