Measure your cabs! A DMM is a handy thing to have.

Discussion in 'Amps and Cabs' started by DonaldDemon, Oct 7, 2016.

  1. DonaldDemon

    DonaldDemon Member

    Messages:
    7,442
    Joined:
    Nov 13, 2007
    Location:
    Fear and Loathing, NJ
    I've been playing my Splawn QR through a Marshall JCM800 412 for almost a year now at my cover band's practice space. It's the bassists cab and he told me it was wired for 16ohms with Greenbacks. A few weeks ago we took it apart to install these speaker baffle rings that angle the speakers up more towards the player.

    After putting it back together (wiring was untouched except at the jack) I measured and not only are they GT75's (surprisingly because they sound really good and I hate those speakers) but they are wired for 8 ohms, so I have been running it mismatched for quite a long time. Luckily no damage to the amp but it does sound better now that it's running matched. Always a good idea to have a DMM on hand and confirm what the actual impedance is on a speaker cab you will running into.
     
  2. metal_murf

    metal_murf Member

    Messages:
    484
    Joined:
    Aug 29, 2013
    Location:
    Live free or die state
    I played a show recently with backlined cabs. Was told it was 8 ohms. Thought it was odd because he said it was a stock 1960a. The switch on back was on mono so I plugged into the 16 ohm jack and checked with my meter. Sure enough it was 14.5 ohms on my meter. The owner must've been reading the 8 ohms for running stereo.
     
  3. sickboy79

    sickboy79 Member

    Messages:
    11,402
    Joined:
    Aug 17, 2006
    Location:
    Chicago
    Agree. I measured the impedance on an early 80s Fender 4x12 that I have and got a funny reading. Turns out one of the speakers was blown. Glad I did it!
     
  4. swiveltung

    swiveltung Member

    Messages:
    14,524
    Joined:
    Feb 5, 2011
    Location:
    PNW
    Yeah, one does have to be careful. Regarding "I measured and not only are they GT75's (surprisingly because they sound really good and I hate those speakers)" , it's amazing what preconceived notions do to our hearing. I tried a Celestion lead 70/80 earlier this year that everyone seems to hate. It was a good sounding speaker I thought.
     
  5. Karl Houseknecht

    Karl Houseknecht Supporting Member

    Messages:
    3,793
    Joined:
    Nov 24, 2008
    Location:
    VA
    I always, always measure, even when it's a brand new cab and I'm the first owner. I've been surprised twice. Once was with a cab I ordered with a multi selector for the jack. The "16" ohm jack was actually 8. Little bit of mis-wiring on the manufacturer's side. The second time was on a cab that didn't have the impedance marked but which the original owner had assumed was 8 ohms. It was 4.
     
    DonaldDemon likes this.
  6. ungarn

    ungarn Member

    Messages:
    3,256
    Joined:
    Jul 23, 2005
    Location:
    Springboro, Ohio USA
    Yup, old broken in G12T75 speakers are great for crunch.
     
    DonaldDemon likes this.
  7. Promit

    Promit Member

    Messages:
    2,319
    Joined:
    Mar 10, 2013
    Location:
    Baltimore, MD
    T75s on their own, eh. Find a 1960AV (V30s) and swap both to X pattern for true glory.
     
  8. DeaconBlues

    DeaconBlues Member

    Messages:
    2,983
    Joined:
    May 2, 2007
    Location:
    way down below the ocean...
    I'm a fan of T-75's.
     
  9. DonaldDemon

    DonaldDemon Member

    Messages:
    7,442
    Joined:
    Nov 13, 2007
    Location:
    Fear and Loathing, NJ
    Another good point. I measured my Acoustic bass cab and the readings kept jumping all over the place, turns out the speaker jack was bad. Sounds much better now that I replaced it and no more risk to the amp.
     
