Acoustic Guitar

Oisín Deignan’s AV Tech Presentation

HOW DOES IT WORK?

BackgroundACOUSTIC GUITAR: HOW DOES IT WORK?

Background to the Guitar•The guitar is one of the most popular musical instruments of all time.

•Known use since as early as the 1500s but some sources suggest it has been around for over 3000 years.

•Musicians in rock, country, and world music use the same acoustic guitar but in different ways to make wildly different sounds.

•Since the 1500s – huge effect on popular music.

The Construction of the Acoustic GuitarACOUSTIC GUITAR: HOW DOES IT WORK?

Guitar PartsHollow BodyBase of the guitar

NeckHolds the frets

HeadContains the tuning pegs

Guitar Parts Soundboard

The most important part of the body.

Job – to make the sound of the guitar loud enough to hear.

Sound board•Soundboard has a large hole called the sound hole.

•Bridge – attached to soundboard, anchors for one end of the six strings.

•Saddle – hard piece that the strings rest on.

•Vibrating strings > saddle > bridge > soundboard.

•Soundboard vibrates – body of guitar forms a hollow sound box that amplifies vibration of soundboard.

Guitar Body•Body of acoustic guitars have two widenings (happens to be a leg rest).

•Two widenings – upper bout and lower bout.

•The tone of a guitar depends on the size and shape of the bouts.

•Lower bout accentuates lower tones. Upper bout accentuates higher tones. (Rattling a plectrum inside demonstrates this).

Neck and Scale Length•Fingerboard/Fretboard - Face of neck containing the frets.

•Pressing fingers onto a fret – changes length of string and the tone it produces.

•Saddle and nut act as two ends of string.

•Scale length – distance between these 2 points.

How the Acoustic Guitar worksACOUSTIC GUITAR: HOW DOES IT WORK?

Sounds, Tones, and Notes

•Sound is any change in air pressure that our ears are able to detect and process.

•For our ears to be able to perceive sound, a sound has to occur in a certain frequency range.

•Human’s perceivable sound: 20-1500 Hz.

Sounds, Tones, and Notes

•A tone is a sound that repeats a certain frequency.

•A tone can be made up of one frequency or a small number of related frequencies - usually a pleasant sound.

•Noise - combination of a number of random frequencies – usually not a pleasant sound.

Sounds, Tones, and Notes•A musical note – collection of tones that are pleasing to the human brain.

•Major sale – certain collection of tones that sound pleasing.

•There certain tones have been given letter names.

264 Hz - C, do (multiply by 9/8 to get:)297 Hz - D, re (multiply by 10/9 to get:)330 Hz - E, mi (multiply by 16/15 to get:)352 Hz - F, fa (multiply by 9/8 to get:)396 Hz - G, so (multiply by 10/9 to get:)440 Hz - A, la (multiply by 9/8 to get:)495 Hz - B, ti (multiply by 16/15 to get:)528 Hz - C, do (multiply by 9/8 to get:)

Sounds, Tones, and Notes•One thing to notice is that the two C notes are separated by exactly a factor of two -- 264 is one half of 528.

•This is the basis of octaves. Any note's frequency can be doubled to "go up an octave," and any note's frequency can be halved to "go down an octave."

264 Hz - C, do (multiply by 9/8 to get:)297 Hz - D, re (multiply by 10/9 to get:)330 Hz - E, mi (multiply by 16/15 to get:)352 Hz - F, fa (multiply by 9/8 to get:)396 Hz - G, so (multiply by 10/9 to get:)440 Hz - A, la (multiply by 9/8 to get:)495 Hz - B, ti (multiply by 16/15 to get:)528 Hz - C, do (multiply by 9/8 to get:)

Tempered Scale•After a long period of time, the musical world came to agree on a scale called the tempered scale.

•All of the notes are offset by the 12th root of 2 (1.0595).

•So if you take any note’s frequency and multiply it by 1.0595, you get the frequency of the next note.

82.4 E - open 6th string87.3 F92.5 F#98.0 G103.8 G#110.0 A - open 5th string116.5 A#123.5 B130.8 C138.6 C#146.8 D - open 4th string155.6 D#164.8 E174.6 F185.0 F#196.0 G - open 3rd string207.6 G#220.0 A233.1 A#246.9 B - open 2nd string

261.6 C - "middle C"277.2 C#293.6 D311.1 D#329.6 E - open 1st string349.2 F370.0 F#392.0 G415.3 G#440.0 A - 5th fret on 1st string466.1 A#493.8 B523.2 C554.3 C#587.3 D622.2 D#659.2 E - 12th fret on 1st string

Tempered Scale•Here is the layout of the notes on the guitar.

•There are 72 fret positions here, but the tempered scale only shows 37 unique notes.

•Therefore there are multiple ways to play identical notes on a guitar.

•Example: Open 5th string tuned to A at 440 Hz = 5th fret on 6th string tuned to E at 329.6 Hz.

Use of the Acoustic GuitarACOUSTIC GUITAR: HOW DOES IT WORK?

Strings & Frets•A guitar uses vibrating strings to generate tones.

•A string under tension will vibrate at a specific frequency that is controlled by the:

• Length of the string.• Amount of tension on the string.• Weight of the string. • Flexibility of the string’s material.

•The tension of the strings is controlled by the tuning pegs.

•The scale length is the distance from the nut to the saddle.

•When you press down on a fret, you change the length of the string and its frequency.

Acoustic Guitar’s Sound

An acoustic guitar generates its sound in the following way:

•Strings vibrate > vibrations transmit to saddle.

•Saddle vibrates > vibrations transmitted to soundboard.

•Soundboard and body amplify the sound.

•Sound comes out through the sound hole.

Harmonics & EnvelopeAcoustic guitars add harmonics to tones.

•When one string is plucked, other strings pick up the vibrations from the saddle.

•Therefore: the sound heard from a guitar note is a blend of many related frequencies.

•The acoustic guitar also adds envelope to any note it plays.

•The sound builds and fades off.

•The amplitude (loudness) of the note changes.