My attempt to soup up a pair of JBL L19s was a mistake. They look and sound amazing down to about 100 hz. The 2118J woofers that I put into the L19 cabinets are much heavier than the stock 116As, and I assumed they would sound better. I said that they were great. Comparing them side by side to other JBLs I had at the time revealed a lack of deep bass response. Frank at the Speaker Shop explained why. The 2118Js were made (and I removed them from) a set of 4612 speakers, professional PA speakers, rated down to 70 hz. As magnificent as they are, they have much shorter voice coils than the 116As, and do not have a long enough excursion to go low. What I ended up with was a beautiful, punchy sound down to the mid-bass frequencies, but an ultimately unsatisfying speaker system. I am about to take delivery of a set of the correct 116A woofers, and know that I will end up with a better sounding system (I've had L19s before). I haven't heard a pair of JBLs in weeks, and am looking forward to hearing the sound I love so much.
UPDATE: They sound great! I love JBL.