Each of these wireless headphones are sold separately and are ideal for language learning, literacy groups, ELL / ELD applications, story-time, audio book listening, and library uses. Their 100' reception range from the matching colorcoded transmitter (which is sold separately, and included with the packaged set of four headphones), helps create flexible learning situations where the students do not need to be next to the media player. There is no limit to the number of headphones which can be added, only that they must match the same color-coded transmitter frequency. Since each colored headphone operates on its own independent frequency, three different groups can enjoy wireless learning in the same room without any interference.