Physics of Music - How a guitar works.

Physics of Music

How a guitar works

A typical guitar has six strings. These are all of the same length, and all under about the same tension, so why do they put out sound of different frequency? If you look at the different strings, they're of different sizes, so the mass/length of all the strings is different. The one at the bottom has the smallest mass/length, so it has the highest frequency. The strings increase in mass/length as you move up, so the top string, the heaviest, has the lowest frequency.

Tuning a guitar simply means setting the fundamental frequency of each string to the correct value. This is done by adjusting the tension in each string. If the tension is increased, the fundamental frequency increases; if the tension is reduced the frequency will decrease.

To obtain different notes (i.e., different frequencies) from a string, the string's length is changed by pressing the string down until it touches a fret. This shortens a string, and the frequency will be increased.

Wind instruments and longitudinal standing waves

Pipes work in a similar way as strings, so we can analyze everything from organ pipes to flutes to trumpets. The big difference between pipes and strings is that while we consider strings to be fixed at both ends, the tube is either free at both ends (if it is open at both ends) or is free at one ...

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Wind instruments and longitudinal standing waves

A pipe organ has an array of different pipes of varying lengths, some open-ended and some closed at one end. Each pipe corresponds to a different fundamental frequency. For an instrument like a flute, on the other hand, there is only a single pipe. Holes can be opened along the flute to reduce the effective length, thereby increasing the frequency. In a trumpet, valves are used to make the air travel through different sections of the trumpet, changing its effective length; with a trombone, the change in length is a little more obvious.

Beats

When two waves which are of slightly different frequency interfere, the interference cycles from constructive to destructive and back again. This is known as beats; two sound waves producing beats will generate a sound with an intensity that continually cycles from loud to soft and back again. The frequency of the sound you hear will be the average of the frequency of the two waves; the intensity will vary with a frequency (known as the beat frequency) that is the difference between the frequencies of the two waves.

Music box

The volume (loudness) of any sound depends upon the amount of sound energy that reaches our ears.

The music box itself produces a quiet sound. It transfers only a small amount of energy to our ears. When it comes in contact with a sound board, the music box transfers its sound energy. If the material has different resonant frequencies than the music box, it will not amplify the music box's sound. If the material has the same resonant frequencies as the music box, it will make the music box's sound louder. This amplification process is called resonance.

Teacher Reviews

Here's what a teacher thought of this essay

Kate Gardiner

13th of Mar 2013

I consider this piece of work to be 4 stars as it displays excellent Physics knowledge on Sound in musical instruments. Very accurate points made and a good understanding of frequency of sound waves shown. An introduction would improve this work as mentioned already at the top of the page and more detailed descriptions of the trombone and music box would improve this essay.

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