What are the main advantages of a concentric driver?
Better imaging, more consistent sound character throughout the listening area, and less influence by the acoustics of the listening space.
First, what is a concentric driver?
In general, it is a driver where the tweeter and bass/midrange driver have been combined into one compound unit. The tweeter is mounted at the apex of the cone, sitting directly on top of the bass driver pole piece, where the dust-cap would normally be found.
The result of this is to match the off-axis characteristics of both drivers so that the sound is more even across the frequency range. The imaging will then be better, the sound character will be more consistent throughout the listening area, and will be less influenced by the acoustics of the listening space.