This article describes the use of different types of tools for the spatialisation of sound in the context of two music theatre projects. In the first part of the article the different types of sonic relationships explored in the projects are outlined, considering a global framework where the voices of performers, transformed sounds and mobile sources can effectively be integrated on stage. In the second part of the article the specific spatial design developed for the two projects is explained in detail, focussing on the advantages and limitations of synchronised and non-synchronised mobile sound sources. The role of mobile technology as a driving force for audience engagement and the interaction with performers in the creative process is discussed considering future developments of the project in the form of a wireless body-worn speaker system.