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Introduction

Welcome to our page dedicated to the world of acoustic, electric and bass guitar.

First up is a bit of information on the theory of sound, then the scientific explanation of how guitars work. Once you've mastered the workings of guitars, there are profiles of several established musicians... much more interesting !


Sound Theory

Sound is any change in air pressure that our ears are able to detect and process. If the change in pressure is strong enough, the eardrum can pick up sound waves and it then vibrates, and this vibration is translated by the brain into sound. The greater the pressure change, the louder we perceive the sound to be.

Sound Waves

A sound wave is introduced into a medium by the vibration of an object following an input of energy. The air molecules surrounding the vibrating object are forced to compress and expand, creating a pressure disturbance consisting of this alternating pattern of areas of compression and rarefaction. The disturbance then travels through the medium by the transportion of energy from particle to particle. This energy originates from the vibrating object. The more energy input into the object, the greater the amplitude of vibration and thus the more energy imparted to the medium. The amplitude of vibration of the particles of the medium is therefore increased.

Aristotle believed that sound and light were carried through air, but could not travel through a vacuum. It was not until the seventeenth century that this theory was proved correct, by Robert Boyle, an Irish scientist. Boyle placed a ticking watch into a jar from which he pumped air, observing that as the amount of air diminished, the ticking sound could no longer be heard.

We now know that sound does indeed require a medium to travel through - this can be gases, solids or liquids. Sound travels in air at approx. 330 m/s.

Frequency and Intensity

For us to be able to hear sound, it has to fall within a certain frequency range. Frequency is measured in Hertz (Hz) and tells us the number of sound waves given off by a vibrating object per second. For most people, the perceivable range of sounds falls between 20 Hz and 15 000 Hz.

The intensity of sound is measured in decibels (dB). The lowest possible sound that can be heard is called the threshold of hearing. The threshold of pain measures at approx. 120 dB, although any sound above 85 dB can damage a person's hearing. Here are some levels of sound intensity encountered in everyday life:

Near total silence - O dB
A whisper - 15 dB
Normal conversation - 60 dB
Motorcycle (up to) - 110 dB
Car horn - 110 dB
Rock concert - 120 dB
Gun shot - 140 dB


Acoustic Guitar

A guitar is made up of three parts - the hollow body, the neck (which holds the frets) and the head (which contains the tuning pegs). The soundboard of a guitar is a wooden piece mounted onto the front of the guitar's body, and it is this that amplifies the sound. Attached to the soundboard is the bridge in which the saddle is embedded, against which the strings rest.

When you pluck or strum the guitar strings, it vibrates at its natural frequency and resonance occurrs, increasing the amplitude. These amplified vibrations are submitted from the saddle to the bridge to the soundboard, which in turn vibrates. The entire body of the guitar forms a hollow soundbox that amplifies the vibrations of the soundboard, and the sound comes out of the sound hole (a large hole in the soundboard).

The vibrating strings of a guitar generate tones (a sound repeated at a certain, specific frequency). The frequency of the vibration of a string under tension is controlled by the length, weight, and springiness of the material of the string, as well as the amount of tension on the string. On a guitar, the first string is the thinnest whereas the sixth string is much heavier and thicker. The tension on the strings can be controlled by the tuning pegs. The frets are metal pieces cut into the fingerboard (the face of the neck), onto which a string can be pressed, altering the string's length and, therefore, the tone it produces when it vibrates. The frets are spaced out in such a way as to allow the proper frequencies to be produced when the string is held down at each fret.


Mark Kulke, former guitarist for Taboo, on acoustic guitar.


Electric Guitar

An electric guitar shares several common features with an acoustic guitar, such as the six strings tuned with the tuning pegs and the frets on the neck of the instrument. However, the body of the guitar differs greatly. Most electric guitars have solid bodies, and so magnetic pickups controlled by several knobs are used to produce the sound.

