7 Jan 2015 Chris A's main rig (5.2)

Where do you have the horn exits on your Thspuds located. 

The SPUDs' mouths are located in the corner of the room just behind the flat back of the Jubilee bass bins, thus forming an additional triangular vertical path behind the Jub bass bin with the sub exit pointed upwards, the SPUD against the front wall, and the side wall stiffened by a piece of plywood.  This adds about 3 feet of additional horn path length to the SPUDs and provides a low cut-off of about 13 Hz in-room (-3 dB). 

I cross over from the SPUDs to the Jub bass bins at 40 Hz.

So if I understand you correctly, the opening is pointing towards the ceiling.  I never thought of that.  What is your ceiling hight, and do you think this would have much to do with it.  As my ceiling is about 8'. I will be adding blocking and plywood in my corners to stiffen them, which should be the same as youadding plywood.

I guess one could always experiment to find what works best.

Nine feet ceiling height for my room.  At the lowest sub frequencies (13-35 Hz), ceiling height isn't significant.  Above 35 Hz, my ceiling height is significant--nearing a quarter wavelength.

 

Most of the room-supported gain is due to its width (18.3 Hz quarter-wave resonance) and length (7.2 Hz quarter-wave resonance). 

 

Stiffening the corners is a good idea: I got more than 7 dB gain at the lowest frequencies just by sliding 1/2 inch plywood stiffeners of about 4 x 4 feet against the side walls using the weight of subs and Jubs only to fix the two plywood stiffeners in place.