How do you put a 16 ohm and an 8ohm speaker in a 212?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by TNJ, Mar 19, 2015.

  1. TNJ

    TNJ Gold Supporting Member

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    I have an elliptical open back 212 cab, and a Celestion Blue (15ohm) and
    a Fane Alnico 8ohm speaker.
    I'm thinking these two speakers would make a great match as a 212 with my ZWreck head.
    Only thing is, how do they get wired for best sound and appropriate matchup with the amp?

    S.
    j
     
  2. mark norwine

    mark norwine Member

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    whether you wire them in series or parallel, you have a bit of a problem brewing: They're not going to "see" (split) the amp's power evenly, and the loudness of each will be different.

    a 15 in parallel with an 8 is seen by the amp as a 5 ohm load.

    a 15 in series with an 8 is seen by the amp as a 23 ohm load.
     
  3. michael patrick

    michael patrick Supporting Member

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    Wired parallel it'd be a total load of 5.33 ohms, and wired series it would be 24 ohms.

    So it'd be best to run it parallel if your amp has either a 4 or 8 ohm tap.
     
  4. AbstractLunatic

    AbstractLunatic Member

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  5. TNJ

    TNJ Gold Supporting Member

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    Z says 16ohms is best with 2 8ohm, speakers.
    Anyone wanna trade my 15ohm Blue for an 8ohm blue?

    S.
    j
     
  6. lemonman

    lemonman Supporting Member

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    You can buy an impedance matching transformer from Weber, if you want to use what you have. WZC-50 for the 50 watts, WZC-100 for 100 watts:

    https://taweber.powweb.com/store/magnetic.htm

    These are what's used in their Z-Matchers.
     
  7. mark norwine

    mark norwine Member

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    Please explain how you'll use a weber product to match 2 unmatched speakers. I'm not seeing it...
     
  8. lemonman

    lemonman Supporting Member

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    You can use the transformer to raise the Fane to 16 ohms, or drop the Blue to 8; IOW you use it on only one of the speakers. I have one, I've done it before; works well.
     
  9. mark norwine

    mark norwine Member

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    so the primary of the weber device is in parallel with the 'other' speaker? Doesn't sound like a great idea to me....
     
  10. drbob1

    drbob1 Silver Supporting Member

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    The Weber is a transformer that converts one impedance to another, just like an OT. It's a reasonable solution to the problem, just VERY clunky!

    Your problem with doing this is that the FANE is a more efficient speaker than the Blue AND at 8 ohms will be getting 2/3 of the watts, so you basically won't hear much contribution from the blue. If you just want two speakers, and volume isn't an issue, you could add a wire-wound, 8 ohm resistance in parallel with the Fane. That'd balance out the watts, sort of like an attenuator on just one speaker...
     
  11. J M Fahey

    J M Fahey Member

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    Sorry, but that's wrong on many counts.

    And I answered such an error less than a week ago ... was it you?

    1) putting a resistor in parallel with a speaker will not "attenuate it" but simply load the amplifier down, not the same thing.

    If the amp is SS or tube but with mid to high NFB, the original speaker will still receive basically the same voltage across its terminals as before.

    Or amp power will go down simply because of the mismatch, not good.

    2) if Fane and Celestion are wired in parallel (nothing makes me think otherwise), putting a resistor in parallel with the Fane will also put it in parallel with the Celestion ... basic Electrical Circuit theory.
     
  12. Tone Meister

    Tone Meister Member

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    [​IMG]
     
  13. teemuk

    teemuk Member

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    With your different impedances power is not shared equally between the speakers. Depending on actual efficiencies of the drivers, this may unbalance - or balance - their perceived loudness.

    Whether wired parallel or series the total impedance will somewhat deviate from standard values. Those values were nominal to begin with, though.

    If you want equal power sharing between the loudspeakers then you need to impedance match. AFAIK, transformer is the most sensible tool for the job. BUT... The higher the power level the impedance conversion is performed at, the clunkier transformer you'll need. Just facts of life.

    IMO, least sensible method is trying to "equalize impedances" with a resistor. Not only are you wasting several watts of power you are also changing load characteristics seen by the amp, which will usually more or less affect the frequency response and tone of the amp. Second, loudspeaker's impedance varies across its bandwidth (why its called "impedance" to begin with) so you can't achieve a "fixed" level of attenuation with just a single resistor. In practice, some frequencies will be attenuated less than others.

    My 2 cents: If you chose a "difficult" pair of loudspeakers to work with why not just face the fact? Don't try a "bubblegum patch" to fix the issue, fix it right. Abandon the other speaker and replace it with something that is more ideal from the get go. IMO, starting point for choosing unidentical drivers is reasonably close match in sensitivity and impedance ratings that fit the overall circuit, not picking everything in random and then wasting tremendous amounts of resources trying to fix all shortcomings.
     
    Last edited: Mar 22, 2015
  14. drbob1

    drbob1 Silver Supporting Member

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    Sorry, typing too fast, too late last night. I meant in series with the Fane, of course. And beyond that I disagree that it's going to change the sound much. You're losing less than 3 dB, using a non-reactive attenuator. I'm pretty sure anyone who has used an old fashioned attenuator set to 2 dB will attest that it's impossible to hear a change in timbre due to that. In fact, one of the amps that's been fairly well received here, the Vox AC4, uses a resistor network to lose 3 dB and 10 dB IIRC, and sounds good. If you have "hound dog" ears you might be able to hear something but I'm skeptical. I have used a similar solution in a 412 cab when I temporarily had 3 16 ohm speakers and one 8, and noticed no problems with sound.

    Of course, the best solution is to find the correct speaker, but if this is a temporary situation while you figure out what sounds good, I'd go for it.
     
  15. AXEnGEAR4J

    AXEnGEAR4J Supporting Member

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    Without going into all the details as others have. For your sound and your amp you are much better off getting the correct impedances in you speakers!
     
  16. TNJ

    TNJ Gold Supporting Member

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    My other question is how a Fane AXA 12" stacks up against a Celestion Gold 12"?

    S.
    j
     

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