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Stage Rig vs. FOH - phasing issues?

Discussion in 'Live Sound [BG]' started by Mr. Pickles, Nov 19, 2010.


  1. Mr. Pickles

    Mr. Pickles Supporting Member

    Nov 11, 2006
    Dutchess County, NY
    Just saw Dub Trio in NYC and I stood directly in front of the bassist and the FOH subwoofer was at my feet. The sub flapped my pants for the whole set, but I simply could not discreetly hear the bass rig (from 10 ft away). Stu used an Aguilar GS412 cab with AG500 head. The mains were slightly behind my right shoulder. The subs looked like 2x15's and their were two- one at each end of the stage. The only time Stu's rig became discernable was when he engaged overdrive as I could hear the high-end, trebley grind.

    More often than not, I experience the same phenomenon in most small-medium sized clubs. Is it possible that there is a phasing issue between the stage rig and the subs that cancels out the low frequencies? Or could it be that the bass rig simply can't compete with the subs.
     
  2. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    if it was phasing, i'd think the foh would have been affected, too. besides, most big acts have time alignment stuff in the pa to minimize phasing. i think either the pa was enough to drown out his amp or he wasn't very loud onstage. not being there it's hard to tell what it was, but i'd suspect the latter two things before i suspected phasing.
     
  3. Vinny D

    Vinny D

    Jan 9, 2007
    Warwick, RI
    That would be my vote.
     
  4. greenboy

    greenboy

    Dec 18, 2000
    remote mountain cabin Montana
    greenboy designs: fEARful, bassic, dually, crazy88 etc
    Not having been there I wouldn't know, but I will note that a bass rig that actually can make a lot of sub-100 Hz energy CAN affect the FOH without being that noticeable to the listeners. And like any subwoofer spacing, it depends on distance what is happening to what frequencies. But to simplify, it's kinda like driving with the emergency brake on: you have to exert more energy to get the same results. And eventually, if pushed hard enough long enough, things burn up.

    So here, the sub amplifiers will be asked to supply more power, and the drivers will be working harder even though you can't hear more SPL. Generally with powerful PA systems a pretty tough bass rig will not be enough to make a real burn-down problem, but there will be extra energy expended, and there will be more chaotic response nulls and resonance buildups generally.
     
  5. Jerry Ziarko

    Jerry Ziarko Supporting Member

    Feb 23, 2003
    Rochester, NY
    While phase issues can be a problem when the backline bass signal arrives at a slightly different time than the FOH, this is not what you were experiencing. Being as close as you said you were to the subs, the backline bass wouldn't be far enough away to cause a discernible difference. If you were farther back in the house it could possibly be a factor, but not that close to the speaker.
     
  6. Phasing, sure. If you were as close as you say you were to the backline, and the FOH subs were flapping your pants, and you heard no bass, do the math.
    The backline was(I'm sure) really loud, and the phase difference between it and FOH subs was such that the low-end killed itself at your location. Bummer.
     
  7. Mmmmm....I doubt that. But, we weren't there. Did you mean close enough?
     
  8. Jerry Ziarko

    Jerry Ziarko Supporting Member

    Feb 23, 2003
    Rochester, NY
    I wouldn't bet the farm on it, but I would wager at least the barn that is what was going on. :D
     
  9. See, I would have 'bet the farm' on the backline and FOH being at similar volumes at the OP's location. Which could certainly lead to low-end cancellations. Am I nuts? Do you disagree?
    It seems to me that, if the OP had pants-flapping stuff going on at his feet, he should have heard it. He says he didn't.
     
  10. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    IMO if there was not enough upper harmonic content, then pants-flapping low fundamentals would just be air without tone, in that type of concert environment. IOW it would not be "heard" because it would not be recognized by our brains as anything other than a low whooshing sound. If the same sounds were made at home or in a non-noisy place, then the ears/brains would probably have heard it properly.
     
  11. D.A.R.K.

    D.A.R.K. Supporting Member

    Aug 20, 2003
    Virginia
    it is quite normal to delay an audio system to the back line, especially in loud situations. so there could very well be phasing issues.
    however, having heard a decent amount of dub trio live stuff,
    quite often the bass is eq'd as something you feel more than hear so that could be another factor.
     
  12. fokof

    fokof One day ,I'll be in the future

    Mar 16, 2007
    Here
    Other variable ;
    Was the OP able to hear the PA's top ?

    If the subs were x-overed low , he could have got a glitch of bass by hearing the tops depending on where it was cutted.
     
  13. Samsound

    Samsound

    Sep 28, 2010
    Could've been room modes, too. He might have been standing in an un-sweet spot.
     
  14. Mr. Pickles

    Mr. Pickles Supporting Member

    Nov 11, 2006
    Dutchess County, NY
    I should have moved around the room, but I was busy watching how Stu used his effects during the set. Bongo has a point - I may have just been feeling the air moving from the subs, and not "hearing" anything.

    FWIW, the mains were flown in front of stage right and left. They sounded good - a nice, clear mix without being overly loud. I was wearing my ER-20 plugs, but I took them out a few times and the noise levels were comfortable.

    I did enjoy myself, though. My main question was regarding my inability to hear the backline bass rig. The sensation of the subs put me in my happy place, so it was all good.
     
  15. TimmyP

    TimmyP

    Nov 4, 2003
    Indianapolis, IN
    I don't care whether it's the backline or the PA that's at work, so long as it sounds and feels right throughout the venue. I've yet to hear the backline sound and feel right other than in a few sweet spots.
     
  16. Jerry Ziarko

    Jerry Ziarko Supporting Member

    Feb 23, 2003
    Rochester, NY
    True dat! So many players seem to fall under the "I need my amp sound to fill the house" and it never sounds the way they think it does out front.
     
  17. Mr. Pickles

    Mr. Pickles Supporting Member

    Nov 11, 2006
    Dutchess County, NY
    Let us proclaim the mystery of low frequencies.
     

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