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Thread: Feedback

  1. #1

    Feedback

    Need help with feedback during live mixing at my church, when the choir sings I have,
    I believe they are two audio technica p48 mics and as soon as I unmute them they start
    feeding back, my room is not treated and is mostly brick and wood on the walls, I seemed to have a little easier go at when I spent more time on my mic placement, would a graphic RTA help my situation. I know the room needs to be treated but that's not in the budget right now. Please help

  2. #2
    First question: Do you really need to amplify the choir? Maybe you do, but at least ask yourself the question. We're so used to sending things thru speakers these days that we do it by reflex. Maybe the choir doesn't sound LOUD without amplification - but does it have to?

    There is no such thing as a sound reinforcement system so good that it doesn't degrade the quality of the music. In particular, if you're not doing a multichannel system for the choir - that is, if you're sending all the sound thru one set of speakers (and almost everybody does) - there's a problem right there. Part of what makes a choir sound good is the massing of voices, spread out acoustically across the width of the choir. When you crunch all those voices together into one speaker, that's like putting the choir in a box with a small hole cut into one side. No way that's going to be an improvement.

    Assuming you do have to amplify the choir, your best weapon is restraint on the gain control. Amplify only as much as you really need to. Lots of operators think they need to squeeze every last dB of gain they can, and push the system into near-feedback. Reducing the gain by as little as 2dB effectively eliminates the ringing, and a 2dB increment is almost nothing in terms of perceived loudness.

    Your next best weapon is mike and speaker placement and aiming. You can't put the mikes really close to the choir - that would only spotlight individual singers - but it might be worth thinking about mic placement with the speakers in mind instead of the choir; that is, try placing the mics for optimum rejection of sound from the speakers, rather than necessarily best placement for choir pickup. A couple of feet difference or a few degrees difference in aiming might help.

    The cheapest processing fix is a 1/3 octave graphic equalizer, which can be had used for not much money. If your mixer permits you to subgroup the choir mics, patch the graphic EQ in so it only affects the choir mics. More sophisticated feedback killing equipment costs more. Some DSP-based units do unfriendly things to the music; if you want to buy one, ask to try it out first.

    Finally, when you do get the budget to do acoustic treatment: do you really want to? The answer depends on what type of service you have. If it's a contemporary, gospel-type service, go ahead and put in padding. But if any of your services are traditional, liturgical style, merely suggesting acoustical "treatment" will cause the organist and choir director to slash your tires. I put "treatment" in quotes because, where liturgical music is concerned, treatment (that is, padding) equals damage.

    Which brings us full circle. If you have a "live" acoustic, that probably means the choir needs little or no amplification. If you put up padding to reduce reverberation, you may find that the choir now needs so much more amplification than before that you've gained nothing, spent a lot of money, and killed congregational singing. (People sing best in a live room.)

    One more thing: are you suffering with bad speakers poorly placed? Even if you had money for acoustic treatment, would it be better spent getting better equipment?

  3. #3
    Thanks, Karl you are right about amplifying the choir that was something I learned a couple of weeks ago my choir would always say we can't hear ourselves then befor the end of the song the monitor gain is jacked up so high you don't have room to open anymore mics without shutting something else off. Lot of good things I'll give a try and let you know how they turn out. Thanks again and have a Blessed holiday.

  4. #4
    AHA! The choir doesn't need amplification for the congregation, but for itself. So I gather the reason you're amplifying is for the choir's benefit.

    I should have guessed. When monitors are in use, they are much more often the source of feedback than the main speakers. If you get a graphic EQ and patch it in just before the monitor amp, so it only affects the monitor speakers, you can get really aggressive with adjustment. Remember, it doesn't need to sound good in the monitors - it just has to be audible. One suggestion - try listening to the monitors playing, say, a CD of orchestral music. Are they smooth and natural sounding, or peaky? An amazing number of monitors are really trashy sounding. They're designed to cut through the noise of a rock band, and the way they achieve that is with midrange-peaked response. A rock band monitor is guaranteed to cause feedback in your application. Just for an experiment, try some home-stereo speakers and see if the feedback problem changes. (Careful with levels - home stereo speakers aren't designed for sustained high power operation.)

