I've been using 4312 (mid-ranges and tweeters removed) with LE85/horns and 2405 bullet tweeter combo for a year now. First order series caps and on each compression driver, L-pads to waste dBs. No iron on the woofer, ala stock 4311. Suits me, my family, and my room quite well.
Love the JBL 123A/2213 tone so I'm trying them in a little bigger cabinet than that in which they normally work. The 4310/11/12 monitors are about 1.5 cubic ft. After reading that the 4311's are tuned around 40hz, I decided, "well, without being greedy and knowing there's no free lunch, how about a little more bass."
I forget who, but someone here suggested that I aim for 2.5 ft. in the new enclosures. I aimed but constraints parked me at about 2.1 in what are now the finished cabinets.
As in the 4311's, the woofers will fly solo in these new ported boxes. JBL LE85's on stereolab round horns will rest on top and outside of the cabinet. Probably the 2405's, too, but that's irrelevant for now.
My goal is to get the woofers to sound a little deeper, a little more open and lifelike than they do in the 4311. I'll run them wide open, ala the 4311/12, with same first order series caps on the upstairs horns.
The new port tube is 4" diameter. After some cypherin', I'd arrived at about 11.75" long, which I believe theoretically tunes the whole shebang to somewhere in the 30-33 hz range.
I've built a phono stage with octal tubes and point-to-point wiring, so I know the meaning of "fine tuning." (my hagerman cornet clone works, sounds good, but I wouldn't advise anyone to follow me down that frustrating path!) I know it may take some tube tweaking but how do I decide what frequency to even aim for?
Help! And thanks in advance.