These headphones feature a remarkably wide 15Hz - 25kHz frequency response, less than 0.2% distortion and 60ohm impedance combined with an open backed design to provide very well balanced and sweet sound with punchy tight base. The sound stage is large and roomy. They are foldable making them very portable and include a 3.5mm jack and 3.5/6.4mm jack adapter on a 1.2meter cord so you can use them with your favourite MP3 player or Hi-Fi system. Included in the price is Koss' No Questions Asked lifetime warranty. Buy Now.