Hello fellow JBL enthusiasts!
Hopefully this post can help other JBL folks as well. I purchased a pair of 4412 studio monitors new about 25 years ago. Noticed some foam rot on the 128h-1 woofers about 8 yrs ago (or so). Had them re-foamed by a factory authorized JBL rep. Haven't really used them mush over the last few years but ever since they were re-foamed I have noticed a lack of bass.
The foam surrounds are put on correctly (glued to the back, etc.). I have checked phase and polarity to the woofers on each side (L/R). Tested with 1.5 v battery (+ to + and - to - pushed woofer to back of frame so we are good there. Just swapped the polarity on the woofers last night to see if there was a difference and there was NO noticeable difference in sound. Seemed odd.
Started thinking that perhaps the crossover network but, and somebody please confirm, I am under the impression that the crossover really shouldn't cause any issues on the low end as the crossover is more or less passing thru the low end frequency unabated (perhaps a little low pass filtering?). So let me say that the surrounds are not very forgiving and seem pretty stiff. Not much movement at all when listening to material. I have plety of amp as I am using a Bryston 4NRB for the power amp. Even pushing a bit on the cone seems fairly stiff with limited movement. Nothing binding up (like voice coil) but just stiffer than I would think they should be.
Starting to think that the material (foam) used may have not been the correct material as the chap that repaired them was mostly into repair of JBL pro (PA, etc.) equipment for rock gigs. I don't know but what do folks think - possible foam issue here?
Also I have read that the original foam is long gone but some folks may have comparable foam (i.e. Rick Cobb perhaps?). Lastly any plugs for some service shops in the USA. I am on the east coast but can ship anywhere domestic US. Well thanks for reading and any comments would be highly appreciated. Thanks!
PM