These Multi channeled cordless systems allow you to have up to four unique listening groups for students to learn different programs, tapes, or lessons. Charge headphones for four hours and they provide 50 hours of continuous operation. Each headphone has individual volume controls and a range of 100 feet. To accommodate more than one listening group at a time, simply switch to a different frequency. Each color represents a different frequency, 4 different frequencies can be used simultaneously in the same room, and any number of headphones will work on the same frequency. Choose a 4 or 6 headphone set, upgrade to include a storage rack, or add an extra headphone. A #308056 wireless transmitter is included with each 4 or 6 headphone sets.