Guitar

How to construct a guitar? And it's overview

How to construct a guitar? What basically, is a guitar?

Guitars are popular music instruments. In fact, they're probably the 'go to' instrument for those who're musically inclined, but have either a budget (pianos are out, then) or a lack of formal tuition (they're easy to learn). For the sake of these people – or just the curious – I will give a brief overview of guitars and how they work.

Firstly, it must be observed that guitars are, broadly, available in two forms: Acoustic and Electric. Acoustic guitars are those which are not powered by any electrical source; they purely produce sound through their hollow bodies, thick strings and resonant woods selected for their build. Electric guitars, on the other hand, have (mainly) solid bodies, lighter strings and (normally two) 'pickups', which are magnetic devices whose function is to convert the electric strings' vibration into an electrical signal, due to the change in the magnetic field caused by the vibrating strings. 

Aside from these differences, there are things that're in common to all guitars, and the first of these is the body. This is the main 'bit' of the guitar that's roughly oval in shape. This carries the bulk of the guitar's weight, and houses either the pickups (on electric guitars), or the sound-hole (on acoustic guitars). Bodies are usually made, in both cases, from specially selected woods, which are then 'plated' with a hardwood (the best being mahogany or maple). The body of a guitar is also where the bridge is located. The bridge is the end-point of the strings. That is, they run down the long neck, over/across the body (and over the pickups or sound-hole), and then finish up at the bridge. The purpose of the bridge, crudely, is so that the strings have somewhere to end. Looking at it in more detail, the bridge is also where action is set.

Action refers to the height that the strings hover from the guitar's body. “Low action” means that the strings are very close to the neck and body, whereas “high action” means they're further away. The differences are often subjective, but broadly speaking, low action is more suited to fast soloing/shredding, and high action offers a more 'bouncy' feel, for playing rhythm guitar (riffs and chords).

From the guitar's body protrudes its neck. This is the long, rather obvious piece of wood over which the strings lay and ones fingers hold them down between the frets to produce particular notes. The neck is straight and is able to withstand the high tension exerted upon it by the tight strings due to containing a metal core, known as a truss-rod. This truss-rod can be tightened/loosened with an allen key (the connection for which is usually in the guitar's head).

Upon the neck are laid small metal strips, perpendicular to the neck's length, and spaced at incrementally more narrow distances apart as one heads away from the guitar's body. These frets are so that, when one 'frets a note' - holds the string down, between (not on) – the string's length is basically shortened (as such), meaning that when plucked, it'll produce a different pitch.

The neck finishes with the guitar's head, where the strings are tuned and wound around the machine heads.

Construction of a guitar - How to construct a guitar (Acoustic & Electric)

Different guitars are constructed in different ways. For ease, space and simplicity, we will here deal with the construction of acoustic guitars and electric guitars, in a general sense, only. There is an assumed basic knowledge of guitar parts.

Acoustic guitars are the more complicated of the two guitars to make, and arguably are affected most by the build quality of the two.

The acoustic guitar's body is produced in four distinct segments. Two plates for the front and back of the body – the soundboards - (one with a sound-hole printed in it), and two side pieces, to form the body. Onto this is glued the neck, which is constructed of a main wooden piece and also another layer, which the frets are embedded in.

Soundboards are intended to absorb and reverberate the sound of the string that's being played, and so must be constructed expertly, with a few supporting pieces of wood glued on the underside (sort of like scaffolding). This process is known as 'plate bracing'. Plate bracing is not just structural though, as the extra stiffness to the soundboard provided by plate bracing can alter the sound through the change in elasticity, both for better or worse depending on the changes made.

Necks must be shaped, usually done roughly with a plane in order to get the general shape, then with a myriad of more precise tools to exactly hone its specific shape/curves. Different woods are usually laminated together for this stage, in order to achieve a different fretboard material. Truss channels are also routed out, and then the final piece of covering wood is added.

