Califone ER1 Single-Sided Mono Headphone, Works with WS-R Wireless Audio System Receiver, Right Ear Only, 20-20000Hz Frequency Range, 32 Ohms Impedance, Sensitivity 105dB&plusmn;2dB Works with WS-R Wireless Audio System Receiver 3 Feet Straight Cord Has a Foam Covering Universal 3.5mm Plug