Audio feedback facts for kids

Audio feedback is a loud, unwanted noise that happens when a sound system gets stuck in a loop. Imagine a microphone picking up sound from a speaker, and that sound then goes back into the microphone, getting louder and louder each time. This creates a screeching or howling sound. It's often called the "Larsen effect" after the scientist who first described it.

This noise usually occurs when a microphone is too close to a loudspeaker that is playing the microphone's sound. The sound travels in a circle: microphone to amplifier, amplifier to speaker, speaker back to microphone. This loop makes the sound grow very quickly, causing the annoying feedback.

How Audio Feedback Works

Audio feedback happens because of a "feedback loop." Think of it like this:

• A microphone picks up a sound, like someone's voice.
• This sound goes through an amplifier, which makes it louder.
• The louder sound comes out of a loudspeaker.
• If the microphone then picks up the sound coming from the loudspeaker, the loop starts again.
• Each time the sound goes around the loop, it gets amplified more. This rapid increase in sound volume creates the loud, high-pitched squeal or hum you hear.

Why Does It Sound So Bad?

The screeching sound of feedback is usually very unpleasant because it's often a very high-pitched tone that grows quickly in volume. It can be startling and painful to listen to, especially in a small room or when it happens suddenly. This is why sound engineers and musicians try to avoid it.

When Feedback is Used on Purpose

While feedback is usually unwanted, some musicians use it as a special effect. Electric guitarists, for example, can create cool, sustained, and distorted sounds by intentionally letting their guitars get close to their amplifiers.

• Electric Guitarists: Famous guitarists like Jimi Hendrix were pioneers in using feedback creatively. They would stand close to their loud amplifiers, letting the sound from the speakers vibrate their guitar strings. This created long, wailing notes and unique sounds that became part of rock music.
• Other Instruments: Sometimes, other instruments or electronic devices can also be set up to create controlled feedback for experimental music or sound art.

This intentional use of feedback is different from the accidental, uncontrolled screech that happens in public address systems.

How to Prevent Audio Feedback

There are several ways to stop or reduce unwanted audio feedback:

• Move the Microphone: The simplest way is to move the microphone further away from the loudspeakers. If the microphone can't "hear" the speaker's output, the feedback loop can't start.
• Change Microphone Direction: Point the microphone away from the speakers. Many microphones are designed to pick up sound mostly from one direction.
• Reduce Volume: Lowering the overall volume of the sound system can help. If the sound isn't loud enough to start the loop, feedback won't occur.
• Use an Equalizer: An equalizer is a device that lets you change the loudness of different sound frequencies. Feedback often happens at specific frequencies. By using an equalizer to slightly reduce those problem frequencies, you can stop the feedback without lowering the overall volume too much.
• Control Room Echo: Rooms with hard surfaces (like concrete walls or glass) can cause sound to bounce around a lot, creating echoes. This can make feedback worse because the sound stays in the air longer. Adding soft materials like carpets, curtains, or acoustic panels can absorb sound and reduce echoes, helping to prevent feedback.
• Use Feedback Suppressors: There are special electronic devices called feedback suppressors or eliminators. These devices automatically detect and reduce the frequencies that are causing feedback, often without anyone noticing.

By understanding how feedback works and using these methods, you can keep sound systems clear and free of annoying noises.

Images for kids

• 

  Block diagram of the signal-flow for a common feedback loop.

• 

  Electric guitarist Jimi Hendrix, pictured here in a 1967 concert, was an innovator in the use of guitar feedback effects.

• 

  The Boss DF-2 Super Feedbacker and Distortion pedal (on the left) helps electric guitarists to create feedback effects.

See also

In Spanish: Efecto Larsen para niños