L212 crossover schematics

[DavidF]

4313B: "Too bad. That could have been fun. You could have whipped up some nice 24 dB/octave LR active filters, put some nice little amps behind them and possibly ended up with something rather spectacular."

That's what I originally thought. I liked the sound of the L212s and used them for many years, but they needed EQ to sound "right" to me. I have moved away from electronics with OP Amps to Class A discrete and you just cannot find reasonably priced active cross over networks with class A discrete circuitry. Plus the cost of six power amps became prohibitive vs what the L212s give you.

Well, what about using a 3rd order network set up for actual driver impedances and the original cross over frequencies? The driver impedances don't vary that much in the vicinity of the cross over points, and the steep slopes of the cross overs networks would minimize this effect more than a few octaves either side of the cross over frequency in any case. You might not even need the Zobel networks if the cross over frequencies are chosen far enough from the resonant frequencies.

You've lost me...sorry.

You were trying to track down JBL xover schematics for reference in constructing replacement xovers. You found some schematics including JBL’s own service guide which is all you need to construct your own mock-ups. But you keep coming back to errors and miss-matches in follow up posts with some component values you expect these schematics to conform to. What values and who came up with them? Now a different design altogether?

[DHL]

You've lost me...sorry.

You were trying to track down JBL xover schematics for reference in constructing replacement xovers. You found some schematics including JBL’s own service guide which is all you need to construct your own mock-ups. But you keep coming back to errors and miss-matches in follow up posts with some component values you expect these schematics to conform to. What values and who came up with them? Now a different design altogether?

Yes, that is still the goal. Building new cross overs. I was checking the values in the published schematic to see if they matched the published spec of cross over points of 800 Hz and 3000 Hz. If those calculations would have checked out I would be a happy camper and that would be the end of it. But they don't even though everyone here says the component values are accurate. Then more mumbo jumbo about acoustic vs electronic cross over points. I my experience, when a manufacturer cites cross over frequencies they are referring to the ones built into the cross overs via the component values. Sometimes they assume resistive loads but if so they are close to the actual speaker impedances or what's the point? Seems to me JBL made a number of design errors in the L212 development and everybody here is trying to justify data that does not add up.

In the quote above I was responding to 4313B response to an ealier post about tri-amping and dumping the passive crossover. Sorry for the confusion.

[DavidF]

Yes, that is still the goal. Building new cross overs. I was checking the values in the published schematic to see if they matched the published spec of cross over points of 800 Hz and 3000 Hz. If those calculations would have checked out I would be a happy camper and that would be the end of it. But they don't even though everyone here says the component values are accurate. Then more mumbo jumbo about acoustic vs electronic cross over points. I my experience, when a manufacturer cites cross over frequencies they are referring to the ones built into the cross overs via the component values. Sometimes they assume resistive loads but if so they are close to the actual speaker impedances or what's the point? Seems to me JBL made a number of design errors in the L212 development and everybody here is trying to justify data that does not add up.

In the quote above I was responding to 4313B response to an ealier post about tri-amping and dumping the passive crossover. Sorry for the confusion.

OK. You are a newbie to the forum. Giving you the benefit of doubt.

Still not sure what you are basing this whole argument about what is correct and what is not correct about the JBL original crossover.

I must be under the wrong impression about your experience with speaker design. It sounds to me as though you are taking the published crossover frequencies and calculating component values using textbook electronic formulas with a fixed load to match up with those frequencies. Your results contradict what the JBL designers came up with for a crossover topology as they naturally would since text book calculations rarely work as predicted on actual speakers. When we respond to you that the values shown in the schematic are correct as originally designed you balk at accepting this answer. The answers we give are trying to explain that there will be considerable deviation from formula calculations in any successful crossover design for many reasons. These responses are “mumbo jumbo” that does not resolve your contradictions. This leads you to believe the original speaker design was faulty and our answers were merely a weak effort to cover up what you see with absolute clarity?

If I am off base it's just what I take literally from your comments.

I admit some bias favoring any design that the engineer who produced L212 comes up with. He contributes directly and indirectly here on occasion. Still I don’t see how anyone could claim he screwed the pooch on one of the company’s top of the line models.

What are the number of errors you have found?

[4313B]

Then more mumbo jumbo about acoustic vs electronic cross over points.

Fail...

What are the number of errors you have found?

His ignorance quite simply isn't our problem. This thread ended at post #2 with the link to the schematic. If someone can't figure it out past that they have no business getting involved in the first place.


I shouldn't have taken the bait when my previous thread was called into question.


There are no errors in the data, deal with it...