Single-sided mono headphone is an ideal tool designed for use with personal receiver or Califone WS-R wireless audio system receiver for students listening to lectures, extended instruction or for smaller groups within an audience being served by a translator. This lightweight headphone can be used in tour groups, classrooms or larger lecture halls where additional audio reinforcement is needed. ER1 has foam covering and its hook comfortably rests around top of the right ear. It includes 3ft straight cord with universal 3.5mm plug that can connect to one of dual 3.5mm headphone jacks on WS-R receiver for multiple simultaneous listeners. Volume is controlled from audio source.