Connects to the headphone jack of your MP3 player or other portable audio device with a 1/8" headphone jack. Folds in half, compact enough to fit in a backpack or purse. Specially designed slot for neat plug and cable storage. Frequency response:200-20,000Hz. Impedance:8 Ohms. Adjust the volume for personal listening or turn it up so all of your friends can listen too. Power supply:3 × AAA batteries.