Giving you access to personal virtual surround-sound, the RS 175 Digital Wireless Headphone System from Sennheiser consists of a pair of HDR 175 headphones, and a TR 175 transmitter. The TR 175 features an analog 1/8" stereo input along with a digital optical input for connectivity to a variety of audio and home entertainment systems, and functions both as a transmitter and charging station for the headphones. You can connect up to 2 headphones to the TR 175, by using an additional set of HDR headphones (not included). The HDR 175 headphones have a closed, circumaural design, and have dynamic bass boost and virtual surround sound modes, allowing you to customize playback. Analog and optical audio cables are included, along with 2 AAA rechargeable batteries. Closed, circumaural headphones with digital wireless audio transmission Digital audio clarity and transmission range of up to 328' (100m) (line of sight) Enables switching between dynamic bass and virtual surround sound listening modes for situational sound customization Supports analog and digital audio inputs and allows toggling between the inputs Intelligently designed controls for ease of use Multi-purpose transmitter also functions as 'easy-charge' cradle and docking station Multi-receiver transmission; transmitter supports up to two pairs of headphones simultaneously Ergonomic design for wearing comfort