Califone's Wireless Headphones are the perfect solution for cordless listening centers. Each transmitter works with a specific frequency, allowing up to four Califone Wireless Headphone systems to operate with the same room. Wireless transmitters broadcast up to 100 feet unobstructed and are powered via AC electricity. The flexible setup allows for some creative uses, including translating religious services on the fly for non-native speakers. Each Wireless Headphone set is powered by a rechargeable battery, which last six hours when fully charged. Individual volume knobs on each headset. The ear cushions are easy to clean replace. Adjust the headband to fit most adults. Califone's Wireless Headphone System carries a full one year warranty.