Headstocks are usually cut out from  the same wood as the neck, so that there's no weakness of joining them on to the neck (this could snap under string tension).

Frets are added to the neck by sawing a small gap and tapping them into place. Their distance apart (which varies) is determined by a mathematical formula. Machineheads are then screwed on to the head, with the nut being applied in a similar way to the frets.

That's the acoustic guitar; the story for the electric guitar is a bit simpler. Here, a body is one solid piece of wood, much as the neck and head also come from one piece of wood and are shaped. The body is shaped (mostly by hand) into the shape required, whereby channels are cut into it for circuitry and necks to screw/glue into place.

The circuitry for an electric guitar can usually be pre-bought, and is a series of wiring, volume pots, tone switches and pick-ups. These are wired in the correct way, and placed inside the body, hidden by scratch plates. Choice of pick-ups can vary to the individual's taste – a 'thinner' tone with 'sharpness' is generated by single coil pick-ups, whereas a warmer, heavier tone can emanate from humbucker pick-ups. Pick-ups are often of different sizes, so need to have their shape cut into the guitar's body (and therefore decided upon in advance).

CONSTRUCTION POINTS:

                                    The starting construction of a “guitar” includes “Coupling”

“Coupling” simply refers to an interaction between two or more vibrating elements. First of all, on a guitar, the string is excited (plucked or picked) by your fingers, vibrating the bridge, which then goes on to vibrate the soundboard and the internal air cavity, then the back and sides and so on. If these elements interact well, the whole system is said to be strongly coupled.
  The body of the guitar acts so that the high pressure vibrations at the bridge are turned into low pressure vibrations of the surrounding air. This is a form of "impedance matching", in much the same way an electrical transformer raises or lowers a potential difference and is the main principle behind speaker cone design.

The higher frequency (pitch) sounds are produced by string interaction with the bridge and then the sound board, whereas the lower frequencies are essentially driven by the internal air cavity/sound hole and ribs/back coupling effects:
The interaction looks roughly like this:
(High Frequencies)
Coupling between parts depends on geometry, sound frequency and the materials used.
Interaction strengths between various components need to be optimised according to taste; a certain amount is needed to radiate the sound transferred from the string's vibration, but too much coupling produces some harsh and very ugly tones*.

Coupling can be, and is to an extent, controlled during construction; luthiers often make use of Chladni pattern diagnosis to check the main resonance symmetries of their instrument and make any necessary changes.
Apart from being sensitively dependent on materials and bracing (see below) various other factors also influence coupling strengths, such as purling and binding (how the sides and top/back plates are connected), bridge type and placement, right down to what sort of adhesive was used during manufacture.

“CONSTRUCTION STEP 2”

The second step includes “Material Composition”.



“Material Composition” The materials from which a guitar is constructed have very direct consequences on its acoustic qualities. Because the traditional material used is wood--- often rare hardwoods and cut from as close to the centre as possible---there are certain economic and conservation issues that would be partly addressed if a more readily obtained and controllable medium were to have the required acoustic properties.   Much work has been done on testing the various acoustic properties of materials that comprise the guitar. Investigations have been carried out using synthesized materials such as fiberglass, carbon fibre and various polymers, in attempts to imitate/replace existing woods. The general rationale was to produce materials with much less variation and at less cost than traditional woods, but so far the results have not been promising:  

1. The attempts studied tended to have as much acoustic variation as traditional woods; and
2. Still didn't have the stiffness-to-mass ratio, elastic module, damping, or longitudinal to lateral grain properties required to compete with traditional timbers.

Despite this, synthetic materials are used successfully in complementing traditional materials (such as carbon-fibre strut reinforcement on some soundboards), but it appears a pure synthetic that has a good sound and yet feels good to play is still some time away. It should also be mentioned that aesthetic considerations also play a large part in purchasing a guitar---even if an instrument sounds good; it won't be very popular if it looks like a politician!  

    
Useful Link :- http://www.phys.unsw.edu.au/music/guitaracoustics/construction.html