The Sennheiser EK IEM G4 is the stereo bodypack receiver of the evolution wireless G4 in-ear monitoring system. Performers, drummers, presenters and church worship teams clip it to a belt or strap and plug in their earphones to hear their own monitor mix from an SR IEM G4 transmitter, instead of relying on floor wedges. This SKU is the A version, tuned to 516 - 558 MHz, so it must be paired with an SR IEM G4 transmitter in the same frequency range. The receiver uses adaptive diversity reception (the headphone cable doubles as a second antenna), has an adjustable squelch, a backlit display, and offers a signal-to-noise ratio of about 90 dB(A) with THD at or below 0.9%. It runs on two AA batteries or Sennheiser's BA 2015 rechargeable pack for roughly four to six hours depending on listening level, in a housing of about 82 x 64 x 24 mm. Check that the A band is permitted for use in your area before buying.