actual ohms on 16 ohm cab

Discussion in 'Amps and Cabs' started by JBPlanck, Feb 3, 2012.

  1. JBPlanck

    JBPlanck Member

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    Just checking the ohms on a 4x12 cab with my ohm meter, reads 14 ohms (Crate 80s 4x12). On my bogner over-sized 2x12 cab it reads 12 ohms.

    Is this OK? How close to 16 ohms should I be seeing? I just read the ohms of a cable plugged into the speaker jack on the back of the each cab individually.
     
  2. Onioner

    Onioner Member

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    Actual measurements will always be lower. I believe it depends on the temperature. Totally normal.
     
  3. JBPlanck

    JBPlanck Member

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    Thanks, after googling a bit more I found the following info at http://www.prestonelectronics.com/audio/Impedance.htm

    "However, with raw speakers and many cabinets, the ohmmeter function of a digital multimeter can help you identify what the impedance of the speaker should be. Generally, the reading given by an ohmmeter will be about 2/3 to 3/4 of the impedance of the speaker. So, a 4 ohm speaker will typically measure about 2.5 - 3 ohms, and an 8 ohm speaker will typically read about 5-6 ohms, while a 16 ohm speaker will measure around 12 ohms."

    I did in fact use a digital ohm meter so I feel a bit better based on your comment and the above information.
     
  4. rockonomics

    rockonomics Member

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    It's gonna vary. You're seeing that on yer meter. Nuttin' to worry about. You have a cumulative total of all speakers. It doesn't surprise me at all that you're seeing such a wide range of readings. I'm looking at a Fleabay 10" 8 ohm speaker that reads 5.1 ohms for a 4 ohm app. I wouldn't consider this a problem at all.
     
  5. rawpower

    rawpower Member

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    there is resistance and then their is inductance, and an ohm meter does not read inductance. Inductance has to do with electrical fields and frequency and gets a little complicated, all you need to know is it works against the flow of electrical current and that speaker that has a 12 ohm resistance will act as if it is 16 ohms when in use and put a 16 ohm load on your amp.
     
  6. Tone_Terrific

    Tone_Terrific Member

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    Plus, impedance has a frequency dependent component.
     
  7. rawpower

    rawpower Member

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    I think i mentioned that, inductance is entirely dependent on frequency I=1/(2πfL)
    and it is the sum of inductance and resistance that makes impedance. I think we are taking this to far. just look at my first post
     
  8. Tone_Terrific

    Tone_Terrific Member

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    That's all I was emphasizing, so you can't measure it with a DC meter...yes, nitty-picky too much info:bonk
     
  9. KWCabs

    KWCabs Member

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    It will vary brand to brand and piece to piece. Most companies will be within 1.5 ohms of the rated number. Is there a problem putting a 12 into a 16 or whatever, that totally depends on the amp build. Some amps can handle a mismatch very well some will blow up and of course there is a range on all. An actual 12 ohm that says 16 well that's a pretty big range, but chances are it won't do anything.
     
  10. JBPlanck

    JBPlanck Member

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    All great info, thanks to all.
     
  11. VaughnC

    VaughnC Supporting Member

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    It's confusing, especially to the layman...DC resistance & AC impedance are different things, but both are measured in "ohms". I often wished they'd label AC impedance something like "aohms"...but it is what it is.
     
  12. mcdes

    mcdes Member of no importance

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    Just think of it like apple products! you buy a 32GIG iPad............. you get a 29GIG iPad actually.......
     
  13. charveldan

    charveldan Senior Member

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    All three of my 16 ohm Vintage Marshall cabs measure between 13 & 14 ohms.
    Things like diameter of voice coil wire & the wire harness can be at play.
     
  14. megatonic

    megatonic Member

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    I just measured my 1960a cab & it read 14.5, so I guess it's fine.
     
  15. Monstercastle

    Monstercastle Supporting Member

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    I predict this thread will be 15 pages by Friday next.
     
  16. rumbletone

    rumbletone Silver Supporting Member

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    Yes, and the vast majority of the posts will refuse to recognize that the reason their dmm is showing a number different from the rating of the speaker is because they are measuring DC resistance ...
     
  17. amptex

    amptex Supporting Member

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    Close...the quantity you're referring to is reactance, not inductance (which is measured in henries). There are two types of reactance - inductive and capacitave.

    Resistance and reactance combine to form impedance, but it's not simply a summation.
     
  18. megatonic

    megatonic Member

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    So, would it be the skin effect that accounts for the 14.5 ohm reading on my 16 ohm cab?
     
  19. rumbletone

    rumbletone Silver Supporting Member

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    What accounts for the difference is that you are not measuring the impedance. You are measuring the DC resistance (assuming you're measuring with a dmm set to measure resistance).
     
  20. megatonic

    megatonic Member

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    In this case, does it really matter as long as we understand that it's normal if we get a reading with a dmm on the impedance (ohm symbol) setting that is slightly less than the cabinet rating?
     
    Last edited: May 10, 2015

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