    Now, when they say they can't hear, what can't they hear? Each other? Then you have a problem. Truly, the only good fix is to put up reflective surfaces around the choir. Acoustic treatments don't feed back.

    But if it's the piano or organ they can't hear, can you do a separate monitor mix that emphasizes those and de-emphasizes the choir?

    One other trick: some mixers permit you to do two monitor mixes. If you mike the left side of the choir and feed it through a right monitor speaker, and vice versa, you'll get a few extra dB of available gain, because each mic is not feeding the nearest monitor, and each section of the choir will hear the other sections they couldn't hear before. This is especially useful in a large church with a choir spread out over fifty feet.

    If this works, and you are in a mega-church, you might consider doing a whole, separate sound system for the choir. Mixers with at least four outputs are cheap. You can set up monitors for every section of the choir, with the nearest mic removed from each of the respective mixes.

  5. #5
    Senior Member SC358's Avatar
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    If this works, and you are in a mega-church, you might consider doing a whole, separate sound system for the choir. Mixers with at least four outputs are cheap. You can set up monitors for every section of the choir, with the nearest mic removed from each of the respective mixes.
    Karl makes a great point. I saw a church's setup several weeks ago. The church is not a traditional building or even modern type - it's actually an old theater. Anyway, their audio system is in two parts with two boards. One board is for the congregation and recording while the other is strictly for monitoring. I was never involved in anything so big myself but it did make technical sense given the size of the stage & audience with instrumental and vocal ramifications.

    Thought I'd just put in my 2 cents
    SC358
    Relationships are based on compromises - behavior accepted is behavior repeated.

  6. #6
    Thanks again Karl, this is something I have to teach the choir and the musicians because the musicians play very loud so now my challenge is to get the musicicans not to play so loud along with getting new equipment and instituting new ways of doing things is one of my biggest problems but I'll keep plugging away at it.

  7. #7
    if you're going to use a mic, try using a shotgun mic thats normally used for tv.

  8. #8

    shotgun

    Smifis has a good idea. A shotgun mic will ruin the intra-section balance of the choir, but that doesn't matter; this isn't the mix the congregation is going to hear.

    A fairly direct rhetorical question to the musicians might be in order: "How do you view your job? Are you supporting the choir or are they supporting you?"

  9. #9
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    Some DSP-based units do unfriendly things to the music; if you want to buy one, ask to try it out first.
    karl eilers is exactly right here. Be very careful of Behringer's early model Feedback destroyers... they've got huge problems with sound distortion.

    I worked with a mega-church in South Florida for about a year, trying to help them get their sound issues fixed. Their sanctuary was about four stories tall and had floor-to-ceiling glass on both sides and no acoustic treatment of the balcony or around the stage.

    When I came on-board they had huge problems with onstage feedback as a direct result of the monitors for the band and choir. One thing I worked on with the choir director was the purpose of the band and choir. Were they there to perform or were they there to help lead the congregation in worship? The answer should be obvious that they are there not to perform for themselves, but to help lead the worship.

    After we got that across, we were able to begin working with the band and getting them to tone down the way they played their instruments. I then introduced small-format sound boards (like, two inputs/one output) for each band member with a set of headphones. My total cost for this was about $80 per member. Then I split their instrument's output, running one into my patch system for the FOH, monitor, and recording mixes; the second output I ran into that mini-mixer. Then I took the second input of that mixer and ran a very basic, low-level monitor mix of the entire band and the worship leader, mixed to the worship leader's request. This then enabled them to control how much of themselves they heard in relation to the band, and it allowed them to control how loud it was without leading to more gain in the sanctuary. Everyone was happy, the feedback issues were eliminated, and the whole mood of the service changed over just a few weeks.

    There are systems out there that do exactly this (Aviom makes several) but they can be out of reach for many smaller churches or even large churches who don't put much of their budget toward the A/V department. The work-around I developed seemed to do a good job.

    Good luck!

  10. #10
    Senior Member SC358's Avatar
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    A shotgun mic will ruin the intra-section balance of the choir, but that doesn't matter...
    Karl -
    Could you please define or expand on "intra-section"? I never came across that term.
    SC358
    Relationships are based on compromises - behavior accepted is behavior repeated.

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