Koss SportaPro Stereo Headphones Headband pivots backward at its base, easily converting from over-the-head style to a behind-the-head style.Connectivity Technology: Wired Foam ear cushions Collapses into a compact, protective package that tucks neatly in a briefcase, gym bag or backpack Frequency response: 5Hz-25kHz Imp: 60? 15 to 25,000 Hz frequency response Flexible headband design, fully collapsible Product description Product Packaging:Standard Packaging Product Description Versatile headphones for any activity Amazon.com The Koss SportaPro portable headphones offer portability, flexibility, and a headband designed to be worn either atop or behind the head. Equally well suited for use at work or on a jogging trail, the SportaPro's open, foam-covered ear cups allow for ambient environmental sounds to be heard, which can be helpful in a recreational environment. The SportaPro's weight is a mere 2.2 ounces, and the headphones boast a frequency response of 15 to 25,000 Hz, delivering (on paper, at least) quite a bit more bass than most home speakers can. Impedance is 60 ohms, with less than a 0.2 percent distortion and sensitivity of 103 dB SPL (with a 1 mW signal). The SportaPro stereophones are collapsible and come with a carrying case, as well as both 0.125-inch and 0.25-inch jacks. Koss covers the headphones with a lifetime warranty.