I have been upgrading a pair of these very fine speakers, with success. The cabinet is 3.5 cu ft, and is on legs and properly bottom ported at the Fs of the woofer, 25Hz. It has a 12 db crossover, of unknown spec, but it seems to be close to the intended points of the more sophisticated Jantzen cross, 1500Hz and 3500Hz. This has made an amazing difference. I rewired them internally, one at a time, with silver sonic hook up wire, the buck a foot stuuff, 16 ga. The clarity and focus is dramatically increased, with a decrease in bass overhang.
Has anyone heard these Jantzen crossovers? They are available at Parts Express. http://www.parts-express.com/pe/show...number=260-896. I have almost a thousand dollars worth of parts, so I tried to buy just the schematic from Jantzen, refused. Here is a link to info. http://www.troelsgravesen.dk/JBL_L100.htm
Cheers.