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PAGE 40 Community Solutions™ Owner’s Manual

13.8 Microphone Feedback

One of the more potentially damaging signals in an audio system is microphone feedback. This

usually results in a high volume level, single-tone signal (essentially a sine wave) being reproduced

through the loudspeakers. This kind of signal can quickly damage the drivers and therefore the

situation should be corrected as quickly as possible.

To avoid this situation the following approaches can be tried. It will be necessary to increase the gain

for the system in order to “test” if there is any improvement in the gain-before-feedback margin as

adjustments are made. During a performance the main recourse to stop feedback or ringing is to

reduce the volume for the offending microphone or, if this cannot be quickly determined, reduce the

volume of the entire system. The following list is in the general order of preference of what to do first.

Note that using equalization is the last thing to do.

1. Use directional microphones (cardiod-types) that have well controlled pick-up patterns.

2. Keep microphones close to the sound sources. The further away they are the more gain that is

needed.

3. Use similar quality microphones. Major problems can be caused by just one poor microphone

that is sensitive to feedback.

4. Use as few microphones as possible. The amount of gain-before-feedback decreases as the

number of “open” microphones increases.

5. When possible, use direct inputs, such as direct boxes, contact pickups, and line feeds from

instrument amplifiers. This will reduce the number of live microphones.

6. Always keep the microphones behind the plane of the loudspeakers and/or aimed away from

them.

7. Reposition the microphone to provide better feedback rejection. Sometimes moving it only a

few inches or re-orienting it will suffice.

8. Mute any microphones when they are not being used.

9. Reverse the polarity of a microphone that is feedback sensitive.

10. Try a different type of microphone in place of one that is feedback sensitive.

11. Use sound absorbing materials like rugs, packing blankets, or sound isolating panels to reduce

sound reflections in hard surfaced stage environments.

12. Use a graphic equalizer, parametric equalizer, or notch filter to reduce the level of frequencies

that are prone to feedback. For best results, it is recommended that a graphic equalizer used

for controlling feedback have filter bandwidths of 1/3 octave or narrower.

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Community SLS Manuel du propriétaire Page 40