The hardanger d'amore is a 10-string bowed instrument made by Salve Håkedal.
Five of the ten strings are bowed, while the remaining five strings function as resonant sympathetic strings. The hardanger d'amore has also been known as a "5+5" fiddle or a "5x5".
As of August 2019, Salve has made 27 of these instruments, the first being finished in 2010.
The hardanger d'amore was first commissioned by Dan Trueman, who had a vision for a hardanger-like instrument with an extra low string, in the Setesdal style, designed to be played at A440, as opposed to the higher pitch hardanger fiddles are usually tuned to.
From Salve's website:
Dan Trueman saw a 5-string Setesdalsfele I made for Vidar Lande. That fiddle had the shape of a normal Setesdalsfele, except that the body was broader. Dan wanted me to make something similar, but with a fatter sound. And it had to be suitable for playing comfortably along with violins..
The result was this fiddle. The body is broader and longer than a 4-string Setesdalsfele, and the string length is like a violin. It can be tuned in A, with normal Hardanger fiddle strings. Or thin violin strings may be used.