Sennheiser HDR120 Supplemental HiFi Wireless Headphone for RS-120 System Sennheiser HDR 120 Headphones, Extra Wireless Headphones for RS110 and 120 Systems (charger not included) Open, stereo, supraaural, wireless RF headphone. Detailed, analytical sound reproduction with strong bass response. Suitable for all types of modern music and TV applications. Wireless freedom with reception through walls and ceilings. Very lightweight headphones, extremely comfortable to wear. Impedance - 24 Ohms