I found this website http://www.volvotreter.de/pics_plans.htm which has plans available for download for a 150Hz tractrix horn using a 12" electrovoice EVM12L driver. Has anyone used this driver before? If so, how high do you think this design can reach? (the actual plans can be downloaded from here http://www.volvotreter.de/files/150Hz_Midbass_Tractrix_Horn_v1.3a.pdf). Is this even a good design? Has anybody got any other designs for 8 to 12" cone drivers for midrange horns with a cutoff around 200Hz?

If anyone has the time to download the plans above, can you please explain what the angles in the bottom left picture means. The diagram looks very similar to the one in the middle right, it is confusing me !!!!!!! please help if you have the time, or if you can!

Thanks in advance!
Adrian