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The following, although not critical for learning how to play, is still good background information which will help you become a well rounded musician.

Fig.1. How the acoustic sound is produced.

-When the string of an Acoustic Guitar is plucked it begins to vibrate between the Nut and the Bridge. This vibrating string in turn vibrates the molecules in the air. As the air vibrates, the particles bump into one another causing sound waves to propagate through the air. These sound waves also enter the Sound Hole of the guitar where they echo in the hollow chamber. The waves of the vibrating string also pass through the Nut and Bridge and sustain within the structure of the wood.  The vibrating wood also vibrates air molecules.  The sound created from this string vibration is projected from the sound hole and the top of the guitar. This is the beauty of an acoustic guitar.  It produces a pure, natural acoustic sound.

-The acoustic guitar is my guitar of personal choice for playing at home.  It lends itself well to vocal accompaniment.

-The type of wood the guitar is made of along with its shape, design and construction will affect the sound produced. String type and gauge also have an effect. Other factors such as room acoustics are at play as well.

Frequency (a little technical theory)

Frequency, as the name implies, is how frequently a sound wave reaches your ear.  Sound travels in waves. One wave is considered to have one cycle.  Frequency is measured in cycles per second (Hertz (Hz)).

The higher the Frequency of a guitar string when picked, the higher the Pitch produced.

The frequency of a guitar string is determined by the String’s Thickness, Tension & Length:

String Thickness: With more mass to the string it will tend to vibrate at a lower frequency under a given tension (this is why string thickness changes from low to high strings on your guitar.  As tension is increased to bring the string into tune it gives a warmer meatier sound.  When selecting your strings, keep in mind that thicker strings are more difficult to bend and changing thickness will change the tension on the neck requiring a Truss Rod adjustment to maintain the same action.

String Tension: As you tighten a guitar string at the Machine Head, the Pitch (Frequency) increases.  This is how the guitar is tuned.  There are numerous frequencies (tensions) however a modern universal standard was set in 1812 at the Paris Conservatoire
at A440.  That is to say that the “A” note has a frequency of 440 Hz.  Each and every standard tuned instrument be it a harmonica or a saxophone and every tuner, tuning fork and pitch pipe is set to this universal standard.  Pitch can be manipulated to express yourself musically using a Whammy bar, Bending behind the Nut, flexing the neck (not recommended) & Turning the Machine Head.

String Length: A shorter string vibrates at a higher Frequency (Pitch).  This is the main concept behind how the guitar produces it’s sound.  An open string (one which you are not pressing down on the fret) is free to vibrate between the Nut & Bridge when played.  When you press on a fret you are effectively shortening the string by changing the end point at the Nut end.  As a result the Frequency increases as does the Pitch.  The frets are precisely positioned so that the perfect melodic Pitch is played when the string is fretted.

 

-The vibrating string is the result of a combination of standing waves containing multiple frequency components at F, 2F, 3F, 4F (Hz) etc. (F being the fundamental and the others harmonics). This harmonic series determines the timbre of the Guitar. The timbre can be changed by plucking the string at a different location. Try plucking a guitar string in the centre where it has lots of depth & bass (fundamental frequencies) and near the bridge where you will find lots of treble (high-order harmonics). Many songs exploit this to manipulate the sound.

-If you pluck the string dead in the middle (12th fret) you’ll mainly excite the fundamental frequency (F) and your tone will be dominated by that frequency and you will get a dull tone. If you hit the strings near the bridge you will excite higher frequencies and you will hear a brighter tone. The placement of pickups at these different positions exploit these characteristics. Multiple pickups are commonly used and are selectable individually or in combination.

-Acoustic guitars are the instrument of choice for many guitarists for the Pure ear pleasing sound they produce. They produce a pleasant volume which lends itself well to vocal accompaniment.

The Electric Guitar is fundamentally the same except instead of a hollow body producing the sound, electronic Pickups are used to sense the string’s vibration. A small electrical signal is induced in the PICKUP. The metal Posts of the Pickup are wrapped with fine wire which is energized to create a magnetic field.  As the vibrating string moves through this magnetic field the field is disrupted causing an electric signal to be induced in the Pickup.  This signal may be manipulated to sound however the guitarist wants. That signal is then amplified to produce the sound through speakers. The solid body of the Electric Guitar allows the string vibrations to resonate. This creates better sustain than an Acoustic Guitar.

-The strings of the guitar get progressively thicker as you move from bottom to top string.
-When set to the correct tension (tuned) the narrow string has a higher pitch than the next  thicker string above it.
-By changing the length of a given string (pressing your finger down directly behind a Fret) the pitch of the string is altered.

 

Fig. 2. Fretting the 1st String at the 1st Fret.

-As the string is made shorter the pitch becomes higher.

-The precise spacing of the frets creates the proper melodic pitch of the note when the string is fretted.

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