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Thread: jBL-UREI 811C crossover options?

  1. #1
    Join Date
    Jun 2009
    Toronto, Canada

    jBL-UREI 811C crossover options?

    I recently acquired a pair of the coaxial drivers used in the UREI 811C monitor: JBL E-145 + 2425.

    The previous owner built a robust pair of cabinets for them using 1.5 inch thick panels all round which reproduce the volume and tuning of the originals.

    However, he contented himself with using a pair of Altec N-604-8A passive crossovers, designed for the 604-8K. The speakers certainly function with this crossover, but it's hardly the optimal solution.

    One option for me is to reproduce the crossover design published by JBL in the 811C "Technical Manual."

    But I'm also wondering if any users have instead used a modern electronic or digital crossover and, if so, what slopes and crossover frequencies they used, and how they implemented the time alignment feature of the original crossover.

    Appreciate any tips or comments!

    Thanks! Joel.

  2. #2
    Senior Member
    Join Date
    Feb 2009
    annapolis, md usa
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    Took a while to find this in my basement. Thought this may help if you decide to go passive. I bought this several years ago to scavenge an L-pad that broke on my 813C. You're welcome to it if you pay the shipping to get it to you.

    My to do list has the digital crossover/multi amp approach on it. I do have friends with knowledge of such things and the measuring equipment necessary to evaluate it. I haven't seen any threads here to date about someone going digital with the UREIs.

    You're probably going to want to use subs with these. I used 2245h woofers in 8 cubic foot boxes with 813Cs and have a friend using the same subs with his 811Cs.

  3. #3
    Senior Member eso's Avatar
    Join Date
    Aug 2009
    Long Beach, CA
    The C series is tricky because Harmon completely redesigned the crossovers with the Tapped inductors making them very hard to replicate.

    To stay passive and time align might require modifying the circuits used in the original A and B series crossovers. This would require re-calculating the inductor and probably cap values to make the correct delay for the 801C coax. On up side to that is the 801C has the smallest physical offset of all of the Urei coax configurations so the time alignment filter should have the least insertion loss.

    I don't have the know-how to make those changes, but Donald Patten on the Altec Users Board does and he's a very helpful guy.

    30Hz Bass Horns/K151, Custom mid bass & midrange horns/Cogent DS 1428 & 1448 field coil drivers, Fostex T925a tweeters.

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