KZ ZST Circle Iron In-ear Mega Bass MP3 Dual Unit Earphone without Microphone (Colour)1. The high pitched moving iron unit + the mid bass moving coil unit complements the sounding advantages of the moving iron unit and the moving coil unit, giving the music a richer detail. 2. The performance of the unit is strong, with a four layer voice coil to bring a stronger driving force, and the low frequency shock is powerful, making the overall listening feeling more appealing. 3. The treble moving iron unit has the high pitched performance