Wiring speakers of different impedance?

Discussion in 'DIY Corner - Tips & Techniques' started by Whitey80, Nov 4, 2013.

  1. Whitey80 Senior Audioholic

    Whitey80
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    So, I luckily came across a pair of JBL 2470 compression drivers set into JBL 2345 radial horns. (at a thrift shop...for $20!) They have fresh diaphragms and sound great.

    I also have laying about, a pair of JBL 123A low frequency drivers that sound great til their roll-off (2500 hz).

    I am thinking of experimenting and setting these up together to take a listen, the question is, the compression drivers are 16ohm rated and the low drivers are 8ohm rated. Would the math still apply as with normal parallel wiring resulting in a total of 5.33ohms?

    And, along the same lines, how would I figure building a simple high pass for the horn? (the 123A low frequency drivers a traditionally allowed to run full range, as JBL had always implemented them) Would it be for 16 ohm?
  2. Swerd Audioholic Ninja

    Swerd
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    It's not going to be so simple, unless you find an already existing design for this combination.

    First, you'll need a cabinet.

    JBL L100 Century

    It describes a closed 65 liter cabinet for that woofer. It will have less boomy bass than the smaller 44 liter ported cabinet used in the L-100.

    And if you haven't seen these, read them too:

    http://www.jblpro.com/pub/obsolete/2470.pdf

    http://www.jblpro.com/pub/obsolete/radial_horns1.pdf

    JBL says the compression tweeter can go as low as 500 Hz, and the horn is made to be crossed over no lower than 800 Hz.

    Once you build a cabinet, measurements will show what diffraction peaks or valleys on the tweeter's low end must be taken into account as you design a crossover. Measurements of these drivers – while mounted in the cabinet – will also give you real world impedance measurements as they vary with frequency. Speakers never have a single impedance value. Designing a good crossover requires knowing impedance vs. frequency for the range of the driver.

    I recommend using a low-pass filter for the woofer too. It will beam noticeably as sound gets higher than 800 Hz. Why have that when it can be avoided? With a proper crossover, the difference in impedance between the woofer and tweeter can be easily taken into account.

    I don't know much about using horn loaded tweeters in a DIY build, but you might get useful suggestions if you ask questions here:

    Lansing Heritage Forums
    Last edited: Nov 4, 2013
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  3. Whitey80 Senior Audioholic

    Whitey80
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    thatnks for the links.
    ive read the jbl spec sheets for them.
    i suppose what im really after for the moment is basically an unrefined slap together sort of deal, to feel out the speakers together and decide if its worth the time and money to go forward with a more complicated build.

    i have a spare pair of L100a cabinets, was thinking of just using them with only the 123 hooked up and building up a very basic crossover to run the horns with them and take a good listen.

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