Amazon.com Koss introduced the PortaPro headphone back in 1984, and they've been a hit ever since. To this day, they still deliver excellent sound quality, particularly for phones in this price range. Phones are collapsible, for maximum portability. Get just the right amount of pressure. The Koss PortaPro collapsible stereophone combines high-quality sound reproduction with a unique design for the ultimate in convenience and comfort. These over-the-head headphones have a dynamic element design for deep bass performance and a frequency response of 15 to 25,000 Hz to ensure the music comes through clear and bright.Also designed for comfort, these headphones have two adjustable temporal-comfort zone pads to shift the pressure and perfectly balance the ear plates on your ear. The open-earphone ear plates are multipivoting and, together with the adjustable headband, allow for maximum comfort.The PortaPros are collapsible and come with a carrying case, so it's still easy to take them with you even when you're not wearing them.Koss offers a lifetime warranty on its PortaPro stereophones.SpecsFrequency Response: 15-25,000 HzImpedance: 60 ohmsSensitivity: 101 dB SPLCord: Straight, Dual Entry, 4 feetWhat's in the Box Koss Porta Pro Headphones Product Description Dynamic element design for deep bass performance; Comfort zone setting on temporal pad for comfortable, secure fit; Multi-pivoting earplates and adjustable headband for added comfort; Collapsible for maximum portability when listening on the go; Includes convenient carrying case; Straight, dual entry 4 foot cord; Frequency response: 15-25,000 Hz. It is not meant for noise isolation. If volume too low, the listener should turn the volume up. This is handled through the device that the headphones are plugged into. The headphones do not have volume control From the Manufacturer Dynamic element design for deep bass performance; Comfort zone setting on temporal pad for comfortable, secure fit; Multi-pivoting earplates and adjustable headband for added comfort; Collapsible for maximum portability when listening on the go; Includes convenient carrying case; Straight, dual entry 4 foot cord; Frequency response: 15-25,000 Hz.