    Last edited: Oct 9, 2016
    sickboy79 likes this.
  10. DonaldDemon

    DonaldDemon Member

    Messages:
    7,442
    Joined:
    Nov 13, 2007
    Location:
    Fear and Loathing, NJ
    I've always hated playing through 1960a cabs because of those speakers. Never sounded good to me, too scooped in the mids and harsh highs. This cab is old so maybe the speakers were better then or it's just that broken in but it sounds awesome.
     
  11. DonaldDemon

    DonaldDemon Member

    Messages:
    7,442
    Joined:
    Nov 13, 2007
    Location:
    Fear and Loathing, NJ
    V30's don't sound good with my amp IME, too much mids for a very mid heavy amp, but I've obviously been proven wrong before!
     
  12. DonaldDemon

    DonaldDemon Member

    Messages:
    7,442
    Joined:
    Nov 13, 2007
    Location:
    Fear and Loathing, NJ
    Also I should probably add, the easy way to do this for those who don't know:

    Hook up your speaker cable to the cab input and leave the other end disconnected. Set your digital multimeter (DMM) to read resistance (Ohms). Some DMMs may be automatic and some may need to be set to a specific value threshold, you will most likely set it 20 ohms. Take the probes and measure the resistance between the tip and sleeve, touching each end with one probe. Your reading sound be about 80-90% of the actual resistance (cable and jack add a slight amount). So, e.g., your 16 ohm cab may read as low as 13ohms, 8 ohms may read 7.xx, etc. That's it!
     
    flantrax likes this.
  13. eclecticsynergy

    eclecticsynergy Member

    Messages:
    5,217
    Joined:
    Mar 17, 2015
    Location:
    NY
    FYI, additional impedance from the cable would result in a higher reading, not lower. But any difference is likely to be negligible. The reason Celestion-loaded cabs sometimes read lower than expected is that in my experience many Celestion speakers actually have a slightly lower impedance than their nominal rating.
     
    flantrax likes this.
  14. fole

    fole Member

    Messages:
    27
    Joined:
    Aug 31, 2016
    That's unfortunate, but you were lucky as the amp was "seeing" a lower impedance than it was "looking" for. If it had been the other way round, that could have caused problems like "Goodby output section".
     
  15. Nebakanezer

    Nebakanezer Silver Supporting Member

    Messages:
    2,584
    Joined:
    Jan 21, 2014
    Location:
    In a geographical anomaly, 2 weeks from everywhere
    I thought we were gonna talk about the Deluxe Memory Man........
     
  16. SirGilmour

    SirGilmour Supporting Member

    Messages:
    9,943
    Joined:
    Aug 8, 2012
    Location:
    Fort Wayne IN
    Me too.
     
  17. ffoont

    ffoont Member

    Messages:
    583
    Joined:
    Dec 10, 2008
    Wait, any more info on these rings?
     
  18. DonaldDemon

    DonaldDemon Member

    Messages:
    7,442
    Joined:
    Nov 13, 2007
    Location:
    Fear and Loathing, NJ
    OK, wasn't sure what the impact was but I knew it changed it slightly. Either way it's rare that you get a reading of exactly 16, 8, 4 or 2 ohms.

    I've read that but I've done it many times without an issue.

    Not the same ones I think but same concept. http://tiltaspeaker.com/about-us/product-description/

    When we added another guitar player I was no longer using the extra cab across the room and was turning my amp louder to hear myself because it was only a few feet behind me. Bassist installed those to help hear and so I wasn't blasting everyone else. I think it helped a bit.
     
  19. DonaldDemon

    DonaldDemon Member

    Messages:
    7,442
    Joined:
    Nov 13, 2007
    Location:
    Fear and Loathing, NJ
    Sure, I think most people use the digital version though, no?
     
  20. keithb7

    keithb7 Member

    Messages:
    1,406
    Joined:
    Feb 16, 2007
    Location:
    Canada
    I concur. A musician using electric gear should have a DMM. Learn how to use it. There are plenty of applications you could use it for. Even a simply continuity test on cables is great.
     
    Last edited: Oct 9, 2016
    DonaldDemon likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice