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 the people occupying a shared social space. These people democratically choose the music played in the shared public space and provide valuable feedback to the musicians by downloading and rating their content.