I wanted to extend the upper frequency response some and to reduce that dip in response near 50 Hz. I used the Horn Response program to test some changes. I increased the rear chamber volume, reduced the throat chamber volume, and increased the compression ratio from 2.0 to 3.0. Then I lengthened and  modified the horn profile. It still conforms to the standard 22.5 X 45 X 45 inch package for truck packing. Here is the v3.0 theoretical result. Note that the analysis now represents four cabinets on an open ground plane, or two cabinets on the floor by a wall, or one cabinet on the floor aimed into a corner. The dark line is v3.0 as compared to v2.0 (light line).
I wanted to extend the bass response a bit further so I also designed a horn extension to combine two cabinets into a single mouth opening. Here are the final results below.
Using the above analysis I designed a new cabinet for the LAB12 driver. The LABsub uses a powerful heavy duty woofer made specifically for it. Here are the specifications. I drilled out the mounting holes to fit 1/4 inch cap screws. The new cabinet was designed using the personal use version of Pro Engineer. The cabinet design has 3/4 inch thick material throughout. I used Europly. I'd use Baltic birch (full 3/4 thick is hard to find) and coat them with truck bed liner for professional use. I built mine for home use.

I designed the cabinets to go together with pocket hole joinery. It worked great and I did not have to use any clamps. Screw the parts together dry a few pieces at a time to make sure they fit properly. Then take them apart and screw them back together with glue. I used Gorilla Glue which seemed to work great for me. For pro use you may want to go with epoxy. The angle on the screws results in a little side slip when you tighten with glue because the glue acts as a lubricant. You need to compensate for this when you dry assemble. Just practice on some scrap pieces. I sealed the access covers with some sealing caulk from Parts Express. It compresses down to form a very thin gasket.
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