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What causes feedback in a guitar or microphone?

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Introduction

Physics Coursework GCSE

What causes feedback in a guitar or microphone?

Just for the record, feedback is actually the mechanism used to control almost every electronic device manufactured. Stability is a critical issue for all of these feedback control systems, and the gain, or level of amplification, used is a critical element in their design. When musicians talk about feedback, however, the connotation is negative because it is the term they use to describe the shreek that results when the gain is too high on the output of an amplified instrument or microphone. There are several potential mechanisms by which feedback can occur when sound is amplified. Let’s deal first with the simple case of a microphone and an amplified speaker. (See the figure, but ignore the guitar for now.)

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Middle

Unlike microphones, guitars (both acoustic and electric) can vibrate and these vibrations occur at particular frequencies. In fact, the structural vibrations of an acoustic guitar and the acoustic resonances of the guitar enclosure are coupled and serve to "color" the sound of the guitar. These harmonics are what distinguish the sound of a particular guitar. The top surface of more expensive acoustic guitars is

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Conclusion

A similar mechanism occurs when amplifying the output of an electric guitar. Structural vibrations induced by acoustic feedback can magnify the signal generated by the sensors embedded in the guitar to "pick up" its sound, which leads to instability. Equalization can control feedback by reducing the gain at the frequency at which this problem occurs. One must take care in setting the equalization so as not to eliminate the natural harmonics of the instrument over a desired frequency range, however.

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Response to the question

The concept of feedback is explained to some degree by the candidate using a variety of examples. The main problem being the confusing nature of some of the examples that were use and lack of support diagrams.

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Response to the question

The concept of feedback is explained to some degree by the candidate using a variety of examples. The main problem being the confusing nature of some of the examples that were use and lack of support diagrams.

Level of analysis

The candidate begins by explaining the concept of feedback. It is a good attempt but it gets slightly confusing to follow in places without any previous knowledge of feedback as there are not base concepts mentioned. No diagrams are used which makes it harder to understand. This is repeated throughout the piece.

Quality of writing

The tone of the piece is wrong from the offset as it is in a very nonchalant and discussion tone manner whereas in a scientific piece the tone should be purely factual with no opinion apart from in the conclusion when all facts have been analysed. Punctuation, grammar and spelling all okay.


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Reviewed by skatealexia 05/08/2012

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