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Problem with mic feedbacking back bass freqs

Discussion in 'Amps and Cabs [BG]' started by morebass!, May 9, 2006.


  1. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    We typically play on small stages and my vocal mic is set up within 5-10 feet of the amp. I sing background vocals. Feedback is so bad that sometimes I turn the mic off for most of the night and only sing when absolutley needed (rare:) ). It's a low-mid kind of muddiness that kills our sound. It's definitely coming from my amp and mic. Is it my amp? Should I get a gramma pad? Is it my mic (SM58) or cable (with on/off switch)? Is it my cheap mic stand? Pointing the amp and/or mic away from each other doesn't seem to matter. Some rooms are much worse than others. Anyone else have this problem? What works?
     
  2. BurningSkies

    BurningSkies CRAZY BALDHEAD

    Feb 20, 2005
    Seweracuse, NY
    Its probably a combination of the things you have listed...your stage volume, and your tone if you're pushing lots of extra lows...and you've combined it with a mic that's pretty close to your amp. I'd think about lowering your volume, working your tone (since it sounds like you're having a problem with it beyond just the mic feeding back) and also look into a mic that has better 'sound rejecting' properties. I'm sure people around here could give you some good options for a 'live sound' vocal mic that would reject more of your bass signal. I personally find that 'in a pinch' switching to a 57 for backups can do the trick...since 57's are pretty plentiful at most gigs.
     
  3. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Speaker pads might help on some stages, Does the stage floor vibrate when your playing? For a test, you could try placing a folded towel under your mic stand and see if your problem is vibration related or volume related.

    Have you tried changing the mixer EQ settings on your vocal mic channel. Try flat, or cutting the freqencies that are causing the feedback problem).

    Some poeple sing softly and stand far behind the mic. This requires a super high mixer channel level. These poeple always seem to have more bleed and feedback problems.

    Poeple that sing louder and closer to the mic, can run the mic channel lower and dont have near as many problems.
     
  4. theshadow2001

    theshadow2001

    Jun 17, 2004
    Ireland
    Here's some suggestions

    Tapping the along mic stand and stomping on the stage with your foot fairly hard are ways of determining if the feedback is being induced by vibration. If it is, a gramma pad might work. If it is vibration then it might not be coming for your cabinet alone but subwoofers from front of house or the kick drum. A graphic eq for the PA might work nicely here as well.

    Try placing your mic and cab so that the least sensitive area of the mic is facing your cab. That said sub frequencies tend to travel in all directions so turning your cabinet away from the mic might not solve the problem

    Or just doing a bit of eqing on the desk. Pump the gain on the mids and sweep through the frequencies and try and find the point where feedback occours and pull that frequency out a bit until it stops.

    Another thing to consider is the position of the mic with regard to front of house.

    Are you using a monitor? Do you use a graphic with the monitor? Is it positioned correctly in relation to the mic?

    Have you tried switching the mic with a different one? Does that make any difference? Do any other singers in the band suffer from feedback? If you do a direct swap of mics with another singer does the problem follow the mic or stay with you?

    How is the gain set on your channel on the desk? A rule of thumb is gain is usually around 10 or 12 o clock on the desk. What you need to do is to keep your input signal to average around 0dB when your singing. If you run it too high it will be easier to get feedback. Do you use a -15dB pad on your channel? If you do is it actually pressed down.
     
  5. el_Kabong

    el_Kabong

    Jul 11, 2005
    Sounds like you've got two problems. One being feedback and the other being mics picking up sonic mud from onstage. Have you made sure the low cut filters on the desk are switched in for every mic other than the kick drum and the bass cab? Flipping the phase on a troublesome mic or the foldback wedge can sometimes help. If you've got any gates, gating the mics pretty hard might both stop the feedback and clean up your sound.
     
  6. Thunder Lizard

    Thunder Lizard

    Dec 7, 2005
    Lethbridge, AB
    Canadian Distributor, Basson Sound Equipment
    HM.
    A few things......switching to an sm57 won't help, because the honest to god only real diff between a classic 57 and a 58 is the shiny silver grille on the 58. If your mixer has a "low end rolloff" or "high pass filter" on your vocal mic. Second, ensure, as many have said, that vibration is not the cause....some people set up tripod style mic stands with the center pole touching the stage....make sure that's not happening. It should rest on the rubber feet....and you should try to make sure those rubber feet are there.
    "Feedback" and "picking up sonic mud" are essentially the same thing..... the mic is picking up non-essential background noise and recycling it... again, check your gain, make sure you don't have a superboost on the bass of your mic channel.
    All this leads to ONE first step..... make sure the mic is just not plain turned up too far....either at the 'gain' or at the fader..then, head for the low end rolloff. Third, reduce the bass EQ control on the offending channel. Fourth, try to remove the frequency from the PA/Monitors using the 31 band equalisers that should be used on them. If none of that helps.....
    Make sure the subwoofers of the PA are not touching the stage. Sometimes this can cause issues. You're not, perhaps, using subwoofers in front of the stage to set mics and monitors on, are you? I know, it sounds NUTS, but sometimes it's that simple. As well, if the venue has set the woofers under the stage to save room, make sure that they're not touching..even the tiniest air gap can damp a lot of sympathetic vibrations.
    The EQ on the PA should be examined to make sure that the 'ringing' frequency is not boosted by accident or design in either the monitors or the main PA.
    If possible, try to isolate your rig from vibrating the stage, too... set it on something that will damp vibration, move it completely away........anything that will seperate your mic stand and the vibrations of your rig.
    Is the stage "bouncy"?? A poorly designed stage can have resonant frequencies that are bounced thru the stage deck to friendly listening devices like microphones, too.
    Place pieces of carpet under your rig, and your mic stand...sometimes it's the tiniest thing that can break a feedback loop.
     
