In this paper we present Fields, a sound diffusion performance implemented with web technologies that run on the mobile devices of audience members. Both a technical system and bespoke composition, Fields allows for a range of sonic diffusions to occur, and therefore has the potential to open up new paradigms for spatialised music and media performances. The project introduces how handheld technology used as a collective array of speakers controlled live by a centralized performer can create alternative types of participation within musical performance. Fields not only offers a new technological approach to sound diffusion, it also provides an alternative way for audiences to participate in live events, and opens up unique forms of engagement within sonic media contexts.