På lördagens konsert improviserar Jan Liljekvist på halldorofon, ett elektroakustiskt instrument byggt av Halldór Úlfarsson. Så här beskriver Halldór själv sitt instrument:
The sound of Halldorophones is achieved by inducing feedback in a string instrument in a controlled way. This is a very basic and known method to color sound and similar to, for example, Jimi Hendrix ramming his Fender Stratocaster into the amplifier stack at Woodstock or a guitarist using innovative gadgets such as the E-bow to feedback the strings magnetically. Halldorophones are unique for including a system for electro-acoustically feedbacking the strings and for having accurate controls to facilitate control and connectivity. The diagram below explains it simply.