Speaker impedance

Discussion in 'Amp Tech Center' started by marshman, Apr 11, 2013.

  1. marshman

    marshman Friend of Leo's

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    So, I have a pair of 15" Eminence Speakers that a friend pirated out of some sort of subwoofer cabinet. The problem is that they are (seriously, I've checked and EMI has conifrmed) 0.8 ohms each. Wired together I get about 1.4 ohms. I happen to have a vintage Univox bass head that has a 2-ohm output selection on the back panel. If we were talking 8 ohm to 4 I'd be ok, but maaaaan, this is LOOOOW. It is still within a 50% tolerance (if we're to believe the 2-ohm output claim on the amp, it's within about 30%), but maaaaaan, this is LOOOOW.

    I had it in to a local, very highly regarded tech about 2 years ago, he replaced a few caps/resistors, corrected some ground problems, gave it a clean bill of health and said it makes 104 watts properly wired into an 8 ohm load.

    http://www.univox.org/pics/schematics/u1050b.gif

    I'm gonna wire it up, then have a beer and think about it. Maybe try it out after I have a chance to sleep on it, maybe hear from a few of our fine tech peeps here.
     
  2. printer2

    printer2 Poster Extraordinaire

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    Put the speakers in series.


    ... and try it. (meant to add that, microwave said time to eat.)
     
  3. PinewoodRo

    PinewoodRo Tele-Afflicted

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    I have seen a 2ohm output on some older studio power amps such as BSS or Turbosound - they worked just fine and allowed you to wire up a big amp to a lot of speakers.
     
  4. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    What you measure with an ohmmeter is DC resistance, not impedance....and what is noted at the speaker output of amplifiers is impedance. 1,4 ohms DC resistance is close enough to 2 ohms impedance - if you measure a Super Reverb or other 4x10 amps' speakers (8 ohms each...but they measure around 7.6 ohms) when wired in parallel you get around 1.6 ohms.

    Just make sure you leave them wired as you did - in series. Parallel wiring wound give you around .4 ohms impedance (and measure around .3 ohms); way too low for that amp.
     
  5. marshman

    marshman Friend of Leo's

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    So I wired up said cab and discovered that the plastic jack was kaput. Turns out the tip connection was just too mung-y to make contact.

    New question is this: can I use a metal jack, like a guitar input jack, in it's place, or will there be an issue with the 'sleeve' connection making contact with the metal of the jackplate?

    Thanks again!
     
  6. BluesAndBooze

    BluesAndBooze TDPRI Member

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    Presume you mean the speaker lead jack going into your amp speaker input?!
    No problem with a metal jack, both my Champ and Lonestar have them, just make sure on your soldering technique, it's the separation of live and ground that counts.
     
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