an earphone produces an intelligently - changing stereo sound effect . the earphone includes an ear cup , at least one speaker disposed in the ear cup , a processing unit disposed in or attached to the ear cup and connected to the speaker , and at least one sensor disposed in or attached to the ear cup and connected to the processing unit . the sensor is configured to sense a movement of the earphone or an environmental change of the earphone and to send the processing unit a signal representing the movement or the environmental change . the processing unit is programmed to process the signal and to generate a changed stereo signal for the speaker . the changed stereo signal is changed according to the movement or the environmental change . the speaker is configured to receive the changed stereo signal and to generate a changed stereo sound effect according to the changed stereo signal .