Sympathetic strings or resonance strings are auxiliary strings found on many Indian musical instruments, as well as some Western Baroque instruments and a variety of folk instruments. They are typically not played directly by the performer, only indirectly through the tones that are played on the main strings, based on the principle of sympathetic resonance. The resonance is most often heard when the fundamental frequency of the string is in unison or an octave lower or higher than the catalyst note, although it can occur for other intervals, such as a fifth, with less effect.

A Hardanger fiddle is a traditional stringed instrument considered to be the national instrument of Norway. In modern designs, this type of fiddle is very similar to the violin, though with eight or nine strings and thinner wood. The earliest known example of the hardingfele is from 1651, made by Ole Jonsen Jaastad in Hardanger, Norway. Originally, the instrument had a rounder, narrower body. Around the year 1850, the modern layout with a body much like the violin became the norm.