Engineering: G is for guitar

The guitar has been the harbinger of the most popular musical genres in the modern world.

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Guitar-led music has defined generations, eras and bred musicians to be superstars.

Yet rock music, country, punk, flamenco and blues all use the same instrument but are polar opposite in style – not many instruments can do that.  

Since the 1500s, the guitar has been reinvented over and over to make all sorts of music. The most recent incarnation, the electric guitar, transformed popular music.

We all know, however, deep down, that there is more to the guitar than just strumming strings. How does the wooden box make particular notes? And why does the electric guitar only sound like its playing when it’s ‘plugged-in’?

All these answers and more will be provided as we discuss the acoustic guitar’s specific features and distinctive sound, and carry on into the amplified world of the electric guitar.

The guitar’s goal in life in to make music, so rock on….

Unplugged and wired – the acoustic guitar

An acoustic guitar can be thought of in three major sections:

- The hollow body

- The neck with frets running up it.

- And the head where the tuning pegs live

Central to the guitar’s sound, however, is the soundboard – the wooden piece hitched on the front of the hollow body. The soundboard makes the guitar sound loud enough to be audible.

In the soundboard is a round and centred hole, which funnily enough, is called the ‘hole’.

Below the hole and on the soundboard is the bridge. The bridge is the anchor-end for all the ends of the six strings. Inside the bridge is a hard piece of material where the string rests, known as the saddle.

When plucked, the strings make a vibration that travels through the saddle, to the bridge and onto the soundboard.  The entire soundboard vibrates making a hollow soundbox out of the body which amplifies the sound.

Tapping a tuning fork against the bridge proves that it is the vibrations of the soundboard that produces the sound of an acoustic guitar.

Other features of the acoustic instrument are concerned with controlling the tone of sound.

The narrowing of the body makes it easy to rest a guitar on the knee but where it widens are called the bouts - the upper bout being where the neck connects and the lower where the bridge is attached.

The shape of the bouts controls the tone the guitar produces – two unalike bodied and sized-bout guitars will sound different.

Bouts influence the sound in two ways: the lower bout accentuates lower tones and the upper bout accentuates higher tones.

Where the strings are located on the face of the neck is called the fretboard and it is where the sound can be manipulated along specific intervals. Pressing a sting down onto a fret changes the length of the string therefore changing the tone it vibrates.

The grooved area where the strings are slotted between the neck and the head is called the nut, therefore, the saddle and the nut are bookends for the strings, and the distance between the two are known as the scale length of the guitar.

As the strings pass over the nut, they are attached to the tuning heads which work as a worm gear that turns a string post that allows the player to ‘tune’ by increasing or decreasing the tension of the strings.

Yeah, but why does it sound like it does?

Because it is a musical instrument, the guitar produces tones. Music is the arrangement of tones into spatial patterns that the human brain finds pleasing or, at least, intriguing.

A tone is made up of one or a few sound frequencies that become a musical note.

A musical note comes from an incremental selection of tones that are pleasing to the ear alone and together with others. The tones run on frequencies such as 264 Hz, 297 Hz, 330 Hz, 352 Hz, 396 Hz, 440 Hz, 495 Hz, and 528 Hz - the frequencies of the major scale.

Each tone is a part of a scale that is multiplied by a certain fraction to make the next tone upwards: such as, 9/8 = 297 Hz, 10/9 = 330 Hz , 16/15 = 352 Hz, 9/8 = 396 Hz , 10/9 = 440 Hz, 9/8 = 495 Hz, 16/15 = 528 Hz – respectively.

The fraction increments are also known as the doh re mi so far la ti doh of music.

The tones are officially written as a scale via a letter of the alphabet starting with the letter C and finishing with G – C, D, E, F, G, A, B, C.

Put simply, the fractions were decided for the major scale because they sounded the best in harmony. 

The space between the first frequency and the last is known as an octave. It is between low and high Cs or the dohs in the rhyming slang. The frequency is separated by a factor of two, where 264 Hz is one half of 528 Hz.

However, semi tones (sharps and flats) are a fraction calculated with C as the starting point. The musical world came to other agreements over time, such as the tempered scale and the minor scale.

These are the foundations on how the guitar is tuned. Twelve frets, three octaves with six different weighted strings make 37 unique notes.  But there are also multiple ways of finding identical notes across the fretboard.

Individual strings are under a specific tension and will vibrate a specific frequency controlled by the string’s length, its tension and its weight. When you press a string down on a fret, you changed its length, its tension and therefore its frequency.

The strings are weighted and spaced so the proper frequencies are produced when it is played along the frets. The guitar can not only make a tone, but add harmonics to it, i.e. plucking one string is a pure note but when strings vibrate harmonically two, three and four times it makes the pure tone.

As different notes start to ring at the saddle at once, the saddle adds its own vibration making the tones sound as many blended frequencies.

The guitar has primitive roots starting in Babylonia, circa 1850 BC, progressing through early Spain until its current electric manifestation today. However, throughout its history, a guitar can still be identified by its body and neck. Even during its time in Egypt, the guitar had frets.

The Guitarra Morisca came to Spain by the Moors and it had an oval soundbox with many sound holes on its soundboard. Despite incarnations as a lute, changing from four to five strings and undergoing heavy Italian influence in the 17th century, Antonio de Torres of Spain developed the Spanish guitar in the 19th century to what we know it today.

An evolution from the Spanish design even provided the model for the electric guitar.

