View Full Version : 4311B crossovers... again!

03-18-2010, 03:12 PM
Greetings all!

I recently picked up a good pair of JBL 4311Bs in excellent condition. I remember this model well from working in studios in the 1980s.

Since purchasing them I have - of course! - been on-line to read up everything I can about these magnificent beasts! I was surprised to learn of the crossover design - woofer wide open and only two caps.

I've also read the thread here, and on other web pages, about improved crossover designs to smooth out the frequency response, especially the peak in the high-mids.

I love the sound of my JBLs and would never go this far (I appreciate the school of thought that says that one should just leave the 4311's alone to be what they are), but I wonder if something as simple as a low-pass cap across the midrange driver might go some ways towards taming that peak?

(As this "solution" has never been mooted (to the best of my knowledge) you can perhaps infer from my question that my crossover design skills are zero!)


03-18-2010, 05:30 PM
Search by-pass, capacitor by pass, bypass caps etc
Much is here on the subject


03-18-2010, 06:09 PM
Hi Thomas - thanks for your quick reply. Not sure if bypassed caps is what I mean here. To my understanding, a bypass cap is a small value cap placed across an existing cap to... do something that supposedly makes it sound better!

I'm talking about actually adding a new capacitor to act as a low-pass filter across the mid-range terminals. Or alternatively a coil on one of the mid-range legs. Just as one would expect a standard crossover to have.


03-18-2010, 06:25 PM
The two forum members that would be most helpful with your question are "4313B" and "Zilch", based on their hands on measurements and experiments with these boxes (the L100 "family" and it's evolution). They are intimately familiar with many, many transducers.

I say this based on what I have read; try searching their posts.


03-18-2010, 06:50 PM
Cheers Thomas.

03-18-2010, 09:06 PM
I would say what you propose is a pretty in-depth crossover revamp that would require measurement capabilities.

I would recommend as was said above, search for posts from the two members noted above.

It would be much easier to follow what has been measured and done already vs stepping "out of the box" without the equipment needed to perform the requisite task.

You could however start here.