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Speakers out of phase with PA?

Discussion in 'Amps and Cabs [BG]' started by Big Benner, Nov 28, 2004.


  1. What happens if your bass amp speakers are out of phase with the PA?

    I played a place last night and had real trouble hearing myself on stage. It was a 150-250 seater with a fairly good PA (I think there were 2x18 subs on either side) and I brought both my 2x10 and 1x15 cabs. We showed up real early and were able to do 3 songs for sound check with a pre EQ D.I. coming off the amp. I try and keep the amp at a quiet volume so my band mates can hear their 1x12 combos and to give the sound man greater control over the full sound of the band, but I was really having trouble hearing myself. I turned the master volume completely off for the last song and I could hear myself coming out of the PA, fairly loudly with lots of bottom. All I needed was more midrange so I could hear the note deffinition.

    During the show I kept adding more mid and high end and taking away low end. It helped somewhat, but for sure everytime I turned up the amp, I really drowned out the guitar player right besied me.

    It was the first show ever where I really wished I had brought my little SWR WM12, titled it up on an angle (usually with a little 2x2 piece of wood) and run the amp flat. I think the band might have been happier without my twiddling knobs every song.
     
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    genrally you shouldn't be out of phase with the pa
    usually you would notice a distinct loss of bass if there was a serious phase problem, but even then you would only notice it in the audience. Even if you were out of phase, the placement of your amp would have an impact upon that, (ditto for being in phase). It sounds liek you were just experiencing the usualy anomaly of the stage sound not being anything like the FOH sound. Last gig i played i had to turn my amp up quite a bit to be loud enough in the room - using a combined total of 33 feet of cord gave me an idea of whatthings really sounded liek out front. Onstage i was louder than i or the others would have liked me to be, but due to room anomalies the overall sound for the audience was great.
     
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It's quite possible you were out of phase with the PA. But it's also possible depending on a number of factors having to do with the distance from your speaker to the walls and ceiling that you may have been standing in a bass 'null' zone. Ceiling height is the usual culprit when this happens. Next time try unplugging the 1x15 and running the 2x10 only, assuming you have the 1x15 on the ground and the 2x10 stacked atop it. With the 1x15 on the floor and a seven foot ceiling you can have a null zone centered at 60 Hz, which would really kill your fundamentals. Another cure would be to have the 1x15 placed face down, with four bricks at the corners spacing it off the floor, to increase the distance to the ceiling and lower the null frequency.
     
  4. Of course your backline is out of phase with the PA, due to the different position of the two sound sources. Yes, there will be cancellation points as a consequence.

    With 4x18 for PA support, the last thing the FOH engineer wants is for you to have a big backline. He knows the conflict that results from this.

    For this kind of PA support, bring only the 2x10 and put it at ear level, not aimed at your legs. It will be easy to hear, and you won't be in conflict with the PA.
     
  5. wwittman

    wwittman

    Apr 21, 2004
    Westchester, NY
    Although odds are you will never be in PERFECT phase match with the PA, it's also unlikely, unless you are at equal VOLUME as well to the PA, that this was the cause of your problem.

    Far more likely that the room had an anomaly where you were standing that prevented you from hearing clearly.

    I'm not personally a fan of leaving it all to the FOH guy.
    I think it's far better to have a good basic balance on stage... that is, with the house and monitors OFF, the band sounds reasonably well balanced on stage.
    Then it's up to the FOH mixer to REINFORCE that sound (that's why they call it "sound reinforcement") to the audience as needed.

    But,
    If the sound out front was good... and you had trouble hearing yourself... why not ask for a monitor wedge pointed back at you to hear yourself better?
    Or, if you HAD a monitor of some sort, why not just ask for bass guitar in your monitor mix?
    One of the advantages of in-ear monitors is that no matter where on stage I roam and no matter what the room is like, I can get a mix in my ears that let's me hear myself, and what I'm playing to, clearly WITHOUT it affecting anyone else.