The USB bin is a high efficiency, high power bass bin designed for general PA use and raves. It uses two 18 drivers in a band-pass horn configuration; that is, it has a short horn which gives it a high efficiency over 80hz, and a band-pass action due to its large rear and front chambers which allow for a shallow roll off extending sub bass response.
The USB is an extremely efficient bass bin, with a very clean sound without any honky peaks or distortions. It works great as a kick bin above subs (like Labs) but also on its own. This is because the horn mouths couple together as you add more bins and the huge power handing allows you to also push the USB low to give out serious sub bass.
Over damped design for better transient response.
Remember to invert the polarity of the driver to keep the phase.
Compact box dimensions.

thanks to Tekasis