A communication system includes: a plurality of mobile communication terminals; a server device; and a plurality of relay devices performing a relay between the plurality of mobile communication terminals and the server device. The device comprises a container housing 12 with an interior volume 24, which may contain an object or a liquid to be disinfected. In one embodiment, the phase of a transducer is sensed, enabling multiple projectors to achieve high acoustic sound pressure levels by beamforming andor modal constructive interference.