Sony MDR-RF970RK Radio Freq Wireless Headphones Enjoy your music without wires. The MDR-RF970RK features noise reduction technology that really lets you listen to your tunes without any unwanted sounds. Travel in freedom up to 150 feet from your sound source while delivering higher fidelity stereo sound. This system includes Ni-MH rechargeable batteries, 900MHz RF wireless transmission and headphones with a 40mm driver for deep bass. An auto tuning feature conveniently scans up and down the band to automatically tune in channels. Hear the difference with the MDR-RF970RK wireless headphones system.