Built in charging function volume control on the headphones 3 transmission channels for avoiding interference elastic headband very high frequency stability thanks to pll system range 100 m in open space 20 30 m in buildings autotuning automatic station search power button with led indicator on the headphones featureproduct featuresmaterialplasticspeaker diameter40colourblackfrequency range20 hz 20 khzdesignover earconnection35 mm jack plugsn ratio gt50modelstereocable length1signal tran