According to the koss website.
http://www.koss.com/koss/kossweb.nsf/02ProductDetailCall? ReadForm&Portabl e+Stereophones^KSC50
I should know all about this kinda stuff from control engineering, but Im was busy sweeing how many pints of beer I could down in the 15 minute lecture break (3) and later, how long I could hold my breath without passing out. (1 minute 10 I think it was, but I passed out shortly after
)