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 A1 version, tuned to 470 - 516 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 A1 band is permitted for use in your area before buying.