Sound


            The purpose of the guitar is to make sound that is pleasing to the player or the listener. In order to understand how a guitar creates music, it is necessary to know a little about what sound is, exactly, and how it works with the guitar.
            According to Webster's dictionary, sound is vibrations in the air, water, etc., that stimulate the auditory nerves and produce the sensation of hearing. For our purposes we will only look at vibrations that occur in the air. The vibrations are caused by air molecules moving back and forth in space. The vibrations travel by the chain reaction of the molecules bouncing into each other in what are called traveling sound waves. The movement of the molecules causes them to compress together and then decompress, thus allowing the wave to travel through space. This movement causes a change in the air pressure. The greater the change the louder our ears perceive the sound to be. The picture below shows how this process works.

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            The number of vibrations per second is called the frequency of the sound. The unit of frequency is the Hertz(Hz). The average person can hear sounds ranging in a frequency of about 20 Hz to 20,000 Hz. E is the lowest note on a standard guitar, and has a frequency of 83 Hz.
            Sound comes in basically two types. One is called tone and the other is called noise. Tone is  sound that repeats at a regular frequency or at similar frequencies. Below is a graph of the sine wave of a 440 Hz tone.

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Noise is the opposite of tone. It is made up of random frequencies that, when graphed, have no pattern. Examples of noise are the static on a radio or tv that is not tuned to a station. The picture shown below is what noise looks like when graphed.

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Musical notes, such as those produced by a guitar, are tones. They are actually made of just a few tones that sound pleasing to our ears when played together. When a guitar plays a tone it takes advantage of  what is called harmonics. That is, when one string is played it rings at multiples of the original tone. In addition, the other strings vibrate a little as well. All of the frequencies that are created are similar and blend together to get the distinctive guitar sound. The picture below is a graph of a 440 Hz frequency blending with an 880 Hz frequency. It is easy to see the repeated pattern in the graph that distinguishes it from just noise.

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            The overall physics of sound is much more complex than what has been presented here. However, this page offers the basics of how sound is involved in the function of the guitar. The following pages will look at how the guitar's various parts work together to create its familiar sound.