I just picked up a pair of JBL Apollo C51 cabs loaded with LX-5 crossovers and D-140 Fs. I installed the H91 horns and 2420 drivers I had lying around. I am not very satisfied with the sound. It is very boxy and unbalanced sounding. Poor low-end. I also have a pair of LX-16 crossovers as well. These cabs have an open square port in the front next to the horn. Is it better to seal it? What other things can I do to improve the sound to an acceptable level? Here are some pics.