<P> In - ear monitors (IEMs) are devices used by musicians, audio engineers and audiophiles to listen to music or to hear a personal mix of vocals and stage instrumentation for live performance or recording studio mixing . They are often custom fitted for an individual's ears to provide comfort and a high level of noise reduction from ambient surroundings . </P> <P> A monitoring system is any system that provides a mix of audio sources to a performer on stage . Traditionally, monitors were loudspeakers placed on stage directed toward the performer (often called floor monitor speakers or wedges). Depending on the sophistication of the audio system, floor wedge speakers can have disadvantages . First, floor wedges greatly increase the onstage volume, in some cases to potential hearing damage levels . Second, while floor wedges can be placed in front of a particular singer, guitarist, bassist or drummer, the other musicians can often hear the other musicians' wedge mixes . In a sophisticated monitoring system, every band member can have their own monitor mix, which is their particular preference of vocals and / or instruments . </P>

What is the thing in the ear of singers