Halldorophones are electro-acoustic string instruments. They get their particular timbre by utilizing the phenomena of feedback. The Halldorophone number 5 is modelled on the cello so that classically
trained musicians can play it. The sound of the instrument is something like a cross between a cello, a pipe organ, the song of a humpback whale and Jimi Hendrix.

The Halldorophone project has been supported by the Finnish Cultural Foundation.