Koss EQ50 3-Band Stereo Equalizer 3-Band Stereo Equalizer For Expanded Frequency Response and Acoustical Contouring Level Controls For Bass, Midrange and Treble Provide Added Sound Definition Provides 2-30 Hours Of Usage Pocket Size 10dB boost or cut per channel Unity gain amplifier limits power output to conserve battery power from the source Ideal for use with laptops or portable DVD &amp; MP3 players Pocket-size for easy travel and portability Requires 2 AAA batteries (not included) for 20-30 hours of usage