4425 level controls

[duaneage]

I see the 4425 schematic has two sets of level controls. Does anyone have a chart showing the transfer characteristics of these controls? It looks like one changes the crossover frequency while another adjusts the level. Or they could be contour controls.

Either way I am working on a crossover for a 2214H monitor and I am curious to see how this crossover works.

Also, there is 50 ohms of resistance across the woofer in the schematic. This is more than the L100T used (39) and I was hoping someone could tell me why they used this resistance across the woofer without a capacitor in series. It does not resemble a Zobel in the true sense.

[rek50]

The NL100t3 network has a pair of 82 ohm (series R1, R2) across the 2214H-1.

I don't see a Zobel, in the true sense, on this one (NL100t3) either.

Did you come up with a Zobel for the 2214H?

[duaneage]

I did come up with a Zobel but I am more curious about the transfer function of the level controls in the circuit.

[grumpy]

http://www.lansingheritage.org/images/jbl/specs/pro-speakers/1985-4425/page4.jpg

[duaneage]

Thanks for the graphs, I searched for something like that and kept finding schematics. If I had SPICE I could model it but I don't.

Nice trick they did providing a midrange control for a 2 way system. JBL always had great networks compared to the competition, most of whom were too lazy to try.

[grumpy]

http://www.audioheritage.org/html/profiles/jbl/4430-35.htm

David Smith explains a similar arrangement for mid/tweet contouring
in the section next to the "How to improve the 4430/35" sidebar.

[duaneage]

I just finished a horn project that could benefit from a variable contour network like that. It's a different horn (2380a) than the 4430 has but the principles are still the same. Sending a portion of voltage through a secondary filter to suppress midrange is an ingenious idea and one I will pursue with the system.