Here I was, reading various extremely technical posts in the archive regarding the calculation of theoretical sound pressure levels (thanks, Joris and bgavin!), and I came to the conclusion I'd have to suck up and ask for help in calculating the expected SPL for my new Bag End S15-D with my G-K 400RB. Then I found this site (thanks, Google!) A cool tool for the rest of us! (In case you care, in my case the calculated 1M SPL for my G-K head and one cab (120W, 103dB published sensitivity) is 124dB, and for a pair of Bag Ends with the same head (100W, 103dB X 2) is 126dB.)
Download my spread sheet and it is directly calculated in the CABS tab, or you can plug in the numbers in the SPL tab for various power ratings. The CABS section uses the manufacturers power rating and calculates the SPL accordingly. http://www.ofgb.org
Bruce - I'd love to see your data, but I can't open the spreadsheet after downloading - "format not valid". I'm only running Excel for Win95.
Sorry, the format is Office 97 / Office 2000 standard XLS file. They changed the file formats after Office 95. Time to upgrade... send $$$ to Bill Gates...