Sound

Getting rid of Feedback – Part 3

We’re in the middle of a series on how to deal with the continual problem of feedback. See the first two instalments here and here. 

We’ve looked at the cause of feedback – a microphone picking up sound from a speaker which is playing an amplified signal from that same microphone. The next step is to understand a little bit more about microphones and two of the main types.

Most microphones are carefully designed so they don’t pickup sound equally from all directions. These so called unidirectional (or cardioid – which means ‘heart shaped’ which will make sense in a sec) microphones are designed to pickup very strongly what they are pointing directly at, only minimal pickup from the sides and virtually none from the back.

Omni-directional microphones, on the other hand, are carefully designed to pickup all directions equally. You can hold the thing backwards, point the cable at your mouth – and it makes little difference.

In the mic manual, you can usually find a diagram (called a polar pickup pattern) which represents this visually. They look like this: (you have to imagine the head of the microphone in the middle pointing upwards.)

 

In a church context, unidirectional mic’s are the way to go for most things, especially for vocalists and mic-ing guitar amps and stuff like that. Unidirectional mics, like the classic Shure SM-58, are much better at rejecting feedback because they only pic up what is in front. So as long as they are not pointing at the speakers, you will have much more scope to crank them up without it feeding back.

The one exception is the lectern mic. Often a more ‘omni’ mic is good here because all sorts of people use the lectern who might not know how to use a microphone. So when 5 ft Janice gets up to do prayers straight after the Bible reading from 6′4″ Bob – there is no problems. One when someone is interviewed and they are standing 2 meters off to the side you can still pick them up alright.

Next time we’ll talk about why feedback sounds the way it sounds. Why it is usually always high pitched, or low pitched. Then we will be ready to get practical and put the pieces together.

© 2008 Check 1-2.