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Checking impedance?

Discussion in 'Amps and Cabs [BG]' started by velvetkevorkian, Feb 9, 2006.


  1. I recently bought an old Peavey Mk IV head, with a Scott Systems 1x15" cab. However, I believe Scott Systems is basically just some guy (apparently an ex-Iron Maiden roadie!), and the impedance of the cab is not specified anywhere on it. Is there any way of checking the impedance of said cab? I wouldn't mind adding a 4x10" on, but I don't wanna blow anything up:)
    For reference, the Mk IV gives 300W into 2 ohms, and 210 into 4.
    Cheers folks
    Kyle
     
  2. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge
    If you have a multi-meter, set it for resistance, set the scale appropriately (10 ohm rather than 10 x1000 for instance...) Plug a cble into the cab and then read the resitance off hte other end of the cable. In the unlikely event that the cable is speakon to speakon, you'll have to disassemble the non-cabinet end connector and read from the wires directly. Does that make sense ?
     
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    You can't measure impedance without special gear but use a DMM to measure the DC resistance, it will be about .8x impedance.
     
  4. 4Mal

    4Mal Supporting Member

    Jun 2, 2002
    Columbia River Gorge

    so an 8 ohm cab would read something like .64 and a 4 ohm cab something like .32 ? Hmmm, didn't know that. I always assumed that my meter needed 'zero'ing ... I use an old analog needle variety no fancy schmancy Digi stuff...
     
  5. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW:

    another thing I do typically when I first get one is crack the cab and have a look, unless impractical for whatever reason. See if it's been jacked with, anything looks amiss, or just to see what it's made of. Pretty much any speaker with any ID will have the ohm rating. You can get the numbers off the speaker and often find out exactly what it is and the parameters if your lucky.

    Oh yeh, I'd put some indication of the rating by the connectors so somebody besides you knows. It may prove beneficial in the future and if someone had done that you'd have known - unless they were screwing with you of course. Always a good to idea know not believe.
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    8 ohms impedance will read somewhere between 5.5 and 6.5 ohms DCR on average, 4 ohms half that. Impedance and resistance isn't the same thing, but don't feel bad, from what I understand no one at AccuGroove is aware of that either.

    Yeah, I know, but I couldn't resist.
     

  7. :D:ninja: :bag:
     
  8. seamonkey

    seamonkey

    Aug 6, 2004
    One way to get close is to put a known impedance in series with the cabinet. Like a cabinet you know to be 8 ohms, or you could use a resistor. Have the keyboard pr PC and play play a steady organ note and measure the AC voltage across each.

    Use a few different frequencies.

    A cabinet with a higher voltage reading than across the known cabinet would be a higher impedance.
     
  9. Nice one, took a peek inside and it's an 8 ohm speaker, rated for up to 400 watts. Sorted! Ta!
    Now I just need to work out what 4x10" I can whack on next to it that'll work out at 2 ohms...:meh:
    Thanks for the help
    Kyle
     
  10. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    None, though a 4 ohm cab will come to 2.7 along with an 8. But all things considered a 2x10 is likely adequate anyway, and don't fall into the "I want to get all the watts out of my amp" myth, a 4 ohm total load is a far wiser move.