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…
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.