Though in-ear monitoring can work perfectly well with cabled systems, particularly for musicians such as drummers and keyboard players who cannot move while playing anyway, singers in particular like to be free to move. Even the most flamboyant on-stage movements are unlikely to affect the performance of a dynamic microphone (and many singers use wireless microphones for even greater freedom of movement), but few singers would move very far with a cable running to a headset (or even a belt pack) for fear of tripping up or getting enmeshed in cable! This is where wireless systems become essential.|
A wireless in-ear system works exactly like a radio mic system but in reverse. The monitor mix is sent from the mixer to a wireless transmitter (usually a 19/1U or half-rack unit). The performer wears a belt pack receiver, which usually incorporates a volume control, to which the headset is connected, usually via 3.5mm stereo mini-jack.
Sennheiser EW 300 IEM System
Shure PSM 200 2-Channel-System
Like wireless mic/instrument systems, wireless in-ear systems are available on a variety of frequencies, and are subject to different national regulations as they constitute a form of local broadcasting. Budget/midrange systems are usually covered by blanket legislation (that is to say, whether it is or is not legal to use a particular frequency for this purpose in a given country), whereas high-end professional systems are allotted a range of licensed frequencies; a licence must be obtained (and usually renewed annually) to use a particular frequency. This may seem arduous but at least goes some way towards guaranteeing that your lead vocal wont suddenly be taken over by the singer in the venue next door!