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Impedance Problem help please

Discussion in 'Amps and Cabs [BG]' started by planitguy, Nov 26, 2017.


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  1. planitguy

    planitguy

    May 24, 2012
    Mid Missouri
    Hello.

    I'm having problems with my ASHDOWN MI550 class D head.

    This head is listed as being 500 watts when run at 4 ohms, and as many have noted....that rating does seem to be a little over exaggerated.

    I have two Eden cabs w a 12" (no horn) in each that are both 8 ohms.

    Now, my understanding is that running the two cabs will show the amp a 4ohm load and produce the full horsepower of the amp (not to mention that two cabs SHOULD be louder than one).

    But here's the deal....using both cabs actually steps down the output of the amp! And the tone thins out some. Unplug one of the cabs (at the amp) and the volume noticeably increases as does bottom end!

    I've tested each cab, each spkr cable, and ea spkr output jack on the amp. All work fine and it's the exact same deal no matter which cab/cable/output jack is used.

    I really love the tone of this amp but would like to get all that's supposed to be there.

    Ideas? Thoughts?

    Thanks for reading and any help.
     
  2. dukeorock

    dukeorock Owner BNA Audio Supporting Member Commercial User

    Mar 8, 2011
    Nashville, TN
    Authorized greenboy designs builder/Owner of BNA Audio
    Speakers out of phase?
     
  3. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    Your cabs may be out of phase. Make sure the + on each cab jack plate goes to the + on the driver. I the event one cab has had a driver replaced and you have no way of verifying the + on one driver is the same as the + on the other, do the 9V battery test. Search for that here.

    One of you speaker cables may be out of phase. Check those too.

    Are you daisy chaining or are both cables going right into the head? If the head has two output jacks, it's also possible the output jacks on the head were worked on and are OOP.
     
  4. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    Reverse polarity, actually, but yes. Wiring is reversed either inside one of the cabs or in one of the cables.
     
  5. planitguy

    planitguy

    May 24, 2012
    Mid Missouri
    Oh, MAN!!!!!

    that's GOTTA be it! i recently changed out the driver in one of those cabs and i bet i got the leads reversed. like DUH!

    you guys are the best....i love this site. post a question/problem and within five min there's my answer!

    thanks so much. of course....now it's gonna be a lot harder to justify going out and buying that Markbass Ninja head i'm jonesing for!

    big thanks, guys.
     
    Last edited: Nov 26, 2017
  6. Coolhandjjl

    Coolhandjjl Supporting Member

    Oct 13, 2010
    Appleton
    Yup, my mistake in nomenclature. Thanks!
     
  7. Which puts the cabs out of phase with each other.
     
  8. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    It does, by 180 degrees at every frequency. But you can have cabs out of phase anywhere from 1 degree to 359 degrees, you can have cabs out of phase by a different angle at every frequency, and you can have cabs 180 degrees out of phase at just one frequency. Phase and polarity aren't the same thing, so you can't use the terms interchangeably.
     
  9. Yes phase differences between two drivers occupying different spaces can be anywhere between 0 and 360.
    But in this special case of out of phase I guess you and I are just going to disagree on what term to use.
    Electrically you are reversing polarity to fix the problem. Acoustically you are changing phase of the one driver's audio output by 180 degrees compared to itself.
    I am talking about the 180 degree phase difference that is introduced by changing speaker polarity.
    Let's not confuse things by throwing in audio phase differences introduced by the fact that the two drivers cannot occupy the exact same space at the exact same time.
    Given the one driver alone you can reverse the polarity and get a 180 degree audio phase shift or you can get a 180 degree audio phase shift by reversing the polarity. So either bit of advice, to reverse polarity or change the speaker phase, in this special case is correct.
     
  10. dukeorock

    dukeorock Owner BNA Audio Supporting Member Commercial User

    Mar 8, 2011
    Nashville, TN
    Authorized greenboy designs builder/Owner of BNA Audio
    Just trying to help some dude in simple terms m, but cool. I'll pay the fine.

    OP, good luck! Hope it was that simple!
     
  11. Shishka Bob

    Shishka Bob

    May 28, 2017
    CT
    OP: Update?
     
  12. No good deed goes unpunished.
    In this special instance, getting both speakers (as close to) in phase as they can possibly be, is the right solution.
    Your advice is cool in my coloring book.
     
    boomertech, soulstew, FenderB and 3 others like this.
  13. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Feel the love.
     
    dukeorock likes this.
  14. Simple test is to place a 9V battery across the tip and sleeve of your plug. Both cones should move in the same direction. Normally with the positive of the battery touching the tip of your plug the cones move out away from the magnet structure.
     
    EatS1stBassist, AE1 and HolmeBass like this.
  15. john m

    john m Supporting Member

    Jan 15, 2006
    Reverse polarity is 180 degrees out of phase .
    Tomayto/tomahto
     
    boomertech and Old Garage-Bander like this.
  16. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    This conforms to modern standards, so I would encourage the OP to correct the one that is wrong rather then reverse the one that is correct and create a "2 wrongs makes a right" (sort of) scenario.

    Convention when discussing speaker polarity is to say that the speakers are "out of phase", which by common usage is assumed to be 180 degrees out of phase at all frequencies (or reversed polarity).
     
  17. Rick James

    Rick James

    Feb 24, 2007
    New Jersey
    If you don't know the difference between phase and polarity then you won't know how to identify, diagnose and fix a problem that's caused by phase.
     
  18. john m

    john m Supporting Member

    Jan 15, 2006
    I remember JBL throwing a wrench in the works years ago. I had to be aware of polarity issues between my rig and my PA system.
    These days I make sure my rig is pushing and pulling in sync with itself.
    I own commercially made stuff and only check when I repair a cable.
     
    roccobass and agedhorse like this.
  19. john m

    john m Supporting Member

    Jan 15, 2006
    With a 2 wire speaker cable ( or driver) there are only 2 choices.
     
    soulstew likes this.
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    DaDo625 and BadExample like this.

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