Three Easy Ways For Preventing Feedback

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Three Ways for Preventing Feedback

Let the worship music be heard without distraction.
Photo provided by David Alan Kidd

You might be suffering from all three of these audio feedback problem areas.  I’ve been emailing a sound tech overseas who has had feedback problems.  In my initial email, I said it could be caused by one of a few things.  As it turned out, he had all three conditions that were causing feedback.  Let’s get it work…

Feedback is caused when a particular frequency becomes excited and is thus astronomically amplified causing the screeching and howling sounds.  Reminds me of Halloween. But seriously folks….the feedback usually occurs when a sound is loud enough to be amplified by a stage monitor and then picked up by a microphone and gets into an amplification loop.  In this loop, the amplified sound gets louder and louder until…

SCREEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEECH!

The Three Easy Ways For Preventing Feedback

1. Place microphones in the right relationships to loudspeakers and monitors.

In the case of my overseas friend, his church setup had the pastor’s vocal microphone out in front of the house speakers.  While such a scenario can work without having feedback, it’s a scenario that’s much more likely to experience feedback.  This is especially true if the pastor moves the microphone or turns in a way that his/her body is no longer blocking sound between the house speakers and the microphone.

Regarding floor monitors, vocalists should be very close to their floor monitor.  The monitor volume should be loud enough that the musician can hear it but not so loud that the microphone picks up the sound when they are holding it up to their lips.

*Tip: Ask your singers not to drop their microphone to their side when they take a break.  Rather, ask them to first move away from the monitors and then they can lower their microphone.  Otherwise, they are essentially stuffing the microphone into the monitors and then it’s feedback city!

2. Teach musicians to use the proper vocal microphone technique.

Last Saturday, I taught a 4-hour audio training course at a local church.  I explained that  anyone using a vocal microphone needs to hold the microphone right up to their mouth.  Immediately, two of the people in the class started talking about how certain people would start with the microphone up to their mouth and slowly lower it as the song went on.  They’d have to turn up the gain until…SCREEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEECH!

People using vocal microphones need to know that audio equipment has its limitations.  Therefore, explain to the singers that if they lower their microphones their voices will drop out of the mix.  Regarding people using vocal microphones for speaking roles, it’s a bit easier.  The problem I’ve observed is, like the singers, they slowly lower the microphone.  As they are using the microphone for a speaking role and will likely be holding a bible, book, or piece of paper, set up a vocal microphone on a stand for them.  Have them read a bit after the sound check to set the gain.

*Tip: If you have more than one person talking into the same vocal microphone during the service, make note of their natural speaking volume level.  This way, when they walk up to the microphone, you can lower the fader before they speak those first words.

3. Use the proper gain setting technique.

Setting the channel gain for any sound source, you want the clearest strongest signal.  You want the best signal-to-noise ratio so that the sound, such as the singer’s voice, is stronger than any line noise that might exist.  However, you don’t want to allow for so much gain that you allow for feedback in the system.

An easy way to get the best signal-to-noise ratio is by using the “gain-before-feedback method” of gain setting.  As you turn up the gain, with the fader at 0, turn it up until you get feedback.  Then turn down the gain a few notches.  Personally, I set the fader at zero and turn up the gain until the sound is about at the volume where I want it in the room.  But if I do experience feedback, I know to turn back the gain.

The Take Away

If you find you are having more than your share of feedback during an event, consider more than one issue might be the problem.  Feedback prevention comes down to placing microphones in the right relationship to monitors and loud speakers, ensuring that microphones are as close to the sound source as possible, and that you are sending the right amount of the audio signal into the mixer.

One last very important piece of information.  As I told my class on Saturday, the entire sanctuary is your responsibility.  This means everything from the stage to the sound booth.  The next time you experience a feedback issue and are asked about it after the service, don’t place blame on someone else or some piece of equipment.  Take ownership of it, apologize for it, and do what you can to prevent it from happening again.

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Comments

  1. says

    I read this “Feed Back” article hoping I can get one of our volunteers better aware of how to control/avoid it. While I can’t say I’ve never encountered feedback, I would say I have it pretty well under control.

    However, I don’t agree with your suggestion to place a microphone to the lips of a singer/speaker. We usually use wired and wireless versions of Shure 87s (old and new wireless versions). All three versions will pick up siblance (sp?) sounds and “P”oping and breath-wind noises when placed directly in front of and close to our singer’s lips. We also bet a much more bassy sound because of being so close to the hollow mouth! I use one of two methods to try and avoid these disturbing sounds. 1: I try to get the user to lower the mic to their chin or 2: move the mic to one side of the mouth. The point is to get the mic out of the direct wind of the users mouth and away from the echo chamber of the mouth.

    One reason this is a constant problem is that users continue to see images of singers ‘eating’ the mic. I don’t know what brand/model mic these singers are using. And the extra bass (presence) is good in certain types of singing, but few churches need a nightclub effect! ;-)

    Do you have a different approach I could use with these mics? Again, we very seldom have feedback problems but I’d like to have another method that could make our job easier AND more successful!

    Thanks for your great site!!

    • says

      Jim, the singers can have the mic up to their lips but still sing over it. The plosives and the proximity effect (more bass the closer to the mic) can be resolved with a little EQ work. The farther away the singer’s voice from the microphone, the more gain you have to give the mic. Then you are picking up more sound on the stage (drums, amp’s, anything else).

      We sometimes put a backing singer near the drummer so listening closely to that singers channel, I can hear the drums. I’ll add a gate to their channel so when they aren’t singing, the channel automatically drop the dB level of the channel so I don’t get the drums coming through that vocal microphone. Check out this article on mixing vocals.

  2. Sujit says

    Hi, Chris

    I had the same problem in my church. But i followed the suggestions and the number of times feedback happens has decreased considerably. I am new and still learning.

  3. says

    Hi,
    Overall this is a good article. The only suggestion I would have is adding to the mic placement relationship section is mentioning something specifically about polar pattern and mic selection. In the spirit of prevention, understanding that using 2 wedges with a supercardioid mic will have less potential for feedback than with a cardioid pattern. Conversely, a supercardioid pattern with a single wedge is less effective that a cardioid mic. Most people don’t have a clue about polar patterns.

    Just a thought

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