The Sony MDR-RF985RK Wireless Radio Frequency Headphone System is designed to transmit analog audio sources wirelessly to its headphones with a range of operation of up to 150-feet. The headphones feature a built-in rechargeable battery that can provide playback for up to 25-hours per charge. They are charged by connecting to the transmitter base station, and produce a full charge in 3.5 hours. The headphones also feature 40mm drivers and an adjustable headband designed to provide comfort for long listening sessions. The system's transmitter features a stereo pair of RCA inputs and a single 1/8" stereo mini-jack input. It broadcasts on an analog 900 MHz radio frequency and has three selectable channels.