The two-channel IRR-20 receiver allows the use of two mics at the same time. Each channel has its own frequency. The receiver's built-in sensor array allows complete freedom of movement in a 1600-sq.ft. room. For larger rooms, up to three wall/ceiling mountable external sensors (IRD-10) increase the working distance. If the receiver is mounted in a secured cabinet the third sensor input disables and replaces the receiver's internal sensor.