cello-like, electro-acoustic string instrument halldorophone produces sounds using ‘feedback’

Halldór Úlfarsson’s string musical instrument, Halldorophone

Halldór Úlfarsson has developed Halldorophone, a cello-like and electro-acoustic string instrument that plays rich sounds using feedback. It is one of the few instruments that is mainly built around the concept of feedback. The design of Halldorophone is based on creating feedback, an intentional decision on the artist’s and designer’s part. It happens when the sound from the instrument is captured by a microphone or pickup, amplified, and sent back into the instrument. This feedback creates a loop, and the sounds the instrument produces come from its coupled strings.

The instrument maker and designer brought his invention to Sónar+D 2024, where Halldorophone was exhibited as part of the Intelligent Instruments Lab, amongst other musical systems designed in the research lab. The visitors were able to try it out, with some of them realizing and jestfully commenting that what they were playing wasn’t a cello. This yellow halldorophone was developed at the lab in close collaboration with Dr. Adam Pulz Melbye, who wrote algorithms, did user experiments, and investigated how people perceive such strange instruments.

all images courtesy of Intelligent Instruments Lab | video filmed and edited by Rafn Rafnsson at The University of Iceland

How does Halldorophone work and produce sounds?

The coupled stings that Halldór Úlfarsson places on the musical instrument consist of four separate strings. The first ones are the main strings the musician plays directly, since they’re right on the body. The rest are the ‘sympathetic’ strings that vibrate on their own when the main strings are played. Each string has its own pickup, which may be comparable to a microphone. This device captures the sounds that the individual strings make, and the performer has control of each string via an inbuilt mixer. There is an amplifier and a speaker that play the amplified sound back into the body of the instrument, thus generating the phenomenon of feedback.

This makes the strings vibrate, resulting in a feedback loop where the sound keeps cycling between the strings, pickups, micro-computer, amplifier, and speaker. The yellow Intelligent Instruments Lab halldorophone has an embedded Bela micro-computer that processes the sound as part of the audio signal chain before it goes back out into the instrument. The Bela microcomputer sits under the mixing board of the instrument. Here, intelligent algorithms augment and control the natural system of feedback so that it can generate more interesting behavior.

Halldór Úlfarsson creates Halldorophone, a cello-like and electro-acoustic string instrument

INTELLIGENT ALGORITHMS FOR RICHER ‘FEEDBACK’ CONTROL

The feedback system allows the Halldorophone to create continuous, rich sounds called drones. The musician can even adjust how loud each string’s sound of the musical instrument is in the overall mix. Aside from the loudness of the string’s sound, they can also toy with the volume of the speaker. By adjusting the speaker’s volume, the player can control how strongly the strings vibrate and how intense the feedback is.

The feedback and electronic components let the musician control the sound to some extent, making the drones have complex, interesting tones. Overall, the cello-like and electro-acoustic string instrument has four main strings. These strings can be played using a bow or by plucking with fingers, but as seen in the video above, the resonant sounds may also be produced by gently and slowly rubbing the strings onto their frame.

the string instrument plays rich sounds using feedback

The fingerboard, or the part where the musician presses the strings, is fretless. It means it doesn’t have metal bars like a guitar, so they can smoothly slide to different notes. Just below the main strings, the sympathetic strings lay, not directly played by the musician.

There’s no bowing or plucking involved for them since they vibrate automatically when the musician plays the main strings. They’re the ones who help create a continuous background sound, as if they were echoes. The player can also connect the sound strings of Halldór Úlfarsson’s musical instrument to external audio equipment.

feedback happens when the pickup captures the sound from Halldorophone

This can allow musicians to use digital sound processors or effects pedals and manipulate or play with the sound. In this way, they can add reverb, delay, distortion, or other effects to the Halldorophone’s sound, similar to how electric guitarists use pedals.

The Halldorophone, designed specifically to feedback the strings and the instrument, gained some recognition in early 2020. It was when Icelandic composer Hildur Guðnadóttir won the Academy Award for her original soundtrack to the movie Joker, some of which was composed using a halldorophone.

the feedback system allows the Halldorophone to create continuous, rich sounds called drones