Career
Thesseling began studying bass in 1988 at the ArtEZ School of Music in Enschede, Netherlands. In 1995 Thesseling started to study microtonality, which resulted in two pieces: Hafnium — study in 72-tone equal temperament (1999) — and Argon — study in 18-tone equal temperament (2000). The period following, microtonal and contemporary classical music inspired him to focus primarily on fretless bass.
In 2005 he recorded with the studio group Ensemble Salazhar.
Despite their highly acclaimed demo "Colors" the group never officially released recordings. Between 2007-2011, he collaborated with and recorded with them and
During the period 2009-2012 he rejoined after a 15-year break and recorded their sixth studio album. Since 2011 German bass luthier Warwick built fretless 7-string instruments for him that are strung with a sub-contra F#-tuning.
Late 2014 Jeroen started working with the jazz/ fusion group Salazh Trio, where piano, drums and electric 7-string bass merge in the vein of the earlier Ensemble Salazhar project
Jeroen is endorsed by Warwick and plays 6-string Thumb neck-through basses since 1993. From 2011 he uses 7-string fretless Thumb Northwest Territories basses with a low F#-tuning.