Califone Switchable Stereo/Mono Headphones can be used with PC, Mac, cassette and CD players and either stereo or mono applications. A 3.5 mm plug and 1/4 inch adapter are included. Features 40 mm mylar dome driver unit transducers, 36 ohms impedance, and 98dB +/- 3 Db at 1 kHz sensitivity. Three-year warranty for school use.