I have no idea what he is and what he is looking for.  He declares himself as “just an average guy in an average basement shop building hi-fi audio horn speakers from wood”.  I do not even know in what country his leaves, not that it is important.  He has a site and a blog:

http://sites.google.com/site/diyfirefly/

http://diyfirefly.blogspot.com/2010/09/horns-are-up.html

Anyhow, he looks like recently made a new installation.

Let see what it is. The playback has 38 Hz tapped horn, 100 Hz Multi-Sided Conical Exponential Horns with unknown drivers, the 320 Hz Round Tractrix Horns with JBL 2446 and some kind of tweeters. It looks an attempt was make to time-alight then in frame – a good sign. The author is concentrated on the wood crafting and provides no information about sound of the thing, crossovering and anything else. The horns are not positioned properly; most likely they are not even connected and juts too fresh.

green heron wrote:

I'm happy with my results midrange on up at the moment, but I'd like more slam from the midbass horns.  The backchamber may be a bit too large, so I'm planning to experiment with the cabinet volume.  Do you have any suggestions to tell what the ideal cabinet volume is and what the typical sound characteristics that indicate if a backchamber is too large?

Yes, you will have more “slam” from the midbass horns if you tune your back chamber. When your backchamber is too large the lower knee of your midbass sound very light, you get more extension and bass accent with back chamber properly tuned. I had guidance how to do it.

http://www.goodsoundclub.com/Forums/ShowPost.aspx?PostID=2991

My article was written for as your midbass that has slow beginning of the opening. Your horn is conical and I do not know how they behave. Conical horns are reportedly very unpredictable and you woeful never know how they behave. So, you need to drive your Fs up and down to see how your conical horns will response to it.