Church Sound and Video Advice > Audio Tips > Feedback Problems
We seem to always be getting feedback in our church's sound system, how can we eliminate this?
A comprehensive examination of Feedback elimination is covered in our Sound Operator's Handbook and Course.
What Causes Feedback:
Feedback occurs when the level on a microphone causes that mic. to pick up sound from the speakers and generate a loop; the speakers feed sound into the microphone which in turn supplies sound to electronics which feeds to the speakers again and again. This loop of sound creates that loud, annoying squeal that everyone dreads. Feedback will always happen at a certain frequency (pitch) depending on which frequency is the most prominent in your room.
How to Eliminate It:
The first thing you need to do is make sure that your room has been properly tuned. This is a process that is done during installation setup. A spectrum analyzer is used to graph the frequencies in your room and a 15 or 31 band graphic equalizer is then adjusted according to the results. This will put all the frequencies at the same level and will help you get more volume before you start getting feedback. It also gives you accurate sound in your room
Placement of the Microphones:
You will still find that after this process you can get feedback if you set the level on the mics high enough. Don't panic! Your next job as a sound tech is to make sure that the placement of the microphones is correct. Most mics are designed to pick up sound within a 60 degrees radius. Make sure you check the data sheet if you are unsure. Use this to your advantage. Try not to set up mics facing into speakers. If you can set the mics up behind them. This way the speakers are not projecting their sound into the microphones. Also instruct anyone using the mics to use them close, about 3 to 6 inches. That way you won't have to crank it up to get the volume and increase your chance of getting feedback.
Presetting the Levels:
Setting your levels properly and knowing what your limit is before you go into feedback is important. When I set up a microphone I like to drive it into feedback. Don't worry I do this before the service when no one is in the room. This lets me know how high it can go. When the service is underway at all cost I stay below this level. If someone is speaking too low, or is too far away from the microphone then it is the fault of the person speaking not of the sound operator. The sound system is half the battle and we need to do everything we can to have the message heard clearly, but good communication skills is the other half of the battle that usually gets left out of the picture when something goes wrong.
Turning Off What You Are Not Using:
Another common mistake that encourages feedback in your church sound system is leaving microphones on when no one is using them. It's not always wrong to do this, depending on the situation, but if you can, turn any mics off completely when no one is using them. Here's the scenario: The worship team has finished the final song before the message. Three or four mics are left on at the front and the pastor gets up to give his sermon. While he is speaking an annoying ring can be slightly heard when he says certain words. That annoying ring means that you are just on the threshold of going into all out feedback You try turning the channel on his microphone down and finally get rid of the ring. BUT!! You just cut his level down. Try turning off the other mics and I'll bet you don't have to touch his level at all.
Always keep your ears peeled, listening for that slight ring. If you hear this, back off on the volume slowly just enough to get rid of it. It may mean that it will be harder for the people at the back to hear the words, but if you don't, no one will be listening to the words anyway. The ring will distract them too much.
If you are using your sound system as a "Turn Key" system, which means that you just turn it on and off, and you don't have a sound operator, or if you want to get the highest possible gain before feedback, especially with a lapel microphone, you might want to consider a Feedback Eliminator. This is an electronic processor which searches for and destroys feedback. There are many different ones available from manufacturers such as Shure, Behringer, Sabine, etc. I have tried many of them, and I believe the best one in terms of cost and performance right now is the AFS224 from dbx.
AFS224 Feedback Eliminator:
The dbx AFS224 is a two channel "state of the art" feedback eliminator with 24 programmable narrow band automatic filters per channel. When the unit "hears" feedback, it automatically finds the feedback frequency and notches it out. When feedback occurs at another frequency, a second filter is sent to the rescue. In this manner, it can find and destroy feedback at up to twelve different frequencies. I find the AFS224 to be the quietest, most transparent and most effective feedback eliminator on the market, out of the ones I have tried.