In this paper we suggest a conceptual architecture for music systems, designed to shift the control over a shared urban space to the users themselves, and also to encourage social interaction between co-located friends and strangers alike. We present UbiRockMachine, a prototype application designed to bring the communities of local, un-signed music producers and music consumers together. The application provides a two-way communications channel where the music producers make their creative content available to people occupying a shared social space. These people then democratically choose the music played in the shared public space and provide valuable feedback to the musicians by downloading and rating their content. We present findings from empirical user testing carried out in three separate locations, and outline directions for future work and further experiments. Categories and Subject Descriptors