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Thread: Cap accross terminals...why?

  1. #1
    Tom Loizeaux
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    Cap accross terminals...why?

    I am re-habbing a commercial sound column and see that they put a 13uf cap accross the speaker terminals!
    What does it do?

    Thanks,

    Tom

  2. #2
    Senior Seņor boputnam's Avatar
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    bo

    "Indeed, not!!"

  3. #3
    Administrator Robh3606's Avatar
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    Maybe it's acting like a Zobel and is counteracting the voice coil Inductance??? There a crossover in there?? An Inductor in series so that's a crossover pole??? You have a driver part number I can throw into Bass Box???

    Rob

  4. #4
    Senior Member frank23's Avatar
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    if they put it at the speaker terminals of the cabinet, it would have the effect of shorting your amplifier output above a certain frequency. That would not seem like a smart thing to do.

    it could only have worked as a crossover if there was an inductor or resistor between the amplifier and the capacitor in either the + or - wire

    if it would have been a zobel, shouldn't there have at least been a resistor in series with the capacitor in between the speaker terminals?

    frank

  5. #5
    RIP 2011 Zilch's Avatar
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    If it's after a passive crossover, it's just adding another pole to the filter.

    If on the woofer and properly chosen, it would steepen the slope of the lowpass.

  6. #6
    Senior Seņor boputnam's Avatar
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    Quote Originally Posted by frank23
    if they put it at the speaker terminals of the cabinet, it would have the effect of shorting your amplifier output above a certain frequency. That would not seem like a smart thing to do.
    That's the direction my " . " post was headed, but the thing doesn't make sense to me.
    bo

    "Indeed, not!!"

  7. #7
    Junior Member P.Warner's Avatar
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    High pass?

    If that capacitor value was series wired, that would seem typical for a PA speaker high pass. Could somebody have rewired it?

  8. #8
    Senior Member 4343's Avatar
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    Question MTM?

    Quote Originally Posted by P.Warner
    If that capacitor value was series wired, that would seem typical for a PA speaker high pass. Could somebody have rewired it?
    If TWO woofers are wired in series, a cap across one will pass the highs to the other woofer.
    Mike Scott in SJ, CA
    Drive 'em to the Xmax!

  9. #9
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    Hello
    What is in the rest of the speaker and how was it wired.
    I may have an idea of what they were/are doing depending
    on how the rest of the cabinet is wired up.

    Let me know
    Mike Caldwell

  10. #10
    Tom Loizeaux
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    6 speaker column

    Sorry I've taken so long to post this photo.
    As you can see, there are 2 caps, one accross each of the bottom 2 speakers. The lower cap is a 50uf and the upper one is a 13uf cap. Though the top 2 speakers are removed, it's pretty clear that the top 4 speakers were wired in series. The bottom 2 are each wired in series with a pair of the top 2 in series. It's confusing...and unlike anything I've seen before. If someone wants, I can try to draw up a wiring diagram.
    All speakers are the same 8 ohm model.

    I'm wanting to replace the 2 missing speakers, but I want to know if a more convential series/parallel wiring plan would be an improvement.

    Tom
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  11. #11
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    Hello
    The cap across the terminals of some speakers will roll the high end off of those speakers. It's not uncommon for many speaker systems to do something like that. JBL did/does the same thing in the older SR series cabinets and many high end line array speakers do the same thing. In the case of your speaker instead of having all the speakers reproducing the full range signal they attenuate the high end by various degrees on some of them to smooth out the response and prevent so much mid and high frequency over lap between speakers. In larger systems it's sometimes referred to shading the drivers.
    The series parallel wiring is common in multiple driver speakers that use all of same driver in order to get the total speaker impeadance that is usable.
    What total impeadance would work for you.

    Mike Caldwell

  12. #12
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    Quote Originally Posted by Tom Loizeaux
    I'm wanting to replace the 2 missing speakers...
    What in the heck are you going to use that thing for?? It looks like something that might go across the inside back of a hippie van or something...

    Edit: Oops - I forgot about your first post - rehab on a commercial system...

    John

  13. #13
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    It actually looks like one of the column speakers that use to hang
    in the four corners of my old high school gym.......till I installed a real sound system for them about 8 years ago.

    Mike Caldwell

  14. #14
    Junior Member P.Warner's Avatar
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    I've been wondering for years why column speakers came to be. Was it simply convenient size, shape and asthetics or were they supposed to have some acoustic behavior besides beamy sibilance?

  15. #15
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    Actually a column of speakers however cheap they maybe has the laws of physics working for them. When speakers are in a vertical column the horizontal coverage is greater while decreasing the vertical coverage, such as throwing sound up into space or onto the ceiling. Also better long throw coverage with less loss. The line array cabinets you see at any major production are nothing more than vertical columns of speakers and drivers coupling together with aid of high tech horns and waveguides. Take a look a the JBL Vertec cabinets.

    Mike Caldwell

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