New technologies allow a stunning possibilities of human being experience, that could be hardly imaginable before. Our project is called to break barriers within people's communication and change urban atmosphere. Jam Machine is an interactive artifact for public spaces that allows dwellers to compose collaboratively music over their smartphones. The interaction with the Jam Machine happens over smartphones that are connected to WLAN. After logging into the WLAN of the Jam Machine, players interact with a JavaScript-based GUI in a browser. The whole process is visualized over a mobile tent made of rear-projection canvas, thus big sectors between intersecting tubes can be used as screens. The project is supported by the RWTH University, Aachen, Germany and Human-Computer- Interaction Centre and is an interdisciplinary art-technologic experiment. Every person, with and without musical experience can participate to jamming process, because the sounds of the jam machine are not discording and sound quite harmonic in any case.