One of the biggest audio challenges for many houses of worship is the issue of feedback. There are lots of reasons why feedback crops up, and many of these reasons are interrelated—meaning, there isn’t always just one issue that’s causing the problem. Part of the role of a technical leader involves finding answers to problematic issues.
Frequently, it’s a combination of factors, and reducing any one of them can reduce the occurrence of feedback.
As an aside that plays well into this topic, Synergetic Audio Concepts (one of the premiere live audio training organizations in the world) once had coffee cups made with the answer to every live audio question printed on it. What was on it? The phrase, “It depends.” This is very true is dealing with the problem of what is causing feedback in your PA system.
So, what IS feedback?
At a basic level, feedback occurs when the sound level from your PA system at a given microphone input approaches or exceeds the direct sound level from an audio source at that source’s microphone.
So, if the sound level of a vocalists’ voice at the point it enters the microphone is lower that that vocalists’ voice from the PA system when it hits the microphone, you’re going to have feedback.
Ringing, where a particular frequency of a sound source sustains for a short while after the sound has stopped, is a type of feedback that indicates your PA system is on the verge of uncontrolled feedback.
There are a variety of things that effect how easily feedback will start. One of these is the number of microphones you have turned on at any given time.
Each time you double the number of microphones that are turned on in your PA system, you reduce the overall volume you will be able to get out of your PA system by 3 dB. So, if you’re having feedback issues, are there microphones turned on at that point in your service that do not need to be on?
The distance from the sound source to the microphone also plays heavily into the point at which you start getting feedback.
Think about what I said earlier—feedback is caused when the level from the PA system approaches or exceeds the actual sound source for a given microphone. Where do churches tend to have the most feedback issues? With podium mics, and choir mics—both of which are relatively far away from their sound sources.
For choir mics, there’s usually not much you can do about that distance. For podium mics, chose a microphone that is very directional (more on this later) and long enough where you can get it closer to the mouths of those speaking from the podium. And, in both these situations, the people singing or speaking need to project strongly.
Just because there’s a microphone in front of you doesn’t mean you can cut the volume of your voice. Quite the opposite. Those in a choir or speaking at a podium need to be trained to always project their voices as if there isn’t a microphone at all.
Next time, we’ll talk more about microphone directivity and choir micing.