Folded-Horn Back-loaded Speakers

After building the smaller 2.1 system, I found the paper "A Method for Designing a Compact Back Loaded Horn Loudspeaker System", by Martin J King. See:

http://www.quarter-wave.com/Horns/BLH_Design_Article.pdf

There is a drawing in the paper that made it look easy to build. It seems "Compact" in the title is a relative term - these speakers are much larger than the last set, but are small in terms of "folded-horns". There are two modifications to the design in the paper:

1) An 8" sub-woofer and 75W amplifier is added to one enclosure.

2) Rather than one 5-1/2" front-facing driver, there are four smaller drivers with angled about 22 degrees off vertical.

To accommodate the four drivers, the width was increased from 8" to 11-3/8", and the height from 38" to 44.5" (including about an inch for the feet). The face holding the four drivers is constructed effectively as a hip roof, in an uneducated attempt at treble dispersion. A small 60 w/ch amplifier is added at the top of the enclosure with the sub-woofer, where the plate amplifier is added to the back. Here's a picture:

"Back-loaded" means the output of the "horn" is out the back. Here's a picture with the sides opened so you can see how the sound flows out the back: