Its a half of an USB bin.
The ES18PHB bin is a high efficiency, high power bass bin designed for general PA use and raves. It use a 18 driver 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 ES18PHB is an extremely efficient bass bin, with a very clean solid sound without any honky peaks or distortions. It works great as a kick bin above subs (like Labs) but also on its own.
Over damped design for better transient response.
Remember to invert the polarity of the driver to keep the phase.
Compact box dimensions.