Björn Hellström, PhD, musician and architect SAR/MSA, is professor in Sound-Art in Urban and Acoustic Environments, Faculty of Art, Konstfack (University College of Arts, Crafts and Design), and docent in architecture at the School of Architecture, Royal Institute of Technology (KTH), Stockholm. He is also acoustic designer at the company Tyréns AB. He is engaged in interdisciplinary research, combining art, urban planning, architecture, music, acoustics and psychology. He has made several sound works in public space, for instance four permanent installations in the city park Mariatorget, Stockholm, and also nine sound works at Arlanda Express, a high-speed rail link between Arlanda airport and Stockholm. The sound works are installed at platforms, elevators, escalators and transport passages.