The Volbox is a simple device that allows easy sound level adjustment without using the music player itself. It has a large, easy to grip volume knob. It has 3.5mm (1/8") sized input and output jacks. This enables you to use your own audio cable for any cable length and quality level you need in your system. No batteries required. Box measures 50mm x 35mm x 11mm tall. Knob measures 20mm x 12mm tall. It can be used between your headphones and MP3 player or iPod, between a music player and a larger home amp or stereo system. With a TV and a set of headphones. On a motorcycle or in your car. The Volbox is hand built with good quality parts to provide many years of service. Use it anywhere you'd like to be able to easily adjust the volume level. Note: This will NOT make the volume louder than the music player's maximum level. For that you would need an amplifier.