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Scratch-plate/finger-rest.

The most common damage to flat-top acoustic guitars is caused by the fingers or pick hitting or resting on the top of the guitar, wearing away the finish and sometimes wearing into the wood of the top. Makers attempt to alleviate or at least slow this process by fixing a ‘scratch guard’ directly to the finish of the top in the areas most commonly damaged. Scratch-plates can be transparent or made of various materials, some are even decorated with complex inlayed motifs.
On instruments with carved tops the scratch-plate is often described as a finger-rest and is usually installed so that it ‘floats’ above and off the instrument surface (such as this example). The finger-rest is also sometimes elaborately decorated or made of exotic figured woods.

On-Board Electronics.

In order to have instruments heard in concert settings, on stage or in a mix of instruments that are played at high volume, amplification is necessary. Amplifying requires that some sort of pick-up must be employed. Generally most instruments that have pick-ups also have some form of on-board electronics.
Most on-board electronics make use of potentiometers (volume and tone knobs) that allow variable adjustment and tone colouring.
In its simplest form on-board electronics may consist of only a single potentiometer acting as a volume control, placed in-line between the pick-up and the output jack and perhaps, if there is more than one pick-up, a pick-up selector switch.
In it’s most complex form there may be an array of switches, potentiometers and a battery powered on-board pre-amp circuit.
This example has a simple single pick-up with a volume and a tone control configuration.

The tailpiece

The primary use of the Tailpiece is to anchor the strings. In a flattop guitar the tailpiece is incorporated into the bridge and strings are held in place by bridge pins. In an arch-top guitar the combined tension of the strings is distributed to the edge of the guitar and via an endpin into the tail-block (an internal block within the sound-box) of the guitar.
Various aspects of the tailpiece can influence the final tone of the guitar: for example, the angle the strings take after the bridge-saddle or the distance of free string between the bridge saddle and tailpiece.

The 'F'-Holes

These serve the same function in an arch-top guitar as the sound-hole does in a flattop guitar. They allow the sound to escape from the sound box, effectively controlling the passage of air ‘agitated’ by the struck string moving the soundboard.
The ‘F’-holes or sound-holes also function in changing the area of ‘flexion’ under and around the bridge.

Pick-up

In order to have instruments heard in concert settings, on stage or in a mix of instruments that are played at high volume, amplification is necessary. To allow amplification an acoustic instrument can be simply amplified via a microphone, but solid-bodied or semi-acoustic instruments must be amplified via a pick-up installed on an instrument.
Pick-ups come in several forms:
1. Magnetic pickups that detect the movement of the strings.
2. Piezo crystal strips or dots that detect changes in pressure which cause the crystals to generate a small voltage. These pick-ups generally give a more ‘acoustic’ sound.
3. On-board miniature microphone.
4. A combination of all or some of the above.
Magnetic pick-ups
Magnetic pick-ups are not normally installed on instruments designed to be played purely acoustically.
Magnetic pick-ups require that the strings used are made of a ferrous metal (steel) in order to react with a magnetic field which implies that bronze strings (used on acoustic instruments), nylon strings and strings made with a silk core and bronze windings (both used on classical acoustic instruments) can not be effectively amplified via a magnetic pick-up. For these a Piezo pick-up must be used. Piezo pick-ups can also be used with steel strings thus allowing a combination of both types of pick-ups to be employed on certain instruments.
A magnetic pick-up is essentially a magnet or set of magnets (most are Alnico) wrapped with a coil of poly-coated 42-gauge (very fine) electric wire. The length or number of wraps normally determines the power and tone of the pick-up. The longer the wrap-wire the higher the DC resistance, power and midrange tone.
There are generally two kinds of magnetic pick-up:
1. Single-coil. These pick-ups hark back to the first pick-ups produced and give a raw bluesy tone. These pick-ups usually give off a low frequency ‘hum’ when not earthed.
2. Humbucker pick-up – which have two or more coils. These have more power and a warmer tone. The coils are oriented in such a way as to cancel out the ‘hum’ normally associated with single coil pick-ups.
Piezo pick-ups
The ‘ribbon’ form of these pick-ups are normally installed under an instrument’s bridge saddle(s) so that the pressure of the vibrating string can be detected. The ‘dot’ form can be installed anywhere and the location will influence the tone produced.
Because these pick-ups generate a strong signal compared to magnetic pick-ups a ‘buffering’ pre-amp is normally required in order to smooth out the signal for amplification. Some amplifiers cater for this by providing a separate input for Piezo pick-ups.

