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Rumble 115 seems out of phase (reverse phased)

Discussion in 'Amps and Cabs [BG]' started by Guapotims123, Jan 8, 2019.

  1. Guapotims123


    Jun 19, 2012
    I pulled the grill off of my Rumble 115 cabinet to observe the speaker under power. It seems to me that the 15" is pulling inward when I play my bass thru it. The ports are blowing mass quantities of air out of them during this and the speaker seems to want to fart out really easily. I have the Rumble 500 amp pushing it with all levels at 12 O'clock except the gain and master are at 9 O'clock I wonder if the polarity of the speaker might be reversed. I doesn't look like the speaker has ever been removed since the manufactures assembly, but I'm not sure as I am not the original purchaser. Should I reverse the wires or just assume this is proper. Any Ideas will be appreciated.
  2. Crater


    Oct 12, 2011
    Dallas, TX area
    You cannot have an out-of-phase condition with a single driver.
    Coolhandjjl, Paulabass and Mushroo like this.
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    What you are seeing is asymmetrical operation, it can be somewhat normal with some drivers/cabinets but it can also be in indication that the driver has been overpowered and the suspension components damaged.

    Try to play a new one and compare. If the new one doesn't do this to the same extent, you driver is likely damaged.
  4. Guapotims123


    Jun 19, 2012
    So are you saying that the polarity of the speaker does not matter. I always thought there was a pos and negative for reason of pushing or pulling in the speaker.
  5. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    That's not what he said.

    The signal is AC, it (generally) pushes and pulls symmetrically except under some amp overdrive conditions where asymmetry is part of the overdrive design. Presumably you are not overdriving your amp (I believe there is some intentional asymmetry in the Rumble overdrive).
  6. Mushroo

    Mushroo Supporting Member

    Apr 2, 2007
    Massachusetts, USA
    It's true, but if there's only 1 speaker driver, then it doesn't really matter whether it pushes then pulls vs. pulls than pushes. Only with 2 or more drivers is there a phase problem.

    As a thought experiment, imagine two boats at sea during a storm. If both boats go up a wave first, then come down the other side of the wave, then that is really no difference vs. if both boats go down first and then up. The waves are the same size whether you start from a peak vs. a trough, no difference in how you experience the storm vs. your friend on the other boat. We are going up and down in synch, so I could yell across to your boat, "hey how's it going?" and you could shout back, "I feel seasick!"

    But if one boat goes up while the other boat goes down, then they are "out of phase." I am at the peak while you are in the trough. We are moving in opposite directions. If I try to shout a warning to you in your boat, you can't hear me if I'm at the top and you're at the bottom. We only line up in the middle of the cycle, passing each other in opposite directions.
    agedhorse likes this.
  7. seamonkey


    Aug 6, 2004
    Let's see it - Shoot a video, but watch out for rolling shutter effect of most cell phones.

    If you have an active bass then watch out for driving too much lows from the built in preamp in the bass. The knobs on the head aren't calibrated to anything so 12 o'clock doesn't mean much.

    Think about it - low B around 30hz you really can't see it. Old time moves were 24 frames per minute and they look like continuous movement.

    There was some problems with early class-d and heads missing HPF. You probably don't have a problem with the Rumble. Don't play anything just push on the strings, do you see the cone move? Probably not on modern class-d heads.
  8. Guapotims123


    Jun 19, 2012
    I guess what I am seeing is "everytime i play a string on my bass, the woofer cone pulls inward. I have always seen them push outward as to move the air. I understand they are a/c driven but the coil should move outward rather than inward. I know when multiple drivers are used you always want them in phase so that they all push together rather than cancelling each other out by some pulling and some pushing.
  9. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    Not true, the voice coil moves both outward and inward, ideally symmetrically. You can't have "push" without a corresponding "pull" in an AC system, otherwise after a few cycles of "push only", the cone would be pushed right out the front of the speaker.

    Please re-read what I posted earlier. If you don't understand it, you might want to study a bit about how a speaker works and why it works the way it does. It will be helpful in your troubleshooting effort.
  10. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    Well, yes... but normally only briefly. When you play a low-E, the woofer cone moves in-and-out (or out-and-in) forty-one times per second. It also moves in-and-out (or out-and-in) a smaller distance eighty-two times per second. It also moves in-and-out (or out-and-in) a yet smaller distance one hundred and twenty-two times per second. These are the fundamental, first overtone, and second overtone. And so on up the spectrum. (I've made some simplifying assumptions here.)

    If your woofer is working properly and your amp is not distorting (intentionally or otherwise), here are two possible explanations for what you are seeing:

    - The lighting makes it easier for you to see the "inward" position of the cone as it cycles in-and-out (or out-and-in), so it looks like the cone has moved inward. It's moving so fast that the rest of its stroke is an almost-invisible blur.

    - It is possible that air flows out of the port more efficiently than it flows into the port, resulting in reduced internal pressure that in effect sucks the woofer cone inward. It's still moving in-and-out (or out-and-in), but the "average" position is inward relative to when the cab is at rest. This is unlikely to happen unless the airflow in the port is high enough for this asymmetry to become significant.
    Last edited: Jan 11, 2019
    michaeln and agedhorse like this.
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    There is also electromagnetic and mechanical asymmetry that can cause this. It's one of the Klippel tests that can be performed on the driver during the design.
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