Cabinet wiring question

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Mark C, Feb 21, 2004.

  1. Mark C

    Mark C Member

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    I am about to order speakers for a 6x10 bass cab. I can get the speakers in 4,8,16 or 32 ohm ratings and I need to wire the cab for a total load of 4 ohms. I have a couple ideas, but I was wondering if any experts out there can contribute some wiring ideas. Thanks
     
  2. Jim Collins

    Jim Collins Member

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    Six, 8-ohm speakers, when wired in series-parallel, will yield about 5.4 ohms, which is about as close as you can get. Three, 8-ohm speakers in parallel will give you about 2.7 ohms. Put two of those in series, and you have about 5.4.
     
  3. Mark C

    Mark C Member

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    Jim, do you think that 5.4 ohms will be safe with a 4 ohm load out of a 70's ampeg SVT tube head? I'm guessing it will be.
     
  4. Jim Collins

    Jim Collins Member

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    You'd be better off getting some real technical advice, as far as that particular rig goes, but if the OT can't handle a mismatch of less than 2 ohms, I'd be surprised. With 6, 4-ohm speakers, wired series-parallel, you'd get a total of about 2.6 ohms. It is actually preferable to have a load that is less than the OT expects rather than greater than the OT expects, so the 4-ohm speakers are probably a safer choice, but we aren't really talking about a huge difference, here.
     
  5. John Phillips

    John Phillips Member

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    What Jim says. Given the degree of mismatching (only 33% in either direction) it probably doesn't matter whether the mismatch is high or low really.

    Fender used the series-parallel arrangement with 8-ohm speakers in their Super Six amps of the 1970s to give a 5.33 ohm load with a 4-ohm transformer, FWIW.

    Another possibility would be six 32-ohm speakers all in parallel, which arguably might sound better for bass (the normal SVT cab has eight parallel-wired 32s as you probably know), but that would be less flexible if you wanted to use the same speakers for some other purpose later.
     
  6. Pedro58

    Pedro58 Supporting Member

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    Mark and I looked at this problem yesterday and found a cool site that calculates everything for you quickly. Arguably unnecessary for those of us who can do math! But fun anyway!
    http://www.eatel.net/~amptech/elecdisc/spkrmlti.htm
    I agree that the 32-Ohm per-speaker choice is the lesser option. That is a difficult thing to find in the case of a blown speaker! Thanks for the help guys!---Peter
     
  7. Mark C

    Mark C Member

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    Ok, I looked at another possibility - running 4 8ohm speakers in parallel for 2 ohms and then a pair of 4ohm speakers in parallel for 2 ohms. Put them together in series and you get 4ohms. Do you guys think there would be any problems with this, such as having some speakers taking on a greater load than others?
     
  8. John Phillips

    John Phillips Member

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    Yes. Power divides according to the impedance, so each 2-ohm combination will take the same amount of power, half of the total from the amp.

    Thus the two 4-ohm speakers will each be taking twice the power (and 1/4 of the total) of any of the 8-ohm speakers.

    Generally it isn't a good idea to mix up impedances and power loadings like this - better to go with a slight impedance mismatch on the amp.
     
  9. Mark C

    Mark C Member

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    Thanks John, that's what I thought, but I wasn't sure.
     

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