Why you use drivers designed for horns in horns a f120a is for AS or sealed cabs not BLH. Thus the poor soud quality in bass. I would suggest adding acusta stuff to BLH mouth and behind driver. Or change driver to 1 designed for BLH use. f120a is a great driver just used wrong like anything else will not perform proper. I seen your BLH for sale on audiogon knew right away this was wrong combo. BLH can add color to sound why I greatly over built our BLH offerings and have now do not offer a BLH. But the main issue with yours is wrong driver used in BLH. Not all wide bands or fullranges are for BLH cabinets.
Like Cain Ben's set up hollow sounding
We have some DIY Cain Ben's with F120A drivers that we just can't seem to tame the hollow sound like listening in a cave? It is a simple system Passion Pak i10 integrated Sony 555es driving the speakers with Element cables. 1st problem noted by others might be the deal breaker the room 25x16 cathedral ceiling 24' up opening to another 25 off the 25 into a lower ceiling room. The speakers are on the 16'x10' heigh wall with the ceiling going up. The speakers they are replacing did quite well Reynaud Twins which were limited in bass but did well other wise. We do not play our music loud but loud or soft the hollow cave effect seems to stay with us. We moved them well into the room helped a little 48" out from the back wall into the room but still there is the sense you are looking into the performance, it kind of brought it out more into the room but still hollow sounding. We stuffed everything we have pillows wool ,,,,,,,,, into them and this helped some but lost some of the live sound? not muffled but not as open? Read one post that said cables Paul Speltz made a difference another post Sistrum stands another thought amp made the difference. Seems this can be a problem with this type of speaker? They look great and at times the sound is right and good bass. Any thoughts I would greatly appreciate them. Thank you