- [Mid-Low] Transparent Vocal sound - [Full Range] Perfectly Balanced and Rich Sound The Coil Parameter Dual Custom BA Driver is a custom-made driver designed to reproduce both full-range and mid-to low-range frequencies.It comes with a total of four drivers: two BA drivers that offer ultra-low distortion to create clear low- to mid-ranged vocal sounds and two BA drivers that offer perfectly balanced rich sounds, uniquely tuned to harmonise each frequency range, playing perfect sounds.