This 4-person wireless listening system is ideal for language learning, literacy groups, ELL / ELD applications, story-time, music and audio book listening, other classroom and library uses, With a 100" range from the transmitter to the headphones, the system creates flexible learning environments where the students do not need to be next to the audio source, There are three different color-coded frequencies with matching hardware to choose from, with an unlimited number of headphones that can be added later for larger sized groups, Since each transmitter and its matching color-coded headphones operate on their own independent frequency, three different groups can enjoy wireless learning in the same room without any interference, The transmitter has a 1/4"" plug to attach a microphone, When connected, this allows announcements to be made which are heard only by students who are wearing headphones that are receiving from that transmitter, Each system includes four wireless headphones, a matching color-coded VHF transmitter that plugs into any audio source (MP3 player, computer, multimedia player, VCR / CD / DVD player, or television monitor), all necessary charging cables, and an AC adapter, For the specialized needs of wireless group or 1:1 instruction with differentiated learning rates for an unlimited number of students, Brings flexible wireless listening to as many as four different groups at the same time, Each of the four frequencies has color-coded hardware for easy identification and use, 100"+ transmitter range for convenience in any setting, Includes all necessary hardware to begin wireless listening from any multimedia source, More students can be included by adding headphones, For four students, yellow, frequency 72, 100 MHz (includes 2003 rack), Contact Califone directly for headphone battery replacement options, SKU: CAFI351