We present the Collective Sound Checks, an exploration of user scenarios based on mobile web applications featuring motion-controlled sound that enable groups of people to engage in spontaneous collaborative sound and music performances. These new forms of musical expression strongly shift the focus of design from human-computer interactions towards the emergence of computer mediated interactions between players based on sonic and social affordances of ubiquitous technologies. At this early stage, our work focuses on experimenting with different user scenarios while observing the relationships between different interactions and affordances.