Microphone feedback has the tendency to damage a soundtrack and will produce a bad sound which is painful for the ears. This generally happens when the signal from the microphone gets amplified and picked up again by the speaker which creates a looping sound. This signal further amplifies extremely fast, thereby creating an extremely bad sound which hurts the ears. This article explains how microphone feedback occurs and what steps must be taken to prevent microphone feedback.
Let’s see what audio feedback is.
What is audio feedback?
Audio feedback occurs when the amplified sound coming from the loudspeaker re-enters the sound system through an open microphone and gets amplified repeatedly. One can call it a kind of positive loop gain that occurs when there is a sound loop between the audio output and audio input. The frequency of the resulting sound is determined by the frequencies of the amplifier, microphone, loudspeaker, and acoustics of the room. An audio feedback is measured in terms of the distance, directivity, and frequency response.
How does it happen?
After you place the microphone in front of the speaker and tap the microphone, the sound coming from the tap spreads through the amplifier then comes out of the speaker and again re-enters the microphone, thereby causing repeated shrilling sound at the same time. The whole thing happens so quickly that it results in a howling shrilling sound.
It is necessary to put the microphone in the right position. Placing it too close to the loudspeaker or too far from the source will create this problem. So following are some steps which will help you to prevent microphone feedback.
Steps to prevent microphone feedback
The microphone should be placed behind the large speakers and in front of the monitor – placing the microphone in front of the speakers will definitely lead to audio feedback because of the repeated amplification. Also, if you place the microphone too far from the monitor, a similar shrill sound will be created due to the pickup patterns of live vocal microphones.
Holding the microphone in the right way – never hold the microphone as you hold a cup. Grabbing it around will lead to the creation of unpleasant sound. For singers, it is recommended to hold the mic from the behind and not just grab it. Also, singers, while moving on the stage, are recommended not to go in front of the main speakers.
Feedback eliminator – utilise the feedback eliminator in the right way. The various switches can detect the frequency and can cut it accordingly to prevent the feedback.
Graphic equaliser- The purpose of the graphic equaliser is to prevent feedback during the show. The technique is known as ‘ringing out’.
How does it work?
The engineer, during the sound check, slowly increases the level as the vocalist sings. This increase in the level creates the feedback. As soon as the feedback starts happening, the engineer again lowers the level, thereby keeping it in check.
Here’s some tips on how to use the technique:
Slowly increase the volume until feedback is created. Next, pull out the offending frequency from the equaliser at 3dB.
If you hear a howling sound keep the range from 250 to 500 Hz. Whistling sound or shrilling sound occurs at 2 kHz. Maintaining the sound range is all about practice. After a few sessions, you will get to know how to check the sound range.
When the first frequency is checked, again increase the volume level to increase the frequency level. Continue this thing until the desired level is reached.
Using the parametric equaliser – some expensive mixing boards come with a parametric equaliser. This can be used to control the frequency level to a great extent. As the parametric equaliser has a smaller bandwidth than the graphic equaliser it gives a better frequency control. The frequency is controlled by degrading the quality of the soundtrack.
Checking the acoustics room – the size and shape of the room has a lot to do with controlling the feedback. Although the size of the room is not always in your hands, if you consider the acoustics, it can prevent excessive reverberation. Here are some DIY tips:
Put foam at the back of the stage and above the stage to decrease the volume of the stage. Hence, the monitors can work even with a low sound. The lesser the sound created, the lesser the feedback.
Always remember your ears are the best detectors of sound. Learn to identify the frequency level by listening to the quality of sound carefully. Tell someone to dial a tone and identify the tone blindly. It’s all about practice. The more you practice, the more efficient you will become.
Apart from following the above tips, you can also check pictures on the internet to get a better idea.