  7. el_Kabong

    el_Kabong

    Jul 11, 2005
    +1 great points. Regarding the feedback/mud thing though, feedback obviously occurs between the mic and the foldback wedge and/or the front of house. It's not happening between the mic and the bass cab. So if the system is feeding back (oscillating, ringing, howling...) that's not the same thing to me as 'a low-mid kinda muddiness that kills our sound'. Of course it's hard to help without hearing/seeing what's happening. On top of all the other tips, have a careful look at the postion of the foldback wedges (try different placements during setup) and make sure your mic line is behind the FOH speakers.

    A couple more things to consider with a muddy/congested sound. What's in the foldback mix? Is your bass in there? Pull out anything that's not essential. Also remember that the amount of gain available before feedback is directly related to the number of open mics on stage so don't mic anything that you don't need, and gate anything you can, especially in a small room. For example you probably won't need drum overheads, they would likely add just to the problem.

    Also when you set up the foldback during soundcheck, do it with the FOH on and at performance volume. It's common to set up monitors with the FOH off. This overlooks the fact that high frequencies are directional. So from on stage, what you hear from the FOH is a lot of low end and short on highs. So when you bring up the monitors you need to add the highs back in and not add too much to the lows you're already hearing. So switch the FOH on too and pull as much bottom out of the monitors as you can till you can't stand it, then sneak a touch back in. Do it at performance volume as your perceptions will change. Get a cheap spl meter if you need one to ensure you soundcheck at performance volume.

    And lastly as others have said, keep your volume in mind. In a small room, especially if it's not full of people, you can play loud or you can sound good, it can be very difficult to get both. You have to play with the venue in mind.
     
  8. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    I've been putting a carpet remnant under my mic stand but not under my amp or under the 18" sub which is usually only a few feet from the mic stand. I'll try that. I don't think it's the sub because my bass only goes through the PA for big gigs and we have this problem in small places more than big places. So it must be some connection between my mic, my monitor, the floor and my amp. I do hear some of that same low-mid ringing from the Toms too but the main problem is my bass and vocals. I can cut my bass signal and it goes away or turn off my mic and it goes away. The Toms ringing goes away when the drummer turns off his mic. Tweaking the low mids on the PA eq sounds like it might help too. Thanks everyone for the help. I'll try these things and report back.
     
  9. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I didn't see any mention of a high-pass filter/low cut on the mic channels of your board. This is exactly the symptom they are intended to prevent. The lows can't feed back if they don't go through the system. Having a gate on each mic to turn them off when not in use is also a good idea.
     
  10. el_Kabong

    el_Kabong

    Jul 11, 2005
    Funny, I thought I said exactly that! Must be the Strine. ;)

    Now there's a really big clue!
     
  11. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    Would the proximity of the sub be an issue even when the bass is not going through the PA?
     
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    No, it wouldn't as far as the bass is concerned. But the sub still shouldn't be there. I'm beginning to question your sound man's level of knowledge. This could be simply a matter of the Peter Principle at work.
     
  13. anderbass

    anderbass

    Dec 20, 2005
    Phoenix. Az.
    Could be, because his (very hot or boosted eq?) vocal mic is picking up bass amp bleed, this mic channel is going through that sub or the mains, then back through the mic over and over...:eek:
     
  14. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    We have no sound man. We are a three-piece and do our own sound. The guitarist owns the PA and has very little knowledge of these things.

    The sub has to go on one side of the "stage" or the other. It's more convenient on my side since the board takes space on the other. If it was on the other then it would be close to the guitarist's mic so I don't think we can get it very far from any mic.
     
  15. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Didn't Dick Smith once publish a book called How to Speak Strine?

    In addition to the low-cut filters on the mixer channels, it's also often useful to attenuate the 200–250 Hz range in the overall mix to help overcome the effect of stage bounce.
     
  16. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    He should read a book on sound system design, Yamaha's is quite good. You can't sound good if you don't know what you're doing, and sounding good is what separates the bands that work from those who don't.
     
  17. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    You guys have been very helpful. Here's my checklist for the gig tonight:
    - check to make sure low cut and pad are used on vocal mics
    - put rug under my amp and sub
    - make sure polarity is right on my amp so that I don't get shocked from mic. That way I can get up on the mic and turn down the level on it.
    - use eq to cut lows on monitors
    - use eq to cut 200-500hz of mains and monitors
    - experiment with placement of sub and mic stand.

    I suppose I should do them one at a time to locate the problem but I'm fed up with this. I'll post later with results
     
  18. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    I still use one of his Co-Tanger antennas! I think he and Benny Hill were the same person.
     
  19. morebass!

    morebass! I'm all ears Supporting Member

    May 31, 2002
    Madison WI
    I did everything below except: 1) didn't change the eq on the mains; 2) the low cut was already in use, and the feedback was gone!:hyper: We sounded as good as ever with a less volume. I'm pleased as punch.

    Of course there are so many changes that I won't know which one fixed it but as someone posted earlier it could likely be many variables that contributed. Three additional tweaks were 1)removing the reverb from the vocals and use of a little digital delay instead; 2) Lowered the crossover point (This clearly made an audible difference) and 3) I used a a fretless active bass instead of a fretted passive.

    The sub was on the otherside of the "stage" because of the club geometry. It'll be interesting to see if putting it back on my side makes a difference next time.

     
  20. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    I think I remember those. Back in the late 70s or early 80s, I think it was, he had a mail-order electronics business in the US that advertised in mags like Popular Electronics and Radio Electonics. His ads were as entertaining as the magazines themselves were.
     

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