Hello! Anyone here with intimate knowledge of early '80's 4312's?
I have a strange low freq. response problem.
My ears have heard it from the beginning, but I finally have the tools to really see it in great detail.
Both speakers now have a sharp 20db dip at 125Hz, and a sharp peak at about 270Hz.I've religiously checked for air leaks and loose joints-none found.The 125/270Hz relationship made me suspicious of this.
For years, I wrote this off as room boundary issues, yet every room I put them in, regardless of room dimensions,I ended up with the same result. I recently tested these 4312's outdoors, one at a time,flush against a large brick wall, a reference mic 3.3 ft. away, the closest north/south hard surface at least 250 ft. away (the only way that I can mimic the original JBL test conditions), and got approximately the same results. SPL level was 80.
The room they live in is treated, with massive bass traps in the rear to reduce room boundary effects.
I found a test graph I made in the '80's with a Goldline RTA in an untreated room, and the dip at 125Hz was 10db down.
Today, in a treated room or outdoors, it's 20 db down.
The testing software I'm using is ETF 5.XXX (demo version).
This software also reveals the 250-270 Hz box resonance that's always bothered me from day one.
Has anyone tested these monitors this extensively?
Has anyone seen this before?
Thanks for everybody's help!