Magnetic Pickups

Most electric guitars are completely passive (ie. they consume no power). The vibration of the strings produces a signal in the coil of the magnetic pickup, an electromagnet consisting of a bar magnet wrapped with up to 7 000 turns of fine wire. The magnetic pickup, which is located under the steel strings, senses these vibrations electronically and routes an electric signal to an amplifier and speaker. The pickup coil sends these signals through a simple circuit:

In an electromagnet, electrical energy can be turned into motion by the coils and the magnet, and vice versa, as in the case of the electric guitar. The vibration of the strings produces a corresponding vibration in the magnet's magnetic field and, therefore, a vibrating current in the coil. A basic pickup isa single magnetic bar under all six strings, although it is possible to have a separate polepiece for each string as below.

Many electric guitars have two or three pickups located at different points of the body, each with its own distinctive sound. Pickups can also be paired to produce additional variations.

Tone, Frequency & Amplitude

Several resistors are used to control the tone, frequency and amplitude. Tone is adjusted by the upper variable resistor, high frequencies can be cut out by using a resistor (~500 kilo-ohms) and a capacitor (0.02 microfarads), and the amplitude of the signal that reaches the jack is controlled by a second resistor. From the jack, the signal runs to an amplifier, which drives a speaker.

Amplifiers and Distortion...

A typical amplifier consists of a pre-amp, a power amplifier and a speaker. Some also include effects and reverb circuits. As it is passive, the electric guitar does not have enough power to drive the power amp directly, and so the boosts the guitar's signal enough to make this possible.

The electric guitar amp is actually part of the instrument, and, unlike a stereo amp which is designed to reproduce and amplify sound with the least distortion possible, for musicians the option of distortion - which occurs when the signal in an amp's circuitry is too powerful - is actually extremely desirable. Depending on the design of the amp, the level of distortion can be controlled by the guitarist. Vacuum tubes can also be used to create distortion patterns and create specific sounds.

Another concept unique to the electric guitar is that of feedback loops between the amp and the guitar. When the sound coming out of the amp and speaker is loud enough, it can cause the guitar's strings to vibrate so that when the musician hits a note with the guitar that string can continue vibrating indefinitely.


Vital Stats

Name DECLAN BENNETT GRAHAM MCGROTTY JUSTIN HOMEWOOD
Nick name Dec Prof Dust
Age/Handspan 21/unknown... 30/unknown...but big enough! 33/8.5"
Instrument Acoustic Guitar Electric Guitar Bass Guitar
How did you get into playing the guitar? 'Cos I couldn't carry my piano around. Can't remember it was too long ago. By mistake.
How long have you played for? Six years. 23 years! Since I was eight.
Specialist/Preferred area A fusion of styles. Blues 70s funk.
Favourite solo A1 - Take on Me "Tunnel of Love" by Dire Straights - it's really beautiful. "Alright Now" bass solo by Andy Fraser of Free. He wrote it when he was 16. I could play it when I was 12. I think that says a lot!?!
Who's your inspiration/fave band? Ani DiFranco Dire Straights and stuff like The Eagles... I like a lot of folk and country & western - NickleCreek are pretty good. Bootsy Collins and Parliment.
Do you play any other instruments? Piano/flute/bodhran/tin whistle... Nope. Solo pink oboe. (!?!)
Career High Having my first solo written song played on radio. Probably has to be playing in the Blues Brothers band, it's always a lot of fun and stuff. Good music. The fans are so cool too! Audtion for kajagoogoo (New Wave band) when I was 14 and doing mock O-levels. Thankfully I didn't get it!
Current jobs/projects Taboo and my solo music project, Sum Lad from Cov. Blues Brothers UK tour 'Out on parole' & my own music, plus I do play with various bands. Declan Bennet Collective and Taboo.
Future Plans Making more music/creating. I'm just gonna keep playing and writing and recording. Build a time machine.
Most interesting fact you know about guitars? They don't make great trainers. They're mostly made out of wood. B demented chord - my favourite.
Say something nice about Science I love geeks, and geeks love Science. I don't really know anything about science - I helped Anna revise for her Physics GCSE though! Science invented the pot noodle.
Say something nice about Anna & Jules I just did but you can't hear me!! (ha ha ha) They made me that really cool mug which I thought about a couple of days ago when I saw it in my cupboard. Great cookies (At last, our talent for baking acknowledged)


Psychology behind the musician...


Mark Kulke and Declan Bennett


Links

Right:
Setup at Taboo -
MD's corner, guitar,
bass and drums.