Feedback is that ringing tone, it varies from a low rumble to a high screeching noise - it is not only annoying, but it can also cause damage to your sound system or ears. A simple PA system consists of a microphone, amplifier and one or more speakers. If you have these three components, you have the potential for feedback. Feedback happens when the sound from the speakers is picked up by the microphone and is re-amplified and sent to the speakers again. With over 50 years experience in supply and system design for many of the UK's largest, high profile audio projects, our AV experts provide a unique level of technical support and customer service.
Subscribe to our YouTube channel now at howtoav. Login Log in to your Account. It is caused by a "looped signal", that is, a signal which travels in a continuous loop. In technical terms, feedback occurs when the gain in the signal loop reaches "unity" 0dB gain. One of the most common feedback situations is shown in the diagram below - a microphone feeds a signal into a sound system, which then amplifies and outputs the signal from a speaker, which is picked up again by the microphone.
Of course, there are many situations which result in feedback. For example, the microphone could be replaced by the pickups of an electric guitar. In fact many guitarists employ controlled feedback to artistic advantage.
You could also try a digital feedback eliminator. There are various models available with varying levels of effectiveness. The better ones are reported to produce reasonable results. Feedback can occur at any frequency. In this post, I will explain several factors that can cause a microphone to feedback so that you can avoid these situations and significantly reduce the occurrence of feedback in your gigs and events.
Plus I have included some tips and solutions that will help you stop microphone feedback. One of the main reasons for audio feedback is because microphones are placed in front or too close to a loudspeaker. If loudspeakers are placed behind the microphone, feedback is almost guaranteed because whatever sound comes out of the speaker will be captured by the mic, and the loop will cause feedback.
Placing a mic to the side of a loudspeaker is another potential reason for feedback because sound can bounce back and forth until it reenters the sound system through a microphone. To help reduce the occurrence of feedback, place all open microphones behind the loudspeakers, making sure that there is enough distance between the mic and the speakers. A rule of thumb commonly used by sound engineers is, if you double the distance between a microphone and the speaker, the volume for that channel can be increased by 6dB, providing you more volume headroom before feedback on that channel.
When setting up your mics, make sure you allow enough time to try different positions until you get the best results. With time and practice, it will become easier because you will understand the behavior of your sound equipment. Another reason that causes feedback is the placement of speakers and monitors.
The dispersion angles for a loudspeaker varies, but typical angles of dispersion are 90 degrees horizontally and 60 degrees vertically. Any microphone located in that dispersion area has the potential for feedback. When setting up a sound system, you want to cover as much space as possible so that your audience can hear everything. This is where it is crucial to place loudspeakers correctly so that they can cover as much area as possible, but staying clear of the pickup pattern of the mic.
When setting up microphones on stage, make sure to keep clear of the dispersion area of the speakers. Place the main loudspeakers as close to the audience as possible. That way, you can decrease the volume in the mixer. Place the monitors exactly behind the mics on stage, especially if you are using cardioid or super-cardioid mics.
A rule of thumb when placing speakers is if the distance between the audience and the main speakers is halved, by keeping the volume constant, the sensed volume by the audience will increase by 6dB. In other words, halving the distance between speakers and the audience increases the sound volume by 6dB. That way, the sensed sound volume increases without actually increasing it on your mixer. Another solution is to use in-ear monitoring systems; that way, stage monitors can be removed entirely, significantly reducing the occurrence of feedback.
The only disadvantage is that in-ear monitoring systems tend to be expensive, but if you can afford them, I highly recommend it. Allow enough time when setting up everything so that each mic is tested with the main speakers and monitors as well.
Simulate a situation so that you know what is your volume headroom before feedback. In other words, slowly increase the volume of all microphones and generate a sound to see how the equipment behaves at higher volumes.
Feedback can be caused by the type of microphone you use.
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