Part number: 505562 Closed back, circumaural headphone system with excellent digital wireless audio transmission delivering range up to 30 meters(100-foot). Connectivity Technology: WirelessHigh-quality Sennheiser transducers and a selectable Bass Boost mode for exceptional sound. Range-Up to 30 m,Max. sound pressure level 106 dB at 1kHz, 3% THDMulti-purpose transmitter with Analog Input - also functions as easy-charge cradle and docking station for the headphonesMulti-receiver transmission - transmitter supports up to two pairs of headphones