The SSR1 utilizes an advanced circuit technology that can reproduce an original multi-channel sound into a personal listening surround sound effect. It also incorporates a built-in amplifier for added volume and a volume control for easy level adjustment. The surround effect control and ON/OFF switch allows the listener to adjust the surround sound experience or simply turn it off. Designed for maximum portability, the pocket size SSR1 has 3.5mm input and output jacks for connecting any headphone to any portable unit. The SSR1 is the perfect travel companion that can bring music, movies and video games to life. Operating on 2 "AAA" alkaline batteries, SSR1 has a 30 hour battery life and is covered by Koss" 90 Day Warranty. SpecificationsFrequency Response 20-20,000 Hz Impedance 10k (output) Distortion <0.3% Cord Straight, Single Entry, 8ft