Microphone feedback is a potential nightmare for bands and sound engineers looking to record or get clean, live sound. While there have been a couple of cases where it as actually been used by some artists, the vast majority want nothing to do with it.
While it sounds awful, the good news is that it is not too hard to eliminate entirely so long as you follow these rules.
What Causes Feedback?
The first step in eliminating any problem is understanding it. Any PA system will contain a minimum of a microphone, an amplifier and at least one speaker. There is also the possibility of other equipment like a mixer.
So now we know what cause feedback we are better equiped to resolve the problem by implementing the steps below.
Interupting the Feedback Loop
The key to dealing with any kind of loop is to find the best place to interrupt it. With feedback that means preventing the noise from the speaker finding the microphone. This can be done as follows:
- Move the mic closer to the sound you want to capture.
- Use a directional microphone to ignore the speaker.
- Turn off any microphones that are not currently being used.
- Avoid boosting tone controls unless absolutely necessary.
- Keep as much distance between the microphone and the speakers as possible
- Keep the speaker output as low as possible.
- Instead of floor monitors, use in-ear monitoring.
- If possible, use sound absorbing materials in the room to prevent echoes from reaching the microphone.
- Avoid walking around to much when using clip on microphones.
Ringing out is a technique often used by sound engineers. The idea is to determine which frequencies are causing feedback and reduce them. Use a graphic equaliser as follows:
- Increase the system volume until you begin to get feedback.
- Reduce the frequency causing it by 3dB.
- Begin to increase the system volume again until the next frequency starts to cause feedback.
- Repeat as necessary until the required levels are reached.
- Remember to avoid over-equalising.
You can tell which frequencing are causing feedback by the type of tone that is being produced:
- “Hooting” or “howling”: The feedback is likely occurring from 250 to 500 Hz.
- “Singing”: The feedback is likely occurring at around 1kHz.
- “Whistling” or “screeching”: The feedback is likely occurring at 2kHz or above.
1. Do not cup the microphone. Some vocalists have gotten into the habit of wrapping their hands around the grill of the mic, probably as some kind of stylistic choice.
Do not let this happen. Changing the microphone’s local environment messes with the way it receives sound. By doing this, a singer is essentially transforming a directional microphone into an omnidirectional one. Not only that, it makes it much more susceptible to feedback.
2. Keep microphones away from monitors. In high-level systems, this does not exclusively mean keeping the two far apart, although that is helpful. Many directional microphones will produce no feedback at all so long as the tail end is always pointed towards the monitors.
3. Listen to everyone who is working. Sometimes someone else is going to have a solution that you are not aware of. This guide is a great way to start but only experience is going to teach you everything you need.
If someone else has a solution that seems wrong and does not require much, let them try it. Worst case they are wrong and you can quickly put everything back. However, if they succeed then you have everything to gain.
4. Remain vigilant always. While we previously said to let people try things, it is always worth remembering that not everyone will ask permission first. There are a lot of people out there who think they know best and will not realise you have set things up the way you have for a good reason.
So you need to double check everything all the time. If you have to leave the mixing console for any length of time, make sure you know where everything should be so you can check when you get back.
5. Practice. With time and experience, your ears will become the greatest tools at your disposal. The best way to practice is to do blind tests with a sine wave or tone generator. Once you can identify the source of a problem automatically, fixing it will become just as automatic