Why mics feedback

Try some of these: Keep the microphone behind the main loudspeakers to minimize the sound that can reenter the microphone. If the microphone is in front of the speakers, then feedback is nearly guaranteed.

You may notice this when a performer or presenter steps out into the crowd and finds themselves in front of the speakers. More often than not the result is that loud, ugly, screeching sound. Use a microphone with a unidirectional cardioid polar pattern. A cardioid microphone has its maximum sound rejection at the rear of the mic.

Keep monitors or loudspeakers aimed at this area of maximum rejection. Please note that an omnidirectional microphone picks up sound equally all around the microphone and has no area of sound rejection. It is much harder to keep sound from reentering an omnidirectional microphone. Place the microphone close to the sound source. Understanding microphone feedback and how to eliminate it comes with experience.

This article will help simplify microphone feedback and offer strategies to help performers and audio technicians eliminate it.

As discussed, microphone feedback is a positive feedback loop that causes the microphone and loudspeaker to rapidly feed each other more and more signal until the system overloads. This loop causes the microphone signal to distort and the loudspeaker to project a gross screeching, humming, or whistling noise. This threshold is often referred to as gain-before-feedback. So what do we do? This is dangerous since an increase in level or even a repositioning of the microphone can send the signal into feedback territory.

So we know what feedback is and the basics of what causes it, but other indirect factors influence microphone feedback. The risk of feedback goes up. After gain is applied, live audio mixers also have channel volumes that adjust the amount of signal sent to the loudspeakers and monitors. Turning up the volume of the loudspeakers creates greater sound intensity in the air.

This, in turn, causes the microphone to produce more signal. Boost the loudspeaker volume too much, and the microphone pickup will surpass the feedback threshold and cause feedback. Of course, conditions are never ideal, but this law is useful in estimating sound intensity as it propagates through air. Therefore, the further the microphone is from a loudspeaker, the smaller the risk of feedback. As the distance between the mic and speaker grows, both the amplification of the mic and the volume of the loudspeakers can be increased!

Typical sound reinforcement microphones have a cardioid polar pattern. They are the most sensitive to where they point, less sensitive to the sides, and barely sensitive to the rear. For more information on directional cardioid microphones, check out my article What Is A Cardioid Microphone? Pointing a directional microphone at a loudspeaker is a surefire way to get microphone feedback. For this reason, foldback monitors can be placed in front of singers.

The directional microphone should point away from the monitor speakers. In this scenario, the feedback threshold is quite high. However, if the singer points the top or front of their microphone at the foldback monitor, feedback would ensue!

Frequency response and tone basically mean the frequency-specific sensitivity of a microphone. Dynamic microphones typically have high-frequency roll-offs well in the audible range of human hearing. The size and shape of the physical space produce particular acoustic characteristics. Standing waves and reflections within an acoustic space have the potential to create microphone feedback.

Standing waves are wavelengths of sound that fit perfectly between two parallel surfaces because the wavelength fits perfectly. The result is a loud rumble or a high pitch ringing noise. 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.