The body

The body is also known as the sound box. It is divided into three main parts:
The upper bout (the slightly smaller 'bulge' at the base of the neck).
The lower bout (the larger bulge) and the waist (the pinched area between the two bouts).
Furthermore the body comprises the top (the ‘plate’ which lies under the strings), the back (the opposite ‘plate’) and the sides.
The top, also known as the 'sound board', is very important to the tone of the instrument, and vibrates to provide the sound. The tone will vary enormously depending on many factors: the timber used, the thickness of the top, and the struts used to reinforce and distribute the string load and sound waves across the instruments soundboard, etc.
This guitar has the top and back carved into an arch, the elements of which control the structural strength and tone of the instrument

The Neck & Fingerboard

The neck is composed of a length of timber topped with another, usually harder layer called the fingerboard. The fingerboard is divided into sections each one of which provides a difference in pitch of a semi-tone. These sections are usually bounded by the frets, strips of metal which provide an ‘edge’ against which to press the strings.
The different sections/frets on the fingerboard are often decorated with small inlays, these serve the dual purposes of decoration and providing the player with reference points. The strings lie very close to the frets but not actually touching them (until played) – the proximity of the strings to the fingerboard is known as the ‘action’ – the smaller the distance, the lighter the action. A light action may cause fret buzz when the instrument is played aggressively.

Scale length
The scale length is the distance between the Nut and the Bridge saddle (excluding a compensation factor). Sometimes referred to as the string swing length. This is the length of the free part of the string that is struck. The measurement of scale length is on a tempered scale and the scale is used to calculate the diminishing distance between the frets as measured from the Nut to the Bridge saddle.
Various scale lengths are used by guitar makers e.g. classical makers prefer 650mm, Gibson have two standards, 25 ½-inches for Jazz guitars and 24 ¾-inches for other guitars, Fender generally use 25 ½-inches, PRS and many current makers are using 25-inches. Bass guitars generally are 34-inches. One can deduce from this that the longer the scale length the larger the distance between neighboring frets.
Custom built guitars can have scale length vary according to the player’s requirements: e.g. 27-inch scale length for a baritone guitar, or for bass guitars it could be 38-inches closer to orchestral double bass (normally about 42-inches). Or an instrument can be built with more than one scale length.

The strings
Most guitars are fitted with six strings (basses usually with four), but this can vary according to function and/or musical requirements.
Strings come in different gauges and with different coverings. Most modern steel string guitars use just that, steel strings, but classical or flamenco guitars use gut or nylon and the string’s core can be wound with metal windings or silk.
Most acoustic steel string guitars are fitted with phosphor bronze medium to light gauge strings, these somehow always feel tighter and hurt the fingers more than other types of string. Most electric solid-bodied guitars are fitted with light gauge round-wound nickel strings with steel cores. Most jazz guitars are fitted with medium to heavy gauge flat-wound or ribbon-wound nickel strings with steel cores. The smooth surface of these strings allows the jazz player to move about the fingerboard without any squeaking noise made by the string windings rubbing and catching against the fingers. Flat wound strings have a less bright tonal colour than round-wound or half-round-wound strings.
String gauges are traditionally measured in imperial thousands of an inch. For example: a medium gauge set 1st (plain steel) - 0.012-inch; 2nd (plain steel) - 0.016-inch; 3rd (wound) - 0.023-inch; 4th (wound) - 0.031-inch; 5th (wound) - 0.042-inch; 6th (wound) - 0.054-inch.
A light gauge may start at 0.010-inch or perhaps 0.009-inch. A heavy gauge set may start at 0.014-inch through to 0.058-inch.

 

The Nut

The Nut is usually made of a dense material such as bone and is located at the furthest end of the fingerboard. It has slots for each string and provides the starting 'edge' for the strings. Its counterpart is the bridge saddle. The depths of the slots in the nut are important in controlling the height of the strings above the frets and thereby creating the action.

The Headstock

The headstock holds the tuning machines upon which the strings are attached and tuned. The headstock is usually inlayed with the maker's logo and the shape is often quite distinctive. There are generally two kinds of headstock: flat (as in this example) with the tuners sticking up through it, and slot head (like most classical guitars) with the tuners going through slots in the headstock.

The Guitar
Most people, when they think of a guitar, think of one of three types of guitar: a six-string steel-string flattop acoustic, a six-string nylon-string ‘Classical’ acoustic or solid-bodied electric guitar. In fact there are many more different kinds of guitar. This one is an arch-top semi-acoustic jazz guitar - it can be played acoustically or through an amp.
Solid-bodied electric guitars must be played through an amplifier, as they are virtually inaudible otherwise.
Bass guitars traditionally have four strings and are tuned an octave lower than the four low strings on a standard guitar. Bass guitars have longer necks to accommodate a longer scale length or open string length to produce deeper notes.
(click on the magnifying glasses on the left for a description of the different parts)