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Thread: JBL 4412A crossover network info

  1. #1
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    JBL 4412A crossover network info

    I'm looking to mimic the passive crossover in the JBL 4412A monitors with an active crossover. I have the schematic and was wondering if anyone generally knows of the characteristics of this passive crossover. Besides functioning as a crossover at 850Hz and 4kHz, what slopes are used? Also, does the passive unit do other things to address time alignment, phase, etc.

    Thanks for your help.
    EJ

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    Senior Member pos's Avatar
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    If going active digital you will have much more freedom and power than the original passive network, and could probably achieve a much better result (optimal crossover points, time alignment using delays, symmetrical LR acoustical slopes, driver response matching, etc.).
    Here is for example what GT did: http://www.audioheritage.org/vbullet...-DriveRack-260
    Do you have measurement gears?
    I am also contemplating the idea of using an active crossover for my beloved 4412...
    Sticking a protection cap in series with the tweeter might be a good idea though.

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    Thanks for that link.

    My main system (non-JBL ) uses a 3-way active crossover. I was considering trying the active crossovers on the 4412 on those occasions I listen to them. The passive crossover in the 4412 would be completely bypassed and the wires from the drive units would be hooked up to a new terminal block with separate HF, MF, LF. But the crossovers are analog not digital so all I can adjust are crossover frequencies, slopes, and S-K/L-R filters. I cannot adjust delays, etc. Thus my question about whether the latter parameters - which I cannot adjust in the analog domain - are an inherent part of the 4412A passive crossovers. I guess it won't hurt that much to try them out but I wanted to get a better idea of how the passive units operate.

    Yea, definitely need measuring instruments for this.
    EJ

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    Senior Member macaroonie's Avatar
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    This is worth a read http://www.troelsgravesen.dk/JBL_L100.htm

    and remember to add a DC blocking cap ahead of the tweet.

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    Quote Originally Posted by macaroonie View Post
    and remember to add a DC blocking cap ahead of the tweet.
    Thanks for the link as well. Nice read.
    As for the blocking cap, I like to live dangerously.
    EJ

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    Senior Member audiomagnate's Avatar
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    Quote Originally Posted by club900fe View Post
    Thanks for the link as well. Nice read.
    As for the blocking cap, I like to live dangerously.
    Hey, I ride bareback as well, and for a pretty good reason. I A/B'd a a 2405 electronically crossed over at 8K, 12 dB/8ve with no "protection" to one crossed over the same way but with an 8uf Solen blocking cap and the difference in sound was huge. It wasn't just sensitivity loss because of the ESR of the cap, the unblocked tweeter sounded more dynamic and alive.

    As far as duplicating JBL crossovers with an EC, it's pretty darn easy. They're almost all very simple 2nd order designs.

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    Senior Member pos's Avatar
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    Adding a protection cap will always change the response and especially phase behavior at the crossover point.
    So if you want to compare with/without a cap you have to take it into account in the electrical crossover design to get the same amplitude and phase acoustical slopes in both cases.

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    I've had no problems going without a blocking cap for many years for the reasons mentioned. This is of course in the appropriate circumstance.

    If the passive unit in the 4412 is a relatively simple second order filter, it would makes things easier. Thanks.
    EJ

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    Senior Member pos's Avatar
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    For one thing I think the 4412 and 4412A have different filters, with a steeper slope on the tweeter for the 4412A, maybe because the tweeter is different.
    So it depends on the exact components you have at hand.
    You can find these network in PDF format online.

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    Yes, I was told that the 4412A crossover was updated from the 4412. Whatever that means.
    EJ

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