Drivers in IEM’s are used to recreate the sound, which means the more drivers, the better the quality of music. While many brands have nailed their single-driver models, some custom-made models can pack as many as eight drivers into a single earpiece.  With standard single-driver in-ears, there is only so much a single driver can do, outputting a limited frequency range and lacking a fair amount of power in the low end. When you add in more drivers, the burden of recreating the audio spectrum rests evenly on every driver, resulting in high-fidelity audio.