The distinctive features of interactive sound installations in public space are considered, with special attention to the rich, if undoubtedly difficult, environments in which they exist. It is argued that such environments, and the social contexts that they imply, are among the most valuable features of these works for the approach that we have adopted to creation as research practice. The discussion is articulated through case studies drawn from two of our installations, Recycled Soundscapes (2004) and Skyhooks (2006). Implications for the broader design of new musical instruments are presented. Keywords Music, Interaction, Urban Design, Architecture, Sound Installation