A close up photo which reveals the internal bracing. The vertical brace extends the full width and height of the enclosure and has a hole behind each driver. It's purpose is to form the back panel of a separate tweeter subenclosure (which eliminated the need for air tight tweeter installation) and to brace the deep (14" for sealed version, 18" for ported shown here) side panels. I also added a cut-out horizontal brace, shown through the lower driver hole, between each second woofer.