The Koss EQP Series is a built-in stereophone equalizer system that delivers expanded frequency response and acoustic contouring to your listening experience. It's ideal for customized sound from your CD, DVD, or MP3 player. The EQP series combines your favorite electronics in a single pack for improved volume output, cord management and lightweight portability from your audio source. The EQP1 system includes a built-in stereo equalizer that has level controls for bass, midrange, and treble. The equalizer provides added sound definition, expanded frequency response and acoustic contouring. A retractable cord mechanism provides efficient cord management. Utilizing 2 'AAA' batteries (not included), the EQP1 delivers approximately 30 hours of play.