[. . . ] [. . . ] Sensitivity: 114dB ±2 dB at F=1KHz Frequency Response:20Hz~20KHz HP- 080 1. Features This item is suitable for any audio devices. (Switch on the noise cancelling function when you are in noisy envoirnment) 5. Working condition Working temperature: -10~60, working humidity:20%~90% When use this item, try to avoid overloading signal input, operate it in the range of the power input extension. 6. Problem and Solution Problem Causes Solutions 2. Parts Introduction Noise cancelling Doesn't mount battery or reverse function doesn't work the polarities, battery run out of , or the power is lower Replace the old battery with new one , meanwhile mount the battery according to the engraved polarities . 3. User's Manual Mount 2 x AAA batteries in the battery case. Connect the audio device with the headphone, adjust the volume properly, you will sense that noise outside is decreased a lot. Try to avoid touching this item with sharp object in order not to influence the appearance. [. . . ] [. . . ]