Simonsen is known as a tuba player, but he also works extensively as a producer, recording engineer, and with modular synths. For the past few years Simonsen has been active with the pioneering microtonal tuba-trio Microtub, a group where he plays with Robin Hayward and Martin Taxt. He has presented sound installations all over Norway, and his work is to be found in the collection of KORO, Norways national body responsible for art in public space.