4x12 cab suddenly has no low end

Discussion in 'Amps and Cabs' started by hbar, Apr 16, 2015.

  1. hbar

    hbar Member

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    My 4x12 had been working fine for about 5 years. One day we load up our gear into the trailer and head off to play. Unfortunately weather did not cooperate, and the gig was cancelled w/o ever even opening up the trailer.

    After unloading the gear back into our practice room (as we have done a thousand times w/o issue), my cabinet suddenly has no low end. It's hard to say if the volume is reduced or not, since half of the audible spectrum simply isn't there. I've tried my amp with different guitars, cables, 4ohm/8ohm/16ohm outputs, etc....I have definitively isolated the problem to the speaker cabinet itself.

    So, what could cause a speaker cabinet to still function, but not have any low end? I opened the thing up, and there is no apparent damage to any of the speakers or wiring. I'm at a loss, and we have a gig Friday night. I've resigned myself to getting either new speakers or a whole new cab, but this seems like it should be easily fixable.
     
  2. Haz

    Haz Member

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    Maybe there is something with the room acoustics? Phasing problems with speakers on in the room?
     
  3. hbar

    hbar Member

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    My gear is set up in the same place it has always been, and even after moving the cabinet around to look at the innards and testing it at what ended up being various locations around the room, the result is the same. The sound is amazingly thin, and it is solved by using a different speaker cabinet.*


    *note I could also solve this by going back in time, but that seems somewhat impractical at the moment.
     
  4. tenchijin2

    tenchijin2 Member

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    Cables and wiring are the only things I can think of that could cause a major signal change like that (since you say it's not the amp). Even though there's no "apparent" damage to those systems I'd replace the jack at least.
     
  5. dayn

    dayn Silver Supporting Member Supporting Member

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    Did you try it with a different head? Maybe it is your tubes.
     
  6. hbar

    hbar Member

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    Why would the tubes work 100% ok with one cabinet, and absolutely terrible with another cabinet (given that they are the same impedance)?


    I'm ok with replacing the jack & wiring being the answer, that's why I used the word 'apparent.' But I'm struggling with how that would produce this effect, especially since I can't find anybody else having posted about this problem, at lest not on the first 10 pages of google results.
     
  7. JDutch

    JDutch Member

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    +1. Loss of bass and/or volume is one of the clearest signs that power tubes need to be changed. I noticed the OP said that he tried the rig with different cables and guitars, but not with different amplifiers.
     
  8. hbar

    hbar Member

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    I did not try with a different amplifier. I didn't have immediate access to one, but I'm not clear how changing the cabinet would solve the problem if the tubes were at fault. I've actually tried 3 cabinets in total, and MY cabinet is the only one that exhibits the problem.
     
  9. tele_player

    tele_player Member

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    I would use a multimeter to check that each driver shows the appropriate DC resistance, and make sure none of the speakers has become disconnected.
     
  10. tenchijin2

    tenchijin2 Member

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    The OP said he tried different cabs with HIS amp though, and they worked. So that would (if his observations are correct) isolate the problem to the cabinet.

    Major weak signal would indicate some kind of fault in the physical connections *as the most obvious starting point* IMO. 4 speakers don't just suddenly stop reproducing low end. One bad jack, though, can interrupt the signal to the whole cab.
     
  11. hbar

    hbar Member

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    I had the cabinet open last night, and all the connections were secure. They actually took some work to get them off to inspect the speakers. They are the slip on clip style, not soldered. But the jack is a soldered connection...both jacks produced the same result if that helps diagnose anything.
     
  12. Bradleyonmic

    Bradleyonmic Member

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    I would check for air leaks if it's a sealed cab. It's hard to believe it could be that bad all at once, but I guess possible.
     
  13. wbm68

    wbm68 Member

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    I had the exact same thing happen with a Marshall 4 x 12 in a rehearsal studio we rented. One day fine, 2 days later the cab had no low end, no punch and just sounded wrong and lifeless. All 4 speakers were working and there was sound etc. etc.
    It turned out that 2 of the 4 speakers were wired out of phase. In my case, somebody had switched wires inside the cab.

    Now if you are the only one who has access to the cab and you know you didn't do anything inside the cab, I would suspect that something on the input plate of the cab may have gotten damaged causing maybe some wires to touch that shouldn't.
     
  14. T Dizz

    T Dizz Member

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  15. RussB

    RussB low rent hobbyist Silver Supporting Member

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    OK, you opened up the cab. Did you test each speaker's resistance with a multi-meter?

    You can also make a speaker cable up and disconnect all the speakers, and play them one at a time
     
  16. SirGilmour

    SirGilmour Supporting Member

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    Time travel is looking more and more attractive isnt it? ;)
     
  17. Tylenol Jones

    Tylenol Jones Member

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    Is it possible it's now working out of phase, therefore reducing the low-end significantly?
     
  18. hbar

    hbar Member

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    No, was expecting the problem to be much more obvious. :(

    Ok, that's something that's easy to test. And whoever asked, no, nobody opened the cabinet and rewired it on me.
     
  19. mix2much

    mix2much Member

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    Sounds like a phasing issue. Hope you figured it out.
     
  20. hbar

    hbar Member

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    I don't disagree, but I don't see how you can SUDDENLY have a phasing issue. Can't wait to get my drill recharged to get the thing open again.
     

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