As for the lower end, IS series is comprised of two passive subwoofers, respectively equipped with a 1x8" or a 1x12" woofer.
The compact size of both boxes is ideal when it comes to integrate a low-end extension cabinet in a venue, without dragging too much attention to it.
Needless to say the keyword here is: ease of installation and unobtrusiveness. Thats why each single system in IS series comes with a smooth design, Phoenix connectors, black or white version.