With a bag at back for your MP3, iPod/Nano Convenient to enjoy the music when going out for a walk, or going to sports, or having a rest Two small bags at two sides When you do not want to listen the music, you can turn off the music player, and put the ears ads in to the small bag Speaker size: 16mm Speaker impedance: 32 ohm Speaker Mylar: 6 Speaker frequency response: 20Hz-20kHz Speaker sensitivity: 113 +/- 3dB Speaker rated power: 10mW Speaker max power: 30mW Speaker distortion degree: < 3%