Larsen Effect – What is it?

Have you ever heard a strong voice which becomes undesirable to hear after some time? Well, all this is nothing but a positive feedback noise and in the world of a sound system, it is popularly known as “Larsen Effect”.  Now the popular question which comes to everyone’s mind is, “what causes feedback?”. All these questions and the related subjects of interests are mentioned here in this post. We will also discuss the factors which contribute to Larsen effect and the popular ways to avoid positive feedback in a sound system.

Larsen Effect and the Factors Which Affect it:

Larsen Effect occurs when sound from an amplified sound source enters the nearby receiver which retransmits it to the amplified sound source. The effect can only take place if both the sound source as well as the receiver is placed in the close vicinity of each other. This process continues in a repetitive manner and leads to an unpleasant sound. Many guitarists use this to create a sound effect which is known as ‘guitar feedback sound effect’. And about the most common feedback frequencies, we can say that feedback occurs at one frequency at a time. However, there are multiple instances of feedback that take place at the same time at various frequencies. Here we have discussed below the factors which we can use to diminish it:

  • Distance – More the distance between input (microphone) and output (loudspeaker), less will be the intensity of feedback. This is so because the sound pressure drops with an increase in distance. So, in order to maximize gain before feedback then it is mandatory to keep the PA system far from the stage.
  • Direction – When your speaker points to the back of the microphone then the effect of feedback decreases significantly. Always keep the directivity of a speaker and polar patter of mic tight in order to avoid feedback. In the higher frequency, speakers are more directive whereas, in the lower frequency, the directivity loses. So, it is advisable to use unidirectional loudspeakers in order to achieve a higher gain even with the lower frequencies of audio. Hence, it is highly important to make a choice of a mic in a careful manner. Also, we should not cover the mic with our hands because if you do so then the mic would become omnidirectional.
  • Frequency Response – All the PA systems have bumps of energy which combines with room modes and ringing to trigger feedback. It is suggested to use a mic with bumps of energy in the same frequency regions and this would solve the problem of feedback to a great extent. ‘Ringing the system’ is the first step to do so
  • Choose Signal Processors – There are a number of dedicated signal processors which offer a facility to reduce feedback significantly. All this process involves is the introduction of feedback into the system and then applying the notches in the equalization to reduce the unwanted frequencies.
  • Choosing Acoustic Instrument – Since every room has certain frequencies that are more resonant than the others. It is advisable to use absorption since hard surfaces in a room contribute to avoiding direct sound from reaching to the audience. It is of great significance to using an acoustic instrument in order to ensure gain before the feedback.

Hence, this is all about the concept of “Larsen Effect” and all the factors which contribute to reducing its effect. So, the next time you encounter the problem of feedback, you can use any of the above-mentioned ways to remove it from your audio system.