i saw this thread just now.
i was searching to see if anyone had discussed using a 90x60 horn instead of a 90x40, i saw the B&C me20 on ebay....i'm guess it would completely alter Wayne's 4pi design since it has different vertical dispersion, but wanted to search and see if it was discussed.anyway here is the link to the B&C 15.
http://www.audioroundtable.com/PiSpeakers/messages/17110.html
would using a 99db woofer in place of the 97db woofer require any crossover changes?
also would it make the efficiency of the 4pi go up a bit or is it a immaterial difference?