Plugged in and synthesised – the electric guitar

The electric guitar is one of the most popular and culturally relevant inventions of the 20th century. It defines the birth of rock’n’roll and all that came after it. The electric guitar hit the streets in the 1930s, but it took 20 years to find its footing in the world.

Now it is the most used instrument in popular music.

Despite functioning basically like an acoustic guitar – with strings, fret board and head and body, it does not make a sound without electric amplification. It has to be plugged in.

When you pluck an unplugged electric guitar string, it won’t make a loud sound – without the soundboard and hollow body, it cannot.

The electric guitar makes its frequency (musical note) electronically as an electronic signal on route to an amplifier and speaker. The guitar senses that plucking has occurred via the string’s vibration alerting a magnetic ‘pickup’ container placed under the strings on its body.

When a string vibrates, it cuts through a bar magnet on the pickup producing a signal in the pickup’s coil.

That is, coils and magnets turn electricity into motion, and in turn, motion into electrical energy – the basis of electronics.

In the case of an electric guitar, the vibrating steel strings produce a corresponding vibration in the magnet's magnetic field and therefore a vibrating current in the coil.

The pickup’s coil sends the vibration as a signal through a circuit.

The electric guitar contains resistors that adjust the tone with filters that cut out uneven frequencies. By adjusting the resistor, the player can control which frequencies get cut out. The second resistor controls the volume that leads to the jack. And from the jack, the signal runs to the amplifier and it comes out as sound through the speaker.

We have delved in deep in a study on amplifiers. Check out A is for Amplifier in scenta’s A to Z of making music series.

There are two types of pickups for the electric guitar: passive and active pickups. Passive pickups don’t need additional power to work but the difference means a lot to the guitar’s tone and overall output.

Passive pickups send a low output (raw signal) to the amp that can only be controlled by the volume and tone resistors on the guitar. Passive pickups tend to send out more midrange frequencies and give players less dynamic control, although the output sound is very desirable as it is.

Active pickups have preamps built into the pickup container so they can push the signal to the amplifier themselves. The preamp needs to run from another power source than the amp, so it has a separate battery. The active pickup sends a high output signal producing a rounded sound with more dynamic projection and controlled tone.

Engineers have been experimenting with automatic music makers for years – player-less pianos and music boxes are some earlier successful attempts of bringing technology to music in the 1800s.

However, it wasn’t until the 1920s when inventors came to grips with amplified equipment with the birth of the radio.

The electric guitar came into being with innovator Lloyd Loar, an engineer at Gibson Guitar. Loar developed the pickup for the electric viola and string bass and had the string vibrations pass through the bridge to magnet and then the coil before carrying on to the amplifier.

Other attempts before the Gibson had the vibrations being picked up from an acoustic-style soundboard. Amplifying the natural sound of the guitar gave a weak signal – engineers had to utilise a more direct pickup system where the electromagnet registered string vibrations from the strings themselves.

The first successful model on the market(1932) was dubbed the ‘frying pan’. The electro Hawaiian model played flat on the lap and was popular among traditional Hawaiian guitarists.

But as time went on, the Spanish guitar influenced the style of the electric model but the significant differences between it and the acoustic guitar meant it took a while to be accepted.

It was Leo Fender who brought the mass produced solid body electric guitar to the world in the 50s just before Gibson released a solid bodied version.

The solid body guitars didn’t have the feedback problems that hollow electric guitars had, it also had a greater sustain.

Then the electric guitar moved into public consciousness as it became the leading instrument in the birth of rock’n’roll.

The early model Stratocaster, by Leo Fender, was famously held by Buddy Holly, and with his horn rimmed glasses, the electric guitar became part of his signature look.

Holly was one of the first to popularise the Stratocaster, but Jimi Hendrix took the instrument to new levels. Eric Clapton became one of the greatest guitarists of all time with the Strat, and the instrument was directed into a new genre in surf culture – a la the Beach Boys and the Ventures.

For better or for worse the Strat was implemented by Hank Marvin of the Shadows (a band originally led by Cliff Richard). His style was so distinctive that many musicians were turned off the Strat – the Beatles didn’t touch the Stratocaster until 1965 with the recording of Rubber Soul.

Fake it to make it

To simulate the sound of a guitar you must get the right harmonics at the right frequencies and amplitudes and blend them. By blending 440-Hz and 880-Hz tones and making it trail off like an acoustic guitar, it sounds very close to the real thing.

By getting the right tonal modifications (bearing in mind that different shaped guitars favour different frequencies and amplifies them better) you would then need to apply distortion to the tones.

By completing this task, you could artificially recreate a note that sounds just like a guitar. Just like what synthesisers do when they simulate the sounds of different instruments.

Click here for more information on how to simulate the guitar.

Rock’n’roll’s best friend

The guitar has been the instrument playing the soundtrack behind the modern generations. Generation after generation have invented new ways and styles to create entire musical genres time and again to suit the feelings and trends of the time.

Although you could say that bands today rehash styles and riffs of decades before, the guitar is still front stage centre driving modern music to new heights.

Even electro producers simulate the guitar with synthesisers and samples – it’s almost as if the modern music as we know it would not exist without a lead-guitarist creating catchy hooks for pop lovers to grasp onto.

Further reading

How stuff works – the acoustic guitar
How stuff works – the electric guitar
History of the acoustic guitar
scenta’s A to Z on making music

 

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